Intradermal injections of bovine collagen are popular, but require testing the patients for an eventual allergy, one month before any injection. Many other surgical uses of animal collagen implants from bovine or porcine origin were developed in the last forty years. They are generally safe. However local immune reactions may develop, particularly after repeated implantations, and may induce significant inflammation with associated proteases and negative consequences on the tissue repair process and its quality.
Recently Xu et al (2008), Sandor et al (2008) in parallel, have compared the host response to a human acellular dermal matrix or to three porcine derived biologic materials transplantation in a primate model of abdominal wall repair. The results clearly show significant immune and inflammatory reactions influencing against the bio-integration of porcine derived materials in contrast with the better biocompatibility and performance of the human derived acellular material in monkeys. Their review also emphasizes the importance of the animal species selection before concluding to the biocompatibility of a given biologic material. Extrapolation of results obtained on genetically distant animal models as predictive of the response in humans may be of limited value.
Khorionyx studies (to be published), comparing porcine and human purified collagens implanted into the dermis of pigs have shown a significant and persistent inflammatory reaction to the human heterologous collagen. On the contrary, they have demonstrated a perfect tolerance to the porcine homologous collagen in the same pig.
For implantation in human patients, we believe that human collagen should be preferable to animal collagen to avoid the immune and associated inflammatory reactions. Human collagen can be extracted from human skin tissues.
However, it is made very difficult since the use of human tissue samples, from plastic surgery and even more from cadavers, poses considerable ethical problems and requires expensive tests in order to eliminate the risks of transmission of infectious diseases, viral diseases or the like.
The preparation of human collagen by the modern methods of genetic recombination or of cell culture is also very expensive, which precludes its long term medical development.
The best economical option is to extract human collagen from specifically collected and screened placentas, according to the past experience of Imedex which is now followed by Albiorex.
Cross-linked hyaluronate (HA) injections are also popular, but do not induce any tissue ingrowth within the implant Fernández-Cossío S. – Castaño-Oreja, M.T. (2006). HA dermal fillers only provide a transient volume correction and must be repeated after progressive hydrolysis of the implant. Some fibrosis is induced at the periphery of the HA implant, mainly due to local dermis dilacerations created by stretching effects during the injection Wang et al. (2007). This is a non specific effect which is probably reproduced with any type of dermal filler.
The ideal biomaterial for tissue augmentation should be “bioactive” and degraded in parallel with induction of tissue ingrowth and new collagen synthesis inside the implanted material. We believe that Human Globin is a new candidate to replace animal collagens and hyaluronate as implants.