Biostable materials

Medical PUs are another subset of PU elastomers. Segmented PUs were first suggested for use in a biomedical application in 1967. ° Early work with PU elastomers showed that these materials could be used for implants without causing a large, unwanted inflammatory response. The first medical devices made of PUs, however, were found to be susceptible to hydrolysis and degraded faster than desired. ° From that time, new biostable materials have been developed for use as pacemaker leads, catheters, vascular grafts. 

An alternative approach is to blend the silk fibroin filaments with more biostable materials. Initial trials in our laboratory have demonstrated that weaving silk fibroin filaments with polyester (PET) yarns to fabricate a 4 mm diameter tubular prosthesis provides both superior mechanical properties and improved cytocompatibility compared to current commercial ePTFE devices. Zhang s group at Soochow University has taken a tissueengineering approach to electrospin a tubular composite scaffold from a... 

The biostable materials such as metals, ceramics, glasses, polymers, and stable composites are intended to stay in a body for the patient s lifetime and function appropriately. They should be physiologically inert, cause only minimal response of the surrounding tissues, and retain their properties for years in vivo. Biostable materials have wide application in permanent prostheses such as joint prostheses, sutures, and other implants. 

Over the past two decades, the trend of using biodegradable materials instead of biostable materials has rapidly emerged in the case of various applications [44]. Because of the diverse features of polymeric materials, biodegradable polymers are rapidly replacing other materials such as metals, alloys, and ceramics [45]. This tremendous increase in the use of biodegradable materials supports the prediction that many of the permanent prosthetic devices used currently will be replaced by biodegradable devices in... 

We were also criticized for implanting materials, but not devices for 2 years prior to clinical use. In fact, it seemed quite reasonable at that time that a biocompatible and biostable material would make a biocompatible and biostable lead. In fact, we now know that even 2-5-year implants of devices in canines may or may not necessarily produce measurable ESC or MIO (depending on the lead model). Nonetheless, lead failure due to ESC, MIO, and crash in humans was reported in... 

Polyurethanes as Biomaterials. Much of the progress in cardiovascular devices can be attributed to advances in preparing biostable polyurethanes. Biostable polycarbonate-based polyurethane materials such as Corethane (9) and ChronoFlex (10) offer far-reaching capabiUties to cardiovascular products. These and other polyurethane materials offer significant advantages for important long-term products, such as implantable ports, hemodialysis, and peripheral catheters pacemaker interfaces and leads and vascular grafts. 

The ability of these peptidomimetic collagen-structures to adopt triple helices portends the development of highly stable biocompatible materials with collagenlike properties. For instance, it has been found that surface-immobilized (Gly-Pro-Meu)io-Gly-Pro-NH2 in its triple-helix conformation stimulated attachment and growth of epithelial cells and fibroblasts in vitro [77]. As a result, one can easily foresee future implementations of biostable collagen mimics such as these, in tissue engineering and for the fabrication of biomedical devices. 

Successful applications of materials in medicine have been experienced in the area of joint replacements, particularly artificial hips. As a joint replacement, an artificial hip must provide structural support as well as smooth functioning. Furthermore, the biomaterial used for such an orthopedic application must be inert, have long-term mechanical and biostability, exhibit biocompatibility with nearby tissue, and have comparable mechanical strength to the attached bone to minimize stress. Modem artificial hips are complex devices to ensure these features. 

Mathur AB, Collier TO, Kao WJ, Wiggins M, Schubert MA, Hiltner A, Anderson JM. In vivo biocompatibility and biostability of modified polyurethanes. Journal of Biomedical Materials Research 1997, 36, 246-257. 

The native properties of high surface area, luminescence, tunable biostability, and reactive surface chemistry identify porous silicon as a potentially useful substrate for a variety of tasks. Presented below are several uses that have been developed by exploiting the chemical reactivity or changes effected by chemical interactions with the nanocrystallites. These applications range from use as a material or structural implant to use as a sensor or analytical support. 

The way to increase the enzyme resistance of cellulose ethers is to limit the amount of unsubstituted anhydroglucose units by adjusting the reaction conditions accordingly. In other words, to increase the degree of substitution rather than the molecular substitution, as is shown in this Fig. 6. The resulting cellulose ether is known as biostable or "B"-grade material. 

The selection of suitable polymers for medical use focuses attention on the inertness of the polymer, its mechaiucal properties, and the extent of its biostability. It is useless implanting a polymer in the body that will be rejected or will degrade to produce toxic materials. The sample should also be pure and free of plasticizer, which might leach out and cause harmful side effects. The polymer has to be resistant to mechanical degradation and particularly abrasion, in case the abraded particles act as irritants. These conditions tend to limit the choice. 

A.J. Coury, Chemical and biochemical degradation of polymers intended to be biostable, in B.D. Ratner, A.S. Hoffman, F.J. Schoen, J.E. Lemons (Eds.), Biomaterials Science An Introduction to Materials in Medicine, third ed.. Academic Press, Elsevier, Waltham, MA, USA, 2013. 

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