17 4月 Functionality, Material Selection & Optimum Process: Is Your Contract Manufacturer Providing the Innovative Solutions You Require?
One of the challenges of designing and manufacturing medical devices is the fact that choices made in the product development effort can have significant impact on regulatory approval lead-time, tooling complexity and cost, and production capabilities. When those choices are made by a cross functional team that reviews potential tradeoffs there is generally balance between features and cost. However, when teams work in functional silos, the end result is often a greater number of design spins or products that are costly to manufacture to desired quality standards.
Forefront Medical Technology, a specialty contract manufacturer with a focus in disposable diagnostic, drug delivery and medical device systems, built its business model around optimizing the product commercialization process. It offers one-stop support for product development, tooling and complete product manufacturing. This paper looks at the benefits of working with a contract manufacturer that takes this type of holistic approach to the process development and commercialization process. It also highlights examples of ways choosing a contract manufacturer with expertise in materials selection, tooling design and manufacturing process selection opens the door to a broader range of choices in product features without sacrificing competitive cost goals.
Design Choices Drive Production Choices
Materials selection has significant impact on a product’s competitive advantages because it can often be factor in added functionality, a unique feel, reduced cost or improved performance over older technology. At the same time, materials choice can often be a gating item in the design process since biocompatibility approvals are needed before a product can be used. To better address the regulatory lead-time factor, Forefront Medical maintains a database of approved materials which includes a full range of medical-grade polymers. While the best material will vary depending on application, cost considerations and desired functionality, the product development team is often able to recommend preapproved materials choices to reduce product development time. Using materials that have previously been tested and approved within the regulatory environments associated with the product can cut 4-5 months from a product development cycle. It’s also important to note that the 4-5 months represents a single testing cycle. If the material has failed testing, a new material must be selected which then restarts the 4-5 month testing cycle.
When material choices are driven by desired features or functionality, it is very important that the design and manufacturing teams work together closely, since the best choice may involve combining material in new ways or designing new production processes to address constraints driven by the design or desired functionality. The following case study examples illustrate the complexity often encountered in this process.
Replacing Metal Components with Precision Molded Plastic Parts
In this case, there was a requirement to design and mold a plastic valve set which was functionally equivalent to
the metal valve set currently used in endoscopes. The challenges included:
- Identifying materials with correct level of rigidity and strength to be functionally equivalent to the metal valve set
- Ensuring that the plastic components performed identically and felt similar to their metal counterparts to a doctor performing an endoscopy
- Designing a complex mold that could produce parts with conformance to extremely fine tolerances.
The valve assembly to be replaced had five separate components: a stem, end cap, snap cap, gasket and spring. Multiple materials were required. The design team began the process with a brainstorming process to determine the likely best materials options. Thermoplastic elastomer (TPE), polypropylene, polycarbonate and acrylonitrile butadiene styrene (ABS) were tested as replacements for the stainless steel parts. ABS offered the lowest cost and the best level of rigidity. This was important because the ABS part was sliding against a metal component during procedures and the plastic part needed to be able to withstand the friction of the sliding motion. Another benefit was the compatibility of ABS with TPE. Components which would come in contact with the doctor’s glove needed to be soft with no sharp edges that could tear the glove. TPE met that criteria and it also provided the best bonding properties with the ABS components.
To better understand the functional requirements, the design team closely studied a working unit in their lab. The plastic valve set not only needed to perform functions identical to those performed by the metal part set, it also needed to feel the same to the doctors using the endoscope.
One area of concern was friction. As mentioned earlier, there is an ABS part sliding against a metal part and that operation needed to be as frictionless as possible. The team found that a lubricated ABS would eliminate the friction and was able to work with ABS supplier to specify a material with an oily property that met the requirement. Design of Experiments (DoE)s were used to fine tune the design of the spring used for a cushioning effect, in order to develop a spring that provided the same “feel” to doctors as the metal spring.
The most significant challenge involved mold design. The design of plastic components is fundamentally different from that of metal components because the manufacturing process is different. Fabricated metal parts are formed through machining, which supports very tight tolerances, precisely formed grooves and sharp corners with 90 degree edges to achieve a tight seal. Conversely, plastic parts are formed via an injection molding process which traditionally has wider tolerances and delivers a less precise cylindrical form.
The tolerance for the components used in the suction valve assembly was 5 microns, which gave a window of +/-2 microns. When a part is injection molded, there is a possibility of non-centering. Additionally, cylindrical molded parts are typically not a perfectly shaped cylinder. The initial parts did not have the required tolerance and as a result, there was leakage in the suction valve. The team decided to change the mold and the molding concept. The two-cavity mold was redesigned to include a slide-core mechanism for forming the cylindrical portion of the part. The critical dimensions of the part were machined inside of the slide-core mechanism during the injection molding process. A high speed computer numerically-controlled (CNC) electronic discharge machine was used for final machining, since it can control tolerance to less than 3 microns.
