69. The influence of non-sulphated polysaccharides on the properties of electro-spun poly(lactic-co-glycolic acid) fibres. Azeem A, Marani L, Fuller K, Spanoudes K, Pandit A, Zeugolis DI. ACS Biomaterials Science & Engineering, Available on line, 2016.

Abstract

Biomimetic tissue engineering aspires to develop bioinspired implantable devices that would positively interact with the host. Given that glycosaminoglycans are involved in many physiological processes, whereas their deprivation is associated with pathophysiologies, functionalization of implantable devices with natural and/or synthetic carbohydrate moieties is at the forefront of scientific research and industrial innovation. Herein, we venture to assess the influence of various concentrations (0.01%, 0.1%, 1%) of hyaluronic acid and Ficoll on the structural, thermal, biomechanical and biological (human osteoblasts) properties of electrospun poly(lactic-co-glycolic acid) fibers. The addition of hyaluronic acid and Ficoll reduced the fiber diameter, with the 1% hyaluronic acid exhibiting the smallest fibers diameter (p < 0.001). Neither the addition of hyaluronic acid nor the addition Ficoll significantly affected the onset and peak temperatures (p > 0.05). All hyaluronic acid and Ficoll treatments significantly reduced stress at break, strain at break and elastic modulus values (p < 0.001). Hyaluronic acid and Ficoll did not affect temperatures (p > 0.05) osteoblast viability and metabolic activity; the 1% hyaluronic acid and Ficoll significantly increased (p < 0.001) osteoblast proliferation at day 21. By day 21, the 1% hyaluronic acid and 1% Ficoll fibers showed the highest alkaline phosphatase activity and calcium deposition. At day 21, osteocalcin was not detected, whereas osteopontin was detected on all samples. Collectively, our data clearly illustrate the biological benefit of nonsulfated polysaccharides as functionalization molecules.

ACS Publications

68. Low oxygen tension and macromolecular crowding accelerate extracellular matrix deposition in human corneal fibroblast culture. Kumar P, Satyam A, Cigognini D, Pandit A, Zeugolis DI. Journal of Tissue Engineering and Regenerative Medicine, Available on line, 2016.

Abstract

Development of implantable devices based on the principles of in vitro organogenesis has been hindered due to the prolonged time required to develop an implantable device. Herein we assessed the influence of serum concentration (0.5 % and 10 %), oxygen tension (0.5 %, 2 % and 20 %) and macromolecular crowding (75 μg/ml carrageenan) in extracellular matrix deposition in human corneal fibroblast culture (3, 7 and 14 days). The highest extracellular matrix deposition was observed after 14 days in culture at 0.5 % serum, 2 % oxygen tension and 75 μg/ml carrageenan. These data indicate that low oxygen tension coupled with macromolecular crowding significantly accelerate the development of scaffold-free tissue-like modules.

PubMed

67. In vitro enzymatic degradation of tissue grafts and collagen biomaterials by matrix metalloproteinases – Improving the collagenase assay. Helling AL, Tsekoura EK, Biggs M, Bayon Y, Pandit A, Zeugolis DI. ACS Biomaterials Science & Engineering, Available on line, 2016.

Abstract

Matrix metalloproteinase-1 and -8 are active during the wound healing and remodelling processes, degrading native extracellular matrix and implantable devices. However, traditional in vitro assays utilize primarily matrix metalloproteinase-1 to mimic the in vivo degradation microenvironment. Herein, we assessed the influence of various concentrations of matrix metalloproteinase- 1 and 8 (50, 100, and 200 U/mL) as a function of pH (5.5 and 7.4) and time (3, 6, 9, 12, and 24 h) on the degradation profile of three tissue grafts (chemically cross-linked Permacol, nonchemically cross-linked Permacol and nonchemically cross-linked Strattice) and a collagen biomaterial (nonchemically cross-linked collagen sponge). Chemically cross-linked and nonchemically cross-linked Permacol samples exhibited the highest resistance to enzymatic degradation, while nonchemically cross-linked collagen sponges exhibited the least resistance to enzymatic degradation. Qualitative and quantitative degradation analysis of all samples revealed a similar degradation profile over time, independently of the matrix metalloproteinase used and its respective concentration and pH. These data indicate that matrix metalloproteinase-1 and matrix metalloproteinase-8 exhibit similar degradation profile in vitro, suggesting that matrix metalloproteinase-8 should be used for collagenase assay.

ACS Publications

66. Collagen cross-linking – Biophysical, biochemical and biological response analysis. Delgado LM, Fuller K, Zeugolis DI. Tissue Engineering Part A, 2017.

Abstract

Extracted forms of collagen are subjected to chemical cross-linking to enhance their stability. However, traditional cross-linking approaches are associated with toxicity and inflammation. This work investigates the stabilization capacity, cytotoxicity and inflammatory response of collagen scaffolds cross-linked with glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, 4-arm polyethylene glycol (PEG) succinimidyl glutarate (4SP), genipin (GEN), and oleuropein. Although all cross-linking methods reduced free amine groups, variable data were obtained with respect to denaturation temperature, resistance to collagenase digestion, and mechanical properties. With respect to biological analysis, fibroblast cultures showed no significant difference between the treatments. Although direct cultures with human-derived leukemic monocyte cells (THP-1) clearly demonstrated the cytotoxic effect of GTA, THP-1 cultures supplemented with conditioned medium from the various groups showed no significant difference between the treatments. With respect to cytokine profile, no significant difference in secretion of proinflammatory (e.g., interleukin [IL]-1β, IL-8, tumor necrosis factor-α) and anti-inflammatory (e.g., vascular endothelial growth factor) cytokines was observed between the noncross-linked and the 4SP and GEN cross-linked groups, suggesting the suitability of these agents as collagen cross-linkers.

PubMed

65. Low, but not too low, oxygen tension and macromolecular crowding accelerate extracellular matrix deposition in human dermal fibroblast culture. Satyam A, Kumar P, Cigognini D, Pandit A, Zeugolis DI. Acta Biomaterialia, Vol. 44, pp. 221-231, 2016.

Abstract

A key challenge of in vitro organogenesis is the development in timely manner tissue equivalents. Herein, we assessed the simultaneous effect of oxygen tension (0.5%, 2% and 20%), foetal bovine serum concentration (0.5% and 10%) and macromolecular crowding (75 μg/ml carrageenan) in human dermal fibroblast culture. Our data demonstrate that cells cultured at 2% oxygen tension, in the presence of carrageenan and at 0.5% serum concentration deposited within 3 days in culture more extracellular matrix than cells grown for 14 days, at 20% oxygen tension, 10% serum concentration and in the absence of carrageenan. These data suggest that optimal oxygen tension coupled with macromolecular crowding are important in vitro microenvironment modulators for accelerated development of tissue-like modules in vitro.

Science Direct

64. Innovating in the medical device industry – Challenges & opportunities ESB 2015 translational research symposium. Bayon Y, Bohner M, Eglin D, Procter P, Richards RG, Weber J, Zeugolis DI. Journal of Materials Science: Materials in Medicine, Vol. 27, No. 9, pp. 144, 2016.

Abstract

The European Society for Biomaterials 2015 Translational Research Symposium focused on ‘Innovating in the Medical Device Industry – Challenges & Opportunities’ from different perspectives, i.e., from a non-profit research organisation to a syndicate of small and medium-sized companies and large companies. Lecturers from regulatory consultants, industry and research institutions described the innovation process and regulatory processes (e.g., 510K, PMA, combination product) towards market approval. The aim of the present article is to summarise and explain the main statements made during the symposium, in terms of challenges and opportunities for medical device industries, in a constantly changing customer and regulatory environment.

PubMed

63. Macromolecular crowding meets oxygen tension in human mesenchymal stem cell culture - A step closer to physiologically relevant in vitro organogenesis. Cigognini D, Gaspar D, Kumar P, Satyam A, Alagesan S, Sanz-Nogues C, Griffin M, O’Brien T, Pandit A, Zeugolis DI. Scientific Reports, Vol. 6, Article Number: 30746, doi: 10.1038/srep30746, 2016.

Abstract

Modular tissue engineering is based on the cells’ innate ability to create bottom-up supramolecular assemblies with efficiency and efficacy still unmatched by man-made devices. Although the regenerative potential of such tissue substitutes has been documented in preclinical and clinical setting, the prolonged culture time required to develop an implantable device is associated with phenotypic drift and/or cell senescence. Herein, we demonstrate that macromolecular crowding significantly enhances extracellular matrix deposition in human bone marrow mesenchymal stem cell culture at both 20% and 2% oxygen tension. Although hypoxia inducible factor – 1α was activated at 2% oxygen tension, increased extracellular matrix synthesis was not observed. The expression of surface markers and transcription factors was not affected as a function of oxygen tension and macromolecular crowding. The multilineage potential was also maintained, albeit adipogenic differentiation was significantly reduced in low oxygen tension cultures, chondrogenic differentiation was significantly increased in macromolecularly crowded cultures and osteogenic differentiation was not affected as a function of oxygen tension and macromolecular crowding. Collectively, these data pave the way for the development of bottom-up tissue equivalents based on physiologically relevant developmental processes.

PubMed

61. Recreating complex pathophysiologies in vitro with extracellular matrix surrogates for anticancer therapeutics screening. Shologu N, Szegezdi E, Lowery A, Kerin M, Pandit A, Zeugolis DI. Drug Discovery Today, Vol. 21, No. 9, pp. 1521-1531, 2016.

