Sabine Fleming, Evonik Health Care, Evonik, explains how medical device companies can use bioresorbable materials to develop devices which improve patient outcomes.
Evonik
Apply and demand: Some of the typical applications for bioabsorable polymers include sutures, rods, plates, screws, and scaffolds for tissue engineering
Medical device manufacturers are challenged to design, develop, and manufacture products which enable the production of innovative therapeutic solutions. In order to ensure the production of these therapeutic solutions, there are many important aspects that must be considered to help facilitate improved patient outcomes. These considerations include device design, material selection, processing, sterilisation, biological response, and end use environment. For this article, we will focus on material selection, namely bioresorbable polymers which are biocompatible materials that offer medical device companies flexibility in design and processing methods.
What are bioresorbable polymers?
Bioresorbable polymers are materials that are absorbed in the body after performing the desired therapeutic function. Implants produced with bioresorbable polymers are decomposed in the body by natural degradation pathways into water and carbon dioxide. There are two kinds of bioresorbable materials, biopolymers which are naturally derived and biopolyesters which are synthetically produced. Biopolyesters include for example polylactide (PLA) poly lactide-co-D, L lactide (PLDL,) poly lactide-co-glycolide (PLGA,) poly lactide-co-caprolactone (PLCL,) poly caprolactone (PCL) poly dioxanone (PDO,) and poly lactide-co-trimethylene carbonate (PL-TMC). These biopolyesters are available as either amorphous or semi-crystalline polymers which provide a range in mechanical strength and degradation profile. Bioresorbable polymers provide the possibility to customize the level of crystallinity, hydrophilicity, molecular weight, and degradation profile of the polymers to further improve mechanical properties and biocompatibility.
Typical applications
Bioresorbable polymers have been successfully used in low load bearing applications due to their mechanical properties and degradation profiles. Some of the typical applications include sutures, rods, plates, screws, and scaffolds for tissue engineering. The possibility to fine tune these polymers based on targeted part performance requirements provide medical device manufacturers flexibility in design for optimal functionality in their device.
Cranio-maxillo-facial (CMF)
Poly L-lactide-co-D, L lactide (PDLLA) have good tensile strength, excellent mechanical and thermal properties and are used in various orthopedic applications including cranio-maxillo-facial devices which are used to treat deformities in the head. Since most of these applications do not require the implant to be placed under an elevated mechanical load, bioresorbable materials used for these treatments have focused on enhancing the biological response and ability to promote healthy bone regeneration without causing any adverse side effects upon degradation. One of the design benefits of such implants made with bioresorbable materials is the possibility to shape the CMF plate to the desired geometry in the operating room using heat to ensure an ideal fit with the patient’s anatomy.
Sutures and suture anchors
Poly dioxanone (PDO) provides medical device manufacturers with a polymer that allows them to manufacture a device requiring flexibility, good mechanical properties, and fast to moderate degradation profile of 6 to 12 months. This material is ideal for sutures because it is able to hold regenerating tissue systems in place long enough to allow for full healing at which point the suture would degrade and be resorbed by the body. Polylactides (PLA,) poly L-lactide-co-D, L lactide (PDLLA,) and poly lactide-co-glycolide (PLGA) materials are options for producing suture anchors due to their mechanical properties and moderate degradation profile. Some medical device manufacturers also offer suture anchors made from a composite blend of bioresorbable polymers with calcium phosphate to enhance bone growth. Such implants help provide quality patient outcomes and improved patient satisfaction.
Material World
Material world: Interference screws are used in reconstructive surgery of the anterior cruciate ligament within the knee. The mechanical properties of bioresorbable materials make PLA, PLGA, and PDLLA particularly advantageous material options.
Interference screw
Interference screws are used in reconstructive surgery of the anterior cruciate ligament (ACL) within the knee. For this particular application, the mechanical properties of bioresorbable materials as well as the ability to prolong the degradation time makes polylactide (PLA) poly(lactide-co-glycolide) (PLGA,) and poly(L-lactide-co-D, L lactide) (PDLLA) particularly advantageous material options. As with suture anchors the addition of calcium phosphate helps promote bone growth, while absorbing at a slow enough rate to allow proper functionality of the implant. This controlled degradation is highly beneficial for this application as the ingrowth of bone tissue into the interference screw region allows for the native tissue fixation of the implanted tendon to occur resulting in better patient outcomes once the bioresorbable screw is completely degraded.
Scaffolds for tissue engineering
Scaffolds are devices which are used for tissue engineering applications such as bone, cartilage, ligament, skin, and vascular tissues. These products are three dimensional structures, typically porous and hydrophilic, which must be biocompatible and should resorb at the same rate as the repair site remodels. Bioresorbable composites highlighted in the above applications are examples of materials which help to provide tissue engineering products for orthopedic applications. Such polymeric structures help promote the regeneration of bone and cartilage while addressing the mechanical need of the targeted repair site. Polycaprolactone is another polymer which is used to manufacture scaffolding for tissue engineering and is different from lactides and glycolides in its’ high elongation and high permeability. All of these bioresorbable polymers are ideal implant materials in terms of biocompatibility and tailorable degradation parameters.
Versatility in processing methods
Bioresorbable materials may be processed via traditional manufacturing methods including injection moulding, extrusion, compression moulding and machining. These polymers may also be used in novel manufacturing methods such as electrospinning, selective laser sintering, and fusion deposition modeling. This versatility in fabrication processes provides device manufacturers the opportunity to produce intricate devices using the method which best meets their part requirements. However, to achieve the targeted mechanical performance of the final device, manufacturers should consider the suitability of the implant design in addition to the material properties and fabrication processes. The degradation profile of the final device depends on multiple factors such as polymer crystallinity, molecular weight, part design, sterilisation method, and in-vivo environment. These considerations are especially important when designing implantable devices with bioresorbable materials.
Benefits of bioresorbable polymers in medical device applications
Bioresorbable materials are used in implant applications because they help facilitate the healing process while temporarily restoring the functionality in targeted areas and eventually absorbing within the body without a trace. Such implantable medical device applications include orthopedic fixation devices, surgical screws, plates, and coronary stents. Unlike other biomaterials, bioresorbables may minimise the need for follow up surgical procedures. Hence, the breadth of commercially available bioresorbable materials along with the possibility to create unique custom polymers offer medical device companies many options in developing devices which deliver life improving therapies.