generation of mis · miniaturisation is key to the evolution of mis instrumentation the rise in the...

Trackwise’s Improved Harness Technology™ Ready to Enable the Next Generation of MIS Instruments

www.trackwise.co.uk 1


www.trackwise.co.uk


www.trackwise.co.uk2

The multiple clinical and economic benefits of minimally invasive surgery (MIS) have seen a dramatic growth in its popularity across a range of medical specialities, including cardiothoracic, orthopaedic, urological, vascular and neurological. The MIS sector is one of the most innovative areas within medicine, and the growth in the numbers of MIS procedures performed globally has driven a corresponding increase in the range of instruments developed to support them.

Catheters and endoscopes are commonly used instruments in MIS, and their sophistication and functionality are improving with each new generation, with electronic components such as microsensors and micro-motors increasingly being built into them. Microwire systems have traditionally been used to provide the electrical pathways within these devices, but the increasing demand for more functionality in these very thin devices is challenging the microwire manufacturing process in a number of ways, with factors such as conductor thickness, insulation performance and overall flexibility and tensile strength being particularly important.

The benefits of flexible printed circuit (FPC) technology have long been understood and FPCs have been integrated into various medical devices but, until recently, their limited length has constrained their use in MIS instruments. However, UK-based company Trackwise has recently patented a process, Improved Harness Technology™ (IHT) that enables production of unlimited length multilayer FPCs.

The capability developed by Trackwise in IHT uses roll-to-roll techniques to enable the cost-effective, high-volume production of long FPCs – a capability now ready to be leveraged to meet the challenges of advanced catheter production.

This paper describes the growth in MIS techniques and the evolution of the associated surgical instruments before examining how recent developments in FPC manufacturing technology are set to benefit the next generation of medical catheters.



The rise of non-invasive surgery

Since it first emerged in the early 1980s, MIS has evolved into one of the fastest growing and most innovative areas in surgery. In MIS, a variety of miniature instruments, along with small cameras are inserted through tiny cuts in the skin to enable the surgeon to see and access the relevant part of the body. MIS can often be performed with the assistance of robotic technology, allowing more precise control over the surgery. By limiting the size and number of cuts required during an operation, MIS can, in some circumstances, offer a number of advantages over open surgery, including less pain and blood loss, shorter recovery times and fewer complications.

As MIS techniques have evolved and the benefits have become more widely understood, non-invasive surgery has become increasingly popular with both surgeons and patients, and the range of medical conditions that can be treated using these techniques has expanded. Today, over 90% of surgical interventions such as appendicectomy, tubal ligation, cholecystectomy, gastric bypass, myomectomy, and prostatectomy are performed using MIS, table 1, and this proportion is projected to grow by up to 15% over the next five decades1.

1 https://spiral.imperial.ac.uk/bitstream/10044/1/43798/2/The%20role%20of%20technology%20in%20minimally%20invasive%20surgery_accepted.pdf



Table 1: Medical conditions treatable using MIS techniques

Surgical area Conditions treatable using MIS

General Pancreatic cancer, benign pancreatic lesions, hernias, severe gastroesophageal reflux disease (GERD), liver tumours (benign and malignant), gallbladder cancer, bariatric surgery – gastric banding and gastric bypass, gastrointestinal/rectal conditions, hernias

Thoracic Surgery Certain types of tumour, oesophageal cancer, and other diseases

Orthopaedic Surgery Minimally Invasive Spine Surgery, including discectomy, laminectomy, spinal fusion Shoulder, knee, hip, and ankle arthroscopy Fracture management Minimally invasive hip and knee replacement

Gynaecological Gynaecological cancer, benign tumours, endometriosis, uterine fibroids, ovarian cysts, benign cervical disorders, conditions requiring hysterectomy, removal of ovaries and staging of lymph nodes

Interventional Cardiology Atrial septal defects, aortic regurgitation, aortic stenosis, mitral valve repair, closure of defects, dilatation of narrowed vessels and valves, valve repair

Neurosurgery/Spine Various spine conditions, including cervical disc hernias, lumbar disc hernias, degenerative disc disease, spinal trauma; skull base brain tumours, anterior cranial fossa (front skull base) tumours, posterior cranial fossa (back of the skull base) tumours

Vascular Abdominal aortic stenting, venous insufficiency, peripheral vascular disease

Urological Kidney cysts, kidney stones, kidney blockage, kidney donation, prostate cancer, incontinence, vaginal prolapse



The endoscope is a key instrument in MIS procedures. Endoscopes use tubes which are only a few millimetres thick to transfer illumination in one direction and high-resolution images in real time in the other direction, enabling indirect observation of the operation site during minimally invasive surgeries. Specialised variants of the endoscope have been developed based on the targeted organ or area of the body and include the arthroscope, (joints), laparoscope, (abdomen/pelvis) and colonoscope, (colon).