Abstract

In vitro tumour models utilise various cancer cells and an appropriate extracellular matrix equivalent to recapitulate the in vivo tumour microenvironment. Three-dimensional tissue surrogates (e.g., decellularised tissue grafts, decellularised monolayers, hydrogels, electrospun fibres and sponges) are increasingly used as alternatives to conventional two-dimensional monolayer cultures to model the tissue environment more faithfully for drug development and screening. Herein, we critically assess the advances and shortfalls of these three-dimensional systems as in vitro models of cancer.

Web of Science

60. Preferential tendon stem cell response to growth factor supplementation. Holladay C, Abbah SA, O’Dowd C, Pandit A, Zeugolis DI. Journal of Tissue Engineering and Regenerative Medicine, Vol. 10, No. 9, pp. 783-798, 2016.

Abstract

Tendon injuries are increasingly prevalent around the world, accounting for more than 100 000 new clinical cases/year in the USA alone. Cell-based therapies have been proposed as a therapeutic strategy, with recent data advocating the use of tendon stem cells (TSCs) as a potential cell source with clinical relevance for tendon regeneration. However, their in vitro expansion is problematic, as they lose their multipotency and change their protein expression profile in culture. Herein, we ventured to assess the influence of insulin-like growth factor 1 (IGF-1), growth and differentiation factor-5 (GDF-5) and transforming growth factor-β1 (TGFβ1) supplementation in TSC culture. IGF-1 preserved multipotency for up to 28 days. Upregulation of decorin and scleraxis expression was observed as compared to freshly isolated cells. GDF-5 treated cells exhibited reduced differentiation along adipogenic and chondrogenic pathways after 28 days, and decorin, scleraxis and collagen type I expression was increased. After 28 days, TGFβ1 supplementation led to increased scleraxis, osteonectin and collagen type II expression. The varied responses to each growth factor may reflect their role in tendon repair, suggesting that: GDF-5 promotes the transition of tendon stem cells towards tenocytes; TGFβ1 induces differentiation along several pathways, including a phenotype indicative of fibrocartilage or calcified tendon, common problems in tendon healing; and IGF-1 promotes proliferation and maintenance of TSC phenotypes, thereby creating a population sufficient to have a beneficial effect.

PubMed

58. Progress in corneal stromal repair – From tissue grafts and biomaterials to modular supramolecular tissue-like assemblies. Kumar P, Pandit A, Zeugolis DI. Advanced Materials, Vol. 28, No. 27, pp. 5381-5399, 2016.

Abstract

Corneal injuries and degenerative conditions have major socioeconomic consequences, given that in most cases, they result in blindness. In the quest of the ideal therapy, tissue grafts, biomaterials, and modular engineering approaches are under intense investigation. Herein, advancements and shortfalls are reviewed and future perspectives for these therapeutic strategies discussed

PubMed

56. Scaffold and scaffold-free self-assembled systems in regenerative medicine. Thomas D, Gaspar D, Sorushanova A, Milcovich G, Spanoudes K, Mullen AM, O’Brien T, Pandit A, Zeugolis DI. Biotechnology and Bioengineering, Vol. 113, No. 6, pp. 1155-1163, 2016.

Abstract

Self-assembly in tissue engineering refers to the spontaneous chemical or biological association of components to form a distinct functional construct, reminiscent of native tissue. Such self-assembled systems have been widely used to develop platforms for the delivery of therapeutic and/or bioactive molecules and various cell populations. Tissue morphology and functional characteristics have been recapitulated in several self-assembled constructs, designed to incorporate stimuli responsiveness and controlled architecture through spatial confinement or field manipulation. In parallel, owing to substantial functional properties, scaffold-free cell-assembled devices have aided in the development of functional neotissues for various clinical targets. Herein, we discuss recent advancements and future aspirations in scaffold and scaffold-free self-assembled devices for regenerative medicine purposes.

PubMed

55. Co-transfection of decorin and interleukin-10 modulates pro-fibrotic extracellular matrix gene expression in human tenocyte culture. Abbah SA, Thomas D, Browne S, O’Brien T, Pandit A, Zeugolis DI. Scientific Reports, Vol. 6, Article Number: 20922, doi: 10.1038/srep20922, 2016.

Abstract

Extracellular matrix synthesis and remodelling are driven by increased activity of transforming growth factor beta 1 (TGF-β1). In tendon tissue repair, increased activity of TGF-β1 leads to progressive fibrosis. Decorin (DCN) and interleukin 10 (IL-10) antagonise pathological collagen synthesis by exerting a neutralising effect via downregulation of TGF-β1. Herein, we report that the delivery of DCN and IL-10 transgenes from a collagen hydrogel system supresses the constitutive expression of TGF-β1 and a range of pro-fibrotic extracellular matrix genes.

PubMed

52. The influence of porosity and pore shape on structural, mechanical and biological properties of poly ε-caprolactone electro-spun fibrous scaffolds. Fuller KP, Gaspar D, Delgado LM, Pandit A, Zeugolis DI. Nanomedicine (London, England), Vol. 11, No. 9, pp. 1031-1040, 2016.

Abstract

BACKGROUND:

Electro-spun scaffolds are utilized in a diverse spectrum of clinical targets, with an ever-increasing quantity of work progressing to clinical studies and commercialization. The limited number of conformations in which the scaffolds can be fabricated hampers their wide acceptance in clinical practice.

MATERIALS & METHODS:

Herein, we assessed a single-strep fabrication process for predesigned electro-spun scaffold preparation and the ramifications of the introduction of porosity (0, 30, 50, 70%) and pore shape (circle, rhomboid, square) on structural, mechanical (tensile and ball burst) and biological (dermal fibroblast and THP-1) properties.

RESULTS:

The collector design did not affect the fibrous nature of the scaffold. Modulation of the porosity and pore shape offered control over the mechanical properties of the scaffolds. Neither the porosity nor the pore shape affected cellular (dermal fibroblast and THP-1) response.

CONCLUSION:

Overall, herein we provide evidence that electro-spun scaffolds of controlled architecture can be fabricated with fibrous fidelity, adequate mechanical properties and acceptable cytocompatibility for a diverse range of clinical targets.

PubMed

51. Biophysical and biological characterisation of collagen / resilin-like protein composite fibres. Sanami M, Shtein Z, Sweeney I, Sorushanova A, Rivkin A, Miraftab M, Shoseyov O, O’Dowd C, Mullen AM, Pandit A, Zeugolis DI. Biomedical Materials, Vol. 10, No. 6, pp. 065005, 2015

Abstract

Collagen type I, in various physical forms, is widely used in tissue engineering and regenerative medicine. To control the mechanical properties and biodegradability of collagen-based devices, exogenous cross-links are introduced into the 3D supramolecular structure. However, potent cross-linking methods are associated with cytotoxicity, whilst mild cross-linking methods are associated with suboptimal mechanical resilience. Herein, we assessed the influence of resilin, a super-elastic and highly stretchable protein found within structures in arthropods where energy storage and long-range elasticity are needed, on the biophysical and biological properties of mildly cross-linked extruded collagen fibres. The addition of resilin-like protein in the 4-arm poly(ethylene glycol) ether tetrasuccinimidyl glutarate cross-linked collagen fibres resulted in a significant increase of stress and strain at break values and a significant decrease of modulus values. The addition of resilin-like protein did not compromise cell metabolic activity and DNA concentration. All groups are supported parallel to the longitudinal fibre axis cell orientation. Herein we provide evidence that the addition of resilin-like protein in mildly cross-linked collagen fibres improves their biomechanical properties, without jeopardising their biological properties

PubMed

49. Harnessing hierarchical nano- and micro- fabrication technologies for musculoskeletal tissue engineering. Abbah SA, Delgado LM, Azeem A, Fuller K, Shologu N, Keeney M, Biggs MJ, Pandit A, Zeugolis DI. Advanced Healthcare Materials, Vol. 4, No. 16, pp. 2488-2499, 2015.

Abstract

Cells within a tissue are able to perceive, interpret and respond to the biophysical, biomechanical, and biochemical properties of the 3D extracellular matrix environment in which they reside. Such stimuli regulate cell adhesion, metabolic state, proliferation, migration, fate and lineage commitment, and ultimately, tissue morphogenesis and function. Current scaffold fabrication strategies in musculoskeletal tissue engineering seek to mimic the sophistication and comprehensiveness of nature to develop hierarchically assembled 3D implantable devices of different geometric dimensions (nano- to macrometric scales) that will offer control over cellular functions and ultimately achieve functional regeneration. Herein, advances and shortfalls of bottom-up (self-assembly, freeze-drying, rapid prototype, electrospinning) and top-down (imprinting) scaffold fabrication approaches, specific to musculoskeletal tissue engineering, are discussed and critically assessed.

PubMed

48. Data on in vitro and in vivo cell orientation on substrates with different topographies. English A, Azeem A, Spanoudes K, Jones E, Tripathi, B, Basu N, McNamara K, Tofail SAM, Rooney N, Riley G, O'Riordan A, Cross G, Hutmacher D, Biggs M, Pandit A, Zeugolis DI. Data in Brief, Vol. 5, pp. 379-382, 2015.

Abstract

This data article contains data related to the research article entitled “Substrate topography: A valuable in vitro tool, but a clinical red herring for in vivo tenogenesis” [1]. We report measurements on tenocyte viability, metabolic activity and proliferation on substrates with different topographies. We also report the effect of substrates with different topographies on host cells in a subcutaneous model.

