Rapid Prototyping Using Medical Grade Silicone by Matthew Bont and Ryan Taylor Executive Summary Albright Technologies Inc

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16 Rubber & Plastics News ● August 8, 2016 www.rubbernews.com Technical Rapid prototyping using medical grade silicone By Matthew Bont and Ryan Taylor Executive summary Albright Technologies Inc. TECHNICAL NOTEBOOK Applications that require silicone pro- Edited by Harold Herzlich The paper reviews processes and materials currently available for rapid proto- totyping range from medical devices to typing using medical grade silicone rubbers bridging from concept feasibility to consumer products to military compo- molded in silicone include cardiac pre-production design validation. It starts with an overview of the various forms of nents and often utilize the good com- catheters, valves, drug delivery devices, medical grade silicone materials, such RTV, HCR and LSR and their properties. pression set, high temperature resist- punctal plugs, diaphragms, ocular im- There is discussion of common approaches to rapid prototyping of silicone medical ance, high elongation and softness, and plants, dental devices, orthodontic devices, devices based on material characteristics and project goals including potential ad- good biocompatibility. laparoscopic lenses, medical device han- vantages, constraints and limitations for several prototyping processes including Liquid silicone prototypes can be mold- dles, handle overmolds, equipment key- casting, compression molding, transfer molding, injection molding and overmolding. ed using compression, transfer and injec- pads and gaskets. This includes expanded discussion of prototyping overmolded devices including tion molding processes. A wide array of ● Industrial parts that are molded in process selection and development, substrate requirements and typical challenges. parts have been manufactured in silicone. silicone include gaskets of all sizes, ● Medical devices that are commonly seals, diaphragms, manifolds, wire con- nectors, lighting assemblies, LED light components, and plugs. ● Consumer products that have been prototyped in liquid silicone include silicone wearables, touch screen surrounds, nasal plugs, aesthetic gaskets and seals, and even shot glasses. ● Aerospace and defense items that have been manufactured using silicone prototyping methods include O-rings, key- pads, antennas, electronic overmoldings, electronic displays, seals and gaskets. Liquid silicone rubber will continue to provide designers with options that push the limits of device functionality. The purpose of prototyping is to answer questions and learn lessons about the design or application functions so that opportu- nities can be identified early in the development process to improve the design. This should start with determining what questions need to be answered in or- der to move to the next stage of the project, and doing so well leads to more efficient, faster and lower cost project success. Medical silicone prototyping generally can be split into two categories: Feasibili- ty testing and design validation/scale-up. The feasibility question generally an- swers questions such as: Can this combination of materials bond? Does silicone work as a material for the potential function? Can this geometry even be made? What is the behavior of the geometry and material combination so that the design may be optimized? Additional common questions answered in this phase are: Which material should be used? Are geometry and wall thickness appropriate for the application? Additionally common feasibility components are used for early stage marketing tools for investors and thought groups. The design validation phase that may include clinical trials tends to have a final design largely determined already and provide feedback for testing performance, production method capability, veri- fying appropriate tolerances and specifi- cations for final design reviews. The intent of this is to ensure the product is capable of completing a successful clinical trial and to produce mar- ketable components to use during scale- up and early production. Prototyping starts with a design intent, which is the root of the medical device. Once a medical device concept has been developed, selecting an appropriate material supports the design intent.

