An online material database says it added about 6,500 new materials during a recent quarter. Its total count is over 65,000. Can you name a new one? Probably not, unless you closely monitor IDES.com or are plugged in to new material introductions from 563 global material suppliers. To keep you materially up to date, the Medical Design Staff has corralled a few recent material releases with the goal of solving at least one nagging design problem.

Should you need wider exposure than those presented here, Mike Kmetz, president of IDES Inc., Laramie, Wyoming, says the firm's search engine for the plastics industry gives users free access and points to articles, technical documents, and other useful websites. The search engine only indexes plastics-related websites, thereby providing specialized content.

“Anyone can register and access is free so you can look up data on a particular material,” says Kmetz. “The search capability in the Prospector product requires a subscription. But then users can conduct a property search to find materials with certain tensile strengths and specific Izod impact values.”

So don't be intimidated by 65,000 materials, says Kmetz. “If an application calls for a thermoplastic, for example, you ignore the thermosets, and even without IDES, you can narrow the field quickly.”

A search might also uncover alternative materials. “If a material has not been working well, another supplier might have a viable substitute at lower cost, or one that offers better performance. A software module on the Website does this rather quickly. A material search based on the datasheets produces a ranked list and alternatives that might work.

“Even free access lets you see the field of potential suppliers. With a subscription you could refine the search and get down to two or three. Then you have to give them a call,” he says.

When silicone makes a best choice

One advantage of silicone is its ability to maintain mechanical properties over a wide temperature range, -80 to 400°F and in some cases even colder or hotter. “Silicone is also naturally UV resistant which makes it ideal for use outdoors,” says Steve Hughes, application engineer at Stockwell Elastomers, Philadelphia, (stockwell.com). A few silicone foams are UL94-V0 rated, a common requirement in the transit and electronic sectors. The material also performs well in compression-set tests when compared to some organic elastomers, such as Neoprene. Silicone gaskets and pads are available in open cell foams, closed cell sponges, various durometer solids, and are readily molded in variety of colors. Silicones can also be reinforced, have high tear strength, and conduct electrically and thermally,” he says.

It's true that silicone is more expensive than some organic materials, he adds, so it's important to understand the demands and performance required. “One brand of urethane foam, for example, absorbs shock or vibration well at room temperature and it's less expensive than other foams. But move the application outdoors and into temperature extremes, and silicone foam or sponge becomes a better material.”

Low outgassing from this packaging material

A low viscosity, thermal-interface material works well at high-temperature and high-stress operating conditions in electronic packaging. EPM-2493 from Nusil Inc., Carpinteria, Calif., (nusil.com) outgasses little, making it ideal for situations, such as electro-optic systems, in which contamination is a concern.

Manufacturing and operating environments can drastically cycle temperatures, thereby embrittling or outgassing the encapsulants.

Micromolded parts as small as 0.0001-in.³

Imagine an injection-molded component comparable in size to a pinhead or one barely visible to the naked eye. Parts this small are made by Phillips Plastics Corp., Hudson, Wis., (phillipsplastics.com). The company builds its own tools and presses to make parts this small. Sizes range from 0.0001 to 0.003-in.³ for plastics and metal. Tolerances can be held to as little as ±0.0005-in.

Superelastic titanium for implants

A superelastic and titanium alloy, Flexium, is well suited for orthodontic, orthopedic, and other medical applications. The material is a metastable titanium-molybdenum based alloy with a good balance of low modulus and high flexibility. Devices and appliances made of it have a low modulus compatible with bone elasticity, excellent biocompatibility, and good strain recovery. The alloy can be used in either cast or wrought condition. Devices made of the material can be cast, cold worked, or machined and are readily joined to other titanium components and coated to finish.

The nickel-free material comes from Memry Corp., Bethel, Conn., (memry.com) and is a single phase titanium alloy of body-center-cubic structure after solution treatment and rapid cooling. The alloy possesses a critical beta stability so deformed crystalline phase change (martensitic transformation) or twining gives rise to superelastic properties.

Critical beta stability lets annealed Flexium recover a strain as high as 3.5%. Cold worked Flexium has a low modulus around 7.5 Msi (50 GPa) and exhibits linear superelasticity that recovers a strain as high as 3.0%.

Soft-tack material allows repositioning

Sil-Pad 1100ST has tack on both sides, dual liners for easy placement, and good thermal performance with an impedance of 0.66°C-in.²/W at 50 psi. The fiberglass reinforced and silicone-based material from Bergquist Co., Chanhassen, Minn., (www.bergquistcompany.com) is aimed at high-volume auto dispensing and works well in low-mounting-pressure applications. Sil-Pad 1100ST's inherent tack requires no additional adhesive layers which makes dispensing easier and interfacial resistance low. Another benefit of the tack is ease of assembly. The material can be repositioned on the target surface without quality problems often associated with PSA-coated products.

Sil-Pad 1100ST comes in sheets, rolls or in die-cut pieces of any shape or size, with a standard thickness of 0.012-in. Standard sheet size is 12 × 12-in., and the standard roll size is 12-in. × 250-ft. Typical applications include power supplies, motor controls, and between an electronic power device and its heat sink.