PubMed

47. Effects of polydopamine functionalization on boron nitride nanotube dispersion and cytocompatibility. Fernandez-Yague MA, Larrañaga A, Gladkovskaya O, Stanley A, Tadayyon G, Guo Y, Sarasua JR, Tofail SA, Zeugolis DI, Pandit A, Biggs MJ. Bioconjugate Chemistry.

Abstract

Boron nitride nanotubes (BNNTs) have unique physical properties, of value in biomedical applications; however, their dispersion and functionalization represent a critical challenge in their successful employment as biomaterials. In the present study, we report a process for the efficient disentanglement of BNNTs via a dual surfactant/polydopamine (PD) process. High-resolution transmission electron microscopy (HR-TEM) indicated that individual BNNTs become coated with a uniform PD nanocoating, which significantly enhanced dispersion of BNNTs in aqueous solutions. Furthermore, the cytocompatibility of PD-coated BNNTs was assessed in vitro with cultured human osteoblasts (HOBs) at concentrations of 1, 10, and 30 μg/mL and over three time-points (24, 48, and 72 h). In this study it was demonstrated that PD-functionalized BNNTs become individually localized within the cytoplasm by endosomal escape and that concentrations of up to 30 μg/mL of PD-BNNTs were cytocompatible in HOBs cells following 72 h of exposure.

PubMed

46. The influence of poly(ethylene glycol) ether tetrasuccinimidyl glutarate on the structural, physical, and biological properties of collagen fibers. Sanami M, Sweeney I, Shtein Z, Meirovich S, Sorushanova A, Mullen AM, Miraftab M, Shoseyov O, O'Dowd C, Pandit A, Zeugolis DI. Journal of Biomedical Materials Research Part B: Applied Biomaterials

Abstract

Tendon injuries are increasingly prevalent around the world, accounting for more than 100 000 new clinical cases/year in the USA alone. Cell-based therapies have been proposed as a therapeutic strategy, with recent data advocating the use of tendon stem cells (TSCs) as a potential cell source with clinical relevance for tendon regeneration. However, their in vitro expansion is problematic, as they lose their multipotency and change their protein expression profile in culture. Herein, we ventured to assess the influence of insulin-like growth factor 1 (IGF-1), growth and differentiation factor-5 (GDF-5) and transforming growth factor-β1 (TGFβ1) supplementation in TSC culture. IGF-1 preserved multipotency for up to 28 days. Upregulation of decorin and scleraxis expression was observed as compared to freshly isolated cells. GDF-5 treated cells exhibited reduced differentiation along adipogenic and chondrogenic pathways after 28 days, and decorin, scleraxis and collagen type I expression was increased. After 28 days, TGFβ1 supplementation led to increased scleraxis, osteonectin and collagen type II expression. The varied responses to each growth factor may reflect their role in tendon repair, suggesting that: GDF-5 promotes the transition of tendon stem cells towards tenocytes; TGFβ1 induces differentiation along several pathways, including a phenotype indicative of fibrocartilage or calcified tendon, common problems in tendon healing; and IGF-1 promotes proliferation and maintenance of TSC phenotypes, thereby creating a population sufficient to have a beneficial effect.

PubMed

45. Substrate topography: A valuable in vitro tool, but a clinical red herring for in vivo tenogenesis. English A, Azeem A, Spanoudes K, Jones E, Tripathi B, Basu N, McNamara K, Tofail SA, Rooney N, Riley G, O'Riordan A, Cross G, Hutmacher D, Biggs M, Pandit A, Zeugolis DI. Acta Biomaterialia, Vol. 27, pp. 3-12, 2015.

Abstract

Controlling the cell-substrate interactions at the bio-interface is becoming an inherent element in the design of implantable devices. Modulation of cellular adhesion in vitro, through topographical cues, is a well-documented process that offers control over subsequent cellular functions. However, it is still unclear whether surface topography can be translated into a clinically functional response in vivo at the tissue/device interface. Herein, we demonstrated that anisotropic substrates with a groove depth of ∼317nm and ∼1988nm promoted human tenocyte alignment parallel to the underlying topography in vitro. However, the rigid poly(lactic-co-glycolic acid) substrates used in this study upregulated the expression of chondrogenic and osteogenic genes, indicating possible tenocyte trans-differentiation. Of significant importance is that none of the topographies assessed (∼37nm, ∼317nm and ∼1988nm groove depth) induced extracellular matrix orientation parallel to the substrate orientation in a rat patellar tendon model. These data indicate that two-dimensional imprinting technologies are useful tools for in vitro cell phenotype maintenance, rather than for organised neotissue formation in vivo, should multifactorial approaches that consider both surface topography and substrate rigidity be established.

STATEMENT OF SIGNIFICANCE:

Herein, we ventured to assess the influence of parallel groves, ranging from nano- to micro-level, on tenocytes response in vitro and on host response using a tendon and a subcutaneous model. In vitro analysis indicates that anisotropically ordered micro-scale grooves, as opposed to nano-scale grooves, maintain physiological cell morphology. The rather rigid PLGA substrates appeared to induce trans-differentiation towards chondrogenic and/or steogenic lineage, as evidence by TILDA gene analysis. In vivo data in both tendon and subcutaneous models indicate that none of the substrates induced bidirectional host cell and tissue growth. Collective, these observations indicate that two-dimensional imprinting technologies are useful tools for in vitro cell phenotype maintenance, rather than for directional neotissue formation, should multifactorial approaches that consider both surface topography and substrate rigidity be established.

PubMed

44. An academic, clinical and industrial update on electrospun, additive manufactured and imprinted medical devices. Ryan CN, Fuller KP, Larrañaga A, Biggs M, Bayon Y, Sarasua JR, Pandit A, Zeugolis DI. Expert Review of Medical Devices, Vol. 12, No. 5, pp. 601-612, 2015.

Abstract

Electrospinning, additive manufacturing and imprint lithography scaffold fabrication technologies have attracted great attention in biomedicine, as they allow production of two- and three- dimensional constructs with tuneable topographical and geometrical features. In vitro data demonstrate that electrospun and imprinted substrates offer control over permanently differentiated and stem cell function. Advancements in functionalisation strategies have further enhanced the bioactivity and reparative capacity of electrospun and additive manufactured devices, as has been evidenced in several preclinical models. Despite this overwhelming success in academic setting, only a few technologies have reached the clinic and only a fraction of them have become commercially available products.

PubMed

42. Glycosaminoglycans in tendon physiology, pathophysiology, and therapy. Ryan CN, Sorushanova A, Lomas AJ, Mullen AM, Pandit A, Zeugolis DI. Bioconjugate Chemistry, Vol. 26, No. 7, pp. 1237-1251, 2015.

Abstract

Although glycosaminoglycans constitute a minor portion of native tissues, they play a crucial role in various physiological processes, while their abnormal expression is associated with numerous pathophysiologies. Glycosaminoglycans have become increasingly prevalent in biomaterial design for tendon repair, given their low immunogenicity and their inherent capacity to stimulate the regenerative processes, while maintaining resident cell phenotype and function. Further, their incorporation into three-dimensional scaffold conformations significantly improves their mechanical properties, while reducing the formation of peritendinous adhesions. Herein, we discuss the role of glycosaminoglycans in tendon physiology and pathophysiology and the advancements achieved to date using glycosaminoglycan-functionalized scaffolds for tendon repair and regeneration. It is evidenced that glycosaminoglycan functionalization has led to many improvements in tendon tissue engineering and it is anticipated to play a pivotal role in future reparative therapies.

PubMed

41. The influence of anisotropic nano- to micro-topography on in vitro and in vivo osteogenesis. Azeem A, English A, Kumar P, Satyam A, Biggs M, Jones E, Tripathi B, Basu N, Henkel J, Vaquette C, Rooney N, Riley G, O'Riordan A, Cross G, Ivanovski S, Hutmacher D, Pandit A, Zeugolis D. Nanomedicine,Vol. 10, No. 5, pp. 693-711, 2015.

Abstract

AIM: Topographically modified substrates are increasingly used in tissue engineering to enhance biomimicry. The overarching hypothesis is that topographical cues will control cellular response at the cell-substrate interface.

MATERIALS & METHODS: The influence of anisotropically ordered poly(lactic-co-glycolic acid) substrates (constant groove width of ~1860 nm; constant line width of ~2220 nm; variable groove depth of ~35, 306 and 2046 nm) on in vitro and in vivo osteogenesis were assessed.

RESULTS & DISCUSSION: We demonstrate that substrates with groove depths of approximately 306 and 2046 nm promote osteoblast alignment parallel to underlined topography in vitro. However, none of the topographies assessed promoted directional osteogenesis in vivo.

CONCLUSION: 2D imprinting technologies are useful tools for in vitro cell phenotype maintenance.

PubMed

40. Macromolecularly crowded in vitro microenvironments accelerate the production of extracellular matrix-rich supramolecular assemblies. Kumar P, Satyam A, Fan X, Collin E, Rochev Y, Rodriguez BJ, Gorelov A, Dillon S, Joshi L, Raghunath M, Pandit A, Zeugolis DI. Scientific Reports, Vol. 5, Article 8729, 2015.

Abstract

Therapeutic strategies based on the principles of tissue engineering by self-assembly put forward the notion that functional regeneration can be achieved by utilising the inherent capacity of cells to create highly sophisticated supramolecular assemblies. However, in dilute ex vivo microenvironments, prolonged culture time is required to develop an extracellular matrix-rich implantable device. Herein, we assessed the influence of macromolecular crowding, a biophysical phenomenon that regulates intra- and extra-cellular activities in multicellular organisms, in human corneal fibroblast culture. In the presence of macromolecules, abundant extracellular matrix deposition was evidenced as fast as 48 h in culture, even at low serum concentration. Temperature responsive copolymers allowed the detachment of dense and cohesive supramolecularly assembled living substitutes within 6 days in culture. Morphological, histological, gene and protein analysis assays demonstrated maintenance of tissue-specific function. Macromolecular crowding opens new avenues for a more rational design in engineering of clinically relevant tissue modules in vitro.

