There is much excitement around the potential capabilities of synthetic biodegradable
polymers and the effect they will have on the design and function of implanted devices. Whether they are used to facilitate a controlled drug delivery function within the body or to
regenerate lost tissue, these materials are crucial to the development of a wide range of new medical applications. The current trend suggests that, in the next few years, permanent prosthetic implants will give way to fully degradable devices.

The year 1969 saw the first approval of a synthetic degradable suture made of poly(glycolic acid). In 1971, an improved suture, containing poly(lactic acid) was approved. Then there was a long wait until polydioxanone appeared as a material for biodegradable
sutures and bone pins in the early 1980s. The next fundamental advance came in 1996 with the development of an implantable drug delivery system using degradable polyanhydrides. The history of synthetic degradable polymers shows that the rate of development is very slow - maybe one fundamentally new polymer system per decade.  Obviously, this rate of development must accelerate to allow the wide use of synthetic degradable in the manufacture of medical implants. 

One of the important goals of our research is to increase the number of viable biomaterials candidates and to accelerate their development into medical devices that alleviate the pain and suffering of patients throughout the world.  Recently, we were able to celebrate a major breakthrough. 

The TyRx Pharma Hernia Repair Device
A biodegradable tyrosine-derived polyarylate, invented in our laboratory,  is a critical component of a new hernia repair device marketed by TyRx Pharma, Inc, a firm that focuses on the development of new drug-eluting medical devices. TyRx used a combinatorially designed library of tyrosine-derived polyarylates from our laboratory to search for suitable polymers for a wide range of applications.  One of the polymers contained in the polyarylate library turned out to have the right properties for use in a hernia repair device.  The polyarylate  improves the handling capabilities of the hernia repair mesh to facilitate precise placement during surgery. The polyarylate coating is then reabsorbed, leaving a smaller
amount of material in the body. This partially degradable implant represents an important step forward in the use of biodegradable polymers.

In the USA alone, about 700,000 patients annually need a hernia repair device, therefore a large number of people will potentially be impacted by the research done in our laboratory.  It is interesting to note that the United States Food and Drug Administration (FDA) granted market clearance for this new device within 90 days of submitting the 510(k) application. Using 510(k) involves showing that a new device is equivalent to an existing device. If this equivalence can be demonstrated, the FDA responds more rapidly and may decide that
it does not require the complex and costly process of establishing safety through extensive clinical trials.  We believe that the successful use of the 510(k) approval mechanism by TyRx is highly significant, as it provides an example for the medical device iindustry fundamentally new polymers can be brought to the market via a 90-day 510(k) application. 

We are now focusing on accelerating the development cycle for new biomaterials by adapting the principles of combinatorial chemistry to biomaterials. In our current research programs, we are producing very large polymer libraries, sometimes containing ten thousands of individual compositions. For such large polymer libraries, it is no longer possible to synthesise each polymer composition contained in these libraries. Therefore we make use of computational modelling techniques to create ‘virtual’ libraries. So far, this technique has found limited use in the biomaterials field, given the difficulty of establishing appropriate models to describe the interaction between biomaterials and living tissue. However, advances in computational modelling techniques may now allow for the elimination of much detailed characterisation of individual polymers by high-throughput screening. For example, predicting the glass-transition temperature of individual polymers contained within one of our large library of polyarylates was based on the "mass-per-flexible-bond" principle which is an empirically derived parameter that can be calculated from a polymer’s chemical structure. The overall effect of starting the discovery process with a visit to a virtual polymer library should enhance the pace at which new biomaterials can be discovered.

Our next goal:  A fully degradable polymer cardiovascular stent that can replace the currently used metal stents:

Rutgers University has already provided a licence to REVA Medical, Inc for a new combinatorially designed polymer library. This library was designed to facilitate the development of degradable stents.  In the USA, about 2.4 million patients annually are diagnosed with cardiovascular disease, requiring some medical treatment.  Many of these patients may be candidates for the new degradable stent being developed by REVA Medical in collaboration with our laboratory.  We believe that other medical device manufacturers will follow in our footsteps:  In the next five years, we will see many pioneering efforts around the
world, aimed at adding drug delivery coatings to existing medical implants or the replacement of non-degradable prostheses by totally degradable regenerative implants.  We hope that in about five to ten years, we will see a larger number of degradable tissue regeneration devices.

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