A minimally invasive procedure typically involves the use of the endoscopic device to observe the operation site in conjunction with a range of miniature instruments which are inserted into the body via very slim tubes or catheters. In knee arthroscopy, for example, two small incisions are made, one for the arthroscope and one for the surgical instruments to be used for operating in the knee cavity. In other areas, including interventional cardiology and interventional neuroradiology instruments are inserted through veins and arteries (figure 1).

Figure 1: Inserting a catheter into the femoral artery

Carotid artery

Aorta

Femoral artery

Catheter



Figure 2: Single-use ablation catheter

Miniaturisation is key to the evolution of MIS instrumentation

The rise in the number of MIS procedures has been accompanied by a growth in the range and sophistication of surgical instruments, with the global market for MIS systems forecast to experience a CAGR of 6.51% over the period 2020 – 2030, to reach a total value of US$55.64 billion2. Instruments used in MIS include trocars, cannulas, laparoscopes and surgical tools such as graspers and forceps.

The use of electro-surgical instruments is also increasing in these procedures, across a growing range of applications, the most common being the ablation and cauterisation of tissues, blood vessels and tumours. In a typical ablation procedure, the surgeon grasps the blood vessel with a clamp and then applies RF current, which energises the electrons within the blood vessel, causing the collagen and elastin in the vessel wall to denature, creating a seal. Ablation procedures were initially developed for the treatment of heart-related issues such as tachycardia and atrial fibrillation but, over time, their use has spread to a much wider range of procedures, as illustrated in Table 1.

Figure 2 shows an example of a catheter used to deliver RF current for cardiac ablations.

2 https://bisresearch.com/industry-report/minimally-invasive-surgical-systems-market.html



Other examples of electro-surgical instruments range from simple electrodes to harmonic scalpels, which convert electrical energy into mechanical motion, enabling tissue to be cut by the high-frequency vibrations of a blade, with lasers also increasingly being used in ablation procedures.

The growing demand for MIS techniques is driving innovation in electro-surgery, and next-generation catheters are being designed to incorporate sensor-signal transmission pathways. Microsensors are increasingly used within catheters to capture vital data such as temperature, pressure and flow rate from the site of the operation, giving surgeons access to more information in real time. Microsensors can also be used to guide catheter placement, with pressure sensor outputs for example alerting the surgeon to risks of vascular damage during this delicate stage of the operation.

Endoscopic techniques for examining internal organs is another rapidly advancing field and, over the last 20 years, a significant amount of research effort has gone into the development of optical coherence tomography (OCT) endoscopes. OCT is a non-contact imaging technique, capable of generating detailed images of body tissues. OCT has become the standard method for scanning the retina and has great potential for use inside the body – for instance in early diagnosis of cancers. Most endoscopic OCT probes use a technique known as helical scanning, where the optics at the distal end are rotated and moved along the axis of the probe in order to scan the surrounding tissues. A variety of such probes have been developed over the years – see figure 3 – with some types relying on a micro-motor, located at the distal end of the probe, to rotate the optics.

Figure 3: Various types of endoscopic OCT probes have been developed(Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5480489/)

Torque Coil

Metal Guard

Torque Coil SMF CF

SMF Glass Rod Microlens

47°

Plastic Sheath MicroReflector

Coupling Optics Ball Bearings

DC motor

Linear StagePulley

Timing Belt

Endoscope

FiberConnector

PolishedSurface

Plastic Sheath Metal Guard Ball Lens

Torque Coil

Metal Guard

SMF Glass Rod Microlens Drive Wire

Inner Shell

Plastic Sheath MicroReflector

MicroMotor

Wires Fibre-optic Cantilever Microlens

PZT

Metal Housing

SMF GRIN Lens 1 GRIN Lens 2

Outer Shell



The ongoing growth in the market for electro-surgical instruments will drive further innovation and a demand for more functionality to be packed into endoscopic systems. In order for them to remain ‘non-invasive’, however, the size of these devices will remain restricted. With the diameter of most catheters currently between 1.6 and 2.3mm, highly innovative miniaturisation techniques are required, not just for components such as motors and sensors but also for the wiring systems that provide power and carry signals.

Innovations in FPC manufacture open up MIS applications

Traditional electro-surgical catheter designs have used microwire systems – with conductor dimensions as small as 0.0254 to 0.0762 mm and insulation thicknesses down to 0.00127 mm. With the ever-increasing demand for greater functionality, in the same or smaller overall catheter form factor, pressure is growing to shrink these dimensions further, to a point where existing manufacturing processes struggle to accommodate them.

Packaging, transport and integration of wires with such small dimensions also becomes very challenging, with wire sizes having to be selected on the basis of required mechanical strength, rather than their electrical performance requirements.