PubMed

38. Progress in cell-based therapies for tendon repair. Gaspar D, Spanoudes K, Holladay C, Pandit A, Zeugolis D. Advanced Drug Delivery Reviews, Vol. 84, pp. 240-256, 2015.

Abstract

The last decade has seen significant developments in cell therapies, based on permanently differentiated, reprogrammed or engineered stem cells, for tendon injuries and degenerative conditions. In vitro studies assess the influence of biophysical, biochemical and biological signals on tenogenic phenotype maintenance and/or differentiation towards tenogenic lineage. However, the ideal culture environment has yet to be identified due to the lack of standardised experimental setup and readout system. Bone marrow mesenchymal stem cells and tenocytes/dermal fibroblasts appear to be the cell populations of choice for clinical translation in equine and human patients respectively based on circumstantial, rather than on hard evidence. Collaborative, inter- and multi-disciplinary efforts are expected to provide clinically relevant and commercially viable cell-based therapies for tendon repair and regeneration in the years to come.

PubMed

37. Accelerated development of supramolecular corneal stromal-like assemblies from corneal fibroblasts in the presence of macromolecular crowders. Kumar P, Satyam A, Fan X, Rochev Y, Rodriguez BJ, Gorelov A, Joshi L, Raghunath M, Pandit A, Zeugolis DI. Tissue Engineering Part C: Methods, Vol. 21, No. 7, pp. 660-670, 2015.

Abstract

Tissue engineering by self-assembly uses the cells’ secretome as a regeneration template and biological factory of trophic factors. Despite the several advantages that have been witnessed in preclinical and clinical settings, the major obstacle for wide acceptance of this technology remains the tardy extracellular matrix formation. In this study, we assessed the influence of macromolecular crowding (MMC)/excluding volume effect, a biophysical phenomenon that accelerates thermodynamic activities and biological processes by several orders of magnitude, in human corneal fibroblast (HCF) culture. Our data indicate that the addition of negatively charged galactose derivative (carrageenan) in HCF culture, even at 0.5% serum, increases by 12-fold tissue-specific matrix deposition, while maintaining physiological cell morphology and protein/gene expression. Gene analysis indicates that a glucose derivative (dextran sulfate) may drive corneal fibroblasts toward a myofibroblast lineage. Collectively, these results indicate that MMC may be suitable not only for clinical translation and commercialization of tissue engineering by self-assembly therapies, but also for the development of in vitro pathophysiology models.

PubMed

36. To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices. Delgado LM, Bayon Y, Pandit A, Zeugolis DI. Tissue Engineering Part B: Reviews, Vol. 21, No. 3, pp. 298-313, 2015.

Abstract

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

PubMed

35. The past, present and future in scaffold-based tendon treatments. Lomas AJ, Ryan CN, Sorushanova A, Shologu N, Sideri AI, Tsioli V, Fthenakis GC, Tzora A, Skoufos I, Quinlan LR, O'Laighin G, Mullen AM, Kelly JL, Kearns S, Biggs M, Pandit A, Zeugolis DI. Advanced Drug Delivery Reviews, Vol. 84, pp. 257-277, 2015

Abstract

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

PubMed

34. Biomimetic approaches in bone tissue engineering: Integrating biological and physicomechanical strategies. Fernandez-Yague MA, Abbah SA, McNamara L, Zeugolis DI, Pandit A, Biggs MJ. Advanced Drug Delivery Reviews, Vol. 84, pp. 1-29, 2015.

Abstract

The development of responsive biomaterials capable of demonstrating modulated function in response to dynamic physiological and mechanical changes in vivo remains an important challenge in bone tissue engineering. To achieve long-term repair and good clinical outcomes, biologically responsive approaches that focus on repair and reconstitution of tissue structure and function through drug release, receptor recognition, environmental responsiveness and tuned biodegradability are required. Traditional orthopedic materials lack biomimicry, and mismatches in tissue morphology, or chemical and mechanical properties ultimately accelerate device failure. Multiple stimuli have been proposed as principal contributors or mediators of cell activity and bone tissue formation, including physical (substrate topography, stiffness, shear stress and electrical forces) and biochemical factors (growth factors, genes or proteins). However, optimal solutions to bone regeneration remain elusive. This review will focus on biological and physicomechanical considerations currently being explored in bone tissue engineering.

PubMed

33. A barbed suture repair for flexor tendons: a novel technique with no exposed barbs. Joyce CW, Sugrue C, Chan JC, Delgado L, Zeugolis D, Carroll SM, Kelly JL. Plastic and Reconstructive Surgery Global Open, Vol 2, No. 10, pp. 237, 2014.

Abstract

BACKGROUND: Barbed suture technology has shown promise in flexor tendon repairs, as there is an even distribution of load and the need for a knot is eliminated. We propose that a quick and simple, novel, barbed technique without any exposed barbs on the tendon surface has comparable strength and a smaller cross-sectional area at the repair site than traditional methods of repair.

METHODS: Forty porcine flexor tendons were randomized to polybutester 4-strand barbed repair or to 4-strand Adelaide monofilament repair. The cross-sectional area was measured before and after repair. Biomechanical testing was carried out and 2-mm gap formation force, ultimate strength of repair, and method of failure were recorded.

RESULTS: The mean ultimate strength of the barbed repairs was 54.51 ± 17.9 while that of the Adelaide repairs was 53.17 ± 16.35. The mean 2-mm gap formation force for the barbed group was 44.71 ± 17.86 whereas that of the Adelaide group was 20.25 ± 4.99. The postrepair percentage change in cross-sectional area at the repair site for the Adelaide group and barbed group was 12.0 ± 2.3 and 4.6 ± 2.8, respectively.

CONCLUSIONS: We demonstrated that a 4-strand knotless, barbed method attained comparable strength to that of the traditional Adelaide repair technique. The barbed method had a significantly reduced cross-sectional area at the repair site compared with the Adelaide group. The 2-mm gap formation force was less in the barbed group than the Adelaide group. Barbed repairs show promise for tendon repairs; this simple method warrants further study in an animal model.

PubMed

32. Assessment of stem cell carriers for tendon tissue engineering in pre-clinical models. Abbah SA, Spanoudes K, O'Brien T, Pandit A, Zeugolis DI. Stem Cell Research & Therapy, Vol. 5, No. 2, pp. 38, 2014.

Abstract

Tendon injuries are prevalent and problematic, especially among young and otherwise healthy individuals. The inherently slow innate healing process combined with the inevitable scar tissue formation compromise functional recovery, imposing the need for the development of therapeutic strategies. The limited number of low activity/reparative capacity tendon-resident cells has directed substantial research efforts towards the exploration of the therapeutic potential of various stem cells in tendon injuries and pathophysiologies. Severe injuries require the use of a stem cell carrier to enable cell localisation at the defect site. The present study describes advancements that injectable carriers, tissue grafts, anisotropically orientated biomaterials, and cell-sheets have achieved in preclinical models as stem cell carriers for tendon repair.

PubMed

31. A shape-controlled tuneable microgel platform to modulate angiogenic paracrine responses in stem cells. Thomas D, Fontana G, Chen X, Sanz-Nogués C, Zeugolis DI, Dockery P, O'Brien T, Pandit A. Biomaterials, Vol. 35, No. 31, pp. 8757-8766, 2014.

Abstract

Development of cell delivery platforms have been driven based on an empirical cytoprotective design. While cell-matrix and cell-cell interactions that influence biochemical effects beyond survival has been limited and overshadowed in an effort to incrementally improve biomimicking properties of the tissue-engineered constructs. Here we demonstrate fabrication of a shape controlled 3D type-I collagen-based microgel platform that can be tuned to modulate angiogenic paracrine- ‘angiocrine’ responses of human mesenchymal stem cells (hMSCs). Furthermore, these microgels were characterized as a 3D cell culture tool to assess optimal biological response as a function of cell-matrix and cell-cell interactions. Finally, optimised hMSC embedded microgels were shown to induce vascular repair and functional improvement in vivo in a mouse model of hind-limb ischemia. The approach described here in designing a tuneable cell delivery platform using naturally occurring extracellular matrix molecules highlights the need for highly customised matrices with an array of self-assembling proteins that dictate specific cell function resembling the native tissue of interest for repair.

PubMed

30. The biophysical, biochemical, and biological toolbox for tenogenic phenotype maintenance in vitro. Spanoudes K, Gaspar D, Pandit A, Zeugolis DI. Trends in Biotechnology, Vol. 32, No. 9, pp. 474-482, 2014.

Abstract

Tendon injuries constitute an unmet clinical need, with 3 to 5 million new incidents occurring annually worldwide. Tissue grafting and biomaterial-based approaches fail to provide environments that are conducive to regeneration; instead they lead to nonspecific cell adhesion and scar tissue formation, which collectively impair functionality. Cell based therapies may potentially recover native tendon function, if tenocyte trans-differentiation can be evaded and stem cell differentiation towards tenogenic lineage is attained. To this end, recreating an artificial in vivo tendon niche by engineering functional in vitro microenvironments is a research priority. Clinically relevant cell based therapies for tendon repair and regeneration could be created using tools that harness biophysical beacons (surface topography, mechanical loading), biochemical cues (oxygen tension), and biological signals (growth factors).

