The importance of hygiene applies to every aspect of patient care – from the sanitary environment where patient treatment takes place to the range of medical devices used in treatment. The quality of materials and equipment used in treatment can also improve patient outcome. For implants, dental care, and medical devices, a smooth surface with fewer burrs reduces the number of surfaces where contaminants can cling, accumulate, and flourish.
Benefits of a smooth surface
– Biocompatibility is a major concern for implantable devices. Materials must be contaminant-free and not produce immunological responses when exposed to bodily tissues or fluids.
Implantable devicesCutting tools, drills, blades – Smooth surfaces promote greater accuracy and minimize risks, including burrs breaking off during use, device corrosion, and contaminant and pathogen contaminant.
Disposable medical devices – Less expensive processes popular with disposables, such as additive manufacturing or metal injection molding, often produce less-than-optimal surface finishes that are not appropriate for medical devices. They often result in inconsistent quality, as well as higher patient rejection rates during testing.
Surgical instruments – Any precision instrument found on an instrument tray needs to be as smooth and clean as possible to meet strict quality and sanitation requirements. Surface anomalies such as threads on bone screws, knurling detail on instruments, or ground points on a trocar can lower precision. Medical imaging and diagnostics – Cathodes, focus cups, and shields provide medical and dental practitioners with data to accurately diagnose conditions. Burrs or imperfections on instrument surfaces can produce arcs in the flow of the electrical current that runs through the X-ray tubes, distorting images. A lack of smooth conductivity that interrupts the path of the current, especially when high voltage is being used, can damage costly equipment.
Laser marking – The U.S. Food and Drug Administration (FDA) has recently updated and made more stringent regulations regarding Unique Device Identification (UDI) on medical devices. To reduce the possibility of identifiers being removed or counterfeited, or interfering with the device’s functionality, they must be applied as laser markings, directly onto each device.
Surface finishing methods
Popular techniques used to finish the surface of metal parts include:
Chemical passivation – Chemical process primarily used to improve the corrosion resistance of metals; may require additional pre-passivation steps; does not remove discoloration or oxide scale; does not result in the smoothest or shiniest surface
Tumbling/vibratory finishing – Abrasive media cleans the surface of metal parts as they are tumbled in a barrel or bowl; typically useful for smaller rigid parts; not suited for fragile, complex parts
Parts blasting – Parts are blasted using aluminum oxide or glass particles; impinges the surface to mask surface defects, creates a matte uniform finish; subsequent cleaning required to remove contaminants
Electropolishing
A process that addresses many issues associated with medical and dental devices manufacturing is electropolishing. Often referred to as a reverse plating process, electropolishing combines chemicals and electrical current to remove the outermost layer of metal in a highly accurate manner per manufacturers’ requirements. Electropolishing removes burrs and surface contaminants, makes the surface smoother, and creates corrosion resistance, resulting in a bright, aesthetically pleasing finish. Electropolishing can accommodate parts of any size and will not damage fragile parts.
Switching to electropolishing
For medical device manufacturers using other methods for finishing, switching to a new process can be daunting. A new process, such as electropolishing, should be tested. Once desired outcomes are achieved, the existing processes can be revisited.
For companies looking for long-term assurance of proper finishing and a simplification of the finishing process, electropolishing may be the best answer.
Smart catheter system: A new bladder control management solution
Features - Contract Manufacturing
With component sourcing and supply chain management support from Trelleborg, Spinal Singularity developed the Connected Catheter to offer improved quality for users.
A fully internal, extended use smart catheter system could provide control for men who face daily challenges of living with a neurogenic bladder – the inability to feel the fullness of their bladder or control their bladder to urinate, leading to chronic urinary retention (CUR). The Connected Catheter, developed by a team at Spinal Singularity and supported with component sourcing and final assembly from Trelleborg, is an approach to overcome the risks and nuances that current bladder management methods present.
“With today’s standard of care, people use a disposable, intermittent catheter that requires them to insert the plastic tubes into their bladder every time they go to the bathroom,” explains Derek Herrera, CTO and founder of Spinal Singularity. “That could be 8 to 10 times a day or 100 times a month. Throughout a lifetime, it becomes a very daunting task.”
An internal, extended use catheter “could potentially replace 50 catheters because our device can safely stay in the body for up to seven days,” Herrera adds. “Instead of having to insert a new catheter every time you go to the bathroom, you can use our device and just open and close a valve to empty the bladder.”
