Dr. Cheng Li has broad experience in developing medical devices and drug delivery systems and currently consults with implantable medical device companies. At www.bio2devicegroup.org, Dr. Li discussed how to use liner and branched cell-binding peptides to enable biomaterials to elicit specific cellular responses and direct new tissue integration mediated by biomolecular recognition for implantable devices. An application for biomimetic vascular grafts developed by Dr. Li was shared as an example.
Most biomaterials used for medical and implantable devices today are not are not biomimetic, but rather biocompatible, or more precisely bioinert. Bioinert materials do not initiate a response or interact when introduced to biological tissue. Therefore, they are non toxic and stable against degradation in the tissues. However, these materials do not fully integrate into the surrounding tissues because of foreign body reaction, inflammatory response, and thrombosis. Physical and chemical properties of implant surfaces can significantly impact basic biological functions and performance of the device. Biointert materials do not fully integrate with the surrounding tissue but biomimetic material can mimic the surrounding tissue and can deliver required intended functional properties and biological responses that can recognize and support the surrounding tissue.
Currently, three approaches are explored to achieve this goal. One approach is to create a tissue like material to incorporate cells and growth functions with biomaterial scaffolds that modulate tissue formation and tissue integration. A second approach is to use materials with biomimetic surface by attaching cell binding peptides or extracellular matrixes (ECMs) onto the surface of the biomaterials. This can improve cell adhesion, wound healing, and tissue integration and reduce inflammation and thrombosis as well as unwanted tissue growth. The third approach is to combine drugs with already existing devices, as in the case of drug eluting stents. This also can reduce unwanted tissue growth, improve cell adhesion and wound healing but may cause poor tissue integration and may have certain immunological challenges.
Recently there has been a strong focus on cell bonding peptides. Cell-binding peptide or ECM molecules can lead to strong biological interactions between surrounding cells and the implant surface because they have specific cell adhesion domains. Therefore, they can promote cell attachment, proliferation, and migration and can be easily synthesized and it is much easier to covalently immobilize cell-bonding peptides onto the surface of biomaterials compared to large ECM molecules, such as fibronectin, vitronectin, or collagen. This approach can significantly improve cell adhesion, wound healing, and tissue integration without altering intended mechanical properties for implant materials.
Each year over 500,000 vascular access procedures are performed for hemodialysis. Many of these patients have poor vessels and therefore require using synthetic grafts which can lead to thrombosis and infections. Replacement of the infected and thrombosed grafts have significantly increased the care costs. Over $1.8 B was spent in 2006 just in vascular graft access, which comes to about 8% of the cost of caring for end stage renal disease patients. Dr. Li shared an example of ePTFE vascular grafts with porous structure and flexible large area for cannulation, for easier access if more than one site is needed. His animal studies data revealed that these grafts did not show thrombosis, and EC indicated endothelial cell proliferation had increased by 800%, compared to controls. Many challenges still remain. The talk was followed by Q&A. Dr. Li can be reached at firstname.lastname@example.org .