Artificial organs and bio-prostheses for reconstructive surgery
At least three decades’ old idea to replace non-functioning organs and tissues of human body by artificial ones has come of age. Inability of organ transplantation to make a more substantial contribution to solving medical problems of seriously ill patients was probably one of the reasons for a medical science to vigorously turn toward artificial organs and tissues.
Various prosthetic materials used in reconstructive surgery can be improved in terms of lowering their immunogenicity and the speed of healing by combining them with fetal cell transplants.
Implantable artificial organs and tissues include all devices which substitute for an organ or tissue function and consist of three-dimensional synthetic matrix made from biodegradable bio-polymers, that provides a template for seeding by live cells. They function primarily by repairing the damage of patient’s organs and tissues, while leaving eventually no residual artificial material in the patient’s body.
Bio-prostheses include nearly all existent non-metallic, and many non-existent, prostheses used in surgery today. Those non-existent prostheses were found to be unusable because of serious healing problems or rejection reaction.
At the end of 1996 the first two U.S. patents on artificial organs were granted. The number of medical reports in MEDLINE computerized medical data base has steadily grown over the past years. The surge in the development of artificial organs and tissues is based on the progress in the field of fetal cell transplantation and in the use of biodegradable biopolymers in medicine.
“Use of bio-degradable bio-polymers combined with fetal cell transplants in medicine and surgery”, is a project of two parts, closely related to each other:
A/ The purpose of reconstructive surgery has been to correct the deformity, or tissue loss, with the best results, without causing additional damage to the patient’s body.
Whenever patient’s own tissues could not be used for such purpose, and use of tissues from another human caused rejection, surgeons have been looking for alternative solutions. One of them was to use bio-compatible artificial materials: metals, ceramics, and polymers.
Over the time metals became the most important artificial material used in orthopedic surgery, and the same applied to ceramics in dentistry, and to polymers in plastic & reconstructive surgery.
Use of metallic bone prostheses have been limited to the bone reconstruction. The main drawback of metals has been the need for their removal after they fulfilled their function. Thereby any long term problems due to the metal remaining in the body have been avoided.
Ceramics, such as hydroxy-apatite, tricalcium phosphate, aluminum oxide, or those containing glass or carbon fibers, have become more popular only lately, and so far have been used more externally than for implantation into internal environment of the body.
Bio-polymers have been used in surgery for decades. Silicones, containing no carbon, were the first, and have remained the most popular. Then came poly-methyl-metacrylates, used at the beginning as external prosthesis only. Next, poly-ethylens were discovered, that became the basis of poly-tetra-fluoro-ethylenes, containing only carbon, oxygen and fluor.
The main problem with all above bio-polymers has been their recognition as foreign by the living body, and so their presence always triggered ‘foreign body reaction’ by immune system of one type or another. Although no one has ever proved that bio-polymers cause auto-immune diseases, it did not stop U.S. courts from giving multi-billion dollar judgment to the recipients of silicone breast implants in the recent past.
Discovery of polyurethanes caused a revolution because of their natural degradation, and eventual disappearance from the body.
Polymers are materials with a wide variety of mechanical and physical properties, readily molded into any desirable shape. Their mechanical properties are derived from their chemical composition and structure, that can be easily manipulated. For example, polyethylene can be made with linear, branched, or cross-linked chains; short chains of low molecular weight are liquids, that turn into viscous – waxy – plastic – and ultimately glass consistency with increase of length of the chain.
The best solution to all problems with bio-compatible polymers appeared ‘bio-degradation’, i.e. gradual disappearance of the prosthesis in the process of bio-destruction by phagocytosis. By combining various plastic materials in the production of final bio-polymer the bio-degradation is assured, without a production of non-compatible disintegration products. Further progress led some 45 years ago to the development of bio-polymers that not only bio-degrade, but do so at the a pre-determined time. It means that their bio-destruction can be pre-programmed.
Best bio-degradable bio-polymers consist of a capron fiber modified by a type of acid treatment and a co-polymer of vinylpyrrolidone and methylmetacrylate. Capron fiber serves as a filling material, while co-polymer of vinylpyrrolidone and methylmetacrylate as a binding material.
Over the last four decades around 60 different products have been created from this type of bio-degradable bio-polymers. Several of them have been patented in many European countries and one of them in the U.S. They could be divided into five groups:
1/ films for timed delivery of various medications: ophthalmologicals, nitroglycerine,anti-nicotine medication, medication for temporary suppression of alcohol intoxication;
2/ implants for osteosynhesis, replacement of vertebral body or disc, covering of skull defects, filling of bone defects, external ear canal reconstruction, vascular prostheses, laryngeal prosthesis;
3/ surgical adhesive tapes for securing surgical anastomosis of hollow internal organs such as intestines, for hemostasis during liver and kidney surgery, etc., and surgical sutures;
4/ surgical glues, with variety of options: such as with long term effect, for treatment of esophageal burns, injectable glues, etc.
5/ foam hydrogel, a water soluble bio-degradable bio-polymer mixture, usable as a filler of veins (bleeding esophageal varices), cavities, etc. More about this unique bio-polymer under B/
Clinical use of bio-degradable bio-polymers showed certain deficiencies, that were rectified by adding to the products various antibiotics to help suppress infection locally, osteogenetic, chondrogenetic, or fibrogenetic additives, chemotherapeutica with local effect for cancer resection surgery, X-ray contrast substances, during manufacturing process.
Binding of live cells, prepared as for fetal precursor cell xeno-transplantation, to the bio-degradable bio-polymers represents the ultimate step in their development because it raises the level of bio-compatibility to presently un-attained levels. Improved bio-compatibility translates into much better and faster healing, with lessened possibility of treatment complications.
This project will revolutionize reconstructive surgery in its entirety.
B/ It is believed that fetal precursor cell transplantation will trigger a rejection reaction by the immune system. Many feel that immunosuppression is not the best option to deal with this problem because drugs used for that purpose are detrimental to the implanted cells. For several years another option has been researched: to protect implanted cells against immune system attack by mechanically shielding them inside of a bio-polymer sponge with opening large enough to permit passage of all biological substances from cell transplants into the recipient organism, but at the same time small enough to prohibit immune system cells and molecules to get to the transplanted cells. Such structure has been called an ‘artificial organ’.
Several bio-polymers have been developed for that purpose. They all have failed to accomplish the task, because within 3 - 4 months the entire structure, consisting of bio-polymer and a cell transplant is surrounded by scar tissue, so that no biological substance produced by cell transplant can get into the recipient organism, thus the positive effect of cell transplant terminates.
Bio-degradable ‘foam hydrogel’ mentioned above under 5/, can be programmed to bio-destruct much earlier than 3 - 4 months after its implantation, and thereby avoid encasement of an ‘artificial organ’ and continuity of function, and ‘foreign body reaction’. Creation of such as ‘artificial organ’ would increase number of implantation sites as well, invaluable for the overall therapeutic effect.