ABSTRACT
In general terms, the goal of tissue engineering is to develop materials and approaches which can be used to facilitate repair, regeneration, or replacement of damaged or diseased tissues. In some applications, reconstitution of tissue function outside the body is the desired goal. In the repair/ regeneration scenario, the goal is to enhance or improve upon natural repair processes which often produce nonfunctional or poorly functional scar in place of normal tissue. In the replacement scenario, the tissue ‘‘foundation’’ may be assembled in vitro and subsequently implanted. This approach may employ a cellular component together with an appropriately shaped structural template or scaffold. Alternatively, a material scaffold may be implanted directly into the desired tissue site and colonized by the target cells. Most tissues are not merely collections of randomly arranged cells, but possess highly detailed organizational features which are closely tied to tissue function. The tissue engineer typically seeks to restore this tissuespecific architecture, and the use of a scaffold provides the means to this end. In order to achieve restoration of tissue architecture, the tissue scaffold may be required to perform a variety of tasks. A porous microstructure which allows cellular ingrowth and scaffold colonization is almost a universal requirement. Enhancements to the microstructure may include spatial variations in pore morphology to help
orient cells or variations in material surface properties to facilitate selective cell adhesion and/or migration. In contrast, inhibition of cell adhesion may be an important performance characteristic for certain locations. Similarly, the scaffold material must be either overtly biodegradable or at least amenable to long-term integration with the host tissue. Biodegradability allows the gradual and orderly replacement of the scaffold with functional tissue, and also prevents the development of adverse chronic responses to the artificial structure. The scaffold material may be required to deliver biologically active agents (for example, growth factors or genes) to the target tissue. The material itself may be required to possess intrinsic biological activity to elicit specific migration or proliferation responses in adjacent cell populations. To this list of cell interaction characteristics may be added certain physical properties such as precise matching of the following: tissue mechanical properties, macromolecular permeability, protein binding or repulsion, tissue adhesion or lubricity, and ease of processing. Since restoration of normal tissue architecture and function is the ultimate goal, the scaffold is usually considered to be a temporary structure. Thus the ability to tune degradation rates to achieve an optimal degradation time profile may greatly broaden the applicability of a particular material.
