Perspectives on Miniaturization
Q: In the effort to make medical devices smaller, what has been the most challenging obstacle you have faced, and how were you able to resolve it?
In our case, power devices such as IGBTs and MOSFETs have the biggest influence on servo drive design. Advances in power device technology have resulted in reductions in size and thermal dissipation. In fact, these improvements have allowed us to increase the power density of our products by 840% over the last four years. To keep the path of miniaturization, we are always on the lookout for characteristic components.
Knowing exactly what the customer requires allows a strip out of anything extra to produce a lean and space efficient design. In many configurations, we hardwire the settings and remove switches and potentiometers to dramatically improve reliability and simplify installation. Strategically placed low-profile connectors have a drastic effect on volume and wiring. Growing trends are PCB 'plug-in' style servo drives that remove wiring considerations altogether.
Responsibilities of other components can also be absorbed. Drives can be expanded to act as a communications node to peripheral devices. Network accessible I/O gives the controller access to sensors without additional wiring or the need for a network I/O board.
Finally, to fit within the allowed footprint, many options are available. With the same volume, a drive can be long and narrow, square, tall, or flat. A heat sink integrated as part of equipment housing decreases weight and adds design flexibility. For example, in one instrument the drive housing was uniquely shaped as part of the cooling tunnel structure.
The push for portable medical products has driven development of highly integrated, application specific IC products. In many cases IC designers are required to develop systems understanding to gain efficiencies from focusing on key application requirements and tradeoff non-critical constraints of general purpose products. Significant cost, power, and size can be obtained from an applications specific design when the requirements can be generalized into a standard set of features and target performance. Unfortunately, even when targeting an IC for a medical application, there may be a broad diversity in performance and feature requirements depending on end-product market targets. For example, ultrasound is an application that is greatly benefiting from higher integrated, application specific ICs for the analog front-end of multi-channel beam-formers. Ultrasound systems may be handheld and battery operated or cart based and line powered. They can be used for pre-diagnosis by EMTs, veterinary diagnosis or screening, or clinical obstetrics or cardiovascular imaging. Ultrasound systems are also used in industrial applications for non-destruct testing. While at a high level, all of these end products may have similar architectures, tradeoffs and priorities vary from one ultrasound manufacturer to another and within these companies, from one product line to another.
There is an obvious trend in hospitals to move to less invasive procedures that reduce patient trauma and enable faster patient recovery times. With this trend comes the need for smaller-sized parts and surgical instruments, many of which require engineering thermoplastics.
The functional challenges for miniaturization are primarily with the medical device manufacturers. The challenges from the material side are limited to moldability and the retention of material performance in very thin walls. Our high-flow Makrolon polycarbonate medical grades have been able to assist in addressing these issues. These grades are able to fill thin, small components and provide exceptional toughness.
For example, Alcon Grieshaber AG, a leading medical technology manufacturer based in Schaffhausen, Switzerland, recently developed a new generation of surgical instruments to help combat vision-impairing retinal disease. The company's Grieshaber Revolution DSP micro forceps and scissors feature eight individual components made of Bayer MaterialScience's Makrolon 2458 polycarbonate. One polycarbonate component of the single-use operating instrument is a basket of thin-walled ribs that forms part of the instrument body. The ribs required sufficient strength, stiffness, and toughness. In addition, the polycarbonate's excellent dimensional stability helped make it possible for this delicate injection-molded component to be easily demolded and for the forceps and scissors to work reliably.
My clients tell me the biggest challenge in making medical devices smaller is probably "produce-ability" as measured by the consistency and reliability of device performance. Miniature devices are exponentially more sensitive to variation
The single largest trend that Memry has seen in recent years from our customers is the trend towards miniaturization. The devices that our customers require are getting smaller, more complicated, and more technically challenging all the time. This trend is clearly driven by the increase in minimally invasive surgical procedures that reduce both patient recovery time and cost.
Dolomite develops microfluidics devices. Microfluidics
Microfluidics is not a new science, but only recently have companies such as Dolomite developed the advanced design and fabrication techniques necessary to make it the mainstream technology available to medical device manufacturers.
