Printer Friendly

Versatile silicones adapt to future healthcare challenges.

Silicones have a long and successful history of utilization in healthcare products, thanks in large part to their documented biocompatibility and demonstrated biostability in various intra- and extra-corporeal applications. Silicone materials also possess additional desirable material properties such as thermal and chemical stability, electrical insulation and low surface tension, as well as high gas permeability which can make them particularly appropriate for a variety of specific uses. Beginning with applications such as syringe coatings and tubing for catheters, drains and shunts, silicone use in medical devices has progressively grown and diversified. Current applications include a wide range of life sustaining and enhancing implants, as well as ophthalmologic, wound care and drug delivery products.

In addition to enabling past and present innovations, silicones offer strong potential for addressing future healthcare challenges. Key reasons include the diverse range of silicone materials, including resins, elastomers, gels, adhesives and fluids, and the exceptional design freedom they offer. Combined with the other unique attributes these products provide, such as comfortable feel and softness, manufacturers are able to address important trends, including the aging of the population and the decentralization from acute to home care settings. Extensively used in electronics, silicones also support new medical devices that incorporate wireless and other advanced technologies, such as remote monitoring devices and point-of-care diagnostics.

Brief history of silicones in healthcare

The initial use of silicones in the medical field was in the prevention of blood coagulation. In the 1940s, Canadian researchers coated syringes, needles and vials with methylchlorosilane. When rinsed with distilled water, the silane hydrolyzed and formed a silicone coating on the glass and metal substrates that delayed blood clotting (ref. 1). A side benefit of coating needles with silicone was reduction in the patient's pain when inserted. Figure 1 shows significant reduction in penetration force associated with the silicone-coated needle, as per DIN 13097 (ref. 2).

Another early silicone application was in long-term implants, including a bile duct stent (ref. 3), an artificial urethra (ref. 4) and the first hydrocephalus shunt with a reliable one-way pressure relief valve (ref. 5). These initial applications generated great interest among members of the medical community, who sent many inquiries about silicone materials to leading silicone manufacturers at the time, including Dow Coming. Over the next several years, catheters, shunts, heart valves, aesthetic implants, orthopedic implants and equipment for kidney dialysis and blood oxygenation were developed using silicones.

Today, the applications for silicone materials in medical devices, pharmaceutical manufacturing and other healthcare fields are extensive and diverse, ranging from silicone pressure-sensitive adhesives used in transdermal drug delivery for conditions such as Alzheimer's disease, to needleless access ports for intravenous fluid delivery.

Silicones have amassed a long and well-documented history in healthcare. Medical silicones possess excellent properties, including chemical and thermal stability, low surface tension, hydrophobicity and gas permeability. These characteristics helped establish silicones as vital resources in the medical field and are key to the materials' apparent biocompatibility and biodurability. Silicones can also bestow desirable tactile properties for sensory advantage. Complementing these characteristics, silicones offer exceptional design freedom, ease of processing and the ability to be preloaded with various agents, such as drugs and excipients to create combination products.

For these and other reasons, silicones are already being drawn upon for next-generation healthcare innovations. In particular, silicones help manufacturers meet current and future healthcare challenges. These include enhancing safety and regulatory compliance, improving patient outcomes, emphasizing diagnostics and prevention, serving the needs of an aging population, managing chronic diseases and accommodating decentralization from acute care settings to home or outpatient facilities.

Silicones align with top healthcare trends

A number of emerging applications for silicones demonstrates their value in addressing macro healthcare trends.

Strengthening safety and compliance

In today's climate of increased regulatory oversight and consumer focus on drug safety, pharmaceutical manufacturers are turning to single-use systems for the production of their products. Single-use systems have been shown to be an effective way to address cleanliness and traceability issues that can prove problematic using traditional manufacturing equipment. By disposing of the system after each batch of a drug has been manufactured, pharmaceutical companies can ensure that there is no cross-contamination or carry-over from a previous batch. Furthermore, it is easier to provide validated assurance of cleanliness and purity to the U.S. Food and Drug Administration and other regulators using a disposable process instead of attempting to fully clean and reuse traditional equipment. Silicone tubing and manifold assemblies are playing an important role in this technology: They are easily sterilized, have limited interaction with the drug product and, importantly, are cost-effective to replace overall.

Improving patient outcomes

The growing emphasis on better patient outcomes and higher quality of care encompasses a range of issues. One is infection prevention. An estimated 44,000 to 98,000 Americans die each year from hospital-acquired infections (HAls) (ref. 6). Plus, with new regulatory mandates for Medicare and Medicaid prohibiting federal payments to states for treatment of certain hospital-acquired conditions, there is increasing financial pressure on hospitals to find new and better solutions for prevention, which supplements their Hippocratic motivation.

To help avoid infections, particularly microbial biofilms, the most prevalent form of medical device-related infection (ref. 7), many device manufacturers use antimicrobials such as antibiotics in their products. A promising new technique is bulk loading the antimicrobial, antibiotic or other active into a silicone elastomer prior to supplying the device manufacturer (ref. 8).

Silicone is widely used in urinary catheters and some small-diameter intravenous catheters, two key focus areas for HAl regulation. Integrating the active into the silicone material at an early stage in the process, rather than applying it afterwards, gives a medical device manufacturer better control of variables to achieve the desired release profile, such as an initial burst of active, a controlled rate of release over months or no release (ref. 8).

