The search for synthetic-based biocompatible materials has posed particular problems for researchers in that no synthetic material is completely accepted and integrated by the body. Therefore, the goal has been to create a replacement tissue that closely mimics natural tissue and will activate normal body healing and tissue reconstruction, and eventually be resorbed harmlessly into the body after normal healing has begun.
Scaffolds used to grow the tissue must be biocompatible, biodegradable, and bioabsorbable and must have a surface chemistry that promotes cell adhesion and growth. They also must have a specific porosity and pore size dependent upon the type of tissue to be grown and be able to degrade within the desired time frame. It must have the capability to be molded into a variety of desired shapes.
The goal in bone tissue engineering is to have a composite with surface and microstructural attributes that promote good cell adhesion and vascularization, that have the necessary transport channels for good cell activity, that has the right three-dimensional network to serve as a substitute for bone under both static and dynamic, weight-bearing conditions, and will be resorbed at an appropriate rate—neither too fast nor too slowly. Even titanium, currently considered virtually the gold standard for implant materials (such as replacement hip joints) is not ideal, and eventually shows failure.
A range of bioceramic and polymer scaffold materials developed so far for bone tissue applications include: coralline hydroxyapatite, calcium carbonate, poly(lactic acid) (PLA), poly(glycolic acid) (PGA) and copolymers of PLA and PGA, as well as new polymer systems like poly(propylene fumarate) and polyarylates. Composites have been used to compensate for the fact that no single material has fulfilled all the necessary functions.
Neuronal tissue is notoriously difficult to replace; even when autologous nerves are used, function is at best about 50% of normal. Again various synthetic materials are being investigated for use as scaffolds, including PLLA poly (L-Lactic Acid) and PLGA poly (DL-glycoloic acid). The ideal scaffold will probably be a combination of synthetic and natural materials.
Source: MedMarket Diligence, LLC; "Tissue Engineering, Cell Therapy and Transplantation: Products, Technologies & Market Opportunities, Worldwide, 2009-2018". Report #S520. (Image source: National Institute of Standards and Technology)