Silicones big ticket to health sector

February 26, 2012

Liquid Silicone RubberLONG associated with feeding bottle nipples and breast implants, silicone rubber is forecast to be the next billion dollar industry to tap the changing yet highly lucrative prospects in the medical and healthcare sectors

A steady pipeline of innovative materials is becoming a prescription for big-ticket health and lifestyle industry and its medical and healthcare sectors. Thanks to the discovery of pathogens and improved management of emerging diseases that call for technical innovations in materials, the healthcare sector is expanding deep and wide.

Alongside this, the silicones industry is filling in created niches by broadening its scope of application as well as improving properties.

The basic raw material for silicone rubber is sand or silicon dioxide (silica). Sand is processed into pure silicone metal and then is reacted with methyl chloride, followed by an additional series of steps to create the many forms of silicone, from fluids and polymers to finished rubber bases and compounds.

Unlike most plastics, silicones have a backbone of alternating atoms of silicon and carbon, with organic side chains that impart curability and other properties.

One such form is liquid silicone rubber (LSR) that has some processing characteristics in common with
thermoplastics, along with some notable differences that are inherent in a thermoset. LSR, thus, offers
properties not obtainable with today’s TPEs.

LSR’s are crosslinked utilising a platinumcatalysed reaction that produces no by-products. Once cured, LSR cannot be reshaped or easily reused or recycled. To do so requires a great deal of energy to overcome and break apart the crosslinks and/or the backbone itself. This same molecular structure makes LSR useful over a wide range of temperatures.

At the same time, the strong bonds between the silicon and oxygen atoms mean that the polymer does not degrade until heated to temperatures above those that most other polymers can withstand.

Another of LSR’s major attributes is its chemical inertness or purity. Coupled with its ability to withstand sterilisation processes, this makes LSR’s ideal for many medical and baby care products.

Healthy Asian market

Just how big the silicone industry has become can be gleaned from a recent global silicone market
report by Freedonia Group. It points to the Asia Pacific region as the largest and fastest-growing outlet for silicones through 2015 that also accounts largely for the 6.2% growth for silicones in various industries including healthcare.

Moreover, the unique properties of silicones, such as thermal stability, good electrical insulation, high
gas permeability, low chemical reactivity, non-stick and water repellent factors, are being sought after in
several types of industries; notwithstanding the bio-friendly nature of the polymer that makes it a viable
option in healthcare.

Freedonia pegs the industry’s worth at US$12.4 billion by 2015, citing also that the growing silicone market in China factors in the double-digit gains despite a slowing from the nearly 20% growth marked during the 2000-2010 period.

The economic recession, particularly in North America and Western Europe, the historical centres of the world silicone industry, as Freedonia says, has slackened demand. But this will be balanced out by the incremental demands in Asian countries such as South Korea, Taiwan, India and Japan and an above-average growth in Central and South America, Eastern Europe and the Africa/Middle-East region, the report also indicates.

Overall, the increased demand for silicone has undergone some baptism of fire. Today’s consumer standards have raised the bar for the silicone industry that it has to keep at stringent materials and environmental regulations as well as standards for biocompatibility, high performance and bacterial resistance.

An alternative to latex

Silicone products for medical and healthcare use vary and include, but are not limited to, tubes, drains, feeding tubes catheters and implants for long and short term use. Exhibiting a unique blend of characteristics including excellent bio-compatibility with human tissue, silicones enable medical devices to be used comfortably and without producing an allergic or negative body reaction, compared to the use of natural rubber latex.

A recent example of the use of silicone use instead of latex comes from US-based medical products maker MedPlast that has devised an assembly for a silicone pessary balloon used in a variety of female gynecological conditions, including prolapse. In years past, such devices were made of latex, which is relatively easy to work with, but from the medical standpoint contains proteins that can cause an allergic reaction.

As a result, medical product makers may now specify silicone, which offers advantages for patients but represent a manufacturing challenge since silicone offers poor tear resistance compared to natural rubber.

MedPlast says that the balloon section of the multi-piece product is thin and has to be stretched and there are difficult de-moulding transitions. For this, the company made a special part to de-mould without over-extending the piece. This Inflat-o-Ball pessary, created by MedPlast for CooperSurgical, includes a moulded part, a check ball and a glued-on silicone extrusion.