PubMed

29. Influence of sterilisation methods on collagen-based devices stability and properties. Delgado LM, Pandit A, Zeugolis DI. Expert Review of Medical Devices, Vol. 11, No. 3, pp. 305-314, 2014.

Abstract

Sterilisation is essential for any implantable medical device in order to prevent infection in patients. The selection of the most appropriate sterilisation method depends on the nature and the physical state of the material to be sterilised; the influence of the sterilisation method on the properties of the device; and the type of the potential contaminant. In this context, herein we review the influence of ethylene oxide, γ-irradiation, e-beam irradiation, gas plasma, peracetic acid and ethanol on structural, biomechanical, biochemical and biological properties of collagen-based devices. Data to-date demonstrate that chemical approaches are associated with cytotoxicity, whilst physical methods are associated with degradation, subject to the device physical characteristics. Thus, the sterilisation method of choice is device dependent.

PubMed

28. Macromolecular crowding meets tissue engineering by self-assembly: a paradigm shift in regenerative medicine. Satyam A, Kumar P, Fan X, Gorelov A, Rochev Y, Joshi L, Peinado H, Lyden D, Thomas B, Rodriguez B, Raghunath M, Pandit A, Zeugolis D. Advanced Materials, Vol. 26, No. 19, pp. 3024-3034, 2014.

Abstract

MMC, the addition of inert polydispersed macromolecules in the culture media, effectively emulates the dense in vivo extracellular space, resulting in amplified deposition of ECM in vitro and subsequent production of cohesive, ECM-rich living substitutes.

PubMed

27. The multifaceted potential of electro-spinning in regenerative medicine. Fuller K, Pandit A, Zeugolis DI. Pharmaceutical Nanotechnology. Vol. 2, No. 1, pp. 23-34, 2014.

Abstract

The increased interest in nanotechnology has resulted in an intense investigation and development of nanofabrication methods. Among the bottom-up approaches, electro-spinning has attracted great interest in recent years. The popularity of electro-spinning lays on the fact that it is a relatively simple and economic technique that enables production of large quantities of nano- to micro-meter range fibrous materials with various morphologies and architectural features. The versatility of electro-spinning is evidenced by the range of applications being utilised, including filtration, textiles, batteries, and tissue engineering and regenerative medicine. Specifically to biomedical applications, advancements in the electro-spinning setup have allowed the development of electro-spun mats that closely imitate native extracellular matrix assemblies and provide opportunities for localised and sustained delivery of therapeutics. Herein, we are discussing different electro-spinning setups and their distinct benefits for regenerative medicine applications.

Bentham Science

26. Surface hierarchical porosity in poly (ε-caprolactone) membranes with potential applications in tissue engineering prepared by foaming in supercritical carbon dioxide. Pintado-Sierra M, Delgado L, Aranaz I, Marcos-Fernandez A, Reinecke H, Gallardo A, Zeugolis D, Elvira C. The Journal of Supercritical Fluids, Vol. 95, pp. 273-284, 2014.

Abstract

This article describes the preparation of porous poly (¿-caprolactone), PCL, membranes by supercritical CO2 (SCCO2) foaming, displaying surface hierarchical macroporosity which could be tailored by careful control of the pressure, in the range of 150¿250 bar, and depressurization processes in several steps, showing also pore interconnectivity between both membrane faces. The membranes exhibited two distinct types of surface macroporosity, the larger with diameter sizes of 300¿500 ¿m were surrounded by and also composed of smaller pores of 15¿50 ¿m (same size as inner pores). Membranes were prepared by solvent casting and submitted to different SCCO2 foaming. Parameters such as membrane thickness, CO2 flow, foaming time, pressure, temperature and the depressurization processes (rate and profiles), were varied to determine their influence on final porosity and to decipher which parameters were the most critical ones in terms of surface hierarchical pore organization. No remarkable changes in PCL crystallinity were found when membranes were processed under SCCO2. Finally, biological evaluation of the porous membranes was achieved by seeding human skin fibroblasts on the prepared membranes. The results, in terms of cell adhesion, spreading, proliferation and metabolic activity indicate that these membranes could hold promise for the fabrication of meshes with controlled porosity for tissue engineering applications.

ScienceDirect

25. In vitro evaluation of Ficoll-enriched and genipin-stabilised collagen scaffolds. Satyam A, Subramanian GS, Raghunath M, Pandit A, Zeugolis DI Journal of Tissue Engineering and Regenerative Medicine, Vol. 8, No. 3, pp. 233-241, 2014

Abstract

Polysaccharides are frequently incorporated into scaffolds for tissue engineering applications to improve mechanical and biological properties. We evaluated the influence of a Ficoll® scaffold on collagen films, a scaffold that is extensively used for soft and hard tissue repair. To avoid cytotoxicity issues associated with chemical reagents, the influence of genipin, a naturally occurring crosslinking agent, was assessed. Ultra-structural level collagen films formed with and without Ficoll showed a fine fibrillar structure whereas genipin crosslinked films showed a coarse fibrillar and partially nodular structure. In contrast, glutaraldehyde crosslinked films lost their fibrillar pattern. Crosslinking significantly increased denaturation temperature (p < 0.001), stress (p < 0.0001) and force (p < 0.0001) at break. Collagen/Ficoll and collagen/Ficoll/genipin films showed the highest WI38 fibroblast attachment than any other scaffold (p < 0.003) and significantly greater WI38 fibroblast metabolic activity than other scaffolds (p < 0.001). By day 6. collagen/Ficoll/genipin films also induced higher and more aligned fibronectin matrix deposition than other scaffolds. Overall, this study indicates the suitability of collagen/Ficoll/genipin for tissue engineering applications.

PubMed

24. Engineering in vitro microenvironments for cell based therapies and drug discovery. Cigognini D, Lomas A, Kumar P, Satyam A, English A, Azeem A, Pandit A, Zeugolis D. Drug Discovery Today, Vol. 18, No. 21-22, pp. 1099-1108, 2013.

Abstract

Traditional ex vivo culture setups fail to imitate the native tissue niche, leading to cellular senescence, phenotypic drift, growth arrest and loss of stem cell multipotency. Growing evidence suggests that surface topography, substrate stiffness, mechanical stimulation, oxygen tension and localised density influence cellular functions and longevity, enhance tissue-specific extracellular matrix deposition and direct stem cell differentiation. In this review, we discuss how these cues will facilitate engineering of physiological in vitro microenvironments to enable clinical translation of cell based therapies and development of in vitro models for drug discovery applications.

PubMed

23. Collagen: Finding a solution for the source. Browne S, Zeugolis DI, Pandit A. Tissue Engineering Part A, Vol. 19, No. 13-14, pp. 1491-1494, 2013.

Abstract

Extracellular matrix (ECM)-based scaffolds, through their inherent bioactivity and molecular recognition signals, provide the ideal substrate for tissue engineering and regenerative applications. Collagen, the most abundant ECM protein, has proven itself to be a very versatile material with applications in many fields, including the leather and food industries, cosmetics, drug delivery, and tissue engineering. However, doubts persist about the optimal source of collagen for tissue engineering applications, given possible immunogenicity and disease transmission associated with animal sources and reduced bioactivity and availability of recombinant technologies. In this special edition, an attempt is made to elucidate the advantages of plant-derived human recombinant collagen and its applications in tissue engineering, particularly skin and wound healing. While results are promising, the widespread use of animal-derived collagen means that recombinant technologies may find applications in niche areas.

PubMed

22. The effect of intraluminal contact mediated guidance signals on axonal mismatch during peripheral nerve repair. Daly WT, Yao L, Abu-rub MT, O'Connell C, Zeugolis DI, Windebank AJ, Pandit AS. Biomaterials, Vol. 33, No. 28, pp. 6660-6671, 2012

Abstract

The current microsurgical gold standard for repairing long gap nerve injuries is the autograft. Autograft provides a protective environment for repair and a natural internal architecture, which is essential for regeneration. Current clinically approved hollow nerve guidance conduits allow provision of this protective environment; however they fail to provide an essential internal architecture to the regenerating nerve. In the present study both structured and unstructured intraluminal collagen fibres are investigated to assess their ability to enhance conduit mediated nerve repair. This study presents a direct comparison of both structured and unstructured fibres in vivo. The addition of intraluminal guidance structures was shown to significantly decrease axonal dispersion within the conduit and reduced axonal mismatch of distal nerve targets (p < 0.05). The intraluminal fibres were shown to be successfully incorporated into the host regenerative process, acting as a platform for Schwann cell migration and axonal regeneration. Ultimately the fibres were able to provide a platform for nerve regeneration in a long term regeneration study (16 weeks) and facilitated increased guidance of regenerating axons towards their distal nerve targets.

PubMed

21. Electromechanical properties of dried tendon and isoelectrically focused collagen hydrogels. Denning D, Abu-Rub MT, Zeugolis DI, Habelitz S, Pandit A, Fertala A, Rodriguez BJ. Acta Biomaterialia, Vol. 8, No. 8, pp. 3073-3079, 2012.

