Applying Tech: Implantable Devices

How are you influencing implantable devices?

Gabriel O. Adusei, MSc, PhD
Independent MedTech Consultant, Founder, International Association of MedTech Consultants 

Over the years, a significant number of implantable devices since their introduction into the market have seen changes from being inert to being bioactive to iterative developments to enhance their efficacy. One area with significant growth and success is the use of hydroxyapatite (HA) and amorphous calcium phosphate nanoparticles in implantology. Many modern implants (e.g., hip replacements and dental implants) are coated with hydroxyapatite. It has been suggested that this may promote osseointegration. The application of nanostructured titanium with nanocrystalline bioactive hydroxyapatite coatings has offered many biocompatibility benefits. For example, nanotubular structured titanium (Ti) substrates coated with nanoparticulate hydroxyapatite (nano-HA) offers a surface that promotes osteoblast cell adhesion and is particularly suitable for orthopedic and dental implants where deposition of osteoblasts and other proteins is important in bone formation. This enhances device-tissue integration. HA nanoparticles can be produced by a process such as sol-gel and plasma spray techniques, chemical and vapour deposition including discrete crystalline deposition (DCD) among a number other methods; however, factors such as the crystallinity, nano-particle size and shape(s) influence the surface area as well as resultant strength if they are to be as stress-bearing composites or as part of drug-release system.

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Joe Pustka
Medical Device Leak Testing Technical Support Manager, Uson

Uson has helped manufacturers to leak test nearly every type of implantable medical device used today. Initially, it was quite common for our team to tell design engineers to go back to the drawing board. The problem had been, and still sometimes is, that in totally sealed components, there is no air gap when there needs to be. Adding a free volume of air into such a sealed part will allow a gross leak to be detected. Sometimes, and especially if the overall size of the part is very small and the acceptable leak rate is comparably small, an alternate approach is to re-design processes to perform leak testing of subassemblies.

Uson’s message to any developer of an implantable device is short and to the point. It is never too early to get your supplier of test equipment involved in helping to design your process and the device itself. If you are dealing with a test equipment supplier that gives you such “advice” at premium cost—sometimes to the tune of six figures—that is money down the drain. Any reputable supplier of test equipment builds up-front consultation on application details into their pricing system.

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Andrew Kelly
Member of Technical Staff, Cactus Semiconductor Inc.

Cactus Semiconductor enables the miniaturization of implantable medical devices (IMDs) by designing customized ICs specifically for the latest battery, MEMs, wireless, and packaging technologies. This miniaturization allows for placement of IMDs near the point of therapy, instead of in the chest or abdomen, thus enabling better performance and less-invasive implant surgery.

Recent advances in battery technology have led to the availability of chip-scale batteries, which can drastically reduce the volume of IMDs. Cactus develops circuits to optimize the charging and monitoring of these unique batteries. In addition, Cactus designs ultra-low power circuits that minimize power consumption to enable use of these lower capacity batteries. One example is our fully-integrated timekeeping solution that consumes less than 200 nW.

MEMs devices are rapidly replacing traditional sensors and actuators in IMDs to enable miniaturization. These MEMs devices are often customized to specific applications so they require customized electronics to optimize power and performance.

Cactus also has wireless solutions that support simultaneous wireless communication and battery charging with a single coil. Our communication solutions employ passive back-telemetry, to minimize battery power, thus enabling the use of smaller batteries.

Finally, Cactus designs custom ICs for multi-chip die-stacks that integrate ASICs with microcontrollers and EEPROMs in a single package. The size of the entire IMD is thus optimized in ways only achievable by customization.

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Tanner Hargens, MS
Senior Biomedical Engineer, Medical Murray Inc.

Medical Murray develops and manufactures medical devices with a focus on complex catheter systems and their components. Our implantable components often intend to repair or regenerate native tissue with absorbable polymers that begin to degrade after accomplishing their initial task. Medical Murray is influencing the bioabsorbable industry through knowledgeable material selection and injection molding of the smallest and most detailed profiles on the market.

Bioabsorbable innovation at Medical Murray has been driven largely by vascular, orthopedic, and surgical applications. The absorbable polymers are initially designed by polymer scientists and engineers to meet the specific mechanical properties and degradation kinetics for each application. Each material will then have its own restrictions when processing to the desired shape. When injection molding absorbables, each material will have limits on the cavity size it is capable of properly filling and must often be processed at the lowest temperatures possible to prevent alteration of the degradation kinetics.

The Sesame nano-molder, invented by Medical Murray, is capable of producing the smallest and most detailed bioabsorbable polymer components by allowing the material to melt to sufficient flow at a lower processing temperature so the material can normalize quicker with a shorter cooling time than is otherwise available. This has also allowed minimal loss of very expensive materials through use of smaller sprues, runners, and reduced melted material in the injection unit. As an example to the understanding the materials and processing, Medical Murray has been able to design and mold the first absorbable living hinges, which allow expansion of a device into the tissue from a small delivery catheter.