Medical silicone materials Silicone materials are polymers that include inert and synthetic compounds made up of repeating units of siloxane. Siloxanes are chains of alternating sili- con and oxygen atoms, and are commonly combined with additional chemical side groups to change properties. Silicone materials are rubber-like in nature and offer a wide operational temperature band and a high degree of heat resistance. In addition, silicone materials benefit from characteristics including P017_RPN_20160808.qxp 8/4/2016 2:24 PM Page 1

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low thermal conductivity, the ability to made of ABS, polyetherimide molds or repel water, as well as the resistance to The authors similar are filled by pouring material oxygen, ozone and UV light. into the mold and curing a solid part. Silicone is commonly used in medical Matt Bont currently serves as the di- The relatively low-cost of these molds al- applications as it is non-toxic and does rector of operations at Albright Tech- lows rapid iteration of basic ideas that not support microbiological growth. nologies Inc., managing daily operations may be relatively complex. Medical grades of silicone have lower at the company while providing strategic Silicone matches surface finish effec- levels of impurities from the material planning and leadership. tively so the resolution of 3D printed and generally have extensive biocompat- Bont began his internship at Albright molds directly affects both the part quali- ibility testing. in 2007 and remained there until earn- ty and accuracy as shown in Fig. 1, the This is the main differentiator being a degree in mechanical engineering layer patterns are transferred to the part. tween medical and non-medical grades from Western New England College in The 3D molds are limited to short runs of silicone. 2009. of a few parts, exhibit poor edge quality Medical grades of silicone commonly After graduation, he started working and surface finish due to plastic strength start at skin contact approval, referenc- Bont full time as a quality engineer at Al- Taylor and printer resolution. ing USP Class 6. bright until he was promoted to senior The temperature and pressure gener- Implantable medical grades, on the project engineer in 2010. ally limit the use of 3D printed molds to other hand, can be used for both short- Bont earned a master’s degree in plastics engineering from the University of RTV materials and some limited LSR term and long-term implantation. Massachusetts Lowell in 2014. materials. Medical grades of silicone are com- Ryan M. Taylor has worked in the manufacturing industry since graduating Better quality printed resins improve monly available from major silicone from Clark University in 2009 with a bachelor’s degree in management. the surface finish as shown in Fig. 2, manufacturers and in different forms of Taylor has worked in technical sales, marketing, operations and most recently but many are restricted significantly by silicone including liquid silicone rubber, at Albright Technologies as director of sales and marketing. temperature and pressure. room temperature vulcanization silicone The relatively low temperature and and high consistency rubber. thermal conductivity drastically in- Implantable grades of silicone are cures at temperatures from 250°F to RTV materials are well suited for low crease the heating and cure duration to available for both short-term and long- 350°F and only requires seconds to a few temperature and low pressure 3D print- a range of minutes to hours and have a term implantable medical devices. The minutes to fully cure. This results in very ed tooling. But for prototypes requiring very short mold life. main difference between the two grades short cycle times and is ideal for proto- clinical testing and high volume produc- The limited pressure and low tool of materials is that the long-term im- types and production molded parts. tion parts, RTV is often not the best fit. rigidity limit the part quality and stabil- plantable grade is more rigorous valida- Liquid silicone rubber materials are High consistency rubber also can be ity required for more advanced prototyp- tion for time frames for acceptable use typically two parts formulations, re- used for prototyping and production molding. Flashing is typically significant due within the body. ferred to as part A and part B. The ma- ing of silicone parts. The main advantage to poor edge quality, low tool rigidity Short-term implantable silicones are terials need to be mixed prior to molding of high consistency rubber over other and the nature of casting. good for use within the body up to 29 or can be mixed live as parts are being forms of silicones is its high strength. days. Long-term implantable materials molded via a static mixer. HCR is for the most part a legacy ma- Compression molding can be used in the body indefinitely. Most liquid silicones are typically mixed terial used prior to the mainstream Silicone compression molding uses Liquid silicone rubber (LSR) offers the 50 percent part A and 50 percent part B, adoption of liquid silicone materials. aluminum or steel molds to form RTV, greatest ease of use when molding sili- however there are exceptions. Colorant However, new versions of high consis- LSR and HCR to the final part shape as cone prototypes and production parts. dispersions can be added to the liquid sili- tency rubber continue to be released by shown in Fig. 3. The mold is filled with The material is available in platinum cone material to provide color and/or tint silicone suppliers for various medical an initial shot or charge and then closed and peroxide curing versions. to the final prototypes and parts. applications that compete more readily to force the material into shape and Platinum curing versions are more Colorant dispersions are typically with LSR materials.l push out excess material. commonly used as they do not outgas like added at a rate of 2 percent. LSR is gen- HCR materials can be molded using Compression molding parts often peroxide types. In addition, platinum erally preferred for manufacturing parts transfer and compression molding tech- serves to achieve design verification and curing versions are relatively inert. over RTV and HCR silicones due to sta- niques. HCR with the addition of spe- validation, functional testing, early clin- LSR materials can be molded into parts bility, efficiency, and ease of processing. cialized raw material handling equip- ical trials with the end product silicone using compression and injection molding Room temperature vulcanization sili- ment can be injection molded. However, material, dimensionally accurate fabri- processes. Liquid silicone