Tissue engineering a ligamentous construct

Tendon and ligament damage causes extreme pain and decreased joint functionality. Current repair methods cannot restore original joint biomechanics nor promote regeneration of native tissue. Recent advances in tendon and ligament repair have involved engineering tissue using cell-seeded scaffolds. Self-aligned cellular structures, similar to those in ligaments and tendons, have been successfully formed, albeit with weak attachment between construct and bone. Calcium phosphates form an intimate bond with both soft and hard tissues and have successfully been used in tissue engineering bone, whilst hydrogels have often been used as cellular scaffolds. This thesis explores agarose, gelatin, carrageenan and fibrin hydrogels as potential soft tissue scaffolds. Fibrin gel exhibited high cellular compatibility with highest metabolic activity on day 14. Although the cellular gel contracted significantly, it was found that the dry weight remained stable in both the acellular and cellular forms. 3D powder printed calcium phosphate scaffolds remained structurally stable after immersion in cell culture media with immersion in protein-rich sera promoting tenocyte attachment. Bracket designs were developed to enhance grip of the cell-seeded fibrin. Ligament constructs were selfsupporting and exhibited structural characteristics similar to native connective tissue. Tenocyte density peaked on day 14, with added L-proline and ascorbic acid inducing a constant level of glycosaminoglycans and 7.4 ± 1.5 % w/w collagen. This research may significantly enhance the clinical application of tissue engineered ligaments and tendons

Silsesquioxane polymer as a potential scaffold for laryngeal reconstruction

Cancer, disease and trauma to the larynx and their treatment can lead to permanent loss of structures critical to voice, breathing and swallowing. Engineered partial or total laryngeal replacements would need to match the ambitious specifications of replicating functionality, outer biocompatibility, and permissiveness for an inner mucosal lining. Here we present porous polyhedral oligomeric silsesquioxane-poly(carbonate urea) urethane (POSS-PCUU) as a potential scaffold for engineering laryngeal tissue. Specifically, we employ a precipitation and porogen leaching technique for manufacturing the polymer. The polymer is chemically consistent across all sample types and produces a foam-like scaffold with two distinct topographies and an internal structure composed of nano- and micro-pores. Whilst the highly porous internal structure of the scaffold contributes to the complex tensile behaviour of the polymer, the surface of the scaffold remains largely non-porous. The low number of pores minimise access for cells, although primary fibroblasts and epithelial cells do attach and proliferate on the polymer surface. Our data show that with a change in manufacturing protocol to produce porous polymer surfaces, POSS-PCUU may be a potential candidate for overcoming some of the limitations associated with laryngeal reconstruction and regeneration

Active screen plasma nitriding enhances cell attachment to polymer surfaces

Active screen plasma nitriding (ASPN) is a well-established technique used for the surface modification of materials, the result of which is often a product with enhanced functional performance. Here we report the modification of the chemical and mechanical properties of ultra-high molecular weight poly(ethylene) (UHMWPE) using 80:20 (v/v) N2/H2 ASPN, followed by growth of 3T3 fibroblasts on the treated and untreated polymer surfaces. ASPN-treated UHMWPE showed extensive fibroblast attachment within 3 h of seeding, whereas fibroblasts did not successfully attach to untreated UHMWPE. Fibroblast coated surfaces were maintained for up to 28 days, monitoring their metabolic activity and morphology throughout. The chemical properties of the ASPN-treated UHMWPE surface were studied using X-ray photoelectron spectroscopy, revealing the presence of C N, C N, and C N chemical bonds. The elastic modulus, surface topography, and adhesion properties of the ASPN-treated UHMWPE surface were studied over 28 days during sample storage under ambient conditions and during immersion in two commonly used cell culture media

Host macrophage response to injectable hydrogels derived from ECM and α-helical peptides

Tissue engineering materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated. Traditional natural and synthetic materials are superseded by bespoke materials that cross the boundary between these two categories. Here we present hydrogels that are derived from decellularised extracellular matrix and those that are synthesised from de novo α-helical peptides. We assess in vitro activation of murine macrophages to our hydrogels and whether these gels induce an M1-like or M2-like phenotype. This was followed by the in vivo immune macrophage response to hydrogels injected into rat partial-thickness abdominal wall defects. Over 28 days we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface without promoting a foreign body reaction and see no evidence of hydrogel encapsulation or formation of multinucleate giant cells. We also note an upregulation of myogenic differentiation markers and the expression of anti-inflammatory markers Arginase1, IL-10, and CD206, indicating pro-remodelling for all injected hydrogels. Furthermore, all hydrogels promote an anti-inflammatory environment after an initial spike in the pro-inflammatory phenotype. No difference between the injected site and the healthy tissue is seen after 28 days, indicating full integration. These materials offer great potential for future applications in regenerative medicine and towards unmet clinical needs

