Regenerative Medicine

John P. Gleeson12 and Fergal J. O'Brien12 1Royal College of Surgeons in Ireland, 2Trinity Centre for Bioengineering

Ireland

1. Introduction

The goal of tissue engineering is to synthesise substitutes that mimic the natural environment to help guide the growth of new functional biological tissue in vitro or in vivo. Tissue engineering relies heavily on the use of porous 3D scaffolds to provide a supportive environment for the regeneration of tissues and organs, acting primarily as a template for de novo tissue formation. However, new advances in fabrication technologies and composite materials are facilitating the rapid development of many novel composites that are beginning to play a more active role in directing the regenerative process. It has been long recognised that the combination of two or more characteristically-distinct materials can often yield composite materials that possess many of the constituent materials mechanical and biological advantages with few of their disadvantages. When applied to regenerative medicine, these new composite materials are beginning to show real potential as bioactive, biodegradable substitute materials, capable of facilitating rapid orthopaedic tissue regeneration, while degrading in parallel with the advancing tissue repair process. These idealised tissue regenerative aids could finally offer clinicians the potential to completely regenerate damaged orthopaedic tissue, leaving no evidence that the tissue was ever damaged in the first instance.

At a simplistic level, biological tissues consist of cells, signalling mechanisms and extracellular matrix (ECM). Tissue engineering technologies are based on this biological triad and consist of (i) the scaffold that holds the cells together to create the tissue's physical form, (ii) the cells that create the tissue, and (iii) the biological signalling mechanisms (such as growth factors or bioreactors) that direct the cells to express the desired tissue phenotype (Figure 1). In native tissues, cells are held within an ECM which guides development and directs regeneration of the tissue. The ECM serves to organise cells in space and provides them with environmental signals to direct cellular behaviour. Consequently, the ECM is responsible for two of the three components in this tissue engineering triad, highlighting the critical role that this extracellular environment plays on tissue formation. What is becoming increasingly evident is that the combination of biomaterials into novel composite scaffolds can result in an engineered biomimicry of this extracellular environment that provide all the environmental cues to promote rapid development of de novo tissue. Consequently, these composites can be designed to act not only as carriers and supporting structures for the associated cells but to play a more active role in the initiation and development of the repair tissue.

Porosity

Mechanical properties

Bioc o mp atib ility

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