Those using standard catheter devices often get infections or face urethra trauma. Unable to control their bladders, individuals may dehydrate themselves to avoid having accidents in public.
The design process
Because the catheter needed to be used as a long-term device, it required a biocompatible material. To meet this standard, the Spinal Singularity team partnered with polymer engineers at Trelleborg Healthcare & Medical for the device’s critical, molded silicone parts and tubing.
“Often, silicone components, whether they are injection molded or extruded components, are chosen because the material attributes provide clinical and design benefits,” says Sean McPherson, sales engineer at Trelleborg Healthcare & Medical. “Silicone is known for long-term stability, is very inert, and can be used and stored under a wide range of temperatures and humidity.”
Medical device makers often use silicone rather than a thermoplastic elastomer (TPE) due to its stability and because it is not affected during sterilization and aging.
Trelleborg was able to manufacture the components in-house and complete final assembly at its Tustin, California facility, streamlining the transition from component manufacturing to final assembly.
An extension of Spinal Singularity’s project team, Trelleborg’s engineers provided design for manufacturability support, demonstrating the risks of bonding silicone materials.
The team used an overmold process that was shorter, less costly, and reduced the likelihood of device failure. Additionally, the Trelleborg team supplied finished product packaging and labeling support.
“Labeling is often looked at as something that can be done last-minute. Because of unique device identifiers, batch numbers, traceability, and other factors, this is not the case,” McPherson says. “Labeling is key because if any part of it is off, then the device will be off.”
The partnership provided Spinal Singularity with rapid prototyping, full component manufacturing, and ultimately full device assembly scale-up and finished device manufacturing.
A smart catheter
The Connected Catheter is fully internal to the male anatomy. The Catheter tip incorporates a magnetic valve-pump, which opens and closes via remote control and enables the bladder to fill naturally. The catheter enables users to empty their bladders comfortably and conveniently without frequent catheterization or an external bag attached to the body to collect urine.
Elasso Surgical Instruments’ Elasso Tissue Removal Device, a single-use electrocautery instrument for adenoid and tonsil surgeries, incorporates medical-grade Ixef GS-1022 polyarylamide resin from Solvay.
Medical device manufacturers are developing and marketing single-procedure instruments – devices used once or multiple times during a single medical procedure – at record high levels. This global trend is driven by the need to reduce hospital-acquired infections (HAIs), reimbursement cost pressures, greater operational efficiency, and the increasing rate of surgical procedures performed at non-hospital facilities, such as ambulatory surgical centers (ASCs).
Historically, most single-use medical products were low-value consumables such as packaging, gloves, collection tubes, or tongue depressors. Today’s trend focuses on offering single-procedure alternatives for demanding medical device applications such as instruments for cardiovascular surgery or guiding and sizing components for orthopedic knee replacement procedures.
High-performance plastics are increasingly relevant for these surgical applications, in conjunction with or to replace metal. However, medical device manufacturers can’t just substitute one type of material for another. Traditional metals such as stainless steel have very different properties than plastics and use different manufacturing processes. With a history in metal-to-plastic conversion for healthcare applications, our experience teaches that failures typically fall into three main – yet avoidable – categories:
Incorrect material selection
Specification of a metal product design for the plastic component(s)
Inexperienced, improper conversion supply chain Following are some current best practices to avoid pitfalls.
Choosing the right medical plastic
Numerous plastic materials are available, each with different performance capabilities. A good place to start is a basic categorization using an industry standard Plastics Pyramid. (See sidebar below)
Regardless of the material’s position on the pyramid, a critical consideration for designers is that the material supplier supports its use for the medical application in question (some do not), and that the material is biologically safe. Standardized biocompatibility testing is required by global regulator’s prior to clearing a device for commercial use. Some material suppliers proactively support their materials by testing in advance and offering those data to customers. More proactive suppliers have a Master Access File of their material on file with the U.S. Food and Drug Administration (FDA). This file contains all relevant toxicological and safety data for FDA reviewers, reducing the risk of regulatory delays when launching a new device.
Plastic choice can also affect ergonomics and surface quality as plastics containing reinforcements may appear rough. Ixef PARA, a gamma-sterilizable plastic material from Solvay used in spinal surgical kits, supports a smooth, aesthetic surface finish. Ixef PARA is also used in single-use instruments featuring an easy-grip handle with waffle-style pattern. When injection molded, this material supports cross-hatched, polished, or whirled patterns and product branding with a logo or image.