Structural changes to resorbable calcium phosphate bioceramic aged <i>in vitro</i>

This work investigates the effect of mammalian cell culture conditions on 3D printed calcium phosphate scaffolds. The purpose of the studies presented was to characterise the changes in scaffold properties in physiologically relevant conditions. Differences in crystal morphologies were observed between foetal bovine serum-supplemented media and their unsupplemented analogues, but not for supplemented media containing tenocytes. Scaffold porosity was found to increase for all conditions studied, except for tenocyte-seeded scaffolds. The presence of tenocytes on the scaffold surface inhibited any increase in scaffold porosity in the presence of extracellular matrix secreted by the tenocytes. For acellular conditions the presence or absence of sera proteins strongly affected the rate of dissolution and the distribution of pore diameters within the scaffold. Exposure to high sera protein concentrations led to the development of significant numbers of sub-micron pores, which was otherwise not observed. The implication of these results for cell culture research employing calcium phosphate scaffolds is discussed

Nitrogen plasma surface modification enhances cellular compatibility of aluminosilicate glass

The effect of Active Screen Plasma Nitriding (ASPN) treatment on the surface-cellular compatibility of an inert aluminosilicate glass surface has been investigated. ASPN is a novel surface engineering technique, the main advantage of which is the capacity to treat homogeneously all kind of materials surfaces of any shape. A conventional direct current nitriding unit has been used together with an active screen experimental arrangement. The material that was treated was an ionomer glass of the composition 4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2. The modified glass surface showed increased hardness and elastic modulus, decreased surface roughness. The incorporation of nitrogen-containing groups was confirmed using X-ray photoelectron spectroscopy. The modified surface favoured attachment and proliferation of NIH 3T3 fibroblasts

Evaluation of iota-carrageenan as a Potential Tissue Engineering Scaffold

The present study evaluates the use of iota-carrageenan as a potential tissue engineering scaffold. Cell viability and cell attachment studies were performed on 3T3 fibroblasts cultured for a period of 12 days on the surface and when encapsulated within a 2% iota-carrageenan hydrogel. It was found that 3T3 fibroblasts seeded onto the surface of the gel did not show signs of attachment and the proportion of live cells decreased by 33% over a period of 12 days. The proportion of live cells encapsulated within the gel remained constant and there was evidence of cell proliferation throughout the 12 day study (4-fold increase in cell number). The extent of degradation of the gel for both encapsulated and non cell-seeded forms was also evaluated and showing no significant degradation for both types. These results indicate that iota-carrageenan may be a suitable scaffold material for use in tissue engineering and a potential tool for studying cell proliferation in three dimensions

Effect of active screen plasma nitriding on the biocompatibility of UHMWPE surfaces

Active screen plasma nitriding (ASPN) is used to chemically modify the surface of UHMWPE. This is an unexplored and new area of research. ASPN allows the homogeneous treatment of any shape or surface at low temperature; therefore, it was thought that ASPN would be an effective technique to modify organic polymer surfaces. ASPN experiments were carried out at 120 °C using a dc plasma nitriding unit with a 25% N(2) and 75% H(2) atmosphere at 2.5 mbar of pressure. UHMWPE samples treated for different time periods were characterized by nanoindentation, FTIR, XPS, interferometry and SEM. A 3T3 fibroblast cell line was used for in vitro cell culture experiments. Nanoindentation of UHMWPE showed that hardness and elastic modulus increased with ASPN treatment compared to the untreated material. FTIR spectra did not show significant differences between the untreated and treated samples; however, some changes were observed at 30 min of treatment in the range of 1500-1700 cm(-1) associated mainly with the presence of N-H groups. XPS studies showed that nitrogen was present on the surface and its amount increased with treatment time. Interferometry showed that no significant changes were observed on the surfaces after the treatment. Finally, cell culture experiments and SEM showed that fibroblasts attached and proliferated to a greater extent on the plasma-treated surfaces leading to the conclusion that ASPN surface treatment can potentially significantly improve the biocompatibility behaviour of polymeric material