This foam can replace screws and rivets

Volara HPT foams rely on advanced extrusion, crosslinking, and foaming processes for tight gauge and density control. Extreme toughness makes the foams from Sekisui Voltek, Lawrence, Mass., (www.sekisuivoltek.com) ideal for low-profile mounting applications, such as mirrors, emblems, and appliqués. Thicker HPT foams can replace screws, rivets, pumpable (caulk) adhesives, as well as more costly urethane and acrylic foams, in a variety of assembly applications. Other uses include manufacturing of electro-medical devices, transdermal-drug delivery, and gaskets.

Precise thickness control allows making roll lengths to 4,500-ft. without gauge banding. The result is fewer roll changes for converters and a better match to release liner roll lengths. Absence of gauge bands also eliminates adhesives puddles while direct coating. Low-gauge variation lets manufacturers of flexographic cushion-mount tapes reduce process time and scrap, especially when they use a secondary converting process. Additional savings come by producing more than one thickness. For example, it is common practice to purchase thick foam and convert it to two mounting tapes of different thickness. The HPT line ranges in thickness from 0.012 to 0.075-in. Densities are available from 8 to 20-lb/ft³. Standard widths are 56 and 60-in., and custom widths are available.

Biocompatible foams absorb shocks

Poron medical urethanes are free of PVC and latex, and contain no solvents. They are medium density and open celled, breathable and fungal resistant for comfort, durability, and biocompatibility. The urethanes from Rogers Corp., Rogers, Conn., (www.rogerscorporation.com) are formulated for body contact uses, and meet ISO 10993 standards for body contact medical devices as defined by FDA G95. They are flexible, resistant to collapse, and possess good shock-absorption, making them ideal for cushioning. These urethanes work well as protective garment padding, monitor-device cushioning, and rehabilitative brace padding. They are available in thicknesses of 1.5 to 12.7 mm.

Bisco medical silicones offer long-term comfort and durability. Both open and closed cell structures maintain dimensional stability even when exposed to dry heat, steam, electron beam, ethylene oxide, alcohol, and gamma radiation. Additional applications include extreme-condition padding, imaging-equipment gaskets, and sterile cleanroom surfaces. The silicones meet ISO 10993 and FDA requirements for rubber articles intended for repeated use (21 CFR 177.2600). They are available in thicknesses of 0.5 to 12 mm.

Compounds for a watertight design

Several compounds from RTP Co., Winona, Minn. (rtpcompany.com) go into a small, watertight, wireless insulin-delivery device for diabetics called the OmniPod Insulin Management System. The Hudson, Wis., facility of Phillips Plastics Corp. worked with the manufacturer to develop the device and suggested a precolored translucent RTP 300 Series polycarbonate for the top housing. The material met specific mechanical-property dictates while having the necessary balance between opacity and clarity. In addition, the housing seal used an RTP Series 6002 colorized elastomer, meeting requirements for an exact color match. Lastly, the chassis used an RTP 2500 Series PC/ABS. It allows precise placement of metal plating.

Tubing doesn't have to be round

A supplier of stainless steel products now produces specialty shaped tubing. The recent profiles from Eagle Stainless Tube & Fabrication Inc., Franklin, Mass., (eagletube.com), include teardrop, hexagonal, square, oval, rectangular, among other shapes in all 300 and 400 series stainless steel, nickel-based and Inconel alloys. The shapes are used in applications ranging from handles and ornamental structural support, to wire and fluid guides.

Two materials make better tubing than one

Coextrusions are two materials simultaneously extruded into two distinct layers in one tube. The layers can be different materials letting each bring distinct properties to the tube. Some applications require a stiff inner material to increase burst strength and a flexible one on the exterior. A variety of co-extruded tubing for medical applications are available from Putnam Plastics, Dayville, Conn., (putnamplastics.com).

Implant-grade alloy well suited to injection molding

A special metal-injection technology (MIT) version of F75, an implant-grade alloy, is suitable for high volume manufacturing and is less costly than materials such as titanium. FlowMet LLC, DeLand, Fla., (flomet.com) developed the material and modified its MIT feed-stock, injection molding, de-binding, and sintering parameters to make F75 components such as hip and knee implants. According to the company, testing showed such parts meet or exceed specifications of the ASTM standard, F75-01 Standard Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants (UNS R30075). Also, F75 MIM properties compare favorably with medical grade titanium, typically Ti-6%V-4%Al.

Biodegradable implant allows pinpoint drug delivery

The Eureka In Situ Forming Matrix, part of the Eureka family of nanoengineered polysaccharides, can be used to create naturally biodegradable implants — drug reservoirs in the body. The Matrix comes from SurModics Inc., Eden Prairie, Minn., (surmodics.com). The development lets healthcare personal deliver a solution of precursor reagents (polysaccharides) and proteins in liquid form to the patient's anatomical location of interest using a minimally invasive procedure. The mixture sets-up in seconds to form the reservoir that releases therapeutic proteins as it degrades by enzyme-mediated digestion.

How Flexium compares to titanium

Property	Flexium	Ti-64
Nominal composition	Ti-9.8, Mo-4, Nb-2, V-3AI	Ti-6 Al-4V
Density, lb/in.3	4.8	4.4
Melting point, °C	1,700	1,650
Annealing temp, °C	870 to 900	700 to 785
Young's modulus, 10 6psi	7 to 10	16.5
Yield strength, 10 3psi	60 to 80	128
Ultimate tensile strength, 10 3psi	110 to 130	138
Tensile elongation, %	15 to 20	14
Reduction of area, %	40 to 45	36
Hardness, Vickers scale	300	350