Plastic single-use instruments provide functionality too, such as color coding. During surgery, blood can cover instrument labels or make lettering hard to read. Plastics formulated in different colors allow designers to communicate characteristics such as size or function, eliminating potential confusion; especially important in kits where several instruments may appear similar. In today’s globally-connected world it’s also key to patient safety with surgeons in Berlin, Boston, Beijing, or Buenos Aries, because color-coding doesn’t require translation.
Plastics-centric design
During design, ensure that the part design and conversion process(es) are optimized in a plastics-centric manner. It’s unfortunately common for a medical device company’s first effort at plastics conversion to fail due to a traditional metal part design being specified and realized in plastic.
Differences can also appear in assembly. Like metal parts, molded plastic products can use threaded fasteners; however, plastic parts can also incorporate snap fits, flash joining, welding, and solvent bonding. With metal, joining or welding requires high heat. However, the heat from a hot plate may be enough to join or weld plastic.
Remember, however, that plastics have different tolerances that could affect product assembly.
ECA Medical Instruments’ Cervical-One single-use surgical instrument set for use in one- and two-level cervical spine implant procedures, made with Solvay’s Ixef polyarylamide. (Photo courtesy of ECA Medical Instruments)
Supply chain
Before replacing metal with plastic, it’s essential to understand all manufacturing considerations and ramifications. Metal instruments feature shapes and structures that are most frequently made by machining, sometimes casting, followed by secondary operations such as milling, boring, anodizing, or polishing. These processes are typically combined into a job shop workflow well suited for low-volume, high-variability production outputs.
A shift to single-procedure instrumentation brings the aspect of increased part volumes. Many instrument categories can then support conversion to more efficient mass production methods. In the case of plastics, part volumes commonly support moving to injection molding. This high-volume process supports greater design freedom and reduced part cost, allowing designers to achieve intricate features and sophisticated geometries not possible with metal manufacturing methods.
Secondary processes using plastic components – printing, joining, packaging, sterilization – can often be efficiently incorporated in line or via dedicated production cells specific to the medical device.
Plastics capabilities have grown and improved throughout medical device supply chains during the past decade. Many machine houses and contract manufacturers have incorporated molding into their operations. Their experience and advice are critical early in the product development process to ensure successful conversion to an all plastic or plastic-metal hybrid single-procedure device.
Metal/plastic hip retractor made with Solvay’s Ixef polyarylamide.
Collaboration
Designers who plan to develop single-use instruments should consider incorporating plastics but need to do more than substitute one type of material for another. In addition to choosing the right polymer, it’s essential to understand the many design and manufacturing differences between metal and plastic materials. Supply chains developed within the industry with plastics expertise assist and enable designers to take advantage of the benefits. By collaborating with material suppliers committed to healthcare, as well as their supply chain partners, medical device manufacturers can create new, innovative designs while increasing efficiency, controlling costs, and helping reduce the risk of HAIs.
Gilbert, Arizona-based Moldworx LLC recently provided a custom solution for a medical manufacturer that automates hypodermic needle production using overmolding to reduce cost and improve productivity. Moldworx engineers designed and developed an A-series, single-cavity injection mold with slides. An operator hand-loaded the needle into the mold, before the machine molded a finished assembly to test the design.
“This allowed us to overmold the needle to eliminate a step in the current manufacturing process, reducing overall production time and cost,” says Moldworx President Jim Taylor. “We encountered some unique issues in the process, including the additional challenge of making this all possible in a horizontal press, not a typical vertical press.”
Next, the team designed a production mold and automation to robotically feed the needles into the mold cavity, eliminating the operator.
“We designed the mold to integrate with the automation and the automation to work in unison with the mold,” Taylor explains. “To accelerate the timeline, the entire automation cell was built in parallel with the mold.”
One challenge for Moldworx was singulating thousands of delicate, tiny, bulk-packed needles. Engineers designed and developed a singulator and hopper to introduce one needle at a time to the assembly cell.
A robot affixed to the injection molding machine picks up each needle and indexes it in front of a set of high-resolution inspection cameras to ensure the needle tip is not damaged or bent, which would cause the needle to be rejected.
The robot places the needle into the mold and the mold closes for the injection cycle. When the mold opens, the robot removes the molded assembly and places a newly inspected needle into the mold. All these actions require inspection and verification to exacting tolerances.
After completing the single- cavity mold and automation, with the customer testing and approving parts, Moldworx built a multi-cavity mold with the required integrated automation cells. The 4-cavity production mold will quadruple the automation cell production to keep up with demand.
Posted by Elizabeth Engler Modic
