Collagen type II: From biosynthesis to advanced biomaterials for cartilage engineering

Collagen type II is the major constituent of cartilage tissue. Yet, cartilage engineering approaches are primarily based on collagen type I devices that are associated with suboptimal functional therapeutic outcomes. Herein, we briefly describe cartilage's development and cellular and extracellular composition and organisation. We also provide an overview of collagen type II biosynthesis and purification protocols from tissues of terrestrial and marine species and recombinant systems. We then advocate the use of collagen type II as a building block in cartilage engineering approaches, based on safety, efficiency and efficacy data that have been derived over the years from numerous in vitro and in vivo studies.

Porcine mesothelium matrix as a biomaterial for wound healing applications

The increasing economic burden of wound healing in healthcare systems requires the development of functional therapies. Xenografts with preserved extracellular matrix (ECM) structure and biofunctional components overcome major limitations of autografts and allografts (e.g. availability) and artificial biomaterials (e.g. foreign body response). Although porcine mesothelium is extensively used in clinical practice, it is under-investigated for wound healing applications. Herein, we compared the biochemical and biological properties of the only two commercially available porcine mesothelium grafts (Meso Biomatrix® and Puracol® Ultra ECM) to traditionally used wound healing grafts (Endoform™, ovine forestomach and MatriStem®, porcine urinary bladder) and biomaterials (Promogran™, collagen/oxidized regenerated cellulose). The Endoform™ and the Puracol® Ultra ECM showed the highest (p<0.05) soluble collagen and elastin content. The MatriStem® had the highest (p<0.05) basic fibroblast growth factor (FGFb) content, whereas the Meso Biomatrix® had the highest (p<0.05) transforming growth factor beta-1 (TGF-β1) and vascular endothelial growth factor (VEGF) content. All materials showed tissue-specific structure and composition. The Endoform™ and the Meso Biomatrix® had some nuclei residual matter. All tissue grafts showed similar (p>0.05) response to enzymatic degradation, whereas the Promogran™ was not completely degraded by matrix metalloproteinase (MMP)-8 and was completely degraded by elastase. The Promogran™ showed the highest (p<0.05) permeability to bacterial infiltration. The Promogran™ showed by far the lowest dermal fibroblast and THP-1 attachment and growth. All tested materials showed significantly lower (p<0.05) tumor necrosis factor-alpha (TNF-α) expression than the lipopolysaccharides group. The MatriStem® and the Puracol® Ultra ECM promoted the highest (p<0.05) number of micro-vessel formation, whereas the Promogran™ the lowest (p<0.05). Collectively, these data confer that porcine mesothelium has the potential to be used as a wound healing material, considering its composition, resistance to enzymatic degradation, cytocompatibility, and angiogenic potential.

Carrageenan enhances chondrogenesis and osteogenesis in human bone marrow stem cell culture

The extracellular matrix is a dynamic and active component of the mesenchymal stem cell niche, which controls their differentiation and self-renewal. Traditional in vitro culture systems are not able to mimic matrix-cell interactions due to the small amount of extracellular matrix present. Macromolecular crowding, a biophysical phenomenon based on the excluded-volume effect, dramatically accelerates and increases tissue-specific extracellular matrix deposition during in vitro culture. Herein, the influence of macromolecular crowding in pre-condition and tri-lineage differentiation of human bone marrow mesenchymal stem cells was investigated. Carrageenan, a sulphated polysaccharide, enhanced chondrogenesis, as evidenced by increased collagen type II and chondroitin sulphate deposition and unaffected Sox-9 expression. Osteogenesis was also enhanced when carrageenan was used only in the differentiation phase, as evidenced by increased mineralisation, collagen type I deposition and osteopontin expression. Adipogenesis was not enhanced in the presence of carrageenan, suggesting that the chemistry of the crowder may affect stem-cell-lineage commitment. In conclusion, carrageenan, a sulphated polysaccharide, enhanced extracellular matrix deposition and promoted chondrogenesis and osteogenesis but not adipogenesis in human bone marrow mesenchymal stem cell cultures.

Environmental fate and effect of biodegradable electro-spun scaffolds (biomaterial)-a case study

Poly-ε-caprolactone (PCL) based medical devices are increasingly produced and thus, their presence in the environment is likely to increase. The present study analysed the biodegradation of PCL electro-spun scaffolds (alone) and PCL electro-spun scaffolds coated with human recombinant (hR) collagen and Bovine Achilles tendon (BAT) collagen in sewage sludge and in soil. Additionally, an eco-toxicological test with the model organism Enchytraeus crypticus was performed to assess environmental hazard of the produced materials in soils. The electro-spun scaffolds were exposed to activated sludge and three different soils for various time periods (0-7-14-21-28-56-180 days); subsequently the degradation was determined by weight loss and microscopical analysis. Although no toxicity occurred in terms of Enchytraeus crypticus reproduction, our data indicate that biodegradation was dependent on the coating of the material and exposure condition. Further, only partial PCL decomposition was possible in sewage treatment plants. Collectively, these data indicate that electro-spun PCL scaffolds are transferred to amended soils.

Innovating in the medical device industry - challenges & opportunities ESB 2015 translational research symposium

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.

In Vitro Enzymatic Degradation of Tissue Grafts and Collagen Biomaterials by Matrix Metalloproteinases: Improving the Collagenase Assay

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.

Electromechanical properties of dried tendon and isoelectrically focused collagen hydrogels

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.

Preferential cell response to anisotropic electro-spun fibrous scaffolds under tension-free conditions

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.

An in situ and in vitro investigation for the transglutaminase potential in tissue engineering

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.

Extruded collagen-polyethylene glycol fibers for tissue engineering applications

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.