Role and future prospect of polymers in frontier medical therapy

With recent remarkable advance of basic biology and medicine of cells, various stem cells of high proliferation and differentiation potentials have been available. However, only by using such cells, it is practically difficult to achieve medical therapy to induce regeneration of tissues and organs. This is because cells basically survive and function interacting with their surrounding environment. Thus, it is indispensable for this cell-based regenerative medical therapy to create a local environment which enables cells to promote their proliferation and differentiation. To this end, polymer biomaterials are being utilized in several shapes or manners. For example, their 3-dimensional formulations are prepared as cell scaffold. The in vivo biological activities of signaling molecules (growth factor and gene etc.) cannot always be expected only by the direct injection in the solution form into the body. One possible way to enhance the therapeutic efficacy of signaling molecules is to utilize drug delivery system which is technology or methodology to supply them to the right place at the right time period and concentration. We have explored biodegradable hydrogels for the controlled release of growth factors and succeeded in the regeneration and repairing of various tissues, while some clinical experiments of regenerative medicine have been started. This controlled release system efficiently enhanced the level and time period of in vivo gene expression. In addition, by the intracellular release of plasmid DNA, stem cells could be genetically engineered to activate their functions at the therapeutic efficacy as high as or higher than cell manipulation by viral vectors. This release system is combined with cells or/and the cell scaffold to realize the regeneration repairing of tissues and organs. This paper introduces several therapeutic trials of regenerative medicine to emphasize the role and future prospect of polymer biomaterial in frontier medical therapy.