Novel Biomaterials for Applications in Cartilage Tissue Engineering

Osteoarthritis is a debilitating joint condition involving the deterioration of cartilage and subchondral bone, which impacts millions of individuals globally. Its high prevalence is attributed to the ineffective intrinsic healing of cartilage due to its avascular nature. Consequently, the limited healing capacity of cartilage, as well as the failure of current surgical interventions, have led to the exploration of tissue engineering strategies that incorporate the use of polymers, biomolecules, and cells to facilitate cartilage regeneration.

The primary aim of this doctorate was to identify or develop novel biomaterials for their application in cartilage tissue engineering in vivo or for ex vivo cell expansion in cell-based industries. The materials selected for evaluation were P(3HO-3HD-3HDD) (a type of polyhydroxyalkanoate), trans-1,4-polyisoprene (TPI), the blend of these (named PHA + TPI), as well as two chemically modified versions of hydroxypropyl methylcellulose, or HPMC (named HPMC 2,6 and HPMC triple). These materials were analysed at various concentrations (2%, 3%, 5%, and 7% w/v), as opposed to the conventional approach of using a single concentration, to explore the potential impact of polymer concentration on the measured parameters.

The initial stage of the study involved the characterisation of the polymers, including mechanical and thermal characterisation, along with an assessment of their wettability and polymer degradation (Chapter 3). The subsequent two studies in this thesis evaluated the application of these materials in vitro with a human chondrocyte cell line known as C-20/A4 (Chapter 4) and immortalised mesenchymal stem cells (iMSCs) from one donor with osteoarthritis and one without (Chapter 5). The findings of the polymer characterisation revealed that HPMC 2,6 and HPMC triple were the most hydrophilic materials, a crucial factor in promoting cell adhesion. However, these materials were also characterised as being the most rigid and least flexible, potentially limiting their suitability for in vivo applications. The outcomes of cell adhesion indicated that HPMC 2,6 and HPMC triple demonstrated superior cell adhesion across all cell lines examined. Cell proliferation was supported on all polymers after 72 hours. However, after 10 days, PHA and PHA + TPI were not able to support cell proliferation, while HPMC 2,6, HPMC triple, and TPI (the latter not assessed with iMSCs) were. Lastly, HPMC 2,6 - 5% w/v supported cell proliferation of all cells most efficiently, resulting in the considerable relative proliferation of C-20/A4 cells (866.91%) compared to conventional tissue culture plastic (312.34%). Comparable outcomes were observed for iMSCs, exhibiting a higher relative increase of cell proliferation on HPMC 2,6 - 5% compared to tissue culture plastic.

The outcomes of this doctorate revealed that TPI, HPMC 2,6 and HPMC triple may be promising for their application in cartilage tissue engineering in vivo or cell expansion in cell-based industries. Particularly, HPMC 2,6, a novel biomaterial, which may be the best-suited polymer due to its potential to efficiently support cell proliferation, resulting in increased cell counts.