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New applications of biodegradable plastics in medical sector gain acceptance


Biodegradable plastics, that had until now found application in packaging, are slowly capturing newer markets, particularly medical products. One reason for the rise in implant use is the performance and outcome advantages over alternative treatments, such as drugs. Another reason is the constant improvement and innovation of devices that keep getting smaller. Applications of biodegradable plastics have gained market acceptance in the medical sector in:
Medical Implants
Biodegradable medical implants is one of the fastest growing areas in the global orthopedics market expected to grow robustly in the next few years. In orthopedics, biomaterials are used in a range of surgical applications, including joint replacements, fracture fixation plates, bone defect fillers, artificial tendons and ligaments and bone cements. Other medical applications include cardiovascular, ophthalmic, sutures, burn and wound dressings, drug delivery systems, cochlear implants, dental implants and more. Implantable medical devices have long been used in orthopedic surgery to hold fractured bones in place. For many years titanium and other metals were widely used for fixing fractures. While titanium possesses the high strength, low weight and excellent corrosion resistance necessary to adequately support the healing process, it also has many disadvantages including: growth restriction; second operation needed for implant removal, implant palpability, temperature sensitivity and visibility; imaging/radiotherapy interference; and potential danger of cross-contamination.
They now have attained the performance properties to gain an inroad in the implant market to give competition to titanium as the preferred choice of implant. Since synthetic biodegradable polymer based medical implants eliminate the need for a second surgical intervention to remove the device, their use reduces the total treatment time of the patient, halves the number of operations required during the care process. It also prevents refracture occurring upon removal of a metal based implant, from the sudden transfer of load, previously borne by the implant, back to the bone. Engineering the biodegradable implant to achieve predictable degradation provides progressive bone loading, leading to better bone healing and a reduction in the risk of refracture. Biodegradable devices can be used as a foundation for drug delivery, so that the degradation rate allows for the optimal release of the drug or agent to further assist the healing process. As the benefits of biodegradable medical implants become more widely known and acceptable to the orthopedic surgeon, demand is expected to grow rapidly relative to the growth rate of the orthopedics market. Inion, a rapidly growing company focused on the development of novel biodegradable medical implants, has received FDA 510(k) clearance of its Trinion Meniscus Screw for use in knee cartilage repair. Trinion screws are used for the fixation of longitudinal vertical meniscus lesions, where the knee cartilage has torn. Inion products use a combination of four polymers--trimethylene carbonate (TMC), L-polylactic acid (LPLA), D, L-polylactic acid (DLPLA), and polyglycolic acid (PGA). Of these biodegradable polymers, highly crystalline LPLA and PGA homopolymers have the highest strength and stiffness. LPLA is a slow-degrading hydrophobic polymer, that takes more than 24 months to fully biodegrade, whereas PGA is more hydrophilic and biodegrades faster, within 6-12 months. By combining (co-polymerizing) LPLA and PGA monomers in varying proportions, Inion has extended the range of polymer properties. The addition of DLPLA, which takes 12-16 months to fully biodegrade, also has an effect on the degradation profile. The properties can be tailored further by incorporating TMC (trimethylene carbonate) into the polymer backbone. The presence of TMC has a strong impact on the malleability (flexibility) of the final products and contributes to the product's ease of use by surgeons. Inion has developed and launched products in four strategic business areas—cranio-maxillofacial surgery, orthopedic trauma, sports medicine and dental surgery. Bioplastics are also being used as suture materials.
Drug Delivery System
There is growing interest in the use of biodegradable polymers for site specific drug delivery--whether as coatings on medical devices or as devices, both fully biodegradable. SurModics, Inc. a leading provider of surface modification and drug delivery solutions to the medical device industry, has an exclusive license from OctoPlus to two novel classes of biodegradable polymers (PolyActive and OctoDEX) for use in the site specific delivery of drugs from medical devices. Privately owned OctoPlus is active in the development of pharmaceutical formulations incorporating their novel biodegradable polymers.
