In September 2021, I contributed an article on medical plastics. While this article is a good general introduction to trends in medical plastics, this new article covers a selection of new developments which have happened since, in what is a fast-moving field. They range from the mundane to the exotic! Innovation by medical device producers continues to accelerate. Plastic materials have a unique and important role to play in the medical field and with appropriate material selection, will continue to be used for the next generation of medical devices.
How to select optimal plastics for medical devices
UL Prospector is fundamentally a selection system for selecting the optimal polymeric material for an application, which is a vital step during the development of a medical device. Rushing, or overlooking a rigorous selection process can lead to unknowns in the performance of materials and ultimately risks to patient health. Corrective measures once a product is in production are very complex and often expensive. Advantages of polymers include:
- Often a cheaper alternative to other materials
- Utilize well-known manufacturing techniques
- Longer shelf life than many other materials
However, the material selection process must include an assessment of both the long-term and short-term mechanical, physical and environmental conditions that may be experienced during processing, assembly, storage, transport and service, including cleaning.
Medical device orthopedics, wireless sensors that monitor implantable medical devices, and cell research involving stem cells and platelets require highly specialized diagnostic tools and techniques. Gauges, measurement and diagnostic equipment that come into contact with body tissues and fluids may require specific properties. These may include biocompatibility, FDA approval, mechanical properties and electrical insulation.
Verification and validation is a key component of this, on top of due diligence when deciding between different polymers. In particular, materials and devices must also be compliant with medical device regulations (MDRs) and legislation, including, where appropriate European Directives. These ensure that patient health is not compromised, and that devices perform as required. But these can also change – if this happens, a rethink of materials specification may be needed.
There is a drive towards medical devices designed to be self-administered at home by the patient. This introduces additional considerations, due to the changing usage profiles and functionality requirements.
In addition to using the UL Prospector, readers may wish to consult independent polymer experts such as Smithers (Ref 1).
Ultra-short forming ‘Med-Cup’ process with high-speed extraction
At the recent K2022 show in Dusseldorf, Sumitomo showcased the latest advances in ultra-short forming medical processing, combining proven machine technology to optimize material use with state-of-the-art quality control and extraction technologies. The shared ‘Med Cup’ project manufactures precision 30ml medication dispensing cups from polypropylene (PP) and enables the release and analysis of 48 high-quality medication dispensing cups in under 3s.
The demonstration deployed a hybrid high-speed El-Exis SP 420, collaborating with an integrated intelligent stacking system from Zubler Handling and a four-axis pick-and-place robot supplied by Pagés. Otto-Hofstetter supplies the 48-cavity tool.
The perfectly balanced hot runner is equipped with individually heated and controllable nozzle tips. This enables the injection of the cup, with a shot weight of around 70g to occur centrally via open nozzles (point gate). A highly efficient, thermally balanced cooling system comprising 29 water cooling circuits, guarantees thermal stability in the mould. The tool is designed to remove moulded parts from the front, making it very easy to service.
Product quality is maintained using a 100% inline control system installed by Zubler Handling. Comprising intelligent high-definition vision cameras placed along the high-speed extraction axis. At an extraction speed of 7.5mm/s, the cameras take an image every 12ms. Anomaly detection and dimension measurements are performed on each image with an accuracy of 0.05mm.
Machine qualifications and validation
Sumitomo also emphasized medical machine qualification and validation and has published a white paper on the subject. Medical Business Development Director at Sumitomo (SHI) Demag, Anatol Sattel, has assembled the company’s qualification and validation experts, including Medical Sales Director Andrew Sargisson, Project Manager Erik Schalle, and UK medical sales specialist Sam Carr to describe how their teams work collaboratively with medical customers to support the entire validation process (Ref 2). It covers the following:
- Where does machine qualification fit into the validation process on medical applications?
- Why is there such an emphasis on documentation?
- What advice is available to help streamline documentation processes?
- Why are preliminary definitions so critical?
- How is GMP Qualification documentation delivered?
- Who should input to URS documentation and SATs?
- Do machinery manufacturers have a responsibility to ‘red flag’ impossible processing requests?
Medical grade nylon 6/6
Ascend Performance Materials has announced a new portfolio of medical grade nylon 6/6 resins for the healthcare market under its HiDura brand, which meet the ISO 10993-5 and 10993-10 testing criteria and can be used in a variety of healthcare applications, including:
- Medical durables: braces, patient support, furniture, mobility aids and other durable equipment.
- Drug delivery: filtration equipment and membranes, tubing, fluid connectors and auto injectors.
- Surgical instruments: scalpel handles, dental instruments, forceps and clamps
- Medical equipment: housings, protective cases, cables, sensors, connectors and wearables.
- Wound care: sutures, tapes and zip ties.
Ascend’s healthcare business manager Dhruv Shah indicated that the company plans to further expand its healthcare portfolio, including the future introduction of long-chain and amorphous polyamide grades.
Sensor encapsulant for prosthetic devices
Researchers at The University of Tennessee (Refs 3 and 4) have employed the Master Bond epoxy resin EP30Med in their measurement tools and gauges in medical device applications, due to its low viscosity, non-rapid setup time, USP Class VI approval and other performance properties.
