Undergoing surgery is a costly procedure, often involving a hospital stay and the ongoing monitoring of the patient after discharge. During and after an operation, the patient is put through considerable stress, both mentally and physiologically, which affects the body’s respiratory, cardiovascular, excretory, and immune systems in particular. Whenever possible, limiting the size and number of incisions made during surgery by using minimally invasive surgery (MIS) techniques is extremely beneficial to the patient’s recovery time.

The benefits of MIS over traditional open surgery are numerous. Because the incisions made by surgeons are smaller and they leave less scarring, patients take less time to recover. MIS procedures are often less painful than traditional procedures so patients don’t need the same level of pain medication and can go home sooner. This frees up space in hospitals for new admissions.

MIS is proving of particular value in gynecological, neurological, orthopedic, thoracic, urological, and vascular surgery, as well as in interventional cardiology. By 2025, the global business for MIS-related equipment will be worth approximately $32.7 billion annually according to analyst firm Market & Markets. 1

The introduction of various types of electrosurgical instruments (arthroscopes, catheters, endoscopes, and laparoscopes etc.) back in the 1980s was pivotal to MIS as we know it today. Over 90 percent of all surgical procedures can be performed by MIS techniques and include appendectomy, arthroscopy, cholecystectomy, gastric bypass/banding, heart valve repair, hysterectomy, myomectomy, prostatectomy, spinal fusion, tubal ligation, and bariatric procedures.

As the supporting technology becomes more sophisticated, it enables surgeons to make even greater use of MIS. This is because innovations in electrosurgical instruments allow the incorporation of elevated levels of functionality making these instruments more effective. Opportunities will also exist for MIS to be applied in treating a wider range of medical conditions. In order to retain their noninvasive properties, the medical devices used in MIS procedures will need to be in the most compact of form factors. This has implications for the constituent electronics in terms of the wiring that delivers the data signals and power to them as well as the component parts (including actuators, microsensors, power management ICs, etc.)

Until now, there has been little focus on the space taken up by the wiring in medical designs. However, by shrinking form factors and simultaneously adding more functional elements, exacting space constraints are being placed onto instrument designs. Consequently, the traditional approach to wiring in medical devices needs to change to respond to this shift.

Conventional electrosurgical instrument designs usually incorporate electrical interconnects that are based on microwire technology. Wires often need to be combined into bundles of around 600 µm in diameter. However, medical engineers should note that microwires have other shortcomings such as their rigidity, which makes them more difficult to apply to enclosure formats with unusual shapes.

The interfaces connecting everything together in modern electrosurgical instruments will need to evolve as the density of the electronic content packed into them keeps increasing. A viable option for replacing microwires is flexible printed circuits (FPCs). FPCs support high degrees of signal integrity and prolonged operational reliability while offering substantial space and weight savings. They have been used in a variety of wearable and implantable medical devices such as blood glucose monitors, hearing aids, and pacemakers to monitor, regulate, and assist many vital physiological processes.

FPCs have the ability to be bent and shaped to exactly fit the dimensions of their enclosure. They are significantly thinner than traditional microwire bundles, yet they have a composite structure that offers considerable mechanical robustness. FPCs also offer medical designers considerable cost savings because a single FPC can replace multiple microwire interfaces. This reduces the bill of materials and the outlay on product assembly.

Fig. 1 - Example of an ultra-thin Improved Harness Technology interconnect. (Credit: Trackwise)

FPCs offer considerable space-saving advantages over microwires and reduce the complexity of the wiring assembly of the instrument they are designed into. In fact, just one FPC can supplant up to 12 microwires because, by using an FPC, a designer can implement conductive traces with a thickness of only 25 µm wide. With the inclusion of the accompanying electrical insulation and protective layers, it is possible to achieve a total interconnect thickness of less than 50 µm — a solution that is in fact thinner than an average human hair.

If FPCs are to replace microwires and be mass produced for design into MIS instruments, it must be possible to manufacture them to any length. This has been an obstacle until now as electrical component manufactures have struggled with manufacturing techniques to achieve this. Most FPC manufacturers are capable of supporting lengths of up to 0.6 m, and a very few companies are able to manufacture solutions of about 2 m long. Until now, FPC manufacturers have been unable to address medical device OEMs’ design criteria.

There is a growing need for longer wiring solutions to address the many MIS application scenarios where this is a requirement. For example, the catheters frequently used in cardiac procedures should be a minimum length of 1.1 m for clinical staff to be able to use them correctly. Even longer wiring lengths are necessary in instruments used for procedures such as interventional neuroradiology where 2 m wiring lengths are required.

UK-based Trackwise, for example, now offers ultra-thin multi-layer FPCs of any length (see Figure 1) achieved through its proprietary Improved Harness Technology™ (IHT) manufacturing techniques. This breakthrough gives medical sector OEMs a weight- and space-saving, length-unlimited alternative to the current solutions on the market.

IHT’s alternative approach to FPC production employs a fully patented, dynamic manufacturing process based on advanced roll-to-roll electrolamination techniques. These cost-effective techniques make it possible to create FPCs of any length that are reliable and repeatable. The planar nature of IHT interconnects allows them to be bonded within the structure they are mounted to, reducing the physical space that they occupy.

Reference

  1. Minimally Invasive Surgical Instruments Market worth $32.7 billion by 2025,” Markets and Markets, Report Code: MD 3177, March 2020.

This article was written by Philip Johnston, CEO, Trackwise, Tewkesbury, UK. A white paper with more information on FPCs for medical applications is available here . For more information, visit here .


Medical Design Briefs Magazine

This article first appeared in the September, 2020 issue of Medical Design Briefs Magazine.

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