Abstract

Assembling artificial collagenous tissues with structural, functional, and mechanical properties which mimic natural tissues is of vital importance for many tissue engineering applications. While the electro-mechanical properties of collagen are thought to play a role in, for example, bone formation and remodeling, this functional property has not been adequately addressed in engineered tissues. Here the electro-mechanical properties of rat tail tendon are compared with those of dried isoelectrically focused collagen hydrogels using piezoresponse force microscopy under ambient conditions. In both the natural tissue and the engineered hydrogel D-periodic type I collagen fibrils are observed, which exhibit shear piezoelectricity. While both tissues also exhibit fibrils with parallel orientations, Fourier transform analysis has revealed that the degree of parallel alignment of the fibrils in the tendon is three times that of the dried hydrogel. The results obtained demonstrate that isoelectrically focused collagen has similar structural and electro-mechanical properties to that of tendon, which is relevant for tissue engineering applications.

PubMed

19. Preferential cell response to anisotropic electro-spun fibrous scaffolds under tension-free conditions. English A, Azeem A, Gaspar DA, Keane K, Kumar P, Keeney M, Rooney N, Pandit A, Zeugolis DI. Journal of Materials Science: Materials in Medicine, Vol. 23, No. 1, pp. 137-148, 2012

Abstract

Anisotropic alignment of collagen fibres in musculoskeletal tissues is responsible for the resistance to mechanical loading, whilst in cornea is responsible for transparency. Herein, we evaluated the response of tenocytes, osteoblasts and corneal fibroblasts to the topographies created through electro-spinning and solvent casting. We also evaluated the influence of topography on mechanical properties. At day 14, human osteoblasts seeded on aligned orientated electro-spun mats exhibited the lowest metabolic activity (P < 0.001). At day 5 and at day 7, no significant difference was observed in metabolic activity of human corneal fibroblasts and bovine tenocytes respectively seeded on different scaffold conformations (P > 0.05). Osteoblasts and corneal fibroblasts aligned parallel to the direction of the aligned orientated electro-spun mats, whilst tenocytes aligned perpendicular to the aligned orientated electro-spun mats. Mechanical evaluation demonstrated that aligned orientated electro-spun fibres exhibited significant higher stress at break values than their random aligned counterparts (P < 0.006) and random orientated electro-spun fibres exhibited significant higher strain at break values than the aligned orientated scaffolds (P < 0.006). While maintaining fibre structure, we also developed a co-deposition method of spraying and electro-spinning, which enables the incorporation of microspheres within the three-dimensional structure of the scaffold.

PubMed

18. A biomaterials approach to peripheral nerve regeneration: bridging the peripheral nerve gap and enhancing functional recovery. Daly W, Yao L, Zeugolis D, Windebank A, Pandit A. Journal of the Royal Society Interface, Vol. 9, No. 67, pp. 202-221, 2012.

Abstract

Microsurgical techniques for the treatment of large peripheral nerve injuries (such as the gold standard autograft) and its main clinically approved alternative–hollow nerve guidance conduits (NGCs)–have a number of limitations that need to be addressed. NGCs, in particular, are limited to treating a relatively short nerve gap (4 cm in length) and are often associated with poor functional recovery. Recent advances in biomaterials and tissue engineering approaches are seeking to overcome the limitations associated with these treatment methods. This review critically discusses the advances in biomaterial-based NGCs, their limitations and where future improvements may be required. Recent developments include the incorporation of topographical guidance features and/or intraluminal structures, which attempt to guide Schwann cell (SC) migration and axonal regrowth towards their distal targets. The use of such strategies requires consideration of the size and distribution of these topographical features, as well as a suitable surface for cell-material interactions. Likewise, cellular and molecular-based therapies are being considered for the creation of a more conductive nerve microenvironment. For example, hurdles associated with the short half-lives and low stability of molecular therapies are being surmounted through the use of controlled delivery systems. Similarly, cells (SCs, stem cells and genetically modified cells) are being delivered with biomaterial matrices in attempts to control their dispersion and to facilitate their incorporation within the host regeneration process. Despite recent advances in peripheral nerve repair, there are a number of key factors that need to be considered in order for these new technologies to reach the clinic.

PubMed

17. Regeneration and repair of tendon and ligament tissue using collagen fibre biomaterials. Kew SJ, Gwynne JH, Enea D, Abu-Rub M, Pandit A, Zeugolis D, Brooks RA, Rushton N, Best SM, Cameron RE. Acta Biomaterialia, Vol. 7, No. 9, pp. 3237-3247, 2011.

Abstract

Collagen fibres are ubiquitous macromolecular assemblies in nature, providing the structures that support tensile mechanical loads within the human body. Aligned type I collagen fibres are the primary structural motif for tendon and ligament, and therefore biomaterials based on these structures are considered promising candidates for mediating regeneration of these tissues. However, despite considerable investigation, there remains no collagen-fibre-based biomaterial that has undergone clinical evaluation for this application. Recent research in this area has significantly enhanced our understanding of these complex and challenging biomaterials, and is reinvigorating interest in the development of such structures to recapitulate mechanical function. In this review we describe the progress to date towards a ligament or tendon regeneration template based on collagen fibre scaffolds. We highlight reports of particular relevance to the development of the underlying biomaterials science in this area. In addition, the potential for tailoring and manipulating the interactions between collagen fibres and biological systems, as hybrid biomaterial-biological ensembles, is discussed in the context of developing novel tissue engineering strategies for tendon and ligament.

PubMed

16. An injectable vehicle for nucleus pulposus cell-based therapy. Collin EC, Grad S, Zeugolis DI, Vinatier CS, Clouet JR, Guicheux JJ, Weiss P, Alini M, Pandit AS. Biomaterials, Vol. 32, No. 11, pp. 2862-2870, 2011.

Abstract

An injectable hydrogel, acting as a reservoir for cell delivery and mimicking the native environment, offers promise for nucleus pulposus (NP) repair and regeneration. Herein, the potential of a stabilised type II collagen hydrogel using poly(ethylene glycol) ether tetrasuccinimidyl glutarate (4S-StarPEG) cross-linker, enriched with hyaluronic acid (HA) was investigated. The optimally stabilised type II collagen hydrogel was determined by assessing free amine groups, resistance to enzymatic degradation, gel point. The potential toxicity of the cross-linker was initially assessed against adipose-derived stem cells (ADSCs). After addition of HA (molar ratio type II collagen:HA 9:0, 9:1, 9:4.5, 9:9) within the hydrogel, the behaviour of the encapsulated NP cells was evaluated using cell proliferation assay, gene expression analysis, cell distribution and cell morphology. A significant decrease (p < 0.05) in the free amine groups of collagen was observed, confirming successful cross-linking. Gelation was independent of the concentration of 4S-StarPEG (8 min at 37 °C). The 1 mm cross-linked hydrogel yielded the most stable after enzymatic degradation (p < 0.05). No toxicity of the 4S-StarPEG was noted for the ADSCs. NP cell viability was high regardless of the concentration of HA (>80%). A cell proliferation was not seen after 14 days in its presence. At a gene expression level, HA did not influence NP cells phenotype after seven days in culture. After seven days in culture, the type I collagen mRNA expression was maintained (p > 0.05). The optimally stabilised and functionalised type II collagen/HA hydrogel system developed in this study shows promise as an injectable reservoir system for intervertebral disc regeneration.

PubMed

15. Nano-textured self-assembled aligned collagen hydrogels promote directional neurite guidance and overcome inhibition by myelin associated glycoprotein. Abu-Rub MT, Billiar KL, van Es MH, Knight A, Rodriguez B, Zeugolis DI, McMahon S, Windebank A, Pandit A. Soft Matter, Vol. 7, No. 6, pp. 2770-2781, 2011.

Abstract

The development of nerve guidance conduits is constantly evolving as the need arises for therapies for spinal cord injury. In addition to providing a path for regrowing axons to reconnect with their appropriate targets, the structural and biochemical cues provided by these conduits should be permissive for directional neurite outgrowth and be protective against inhibition in the vicinity of the injury site. Here, we adapted the use of iso-electric focusing to drive the alignment of supramolecular fibrils into self-assembled collagen hydrogels (300 µm diameter), and tested those hydrogels for the ability to direct and enhance the migration of neurites. Structural characterization revealed anisotropic alignment of nanofibrillar aggregates (20 nm diameter), arranged in micron-scale bundles (1 to 2 µm diameter) similar to the hierarchical size scales observed in native tissues. Neurite outgrowth extended bidirectionally along the axes of aligned hydrogels. Furthermore, it was shown that, as opposed to poly-D-lysine, neurite outgrowth on aligned hydrogels is not inhibited in the presence of myelin-associated glycoprotein (p > 0.05). These results highlight for the first time a structural and biochemical role for iso-electrically aligned collagen hydrogels in controlling neuronal growth, and indicate that the short-term signaling associated with these hydrogels can be used in adjunct therapy following injury to the spinal cord.

Royal Society of Chemistry

14. Amine functionalization of collagen matrices with multifunctional polyethylene glycol systems. Ward J, Kelly J, Wang W, Zeugolis DI, Pandit A. Biomacromolecules, Vol .11, No. 11, pp. 3093-3101, 2010.

Abstract

A method to functionalize collagen-based biomaterials with free amine groups was established in an attempt to improve their potential for tethering of bioactive molecules. Collagen sponges were incorporated with amine-terminated multifunctional polyethylene glycol (PEG) derivatives after N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide and N-hydroxysuccinimide (EDC/NHS) cross-linking. The extent of the incorporation of different amounts and different numbers of active moieties of amine-terminated PEG systems into the collagen scaffolds was evaluated using ninhydrin assay, Fourier transform infrared spectrophotometry (FTIR), collagenase degradation assay, denaturation temperature measurements, and in vitro cell studies. A 3% 8-arm amine-terminated PEG was found to be the minimum required effective concentration to functionalize EDC/NHS stabilized collagen scaffolds. EDC/NHS stabilized scaffolds treated with 3% 8-arm amine-terminated PEG exhibited significantly improved denaturation temperature and resistance to collagenase degradation over non-cross-linked scaffolds (p < 0.002). Biological evaluation using 3T3 cells demonstrated that the produced scaffolds facilitated maintenance of the cells’ morphology, metabolic activity, and ability to proliferate in vitro. Overall, our results indicate that amine-terminated PEG systems can be used as means to enhance the functionality of collagenous structures.

