Rapid Prototyping Using Medical Grade Silicone by Matthew Bont and Ryan Taylor Executive Summary Albright Technologies Inc
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P016_RPN_20160808.qxp 8/3/2016 3:48 PM Page 1 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 sili- cone 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 ques- tions and learn lessons about the design or application functions so that opportu- nities can be identified early in the de- velopment 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 com- bination of materials bond? Does sili- cone work as a material for the potential function? Can this geometry even be made? What is the behavior of the geom- etry and material combination so that the design may be optimized? Additional common questions an- swered in this phase are: Which material should be used? Are geometry and wall thickness appropriate for the application? Additionally common feasibility compo- nents 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 fi- nal design largely determined already and provide feedback for testing perform- ance, 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 suc- cessful clinical trial and to produce mar- ketable components to use during scale- up and early production. Prototyping starts with a design in- tent, which is the root of the medical de- vice. 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 common- ly combined with additional chemical side groups to change properties. Silicone materials are rubber-like in nature and offer a wide operational tem- perature band and a high degree of heat resistance. In addition, silicone materi- als benefit from characteristics including P017_RPN_20160808.qxp 8/4/2016 2:24 PM Page 1 www.rubbernews.com Rubber & Plastics News ● August 8, 2016 17 Technical 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 be- ing 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 mold- ing. 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.