Redesign to Improve Product Performance
In another case, a device used in foreign particle management needed a redesign to increase market share. The design team recommended converting the manufacturing process used for the device’s tubing from a dipping process to the combined use of extrusion molding and injection molding. The team also recommended changes in the materials composition for other components used in the product.
The old product used a dipping process involved dipping the product multiple times to form layers. There were three primary disadvantages of the dipping process. First, it produced a sticky tube, which created a high frictional force during insertion of the endoscope and impaired its key function of serving as a guide for insertion of the endoscope. Second, the sticky tube also was difficult to insert in patients. Finally, it was costly since manufacturing the tubing involved several rounds of dipping.
The dipping process also limited the device to a single material type of same shore hardness on the entire device, whereas the proposed process of vertical extrusion molding and injection molding allowed the use of different types of material and concomitant shore hardness at different parts of the device, based on the functional requirement.
The product line included 25-centimeter and 50-centimeter versions. Components included inner tubing, outer tubing with a tapered tip, a distal cuff and a spring. Under the redesign, the wire-reinforced outer tube and the inner tube were extrusion molded and the distal tip and cuff were injection molded. The taper on the tip enabled the tube to be inserted without mucosal tearing and/or shearing. To cater this requirement, this distal tip was injection overmolded with a softer PVC resin on the reinforced body. The cuff needed to tightly seal to minimize the risk of body fluid contamination.
Finding the right material combination to achieve those functional requirements required several rounds of testing material combination selections.
Extrusion with spring reinforcing was selected as preferred process for the outer tube because a normal extruded tube wouldn’t work well with the spring. That said, in initial molding tests, the spring wasn’t getting into the right pitch. The team had two options: lock the spring into position or have it loose in the inner tube. They chose to develop a proprietary process to mount the tube for the spring, insert the spring and then overmold.
Forefront’s electro discharge machining capability enables fabrication of molds with tolerances of three microns. One challenge was the gauging inside the mold. The tube needed to have a smoother finish since it would have tissue contact. This meant that only a single point gauge could be used in mold for in-process measurement. Moldflow analysis software was used to optimize the molding parameters to the point where a single point gauge was acceptable.
Forefront’s vertical extrusion machine capability was also beneficial. Vertical extrusion improves quality in thinwalled tubing by having easier alignment between the press ram and tools and uniform deformation due to uniform cooling of the billet in the container.
Specialty Pharmaceutical Bottle Production
In a third case, the project involved design of a pharmaceutical bottle made of a flexible, medical grade PVC material. While blow molding is the preferred choice for bottles utilizing low density polyethylene, the flexible PVC material required an injection blow molding process.
There were several advantages with driving this choice:
- Quality and repeatability: Utilizing this process the bottles met exacting standards of consistent weight, volume and tolerance. It also allowed for an exact neck dimensions to ensure bottle and cap had a proper fit and seal.
- Cosmetic factors: This process gives the bottle thick even walls with nearly invisible parting lines. The process also allowed for a variety of surface finishes.
- Cost effectiveness: While blow molding requires a single cavity, injection blow molding utilizes molds with as many as 12-16 cavities. The process generates no wasted material. Additionally, this process is accurate enough that secondary processes such as trimming are unnecessary. Auxiliary machines are not required for additional operations.
In injection blow molding, the process begins by melting down the flexible PVC and forming it into a parison or preform, which is a tube-like mini bottle which a hole in one end through which compressed air can pass.
While the customer gives the final geometry of the bottle, it was up to the design team at Forefront to develop the parison geometry and design the mold. This required extensive moldflow analysis of the proposed injection blow molding process and product characteristics. The customer’s target cost in volume production also needed to be considered in determining the ideal mold design and molding process, since cavitation and cycle time would drive production cost.
The design team also specified the flexible PVC material, matching the clarity, hue and durometer of the customer’s current product. The prototype mold was designed with a single cavity. The production mold was multi-cavity. There were three stations incorporated in this process. The first station had injection-core cavities and a slider. In this step the molten material is fed into a hot runner manifold where it is injected through nozzles into a heated cavity and blow stem. The blow stem forms the neck and internal shape of the parison. This process takes about 8-9 seconds to form the shape and cool to 190 degrees C. The second station is called the blow station and in this step the parison is clamped into a chilled mold and air is blown into it through the blow stem. A bottle shape is formed that matches the mold cavity. The cycle time on the blow station is 12 seconds. In the final step the bottle is transferred to the ejection station. Once cooled and hardened the part is ejected from the open mold. While the injection blow molding process takes slightly more time than an extrusion blow molding process, it offered a higher degree of accuracy and repeatability.