As catheter design requirements have become more challenging, the attractiveness of using flexible printed circuits (FPCs) in their construction has grown. FPCs are widely used within electrical and electronic systems and can already be found in a range of medical equipment, including various health-monitoring devices and wearable applications as well as in miniature devices such as medical pumps, heart pacemakers and hearing aids. Their popularity is based primarily on their weight- and space-saving benefits, with their ability to be bent and shaped to fit into almost any shape of housing. With conductive traces as fine as 25μm and total thicknesses including insulation, (cover layers), of less than 50μm, a single FPC can replace up to 12 microwires, significantly reducing the complexity of catheter assembly. Additionally, the composite structure of the FPC gives it its mechanical properties, eliminating the need to select larger conductors for strength; the cross-section of the conductor can be based on the electrical characteristics of the catheter application, enabling further space and cost reductions. It should also be noted that the cost savings achievable by using FPCs in catheters and other medical devices are substantial; one FPC replaces multiple wires, thereby reducing product assembly costs. FPCs are also very tolerant of operating temperatures and their construction facilitates simple and reliable installation, with fewer component parts, requiring less manual intervention and improving repeatability.

The biggest barrier to widespread adoption of FPCs in catheter designs has, until recently, been the limitation imposed on their length by their manufacturing processes. The majority of FPC manufacturers have only been able to produce lengths of up to 600mm, with a small number achieving 1 metre, significantly limiting their use in catheters. As discussed above, the use of catheters is commonplace in cardiac procedures, where a length of around 110cm is required, and, in procedures such as interventional neuroradiology, access via the femoral artery requires lengths up to 2 metres.



These barriers are beginning to fall, however, as some manufacturers – including the UK’s Trackwise, a market leader in this field – are beginning to produce longer FPCs. Trackwise has recently patented its innovative IHT technology, which enables the production of FPCs of unlimited length. In the short time since its introduction, IHT has disrupted the FPC market, enabling a wide variety of new applications to access the benefits of FPCs. Having successfully demonstrated substantial space, weight and cost advantages through a number of projects in sectors such as the automotive and aerospace industries, Trackwise is now in a position to apply its new FPC technology to the MIS instrument market with its roll-to-roll manufacturing (length-unlimited) being a very cost-effective means of manufacturing at volume – which is needed for devices like catheters.

A global leader in FPCs, Trackwise is committed to the medical sector

Trackwise has over 30 years of experience in the PCB industry and, with its IHT process, was one of the first manufacturers to break through the length limitations of FPC production. The company continues to push the boundaries of PCB manufacture, making significant investments in state-of-the-art manufacturing capabilities at its factory in Tewkesbury, UK. Trackwise’s range of Industry 4.0-level machinery has equipped it with advanced FPC manufacturing capabilities, enabling the delivery of flexible printed circuit boards of any length and with industry-leading levels of quality, precision and consistency. Combining world-class PCB expertise with an extensive range of laminates in stock, Trackwise has earned a global reputation for short lead times and consistent delivery of high-quality products into multiple industries, including the automotive and aerospace sectors.

In aerospace, for example, the space- and weight-saving benefits of FPCs translate directly into fuel and cost savings, and Trackwise has been heavily involved in a number of projects where IHT FPCs have replaced traditional wire harnesses. Projects in this field include the delivery of a 10m-long, six-layer, arc-tracking compliant harness for a commercial airliner, production of a 42m, multi-layer circuit designed for a power-transfer harness for a roll-out solar array for spacecraft, and the manufacture of a 26m-long shielded FPC intended for transferring power and signals across the wingspan of an unmanned aerial vehicle (UAV) – figure 4.

Figure 4: Aerospace application: 26m-long, multi-layer FPC for a UAV



Having proven the capabilities of IHT in these sectors, Trackwise is now ready to bring the benefits of unlimited-length FPCs to other applications and sees significant opportunities within the medical device sector. With recent investments in the installation of an ISO Class 7 clean room and also in an extremely high-resolution reel-to-reel direct-imaging process, Trackwise’s manufacturing processes are now ready to meet the high-precision and miniaturisation requirements of MIS instruments.

Conclusion

The popularity of minimally invasive surgery is driving high levels of innovation in the medical instruments sector, and electro-surgical devices are becoming increasingly sophisticated, packing more and more functionality into the tiny diameters of endoscopic devices. Traditional microwire manufacturing techniques are challenged by the advanced miniaturisation requirements of next-generation devices, but new developments in manufacturing techniques have positioned FPCs as a viable alternative for catheter and endoscope design.

Trackwise is a global leader in FPC manufacture, with its cost-effective IHT process leading the way in the production of FPCs of unlimited length. Trackwise’s advanced manufacturing capabilities along with its experience of delivering leading-edge FPC solutions into other sectors makes it the ideal partner for manufacturers of precision medical instruments.



1 Ashvale, Alexandra Way, Tewkesbury,Gloucestershire GL20 8NB, UK

+44 (0) 1684 [email protected]

Connected Technology

Trackwise manufactures specialist products using printed circuit technology. With a wide range of potential applications including medical, telecommunications, aviation, automotive and defence, our products are exported around the world, including the USA, Australia, Europe and Asia.

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