Safe materials

With inherently low toxicity, pure silicones present a low risk of unfavourable biological reactions and have gained widespread medical recognition and acceptance. Medical grade silicones, classified as non-implantable, short-term implantable and long-term implantable, have been tested for bio-compatibility and are appropriate to be used for medical applications. In the US, the Food and Drug Administration (FDA)
regulates materials implanted into the body. Medical grades are approved as USP Class V and VI with most medical silicones falling in the Class VI certification. While the latter can be in contact with human tissue no longer than 29 days, implantable silicone grades can be implanted in the human body indefinitely.

Several companies are engaged in manufacturing raw silicones, which include Wacker Chemie, Bayer, Dow Corning, Shin Etsu, NuSil Technologies and Momentive Performance Materials. For these companies testing is continuously done to ensure material safety.

Over the years, there have been concerns over potential liability and risk of silicone use and that has prompted several large providers to stop producing long-term implantable silicones.

US-based NuSil Technologies, a manufacturer of silicone compounds for the healthcare and pharmaceutical industries, is one company that still continues to manufacture silicones for long-term implants.

Continuously innovating long-term implant silicones, the company announced recently the release of MED-6671, a room temperature curable coating that is said to significantly decrease the coefficient of friction of a cured silicone surface. The new product is designated unrestricted and may be considered for long-term implant applications of 29 days or longer.

A one-part silicone coating, it is dispersed in tert-butyl acetate. Once cured, the coating chemically bonds to the silicone elastomer substrate, imitating its mechanical properties. This results in a smooth finish with a durable, yet flexible coating that resists abrasion from moving, sliding and rubbing parts.

New silicone grades

At the K2010 show, German chemical firm Wacker introduced a range of silicones for the medical industry. Included are solid silicone rubber grades that cure to elastomers of low surface friction. Of this, Silpuran 8630/60 is a high-purity silicone product developed specifically for medical applications. The low friction effect of the solid silicone is based on a special formulation concept that circumvents the drawbacks of traditional oil exuding silicones.

Last year, Wacker also introduced a LSR grade for radiation-sterilisable silicone valves used in medical devices. Silpuran 6610/40 serves in the production of bio-compatible silicone valves whose slits do not close up or “heal” during radiation sterilisation. The company says it, thus, allows such valves to be made without the use of additional auxiliaries. For instance, silicone valves ensure that infusion systems administer the correct dose of liquid medication.

It also introduced Silpuran 4200 single component adhesive, which is a condensation curing silicone rubber formulation. Upon vulcanisation, it forms a silicone elastomer with mechanical strength, making it ideal for
permanently bonding components of medical devices.

At a recent medical exhibition in the US, Momentive Performance Materials presented a case study that demonstrates the ability to use UV light to vulcanise silicone elastomers that contain different thermally sensitive materials at multiple concentrations. The new Addisil UV60EX elastomer can be cured on demand by exposure to UV light, making it an ideal candidate in medical applications where lower temperatures during the
manufacturing process and typical silicone rubber physical properties are required.

UV cure silicone elastomers are just one of the proprietary platforms of enabling technology and Momentive says it is helping drive innovation in the medical device industry.

StatSil antimicrobial elastomer, developed using a technology that provides built-in antimicrobial protection in silicone-based elastomers, continues to be a featured product line. Responding to the medical industry’s heightened concern over bacterial contamination on critical device surfaces, StatSil elastomer may allow product designers to incorporate into the medical device itself antimicrobial protection for the purpose of controlling microbes in or on the human body, in examples such as catheters and wound drains.

The firm says that representative samples of StatSil HCR 50 HC and StatSil HCR 55 HC have passed USP Class VI and ISO 10993 tests.

Future of silicones There are two issues that affect the future of silicones as a biomedical product. The first is the continued availability of its component silicon. Environmentalists are now very concerned about the rapid depletion of oil, and, to a lesser extent coal, and many other non-renewable minerals mined from the planet.

Silicon is also used in the telecommunications and IT industries and since it is a non-renewable resource, it will eventually become more difficult to find and extract and thus become increasingly expensive. It is probable that the more commercial telecoms and IT sectors may be better able to carry price increases than the medical sector, whose customers tend to be government- financed healthcare systems.

The second issue, also environmental, is the disposability of waste silicone. This is the lesser of the problems, since silicone is not regarded as a toxic substance and is therefore safe if it finishes up as landfill. However, the whole issue of waste creation and disposal are also under review and may become a more serious issue later.(PRA)

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