Endotracheal Tube Redesign
In a final case, the project involved development of a single-use portion of new endotracheal tube designed to mitigate the incidence of ventilator-associated pneumonia (VAP) by maintaining constant pressure within the tube and providing a collection point for oropharyngeal secretions that could easily be drained and cleaned by the hospital’s nursing staff. Forefront supported the development of the single-use components for two models of endotracheal tubes. The complete product combines endotracheal tubes with tracheometry drain tubes made from silicone, along with a tracheal seal monitor which continuously measures the pressure between the cuff and the trachea, enabling it to generate maximum cuff pressure. The resultant optimal tracheal seal significantly helps reduce the risk of aspiration. Key product features included:
- Non-stick coating inside the tube to reduce the formation of biofilm
- An adjustable flange and safety system to prevent any unforeseen extubations
- A silicon spiral tube which can adapt flexibly to airways
- Triple subglottic flushing suction pipes to collect and clear secretions
- A low-volume, low-pressure silicon cuff to provide optimum tracheal sealing and minimize injury to the tracheal mucosa
- A special atraumatic tip for atraumatic intubation and optimum adaptation to airways.
From a design and manufacturing standpoint, the single-use portion of the product required 14 different components which utilized a variety of materials. Achieving the customers’ form, functionality and fit goals required an innovative approach to material selection plus use of specialized molding processes with very critical tolerances. The assembly process also included a specialized dipping process.
There were several design issues to address. First, the mouthpiece included a locking nut to lock the tube into position and keep it from moving as the patient moves. Developing the optimum design required a redesign of the original concept. Second, the device was designed with a multi-lumen tube to facilitate collection and removal of secretions. Silicone was selected as the preferred material. While this is an optimum material for the device in terms of fit and function, it increased the complexity of mold design and fabrication. The cavity design needed to maintain the correct dimensions of the multi-lumen tube and use of liquid silicone resin (LSR) drove a requirement for much tighter mold machining tolerances than required in injection molds for other materials.
Finally, the tubes needed to be MRI-compatible. The traditional tube design has an outer layer with a wire spring and then an inner layer. These tubes need to be removed during MRI. The design team recommended nitinol (nickel-titanium) springs, which are MRI-compatible. In the new design there is an outer layer, the nitinol spring and a coating that comprises the inner layer. The non-stick coating also helps reduce the formation of biofilm. The coating requires a dipping process during assembly, which added process development complexity since the pitch of the nitinol spring must be controlled as the inner layer is formed through the dipping process.
Following a design review, mold fabrication began. This was followed by a testing and debugging phase which included a dry run and analysis of product first off the tool. This was a fairly complex process, as the devices used different materials for different components including silicone and polycarbonate. There was also component requiring polypropylene overmolding metal. The LSR molds presented some design and production challenges. A key benefit of LSR molded components is that they are fully cured and pliable after the press cure. This enables the parts to be demolded without the use of ejector pins. However, uncured silicone is a low viscosity polymer that under pressure will flow out any opening greater than three microns. As a result, machinability tolerances within the mold are less than three microns. Forefront uses CNC machines for this type of mold fabrication. There are only a limited number of mold fabrication houses capable of fabricating LSR molds.
Production processes underwent a similar development and validation phase with performance qualification to user requirements, operational qualification to functional requirements, installation qualification to design specification and installations. The dipping process for the inner coating required DoEs to determine the optimum process parameters for correctly pitching the nitinol spring within the tube.
A Holistic, Cross Functional Approach Improves Quality, While Reducing Cost and Development Time
In each of these cases, functionality, cost considerations or performance considerations drove the selection of specific types of materials. This in turn drove production choices and mold design constraints. In several instances, the combination of choices drove development of highly customized processes requiring DoEs to fine tune to the optimum process. The cases also illustrate a very broad range of production capabilities. Utilizing a single supplier for design, mold design and fabrication, and production streamlines the communication processes needed achieve an efficient product development process that rapidly generates a manufacturable design and ultimately a cost competitive product. And, the broader the range of fabrication and production capabilities at the contract manufacturer, the more focus can be put on designing in the required functionality and performance characteristics as opposed to designing only within limited production capability parameters.
About Forefront Medical Technology
Forefront Medical Technology is a global medical device contract manufacturer with five locations. Singapore is Forefront’s headquarters, as well as home to our Design Engineering Center and specialty manufacturing. JiangSu and Xiamen, China, are additional manufacturing locations and are also China FDA Registered. Shanghai, China, Farmington, CT USA are regional Business Development offices which assure our technical sales teams are close to our customers for local, responsive assistance.
We have developed extensive capabilities with laryngeal mask airways, diagnostic devices, drug delivery systems, enteral feeding catheters, infusion sets, wire reinforced tubes, optically clear components, patient monitoring devices and other specialty products. Each of our locations has state of the art manufacturing capabilities that include class 100K clean rooms for extrusion and injection molding, complimented by class 10K clean rooms for assembly and packaging. Forefront Medical’s integrated technical approach provides customers the total manufacturing solution and global supply chain. Our facilities are TUV ISO 13485:2016, ISO 9001 and FDA Registered. Forefront is a wholly owned subsidiary of VicPlas International Ltd, who is listed on the SGX Main Board, Singapore stock exchange.