rubber typically cones are widely available from all of the these systems are not as common or cation, and with the surface finish in- major silicone suppliers and many RTVs widely available as processing equip- tended for the final design. Fig. 1. Silicone casting using 3D print- are available in medical grades as well. ment for liquid silicone rubber. The compression molding process can ed molding. RTVs typically take a few hours to a create a complex part with excellent few days to cure at room temperature Prototyping processes quality as shown in Figs. 4 and 5 but is are commonly used in feasibility testing. Medical silicone device prototyping limited by handling to lower volumes in Depending on the cure system, the spans 3D printed molds and potentially the hundreds or thousands of parts. curing process can be accelerated by ap- handcrafted or cut rough geometries to The major benefit is the final produc- plying heat significantly reducing the injection molding scale-up processes. tion such as parts that are dimensional- cure time. Based on the material and intent then the ly accurate components with full surface Room temperature vulcanization ma- following general overview covers major finish controls, where the biggest advan- terials are for the most part inexpensive processes and typical stage each is used. tage is simple and economic tooling and and widely available in small kits lead- Molding typically breaks down into rapid color and material changes. ing to being commonly used for silicone casting, compression molding, transfer prototyping needs. molding and injection molding. Extrusion Transfer molding RTV has many drawbacks as compared is also common but beyond the scope of Silicone transfer molding is similar to to liquid silicone rubber and high consis- this paper. compression molding except the charge tency rubber. RTV materials typically is loaded into a transfer pot or zone out- have lower performance properties when 3D Casting side the cavity. The mold closes, and a compared to other silicone materials. Crude initial casting is often the first piston typically actuates driving the ma- approach used by developers for early terial into the cavity though a runner Fig. 2. Compression casting using synthetic ABS. feasilibity testing. 3D printed molds and gate system. See Silicone, page 18 Fig. 3. Silicone compression molding. Fig. 4. Compression molded silicone housing cap. P018_RPN_20160808.qxp 8/4/2016 3:03 PM Page 1

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Mettler Toledo has launched its standard printouts. These can be trans- newest halogen moisture analyzer, the Larson ferred via the RS232 or USB ports to fulfill Products HC103, which measures moisture content Electronics’ documentation and traceability. in minutes, enabling fast response times portable pedestal base stand with a convenient New drying methods are easily up- for quality control and in-process control. explosion carrying handle built into the top of the loaded to the HC103 via the USB port. A color touchscreen, graphical user proof LED stand. Mettler Toledo provides a collection of guidance and real-time drying curve work light The A-frame portable stand is con- validated drying methods for more than make the HC103 easy to use, Mettler with a mag- structed from non-sparking aluminum, 100 different samples. Toledo said. netic base. Larson said, and powder coated for in- For more information on the HC103, creased durability and corrosion resist- visit www.mt.com/moisture. ance. The lamp can be adjusted up or down 90 degrees and locked into position. The Wacker Silicones unit of Wacker More information can be found at Chemie A.G. has launched two high-re- www.larsonelectronics.com. fractive-index silicone elastomers for use in light emitting diodes and optical compo- Automator America Inc. has rolled nents. out a new line of marking machines for hot Lumisil 590 and 591 are transparent, Larson Electronics L.L.C. has in- stamping presses that are available for addition-curing silicone elastomers with troduced a portable explosion proof LED manual and pneumatic operation. The ma- a refractive index of 1.52, which the com- work light with a magnetic base. chines can be bench mounted or mounted pany said ranks them among the HRI Larson said the EPL-MPM-150LED- for in-line production and are ideal for encapsulants. 100 explosion proof LED light is Class 1 marking fabric, plastics and wood, it said. The products can withstand high oper- Division 1 and 2 and Class 2 Division 1 Automator said its MB20/21E series hot ating temperature and strong light radi- and 2 rated and is capable of illuminat- stamping presses are designed for high Mettler Toledo halogen moisture analyzer. ation without yellowing. Wacker said ing up to 10,000 square feet of work production environments with a cast base that makes them suitable for producing space. that includes standard T-slots for tooling. Operators can access drying methods LEDs with high light efficiency. It said This LED work light produces a bril- Equipped with an automatic ribbon ad- directly from the home screen with just the elastomers also protect the LED chip liant flood pattern for illuminating en- vancement package and temperature con- one click, the company maintained, and against corrosive gases, which will ex- closed areas and hazardous locations trol regulator, Automator said its hot can just add the sample to the weighing tend the component’s service life. where flammable vapors, gases and stamping machines apply consistent per- pan, tare and press start. The new Lumisil lines are easy to dusts may be present, Larson said. sonalization of products with colored foil As the drying program is running, process, heat resistant and tack-free after The LED lamp produces 13,000 lu- imprints. Mettler Toledo said a real-time drying curing, according to the company. Lumisil mens of light with a color temperature Many accessories for marking details curve is displayed on the screen to pro- 590 and 591 form cured rubber grades of of 6000K, the company said, and a color are available that include cliche, type and vide an overview of the progress. varying hardness. Lumisil 590 is relative- rendering index of 70. type holders, numbering heads and custom There is no need to record the results ly soft, with a hardness of Shore A 65, The EPL-MPM-150LED-100 is made hot stamping dies. manually, Mettler Toledo said, as the while 591 is harder at Shore D40. of a 16-inch wide by 14-inch tall rectan- Visit www.automator.com for more in- HC103 can generate result reports in the For more information, go to www.wack- gle light head mounted within a formation. form of PDF or CSV files in addition to er.com.