PolyActive is a biodegradable polymeric drug delivery system. Its biodegradability and linear release properties make it an excellent technology for the controlled release of proteins and lipophilic small molecules for both local and systemic administration, and have applications in pharmaceuticals and medical technology. PolyActive represents a series of poly (ether ester) multiblock copolymers, based on polyethylene glycol (PEG) and PBT major advantage of this system is the ability to vary the amount and length of each of the two building blocks, creating a diverse family of customized polymers. Polymer matrix characteristics such as rate of controlled release, degradation, swelling and strength can be precisely controlled by the appropriate combination of the two copolymer segments. Products made from PolyActive can be processed into various shapes and configurations, thereby allowing them to be used in a wide range of applications.
The OctoDEX drug delivery system is based on crosslinked dextran microspheres, prepared without organic solvents. The absence of organic solvents in the manufacturing process of OctoDEX microspheres enables the encapsulation of fragile proteins. The system enables high protein loading; up to 15% of protein (dry weight) can be loaded in OctoDEX microspheres. The encapsulation efficiency is very high, typically >90%. The microspheres produced are 10-50 µm in size, facilitating subcutaneous injection through a 25G needle. One of the main advantages of the OctoDEX drug delivery system over other drug delivery technologies is that it shows no burst effect, i.e. no high initial release of the encapsulated drug. The release profile can be completely controlled and after the designated release time, the active ingredient will have been fully released from the OctoDEX matrix.
Hernia Repair Device
TyRx Pharma, Inc, markets a biodegradable tyrosine-derived polyarylate component of a new hernia repair device. The company uses a combinatorially designed library of tyrosine-derived polyarylates developed by a team at Rutgers . These polymers were developed after a thorough examination of the body's natural metabolites, which highlighted that derivatives of tyrosine dipeptide were a close natural, non-toxic mimic to diphenols used in industrial plastics. The resulting tyrosine-derived polyarylates have shown strong structural and drug delivery capabilities for implants. In vivo animal testing suggests minimal tissue and blood response, even at full degradation. Developed as a coating on a surgical mesh, these polymers improve the handling capabilities of the mesh to facilitate precise placement during surgery. The coating is then reabsorbed, leaving a smaller amount of material in the body. While this partially degradable implant represents a step forward in the use of biodegradable polymers, perhaps the most significant factor is the route by which the polymer has become part of an approved medical device. The hernia device was granted clearance by the FDA using the 510(k) mechanism. 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.
Parietex ProGrip™ mesh is the first bicomponent mesh composed of monofilament polyester and a resorbable polylactic acid gripping system that facilitates a tension-free repair. This secure, self-gripping, biocompatible solution is positioned and placed in the same manner as in a standard open patch repair. The mesh's self-gripping feature provides secure fixation, reducing or possibly eliminating the need to place supplemental fixation. Made of lightweight, hydrophilic polyester, the mesh provides optimal porosity, which, in turn, fosters better tissue in-growth and may reduce pain. In addition, by working with the body's natural systems, this innovative new product reduces the amount of foreign material left in the body.

Demand for medical implants is estimated to increase 9.3% annually to US$43.6 bln in 2011, according to a report by Freedonia Group. Cardiac implants are expected to remain the top-selling group, led by stents and defibrillators, with demand expanding 9% pa to almost US$20 bln in 2011. Demand for orthopedic implants is forecast to exceed US$19 bln in 2011, up about 9% pa from 2006. Other fast-growing segments include neurological stimulators, cochlear devices and gastric bands, expected to be worth US$5 bln in 2011, up more than 13% pa from 2006. Orthopedic trauma, the largest of the four areas is a $1.7 billion market, with the plates, screws and pins portion valued at $680 million. The second biggest market is the maxillofacial market, worth $430 million annually. The two other prominent markets are sports medicine at US$250 mln and dental at about US$700 mln.

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