PubMed

13. The physiological relevance of wet versus dry differential scanning calorimetry for biomaterial evaluation: A technical note. Zeugolis DI, Raghunath M. Polymer International, Vol. 59, No. 10, pp. 1403-1407, 2010

Abstract

Collagen and its denatured form, gelatin, have been extensively used as scaffolds for tissue engineering and tissue repair applications. Denaturation temperature, commonly measured using differential scanning calorimetry (DSC), for biomaterial applications is a significant physical property that will determine the stability of a potential implant at body temperature. In order to imitate a clinical setting, DSC should be run under fully hydrated conditions. We show here that for hydrophobic polymers such as poly(ε-caprolactone) and chitosan there is no significant difference between dry and wet DSC operation (p > 0.05). In contrast, for hydrophilic polymers such as collagen, gelatin, poly(ethylene glycol) (40 kDa) and poly(ethylene oxide) (900 kDa) significant differences occur between measurements in the dry and the wet state (p < 0.0011). Moreover, we demonstrate that only when wet DSC is carried out are we able to separate the unique crystalline structure of collagen from its randomly coiled heat-denatured by-product gelatin (p < 0.0005). We therefore recommend running DSC under fully hydrated conditions when the function and properties of a biomaterial are under investigation.

Wiley Online Library

12. Spinal cord injury in vitro: modelling axon growth inhibition. Abu-Rub M, McMahon S, Zeugolis DI, Windebank A, Pandit A. Drug Discovery Today, Vol. 15, No. 11-12, pp. 436-443, 2010.

Abstract

Over the past three decades, tremendous progress has been made in elucidating mechanisms underlying regenerative failure after spinal cord injury and in devising therapeutic approaches to promote functional nerve regeneration. Various in vitro assays have been developed using brain and/or spinal cord neuronal cells to study axon growth in conditions that represent the post-injury environment. This review outlines the current models used to dissect, analyze and manipulate specific aspects of spinal cord injury leading to axon growth inhibition.

PubMed

11. Essential modification of the Sircol Collagen Assay for the accurate quantification of collagen content in complex protein solutions. Lareu RR, Zeugolis DI, Abu-Rub M, Pandit A, Raghunath M. Acta Biomaterialia, Vol. 6, No. 8, pp. 3146-3151, 2010.

Abstract

Collagen contains the unique imino acid hydroxyproline (HyPro), which is involved in the stabilization of this triple helical molecule. The concentration of HyPro is customarily used to calculate the total collagen content in a cell culture environment and in acid hydrolysates of normal and pathophysiological tissues. Radiolabelling, chromatographic and calorimetric assays have been developed over the years for the accurate determination of collagen content through HyPro estimation. Recently, the Sircol Collagen Assay (SCA) has been almost exclusively adopted as the fastest and simplest colorimetric method for the determination of collagen concentration in complex protein solutions. We show here that the colorimetric SCA, which is based on the binding of Sirius red (SR) to collagen, is flawed by interference of non-collagenous proteins (e.g. serum). In fact, we demonstrate that SCA in cell culture systems and tissue hydrolysates results in a dramatic overestimation of collagen content ranging from 3- to 24-fold. In order to rescue this otherwise very practical assay, we introduce a simple purification procedure that allows the removal of interfering non-collagenous proteins from culture media and tissue samples so that accurate measurements with SCA are now possible.

PubMed

10. An in situ and in vitro investigation for the transglutaminase potential in tissue engineering. Zeugolis DI, Panengad PP, Yew ES, Sheppard C, Phan TT, Raghunath M. Journal of Biomedical Materials Research Part A, Vol. 92, No. 4, pp. 1310-1320, 2010.

Abstract

Transglutaminases (TGases) constitute a family of enzymes that stabilize protein assemblies by gamma-glutamyl-epsilon-lysine crosslinks. The role of tissue transglutaminase (TGase 2) in several pathophysiologies, wound healing applications, biomaterials functionalization, and drug delivery systems provides grounds for its use in tissue engineering. Herein, we initially studied the endogenous TGase activity and expression under normal (skin, duodenum, colon, and small bowel) and pathophysiological (keloid scar) conditions on cadaveric human tissues. Successful inhibition was achieved using low concentrations of BOC-DON-QIV-OMe (0.1 mM and 1 mM for normal skin and keloid scar, respectively), iodoacetamide (0.1 mM and 1 mM for normal skin and keloid scar, respectively), and cystamine dihydrochloride (1 mM and 10 mM for normal skin and keloid scar, respectively), whilst di-BOC-cystamine was found ineffective even at 100 mM concentration. Secondly, the addition of exogenous guinea pig liver transglutaminase (gpTGase) onto the inhibited tissues and collagen scaffolds was studied, and results presented advocate its use as potential tissue adhesive and drug delivery tool. However, the investigation of its crosslinking extent using second harmonic generation microscopy and differentially scanning calorimetry revealed rather poor stabilization function. Overall, our study indicates that TGase 2 has a role as a biological glue to consolidate various micro-structural components of tissues and biomaterials.

PubMed

9. The influence of a natural cross-linking agent (Myrica rubra) on the properties of extruded collagen fibres for tissue engineering applications. Zeugolis DI, Paul RG, Attenburrow G. Materials Science and Engineering - Part C, Vol. 30, No. 1, pp. 190-195, 2010.

Abstract

Extruded collagen fibres have been shown to be a competitive biomaterial for both soft and hard tissue repair. The natural cross-linking pathway of collagen does not occur in vitro and consequently reconstituted forms of collagen lack sufficient strength. Numerous cross-linking approaches have been investigated through the years, but still there is no ideal method accepted. The use of plant extracts to cross-link collagen scaffolds has been advocated due to superior mechanical properties. As first herein we investigate the stabilisation effect of Myrica rubra on extruded collagen fibres. Fibres treated with M.rubra exhibited higher denaturation temperature (p < 0.005) and lower enthalpy of denaturation (p < 0.034) than formaldehyde of glutaraldehyde. Uniaxial tensile tests of wet tested fibres revealed j-shape curves similar to those of native tissues. Thin fibres exhibited high stress/low strain graphs, whilst thick fibres yielded low stress/high strain graphs. Cross-linking reduced significantly the fibre diameter (p < 0.005) and increased significantly the stress (p < 0.004) and force (p < 0.001) at break and the modulus at 2.0% strain (p < 0.003). An inverse relationship between stress at break and fibre diameter was observed for every treatment. Overall, our findings demonstrate the potential of M.rubra in stabilisation of collagen-based materials for tissue engineering applications.

ScienceDirect

8. Extruded collagen fibres for tissue-engineering applications: influence of collagen concentration and NaCl amount. Zeugolis DI, Paul RG, Attenburrow G. Journal of Biomaterials Science, Polymer Edition, Vol. 20, No. 2, pp. 219-234, 2009.

Abstract

Extruded collagen fibres have been shown to be a competitive biomaterial for tissue-engineering applications. Since different tissues are coming in different textures, as far as it is concerned their fibre diameter and consequently their mechanical properties, herein we aim to investigate the influence of the collagen concentration and the amount of NaCl on the properties of these fibres. Scanning electron microscopy study revealed that the substructure of the collagen fibres was the same, regardless of the treatment. The thermal properties were found to be independent of the collagen concentration or the amount of NaCl utilized (P > 0.05). An inversely proportional relationship between dry fibre diameter and stress at break was observed. Increasing the collagen concentration yielded fibres with significant higher diameter (P < 0.002), strain (P < 0.009) and force (P < 0.001) values, whilst the stress (P < 0.008) and modulus (P < 0.009) values were decreased. For the fabrication of fibres with reproducible properties, 20% NaCl was found to be the optimum. Overall, reconstituted collagen fibres were produced with properties similar to native or synthetic fibres to suit a wide range of tissue-engineering applications.

PubMed

7. Cross-linking of extruded collagen fibers -- A biomimetic three-dimensional scaffold for tissue engineering applications. Zeugolis DI, Paul GR, Attenburrow G. Journal of Biomedical Materials Research Part A, Vol. 89, No. 4, pp. 895-908.

Abstract

The repair of tissue defects remains a challenging clinical problem. Extruded collagen fibers comprise a promising scaffold for anterior cruciate ligament and tendon reconstruction; however the engineering of these fibers has still to be improved to bring this material to clinical practice. In this study, for the first time we investigated the influence of a wide range of cross-linking approaches (chemical, physical, and biological) on the properties of these fibers. Ultrastructural evaluation revealed a closely packed interfiber structure independent of the cross-linking method employed. The thermal properties were dependent on the cross-linking method employed and closely matched native tissues. The stress-strain curves were found to depend on the water content of the fibers, which was influenced by the cross-linking method. An inversely proportional relationship between both dry and wet fiber diameter and stress at break was found, which indicates that tailored-made biomaterials can be produced. Overall, the chemical stabilizations were more potent than both physical and biological approaches. Bifunctional agents such as hexamethylene diisocyanate and ethylene glycol diglycidyl ether or agents that promote matrix formation such as glutaraldehyde produced fibers with properties similar to those of native or synthetic fibers to suit a wide range of tissue engineering applications.

