New Biomaterials For Tissue Engineering

The success of tissue engineering rests on the ability to direct specific cell types to multiply, migrate, and express normal physiologic behaviors in order to yield a cellular organization that performs the functions of the desired tissue. For example the engineering of living bone to repair skeletal defects has focused on growing osteoblasts—the cells responsible for bone formation—on degradable polymer matrices in vitro. The polymer matrix initially serves as the scaffold for bone-cell proliferation and maturation. Ideally the cells form a bonelike tissue that after implantation is fully integrated into the patient's own bone, thus repairing the bone injury or defect. Soon thereafter, its function complete, the polymer scaffold resorbs away. Readily apparent is the crucial role the scaffold material occupies in tissue engineering since it serves as the template for cell growth and tissue formation. It is the interaction between the cell and the material that dictates whether the cells will proliferate, mature, and express the desired tissue characteristics.A critical issue facing the biomedical industry today is the availability of raw materials for medical-device manufacture. Furthermore it is now recognized that the materials base of the medical-device industry is outdated. Metals and various industrial plastics (e.g., polysiloxanes, polyurethanes, Dacron®, Teflon®, polyethylene) are the most commonly used biomaterials. These biostable, synthetic implant materials lack the biological sequences and patterns crucial to normal cell function and can trigger aberrant cell responses. Likewise few degradable polymers are available to the medical-device designer and tissue engineer, representing another limitation of the materials base of the medical-device industry (Table I).