One major challenge has been that fluids behave very differently in the micro-scale, with surface tension and viscosity dominating their dynamics. This means that the design of these devices is a complex business that applies fluid dynamics, thermo dynamics, and considerable engineering and modeling expertise.
As the range of applications for microfluidics in the medical device field increases, rapid prototyping is another major challenge. At Dolomite, glass substrates are most often used due to the speed with which devices can be prototyped and the optical transparency of this material. Novel microfabrication techniques have had to be developed, which are capable of creating microchannels and complex structures in the glass (or sometimes quartz or polymer). The main fabrication processes are photolithography, wet etching of microchannel structures, micro-drilling of fluid ports, thermal bonding, and surface modification.
Dolomite's investment in the equipment, expertise, and software that is required to deliver this technology has been considerable, but the growth in new projects and the long term, commercial potential of this emerging technology is easily justifying Dolomite's decision to create one of the best facilities available worldwide.
Miniaturization of medical devices that include microporous membranes presents a unique manufacturing challenge. The membrane must be adhered or affixed to the housing without damaging the membrane's microscopic pore structure. With typical medical device manufacturing, membranes are attached to the housings using standard heat sealing methods. As the device is miniaturized, the size of the membrane is reduced, causing the same amount of heat energy to be focused on a much smaller membrane surface area during the sealing process. Overheating and melting of the membrane surface can occur. Once this happens, the pore structure of the membrane collapses, leaving a solid film. The way to avoid this problem is to search for other means of sealing.
In summary, designing smaller, less obtrusive medical devices requires creativity and innovation. To help you through these challenges, seek out and apply new technologies and methods for your manufacturing needs.
Chip technology has allowed medical electronic devices significant increases in the functions they provide and an increase in portability for the body, in the catheter, or the portable equipment they serve. Probes, catheters, scopes, and cameras all require highly miniaturized connector and cable interconnecting systems to serve the main control instruments. Those connectors and cable systems must be dramatically changed to serve many of these applications. Examples include dental camera chips that are placed in the mouth for image processing, catheters containing temperature probes inserted into the brain, or wiring to cochlear implants that must fit behind the ear and yet withstand daily abuse of external wear by highly active children. The wiring must be small, feel good, look excellent, have high flexibility, and yet, withstand shock, vibration, and high moisture exposure. The connectors must function over long periods with a high rate of mating cycles by the user. Often the connector and wires are highly miniaturized custom systems designed to look as one unit. The combination of the probe, connector and cable must flow together as one completed, high quality integral unit. It must look "medical" and be acceptable to the daily practitioner and the patient. To solve this problem, we used solid modeling systems and developed a family of nano-sized connectors that can be "built-in" to the probe tip, catheter, or instrument handle. These mini-connectors, with cable attached are then over-molded with very thin wall thicknesses to keep the product miniaturized. Medical instrument designers can go online and interact with the solid model connectors to customize their shape and size to fit into their systems needs.
The demand for portable and miniaturized medical electronic devices has impacted everything from semiconductor packaging to communication interfaces, battery, and display technologies.
Even with these advances, miniaturizing portable electronics remains limited by the size of the human interface (keypad), battery, and power supply. The human interface size is easily reduced by leveraging touch screen controls. This completely eliminates the need for any keys or buttons on the medical device, and even allows for multilevel, customizable menus. This can be taken a step further by leveraging low power wireless interfaces for near-field communication to a remote display and human interface. With this, patients will be able to wear medical devices such as monitors that synchronize with a display in the doctor's clip board, optimizing size and cost of the entire monitoring infrastructure.
For portable electronics, operational runtime truly is a key concern. Reducing the battery size and power supply can impact this. Many of today's semiconductor solutions have been optimized for portable electronics. Thus, realizing great performance takes fractions of the power needed just five years ago. This, added to new battery chemistries as well as improvements in battery management techniques such as impedance tracking, allows us to achieve the same number of amp hours out of much less battery volume than ever before.
In short; the technology exists today in terms of packaging, assembly, usability, and power management to take many applications far beyond simply being portable into a world of miniaturization.