Shape Memory Polymers in biomedical applications and beyond

A number of research studies are on stream to use the unique characteristics of shape memory polymers (SMP) in biomedical applications. Recent works are examining how the changes in chemistry and structure of SMPs have a bearing on their chemical, biological and mechanical properties in order to be used in biomedical devices for treatment of circulatory, nervous and skeletal systems.
SMPs have both a visible, temporary form and a stored, permanent form. Once in its original form, the shape memory material is molded into a second temporary form by skillful heating, deformation, and finally, cooling. These polymers can be provisionally stretched or compressed into forms larger or smaller than their final shape and further get restored to their permanent shape due to the heat, light, local chemical environment or any other change in stimulus. A shape memory polymer (SMP) is composed of two components with different thermal characteristics, oligo(e-caprolactone)diol and crystallisable oligo(?-dioxanone)diol, each already used separately in clinical applications such as drug delivery. The biodegradable multiblock copolymer features a hard segment and a �switching� segment, which are linked together in linear chains. The higher-temperature shape is its permanent form, which it assumes after heating or any other stimulus change. Smart polymers may change conformation, adhesiveness or water retention properties, due to slight changes in pH, ionic strength, temperature or other triggers.

According to its developers, Dr Andreas Lendlein and Dr Robert Langer, SMPs can find their way into modern and minimal invasive medical devices such as surgical sutures that allow an optimized tightening of the knot or in allowing bulky implants to be placed in the body through small incisions. This can largely result in reducing the scars, speeds the healing process and reduces the risk of foreign infection. Further, these intellectual polymers can expectedly aid in opening blocked arteries, probe neurons in the brain and engineer a tougher spine. Also, targeted drug delivery has been a widely used application of these SMPs. SMP matrices release drugs by a chemical or physiological structure-altering reaction, often a hydrolysis reaction resulting in cleavage of bonds and release of drug as the matrix breaks down into biodegradable components.
教授Ken Gall乔治亚理工学院的技术nology feels that the mechanical properties of the SMPs make them a lucrative prospect in developing ultra generation biomedical devices. He emphasizes his research on how to enhance the effectiveness of such SMPs for applications in biomedical devices, and believes that the metallic cardiovascular stents can be overridden by the SMPs as polymers more closely resemble soft biological tissue. However, special heed should be given to biofunctionality, biostability and biocompatibility of the SMPs which come into close proximity with tissue and body fluids. This research group has designed a shape-memory polymer stent that can be compressed and fed through a tiny hole in the body into a blocked artery, just like a conventional metallic stent. Thereafter, temperature inside the body makes the polymer expand into its permanent (original) shape, resulting in a natural operation without supplementary devices.

MedShape Solutions, an early stage medical-materials company based in Atlanta, is developing devices to improve the treatment of human orthopedic conditions. The company�s research is streamlined and includes shape memory polymers and alloys � solid materials that change shape on demand. The ability of these materials to mold actively to human bone and tissue is expected to make them useful in several types of reconstructive surgery.
Germany�s mNEMOSCIENCE GmbH is a company that specializes in the design, manufacture and commercialization of innovative biocompatible shape memory polymers (BIO-SMP�) which may be applied to various industries such as medical devices, automotive, electronics, textiles or packaging, and may enable the development of ground-breaking products and therapies. The company recently announced the completion of a global licensing agreement for an application of its BIO-SMP� with Aporo Biomedical. Aporo Biomedical will use the BIO-SMP� in both patent foramen ovale (PFO) and femoral artery closure devices. Initially, the BIO-SMP� will be commercialised in absorbable surgical sutures and vascular stents, and later expanded into other applications, such as non-absorbable sutures and non-vascular stents, and other industries.

Changing the chemistry of SMPs in order to tailor its strength, stiffness, stretchiness and expansion rate is another imperative area of research. Researchers have found that altering the backbone of SMPs influences the stiffness of polymer thereby allowing it to resist immense strain before falling. Such alterations in polymers can lead to applications where rapid recovery is required. Also, researchers are working to develop polymer materials having size of a single strand of hair (around 100 microns) for insertion into the brain tissue, which would change shape inside the brain due to change in temperature without affecting the adjoining tissues. Such materials can also be applied in minimal invasive spinal surgery. More and more research is being commissioned in the US to develop SMPs for spinal surgery which exhibit high stretchiness and weight carrying ability as seen in the spinal disks. Nevertheless, changing the stiffness of the polymers used in implants could also aid in fighting or sustaining biofilm formation. Researchers from the Massachusetts Institute of Technology have discovered that bacteria use a sense of touch in deciding where to form biofilms, which are colonies of microbes that grow on medical implants and other devices, and play a key role in hospital acquired infections, HAI. This will surely result in more secure implants which use SMPs, for fighting biofilms. On the other hand, SMPs could also be used to develop materials capable of sustaining cultures of beneficial bacteria.

Besides biomedical applications, SMPs are increasingly expected to enter wide ranging applications including components in automotive, electronics, aviation and other industries. In automotive industries, these polymers could find its way in bumpers, fascia panels or any other exterior car body sheath which are vulnerable to crashes and deformations leading to dents. In the case of a deformation in a fender, the undamaged original shape is of vital importance. The impact (in form of a crash or accidents) results in a temporary form, which changes back to the original form upon heating � in effect, the plastic repairs itself. In aviation industry, SMPs can aid in developing the morphing wing technology which are of immense significance for personal aviation vehicles (PAVs).
Airplanes are designed to cruise at one altitude and one Mach number. However, with change in flight conditions, planes could change shape continuously to maximize efficiency at all times. To accomplish this feat, aircraft will be built of not only aluminum alloys and advanced composites, but of SMPs and plastics. Like a bird in flight, which constantly adjusts its wings to compensate for gusts and patches of lift, the aircraft of the future will be in a constant state of change, altering the shape of its wings and control surfaces, and narrowing or flaring its engine exhausts.

总之,在biomedi smp的应用cine are expected to increase due to their programmability and unique mechanical properties. Importantly, biocompatibility, biodegrability and ease of processing are vital factors for their acceptance in a number of applications. Altering the SMP�s chemistry can further enhance their applications in drug delivery, spinal surgery, probing brain cells, fighting or sustaining biofilm formations and the like. Nevertheless, these smart polymers can also be stretched beyond biomedical applications for automotive, aviation and other industries which can benefit from its intrinsic shape changing properties.