Biofunctionalised electrospun scaffolds for cartilage tissue engineering

Abstract

The field of tissue engineering has advanced and evolved to focus on biomimetic strategies to meet the rise in demands of tissue replacements for surgical reconstruction. One of the key strategies focuses on developing growth factor delivery systems, by incorporating growth factors into tissue scaffolds. While growth factors are crucial cell-inducing components, their limitations such as short half-lives and dose related adverse effects remain a challenge. To overcome these challenges, this thesis is focused on the development of a novel biomimetic tissue scaffold concept incorporating cell-mediated activation of growth factors for cartilage regeneration. The latent transforming growth factor-β1 (TGF-β1) was selected as a model latent protein due to its well established effects on cartilage as well as its ubiquity in many other tissue types. The thesis first focused on the development and characterisation of the tissue scaffold. A non-woven fibrous scaffold was fabricated by electrospinning, surface modified using ammonia plasma, followed by scaffold surface biofunctionalisation with the latent TGF-β1. Physiochemical characterisation revealed that: (1) the scaffold architecture closely resembled that of the native cartilage extracellular matrix; (2) the scaffold surface was chemically modified for subsequent biofunctionalisation reaction; and (3) the latent TGF-β1 was incorporated onto the scaffold and the active TGF-β1 was detected upon acid and enzymatic activation. Biological effects of the biofunctionalised scaffold were assessed using human nasal chondrocytes in a serum free environment and compared with conventional TGF-β1 supplementation on non-biofunctionalised scaffolds (as control). The biofunctionalised scaffold group induced a lower cell metabolic activity and significantly higher gene expression of cartilage specific transcription factor Sox9 after 14 days. The second part of the thesis evaluated the chondrogenic efficacy of the biofunctionalised scaffolds, using the aforementioned chondrocytes and human mesenchymal stem cells (MSC), in an in-vivo rat model. Cell-scaffold constructs were implanted into subcutaneous pockets of athymic rats for six weeks. Gene expression and immunohistochemistry showed that the biofunctionalised group induced significant chondrogenic differentiation in chondrocytes and type II collagen production when compared to controls. Interestingly, a converse response was observed in MSC where the control group induced relatively higher chondrogenic potentials that the biofunctionalised group. This thesis demonstrates that the latent TGF-β1 biofunctionalised scaffolds induced chondrocytic differentiation in chondrocytes and more importantly the proof of concept of cell-mediated activation of growth factors as a novel approach for functional tissue regeneration.