PubMed

6. Collagen solubility testing, a quality assurance step for reproducible electro-spun nano-fibre fabrication. A technical note. Zeugolis DI, Li B, Lareu RR, Chan CK, Raghunath M. Journal of Biomaterials Science, Polymer Edition, Vol. 19, No. 10, pp. 1307-1317, 2008.

Abstract

Collagen is the main component of the extra-cellular matrix and has been utilised for numerous clinical applications in many forms and products. However, since collagen remains a natural animal-derived biopolymer, variation between batches should be addressed and minimised to ensure reproducibility of the fabrication process. Recently, electro-spinning of collagen has been introduced as a leading technique for the production of bio-mimetic nano-scale scaffolds for tissue-engineering applications. However, no protocols are available that would allow comparisons of the quality of different collagen raw materials prior to the electro-spinning process. In order to bridge this gap we assessed the solubility of various freeze-dried collagens in 0.5 M acetic acid and analysed the solved collagen by gel electrophoresis. We show that raw material of limited solubility in acetic acid will not render high quality electro-spun nano-fibres using hexafluoropropanol. In particular, insoluble collagen directly failed to produce nano-fibres, collagen of reduced solubility produced fused nano-fibres with limited inter-nano-fibre space, whilst purified type-I collagen of high solubility produced smooth, reproducible nano-fibres. Gel electrophoresis confirmed the amount of solubility, as well as qualitative differences in terms of collagen cross-links and collagen types. We recommend this simple and fast step to save costs and to enhance control over the electro-spinning process of collagen. Furthermore, we believe that the solubility test should be introduced prior to any collagenous matrix preparation in order to ensure reproducibility and accuracy.

PubMed

5. Post-self-assembly experimentation on extruded collagen fibres for tissue engineering applications. Zeugolis DI, Paul RG, Attenburrow G. Acta Biomaterialia, Vol. 4, No. 6, pp.1646-1656, 2008.

Abstract

Extruded collagen fibres have been shown to constitute a biomimetic three-dimensional scaffold with numerous tissue engineering applications. The multi-step fabrication process of this material provides opportunities for further advancements to improve the properties of the final product. Herein we investigated the influence of the post-self-assembly washing baths on the structural, mechanical and thermal properties of these fibres. The surface morphology and the inter-fibre packing were similar for every treatment. The overnight incubation in isopropanol yielded fibres with the highest temperature and energy of denaturation (p<0.013). Typical s- and j-shape stress-strain curves were obtained for all treatments in the dry and wet state respectively. Rehydration of the fibres resulted in increased fibre diameter (p<0.006) and reduced stress (p<0.001), force (p<0.001) and modulus (p<0.002) values for every treatment. In the dry state, the alcohol-treated fibres were characterized by the highest stress (p<0.002) values; whilst in the wet state the Tris-HCl-treated fibres were the weakest (p<0.006). For every treatment, in both dry and wet state, a strong and inverse relationship between the fibre diameter and the stress at break was observed. Overall, the fibres produced were characterized by properties similar to those of native tissues.

PubMed

4. Electro-spinning of pure collagen nano-fibres - just an expensive way to make gelatin? Zeugolis DI, Khew ST, Yew ES, Ekaputra AK, Tong YW, Yung LY, Hutmacher DW, Sheppard C, Raghunath M. Biomaterials. Vol. 29, No. 15, pp. 2293-2305, 2008.

Abstract

Scaffolds manufactured from biological materials promise better clinical functionality, providing that characteristic features are preserved. Collagen, a prominent biopolymer, is used extensively for tissue engineering applications, because its signature biological and physico-chemical properties are retained in in vitro preparations. We show here for the first time that the very properties that have established collagen as the leading natural biomaterial are lost when it is electro-spun into nano-fibres out of fluoroalcohols such as 1,1,1,3,3,3-hexafluoro-2-propanol or 2,2,2-trifluoroethanol. We further identify the use of fluoroalcohols as the major culprit in the process. The resultant nano-scaffolds lack the unique ultra-structural axial periodicity that confirms quarter-staggered supramolecular assemblies and the capacity to generate second harmonic signals, representing the typical crystalline triple-helical structure. They were also characterised by low denaturation temperatures, similar to those obtained from gelatin preparations (p>0.05). Likewise, circular dichroism spectra revealed extensive denaturation of the electro-spun collagen. Using pepsin digestion in combination with quantitative SDS-PAGE, we corroborate great losses of up to 99% of triple-helical collagen. In conclusion, electro-spinning of collagen out of fluoroalcohols effectively denatures this biopolymer, and thus appears to defeat its purpose, namely to create biomimetic scaffolds emulating the collagen structure and function of the extracellular matrix.

PubMed

3. Factors influencing the properties of reconstituted collagen fibers prior to self-assembly: animal species and collagen extraction method. Zeugolis DI, Paul RG, Attenburrow G. Journal of Biomedical Materials Research Part A, Vol. 86, No. 4, pp. 892-904, 2008

Abstract

This research work allows a direct comparison between collagen solutions of equal concentration derived from the two widely used collagen sources: bovine Achilles tendon (BAT) and rat tail tendon (RTT), and extraction methods: acid (AS) and pepsin (PS) solubilization on the properties of extruded collagen fibers. Scanning electron microscopy revealed that the substructure of the collagen fibers was the same independent of the treatment. Transmission electron microscopy revealed that the AS collagen-derived fibers were comprised of thick quarter-staggered fibrils, while the coexistence of thin nonbanded and thick banded fibrils was apparent for the PS collagen-derived fibers. The BAT-derived fibers demonstrated higher denaturation temperature than the RTT-derived ones (p < 0.05). The extraction method had no influence on the thermal characteristics of the fibers produced (p > 0.05). ASBAT collagen was of higher viscosity than both ASRTT and PSBAT (p < 0.002), and therefore larger diameter fibers were obtained (p < 0.001). An inversely proportional relationship between dry-fiber diameter and stress at break was observed within the treatments. The PS yielded 10 times more soluble collagen from BAT and the derived fibers were of similar tensile strength, stiffness, and elongation (p > 0.05) as those derived from the AS collagen. No significant difference was observed for the stress at break for the ASBAT and the ASRTT, while significant difference was observed for the elongation and modulus values (p < 0.005). Overall, reconstituted collagen fibers were produced with properties similar to native or synthetic fibers to suit a wide range of tissue engineering applications.

PubMed

2. Extruded collagen-polyethylene glycol fibers for tissue engineering applications. Zeugolis DI, Paul RG, Attenburrow G. Journal of Biomedical Materials Research Part B: Applied Biomaterials, Vol. 85, No. 2, pp. 343-352, 2008.

Abstract

The repair of anterior cruciate ligament, skin, tendon and cartilage remains a challenging clinical problem. Extruded collagen fibers comprise a promising scaffold for tissue engineering applications; however the engineering of these fibers has still to be improved to bring this material to clinical practice. Herein we investigate the influence of collagen concentration, the amount of PEG Mw 8K and the extrusion tube internal diameter on the properties of these fibers. Ultrastructural evaluation revealed packed intra-fibrillar structure. The thermal properties were found to be independent of the collagen concentration, the amount of PEG or the extrusion tube internal diameter (p > 0.05). An inversely proportional relationship between dry fiber diameter and stress at break was found. The 20% PEG was identified as the optimal amount required for the production of reproducible fibers. Increasing the collagen concentration resulted in fibers with higher diameter (p < 0.001), force (p < 0.001) and strain at break (p < 0.02) values, whilst the stress at break (p < 0.001) and the modulus (p < 0.007) values were decreased. Increasing the extrusion tube internal diameter influence significantly (p < 0.001) all the investigated mechanical properties. Overall, extruded collagen fibers were produced with properties similar to those of native or synthetic fibers to suit a wide range of tissue engineering applications.

PubMed

1. Engineering extruded collagen fibres for biomedical applications. Zeugolis DI, Paul RG, Attenburrow G. Journal of Applied Polymer Science, Vol. 108, No. 5, pp. 2886-2894, 2008.

Abstract

Extruded collagen fibers constitute a promising biomimetic scaffold for tissue engineering applications. In this study, we compared the structural, thermal, and mechanical properties of fibers produced from either NaCl or poly(ethylene glycol) with a number-average molecular weight of 8000 (PEG 8K), the only two coagents that have been used in the fabrication process. As novel, we report the fabrication of fibers with properties similar to native or synthetic fibers using other coagents. NaCl derived fibers were characterized by higher thermal stability (p < 0.026), stress (p < 0.001), and modulus (p < 0.0025) values than PEG 8K, whereas the latter yielded more extendable fibers (p < 0.012). Poly(ethylene glycol)s with number-average molecular weights of 200 and 1000 produced fibers with similar mechanical properties (p > 0.05) that were thinner (p < 0.033), stiffer (p < 0.022), and less extendable (p < 0.0002) than those of PEG 8K. Poly(vinyl alcohol) (PVA) with a number-average average molecular weight of 9–10,000 and PEG 8K yielded fibers with similar diameters and stress-at-break values (p > 0.05); however, the poly(ethylene glycol) derived fibers were more extendable (p < 0.0003), whereas the PVA fibers were stiffer (p < 0.029). Gum-arabic- and soluble-starch-derived fibers were of similar tensile strength, extendibility, and stiffness (p > 0.05). In this in vitro study, the thickest (p < 0.011) and the weakest (p < 0.0066) fibers were produced in the presence of sodium sulfate.

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