Total knee arthroplasty is a widely popular application of joint replacement. The procedure alleviates arthritic knee joint pain by capping the ends of the bones that form the joint and kneecap with metal and plastic. An invasive surgery, total knee arthroplasty addresses multiple forms of arthritic pain, including osteoarthritis (a degenerative joint disease), rheumatoid arthritis (pain due to inflammation), and traumatic arthritis (due to injury). Total knee arthroplasty resurfaces the damaged segments of the knee joint, generally following unsuccessful attempts to treat the existing bones.
To verify the success of the surgery, medical device designers created several diagnostic tools. In one such application, researchers installed strain gauges into the prosthetic component on the tibia. The gauges measure the impact on the joint by reading strain data through a strain-mapping wireless sensor array that could feed information on how the repaired joint performs following the knee replacement surgery.
Microcantilever-based sensors are the key to creating an accurate yet computationally efficient data map. Optimizing sensor quantity and size are significant challenges to the success of the application. The sensors must record accurate information without carrying a prohibitive computational cost. The sensors need to be encapsulated with medical grade adhesive to both protect them from damage and to form an appropriate interface between the implanted device and the bone tissue. Researchers tested a few epoxies for suitability of sensor encapsulation to select the most advantaged product to record the optimal amount of data.
Among the epoxies tested, EP30Med proved to be the best choice of the four epoxies evaluated due its low viscosity, a non-rapid cure time, and a minimal amount of air bubbles present in the mixed epoxy during the curing process, creating a durable, homogenous consistency.
3D printed eyes
Fraunhofer IGD reports the development of a 3D printed prosthetic eye. Not only is a 3D-printed prosthetic eye produced in a fraction of the time taken by the conventional process, but the resulting prosthesis also looks more realistic (see Ref 5).
The breakthrough technology to produce prostheses is now being fitted in patients for the first time in a clinical trial at Moorfields Eye Hospital in London.
“We are excited about the potential for this fully digital eye,” said Moorfields consultant ophthalmologist Professor Mandeep Sagoo. “This has been a culmination of four years of development of sophisticated technology between Moorfields Eye Hospital, UCL Institute of Ophthalmology, British company Ocupeye and Fraunhofer. We hope the forthcoming clinical trial will provide us with robust evidence about the value of this new technology, showing what a difference it makes for patients. It clearly has the potential to reduce waiting lists.”
The patient’s 3D prosthesis initial appointment begins with a 2.4s, non-invasive, non-ionizing scan from a specially modified Optical Coherence Tomography ophthalmic scanner, which is manufactured by Tomey (Japan) and is routinely used in a hospital environment. The resultant scan of the eye socket and color-calibrated image of the healthy eye is seamlessly and digitally transferred to Fraunhofer IGD.
The Fraunhofer software program Cuttlefish:Eye creates a 3D print model from this data in an equally short time. The printers are controlled by the Cuttlefish universal 3D printer driver, which is characterized by its color consistency as well as realistic representation of even transparent polymeric materials. Fraunhofer IGD technology is used worldwide with many different types of printers. The 3D prostheses are printed by Lupburg based Fit AG which has many years of experience in additive manufacturing, especially in the field of medical technology. Once printed, the prostheses are inspected and given final polishing by a team of experienced ocularists. With a single 3D multi-material printer, Ocupeye can potentially fulfill the annual requirement of around 10,000 prostheses required, just for the UK market.
Every step of the new manufacturing procedure has been subjected to strict quality controls. The Cuttlefish: Eye software is certified as a Class 1 medical device. Extensive and exhaustive biocompatibility tests were performed on the 3D printing materials, before the UK Medicines and Healthcare products Regulatory Agency – MHRA – provided a letter of approval for a clinical trial. The clinical trial will recruit around 40 patients to receive a 3D-printed ocular prosthesis; they will be examined several times by qualified clinical staff over the course of a year and be asked to report back on their experiences.
Speculating on the next steps, 3D printing technology can already accommodate electronics, so how long will it take before a 3D printed prosthetic eye can deliver visual information to the recipient’s brain?
Stents produced by short pulse lasers
Stents are tiny tubes with a lattice structure that are implanted into blood vessels to relieve or prevent vascular constructions. Plastic is commonly used for stents due to its biocompatibility, visibility during x-rays, mechanical properties for expansion, and if necessary, degradation in resorbable stents.
These intricate devices require precision manufacturing techniques – size and thickness are critical parameters in order to achieve the required flexibility and strength. In most cases, lasers are used to cut stents to an accuracy of a few µm. Now new developments with ultra-short pulse lasers having pulse durations in the picosecond or femtosecond range have opened new possibilities in the manufacture of medical components, allowing not just more precise, but also more economical production.
In laser cutting, for example, cuts and holes can be made with an accuracy in the µm range. The laser produces clean and almost perfect cutting edges. It also offers a high degree of flexibility when cutting different shapes and bodies. In addition to stents, other typical components include components for minimally invasive surgery, stone trapping baskets, bone saws, orthopedic devices, and numerous implants (Ref 6).
Add medical plastics and biopolymer filters to your Prospector account by upgrading to our Unlimited level account. Learn more.
References
- How to select the optimal plastics for medical devices
- Sumitomo Demag: Making sense of medical GMP machine qualifications and validations
- Multi-channels wireless strain mapping instrument for total knee arthoplasty with 30 microcantilevers and ASIC Technology. Center for Musculoskeletal Research. University of Tennessee.
- The Future of Ultra Wideband Systems in Medicine: Orthopedic Surgical Navigation. Pages 307-308.
- Leslie Langnau. The first ever patient with a fully digital 3D printed prosthetic eye.
- Laser Optics by Laser Components
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