Mitchell R. Ladd

Bioreactor Maintained Living Skin Matrix

Numerous reconstructive procedures result in wounds that require skin grafting. Often, the amount of tissue available from donor sites is limited. In vivo tissue expanders have been used clinically to generate larger sections of skin, and other methods exist to cover large wounds, but all have significant limitations. We investigated whether these difficulties could be overcome by increasing the surface area of skin in vitro while maintaining tissue viability. Human foreskin was incrementally expanded in a computer-controlled bioreactor system over 6 days to increase its surface dimensions under culture conditions. Morphological, ultrastructural, and mechanical properties of the foreskin were evaluated before and after expansion using histology, scanning electron microscopy, mercury porosimetry, and tensile testing. The surface area of the tissue was 110.7% +/- 12.2% greater, with maintenance of cell viability and proliferative potential. Histomorphological and ultrastructural analyses showed that dermal structural integrity was preserved. The pore diameter of the expanded skin was 64.49% +/- 32.8% greater. The mechanical properties were not adversely affected. These findings show that expansion of living skin matrices can be achieved using a computer-controlled bioreactor system. This technique provides an opportunity to generate large amounts of skin for reconstructive procedures.

Electrospun Nanofibers in Tissue Engineering

The field of tissue engineering and regenerative medicine is a fast growing scientific field. Many diseases and injuries that result in the loss of organ or tissue functions currently lack treatments which restore those functions and the patient to a desirable quality of life. Many current treatments could greatly benefit from incorporation of bioengineered organs and tissues, and investigation into this field shows great promise for modern medicine. Tissue engineering hypothesizes that by incorporating appropriate cells in the context of a threedimensional scaffold and then implanting the cell-scaffold construct into an injury or defect, that the cells and scaffold will provide both active and passive healing properties. Various scaffolding systems exist and are generally made from natural and/or synthetic polymers. Scaffolds can be fabricated by many methods including solvent casting and particulate leaching, melt molding, rapid prototyping, phase separation, and many others (Yang et al., 2001). Of particular interest to the subject of nanofibers is electrospinning, which has seen widespread use in the field of tissue engineering due to the ease of use, scalability, adaptability, and capacity to form fibers on both the micro and nano scale (Sill & von Recum, 2008). In constructing scaffolds for tissue engineering it is ideal to provide cells with an environment which closely resembles their native extracellular matrix (ECM). The spinning of nanofibers allows for a connected and porous scaffold which can mimic the ECM of many tissue types structurally, chemically, and mechanically. The ECM is a largely proteinaceous cellular environment that varies greatly between tissue types. In most tissue types the ECM is composed of a highly interconnected network of proteins such as collagen and elastin, and proteoglycans such as perlecan (Lodish et al., 2008). These molecules link together to form a functional environment in which cells live, move, receive and transmit signals, and which provides structural support to the cells, tissue, and organ as a whole. The composition of molecules in the ECM has a strong influence on the structural properties of the tissue which it helps compose. For example, in tissues which must stretch and bend, such as the muscle of the heart, elastin is a necessary ECM component which lends elasticity to the tissue when found in sufficient quantities (Lodish et al., 2008). Similar examples may be found in all tissue types, exemplifying the common theme of structure supplying function found throughout biology. The ECM is approximately nano scale and fibrous, though the fiber orientation depends on the tissue type. For example, dermis has randomly oriented fibers so as to provide structural support when stretched in different directions, while ligaments have a highly directional ECM so as to provide support in the direction of stress.