Another aspect of improving outcomes is faster recovery after a surgical procedure. Drugs preloaded into silicone rubber components used in implanted devices can deliver a focused local dose at the operative site, possibly avoiding complications such as infection, resolving inflammation and accelerating the post-surgical recovery process. Cardiac rhythm management is just one of many healthcare disciplines benefiting from this drug/device combination approach.

Chronic disease management

With the aging of the population and the increase in obesity rates, the prevalence of chronic diseases is on the rise. Silicones are being used in certain bariatric surgeries to treat obesity, a risk factor in chronic illnesses such as diabetes and heart disease. Silicones are used to manufacture gastric bands, thanks to their elastomeric properties, inertness in the body and long history of successful use in implantation.

The electrical insulation properties of silicones are used in neuromodulation therapies for chronic pain and movement disorders such as Parkinson's disease. In the latter instance, a small electronic device, similar to a pacemaker, is implanted in the body and transmits electrical signals to electrodes in specific areas of the brain, allowing the patient better movement control. Silicones are highly effective for insulating the leads that carry these signals.

Increase in non-acute and home care

To reduce costs and accommodate patient preferences, healthcare delivery is moving from the hospital to the home or non-acute care setting. This decentralization trend is driving the need for portable, consumer-friendly devices and equipment. The design flexibility of silicones helps enable compact designs, and their attractive tactile sensory attributes (smoothness, softness, resilience) make them appealing to consumers. Silicones have already been proven effective in the diaphragms of infusion pumps, enabling precise dosages of needed medication and nutrition. Now, the design freedom afforded by these materials is helping engineers create portable versions. In one case, silicones are being used in the cassettes of home dialysis equipment, which promises to free patients with renal problems from spending many hours in a dialysis clinic.

Related to the non-acute care movement is the continuing increase of non-invasive or minimally invasive procedures done on an outpatient basis. Advancements in technologies such as endoscopy allow clinicians to perform a wide array of procedures with minimal and smaller incisions. Silicones are a preferred material for the seals between the endoscope housing and working channels of the tools because they help prevent leaks in the flexible instruments, helping the clinician focus more on the procedure to achieve the necessary precision and effectiveness.

Emphasis on prevention

Two key healthcare drivers, cost reduction and better patient outcomes, converge in the shift to prevention and early diagnosis efforts. Here, silicones are playing a part in streamlining laboratory testing for the patient. The concept of the laboratory on a chip is delivering on its promise to accelerate testing and minimize the amount of sample drawn from the patient. One small blood sample, in many cases a single drop, can be analyzed using a specialized glass slide or chip to perform a number of different diagnostic tests. Silicones are being used in these up-and-coming devices due to their relative inertness and ability to be molded into small, precise geometries needed to process and test the patient's sample.

More efficient laboratory tests, and the data they supply, also support the strong movement toward evidence-based medicine. The accumulation of volumes of accurate data can help physicians document best practices.

Conclusion

Today, silicones are among the most thoroughly tested and successful materials used in healthcare applications. The valuable properties of silicones that led to noteworthy innovations since the 1940s continue to drive new designs in medical devices, equipment and patient diagnostic processes. Ongoing advancements in silicone materials, including new technologies for the loading of actives and other agents, are enabling the next wave of healthcare technologies.

References

(1.) L.B. Jaques, E. Fidlar, E.T. Feldsted and A.G. MacDonald (1946). Silicones and blood coagulation. Can. Med. Assoc. J., 55:26.

(2.) Jim Curtis and Andre Colas (2013). "Medical applications of silicones, "Biomaterials Science: An Introduction to Materials in Medicine. Third edition. Eds. Buddy D. Ratner, Allan S. Hoffman, Frederick J. Schoen and Jack E. Lemons. Amsterdam: Academic Press/Elsevier, pp. 1,106-1,118.

(3.) F.H. Lahey (1946). Comments made following the speech, "Results from using Vitallium tubes in biliary surgery," read by H.E. Pearse before the American Surgical Association, Hot Springs, VA. Ann. Surg., 124:1,027.

(4.) R.R. DeNicola (1950). Permanent artificial (silicone) urethra. J. Urol., 63 (1):168-172.

(5.) J.S. Baru, D.A. Bloom, K. Muraszko and C.E. Koop (2001). John Holter's Shunt. J. Am. Coll. Surgeons, 192: 79.

(6.) D.J. Murphy and P J. Pronovost (2010). Reducing Preventable Harm. Arch. Intern. Med. 170 (4).

(7.) M. Shirtliff and J.G. Leid (2009). The Role of Biofilms in Device-Related Infections. Springer Series on Biofilms, Vol. 3.

(8.) J. Curtis (2013). Active-Loaded Silicone Materials for Medical Devices to Help Prevent Hospital Acquired Infections. Medical Design Briefs, in press.
COPYRIGHT 2013 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Curtis, Jim; Inman, William, Jr.
Publication:Rubber World
Date:Jun 1, 2013
Words:1796
Previous Article:Designing silicones for medical device applications: an overview.
Next Article:Extrusion of low friction and low tack microstructured surfaces on silicone rubber.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters