The challenges and opportunities of bioresorbable polymers in medical technology

While bioresorbable materials have been getting a great deal of attention in the medical arena during the last 10 to 15 years, relatively few have been adopted for use in marketable products. That may change, as production efficiencies and economies of scale improve. Materials expert Len Czuba, who heads product design and development firm Czuba Enterprises, explains.

PlasticsToday: What are the primary bioresorbable materials in use today and what are some typical applications? What are the benefits for the patient?

Len Czuba: There are about a dozen materials commonly considered as “bioresorbable” but, of these, only a few are commonly used in medical device applications. Most resorbable medical devices are made from glycolide-lactide polymers and copolymers, polycaprolactone, polydioxanone and polytrimethylene carbonate. Applications include surgical sutures, orthopedic pins, screws, rods and plates, cardiovascular stents, hernia repair and reinforcement meshes and tissue anchors. In every case just mentioned, the medical device is needed to help the recipient recover from an injury or to allow healing of a suture, tear, break or other deficiency in the tissue or to allow healing of a reopened blood vessel or repositioned tissue.

It stands to reason that after the bone or blood vessel or sutured tissue is healed, the medical device providing the support needed during that healing is no longer needed. If it were to remain in place, in the long term, the body would begin to react to it as it would to any other foreign object. A dramatic example is cardiovascular stents made from nitinol metal. They provide life-saving intervention into otherwise blocked blood vessels allowing immediate return of normal blood flow, usually to the heart. But after the blood vessel “heals” in the new opened position, the metal stent becomes a foreign body that can lead to restenosis, or re-formation of blood clots, unless the patient is otherwise treated. The resorbable stents will be eliminated and not lead to complications typical with metal stents. Similar benefits are found with resorbables in orthopedic applications, surgical repairs and tissue reinforcements and anchors.

PlasticsToday: What are some of the challenges associated with sourcing the materials and processing them, especially when it comes to molding the parts?

Czuba: I believe that there are two or three major challenges related to the use of bioresorbables for implantable medical devices.

First, recognize that in most cases, the resorbable device is intended to be placed in the patient to assist in the healing process, which can be weeks to months. After the healing period, there is then the extended time that it takes for the implanted device to be resorbed and eliminated from the tissue and the body which can be at least double the healing time. So these devices are all considered long-term implants. This means that besides selecting materials that are shown to be safe and effective, these materials must be sourced from suppliers that are willing to supply materials for long-term implantable medical device applications. My experience is that there is still quite a bit of reluctance from suppliers to allow their materials to be used in these types of medical devices. This is in large part because of the misunderstanding of the potential liability they face if there were to be found a problem caused by the device made with their material. (If they understood how the Biomaterials Access Assurance Act of 1998 has shielded them from liability, they would realize that they have no liability as long as they maintained compliance to the originally agreed-upon specifications.)

The second major challenge facing users of bioresorbables for medical devices (not even mentioning the extremely high cost of the materials) is the difficulty that comes with processing these materials and making them into the intended medical device. These materials are extremely heat sensitive and tend to rapidly lose molecular weight (meaning polymer strength) during the extrusion or injection molding process as well as during sterilization and even during storage. Care must be taken in the design of the medical device, selecting just the right bioresorbable polymer and in making that polymer into the intended medical device having the properties necessary for the device to be effective. For injection molded components using bioresorbables, great care must be taken to minimize the heat exposure of the material and to keep the time at melt temperature as short as possible while also avoiding any exposure to moisture. Heat and moisture lead to hydrolysis of the polymer chains, thereby reducing the molecular weight of the polymer resulting in a lower strength part. To make a successful part, this loss of molecular weight must be anticipated and designed into the part well before injection molding.

Finally, the last significant challenge faced by anyone planning to use these bioresorbable materials is the extremely high cost of the polymer. Coupled with the difficulty in processing the material, this often results in significant cost during the development and scale-up of the newly developed product.

Manufacturers must be aware of and willing to work through these high material costs and processing challenges from the start of developing the new medical device. Otherwise they are in for a disappointing surprise.

PlasticsToday: Do you have any insights on the growth of bioresorbables in the medical market?

Czuba: I believe that even though these materials have been around for almost 40 years and have been getting much more attention in the last 10 to 15 years, there has been little in the way of new products made from them introduced into the marketplace. Start-up and small companies have produced a number of newer materials and there has been published research done on a variety of newer materials, but few have caught on or been adopted for use in marketable products. This has resulted in a reduction in the number of companies supplying these new materials, and even the variety of bioresorbable materials available for use has shrunk.

But for the few major suppliers out there, they are becoming more efficient at making these materials and as their production volumes grow, there is an improvement in economies of scale leading me to believe that there is an optimistic future for these materials, at least the popular ones.

I also believe that as more and more information becomes available about products made from these bioresorbables, other companies and entrepreneurs will become familiar with using these materials and comfortable with their use in long-term implantable medical devices. I do believe that their use and adoption in implantable medical devices will grow in the near future based on all the activity that I currently am witnessing.

PlasticsToday: A recent milestone in bioresorbable medical products is FDA’s approval of Abbott’s Absorb GT1 Bioresorbable Vascular Scaffold. Are there any other products in the pipeline that we should be aware of?

Czuba: For the last several years, researchers primarily in university research labs have been investigating the use of bioresorbables in implantable electrical circuits. These carefully designed implants are intended to be put in place in the body and perform some function for the short time they were designed to be used. After their intended function is completed, the implant would then be resorbed (electrical circuit and all!) by the normal process, which make these materials so useful and promising in these applications. I am also aware that there are bioresorbables being developed and used as liquid adhesives for surgical wound sealing, tissue coating and tissue scaffolding and the products being conceived are exciting and eventually will bring many new applications to the healthcare industry.

PlasticsToday: Looking further ahead, what would you like to see in terms of future breakthroughs in bioresorbable technology?

Czuba: I think that until the material pricing can be brought down via a combination of increased volume requirements throughout the industry and by additional suppliers entering the marketplace resulting in more competitive pricing, these materials will only gain a very slight foothold in the industry. But with lower prices and increased supply, I can envision that these materials could even become useful as possible “sharps” products. Imagine a scalpel blade or a needle used for drug injection which after use is placed in a pan of water and the sharp part is dissolved or melted away and is no longer sharp! In existing metal products, these sharps often lead to so-called “needle stick injuries” in the healthcare workers community, which would be resolved if the resorbable tip, point or sharp part of the blade dissolved.

Another application that is likely to become useful in the future is in drug delivery, especially in slow-release medication delivery. Much like existing slow release medication capsules, these resorbable polymers could be adapted to even longer-term drug release. The beauty of bioresorbables is that, depending on the polymer selected for use, the time for dissolution can be designed into the product and for long-term requirements will offer dialed-in product delivery. I really think that this specialty material will be the newest material technology of the future upon which many new products in the healthcare industry will be based.

Len Czuba is President of Czuba Enterprises (Lombard, IL), a product development organization specializing in plastics and medical devices. He can be reached at 630/627-9242 or via e-mail at [email protected].

Steve Coulter, PhD, Senior Associate at Fallbrook Engineering (LaQuinta, CA) contributed to this article. He can be reached via e-mail at [email protected].