When prototyping, aluminum or steel Generally plastics such as ABS, ny- bonded to, but require more specialized tools are used depending on tool strength lon, peek, polysulfone and polycarbon- primers or approaches. Silicone and quantity of parts required. ates have been shown to bond well with Silicone to silicone bonding presents sev- Setup generally takes longer than the silicone. Primer may be needed to achieve eral unique challenges. Generally, flashing Continued from page 17 previous processing methods but silicone a strong bond and the addition of mold and deformation are common in composite Transfer molding typically performs injection molding can most closely repre- release into the base resin often causes silicone devices comprised of different ma- well for hundreds to thousands of parts. sent production processes for the purpose bonding failure. terials, but the advantage is creating Transfer molding is often used for HCR of scalability and validation. The heat deflection temperature or Vi- unique performance devices. Some sili- materials and in limited LSR applica- Injection molding generally produces cat softening point for a plastic grade in- cone chemistries when fully post-cured tions. RTV and LSR materials are often high dimensional stability and good edge dicates the temperature were the plastic bond poorly to other silicones. Mold release not well suited to transfer molding due quality. component is rigid enough to overmold and differences in chemistry between ma- to low viscosity and high reactivity. Material changes often require clean- and provides a good reference tempera- terials have also caused bonding failure. Molds are good for design verification ing the barrel to ensure a complete switch ture to compare against cure conditions. and validation, functionality testing, and between materials leading to longer and Olifins such as polypropylene and Conclusions early clinical trials. Materials can often be more costly setups and switchovers. polyethylene do not bond in general to The basic silicone material selections easily changed in transfer molding. The The quality and cost vary significantly silicone and generally melt at hotter available from suppliers provide devel- molds are typically made of aluminum or in silicone injection molding based on temperatures required for processing. opers with high performance options to steel and can produce good edge quality as the quantity and intent of the molding, 3D printing offers a rapid and inexpen- meet temperature, biocompatibility, and compared to casting. as well as the complexity of the part and sive method for prototyping inserts for other elastic and sealing requirements. Transfer molding allows for insert investment in tooling. complex component geometries and can Prototyping methodology should be molding with tight shutoff zones to limit provide early stage function testing and chosen based on the intent between fea- material to functional areas (Fig 6). Molding substrates marketing feedback with the right grades. sibility and production scale-up. Transfer molding is often less utilized in Silicone is often used in multi-compo- The printed plastic components have Answering these questions deter- favor of compression or injection molding. nent and composite devices combined some of the same challenges as molding mines which process is the best fit to with electronics, plastic, metal, ceram- grade plastics, where some grades have achieve the intent of the work and pro- Injection molding ics, and other silicones. low melting temperatures and may con- vide the best path forward for successful Silicone injection molding shown in Fig. A few common prototyping methods in- tain additives that may cause inhibition development of a silicone device. 7 is ideal for LSR and with more special- clude overmolding silicone onto 3D printed during curing. ized material handling equipment HCR is inserts, pre-molded plastic or silicone, ce- Silicone can generally be bonded to met- References also possible.2 Typically, injection molding ramic and metal inserts where the three al with the use of primers. Some grades 1. Albright Technologies. Silicone Compression lends itself to orders requiring several major challenges are bonding, tempera- with very high oil content and certain Molding. (Online) http://albright1.com/silicone-com- ture limitations for processing, and cure chemistries cause cure inhibition or in the pression-molding/. hundred to thousands or more parts. 2. Albright Technologies. Liquid Silicone Injection inhibition. least bonding failure. Molding. (Online) http://albright1.com/liquid-silicone- Some metals such as titanium can be injection-molding. Fig. 5. Compression molded silicone wire seal. Fig. 6. HCR Silicone overmolded on a steel frame. Figure 7. Silicone injection molding equipment diagram.