Plastic injection molding is an effective and popular method of producing large quantities of identical components with high precision. This process entails melting thermoplastic flakes or pellets before injecting them into a mold. After the mixture cools or hardens, ejector pins push the finished part out.
Injection-molded parts can have intricate structures, and making design changes after manufacturing the product is difficult. As such, it is critical to carefully craft and lay out the plastic component to reduce the likelihood of tool issues, achieve the desired results, and save injection molding costs.
Here are ten design tips for plastic injection molding:
1. Choose the Most Appropriate Surface Finish for the Design
Making the right decision regarding the surface finish is vital to ensure a proper molding design. Aside from its aesthetic value, it improves grip, increases paint adhesion, and allows gases to escape the mold during the process. However, the surface finish you select is related to the molding type required based on production volume and the material type from which you will make it. For instance, steels are more durable and have more surface finish options than aluminum ones. You can also polish them for a smoother finish.
2. Uniformly Design the Parts
Any thickness limitations or changes in the components can disrupt the injection molding flow, potentially leading to other negative consequences. Therefore, keeping the thickness constant between 2 mm. and 3 mm. is recommended because layer thicknesses less than 1 mm. or greater than 4 mm. might lead to manufacturing issues.
3. Add Drafting to the Parts
Adding a draft angle allows the parts to be ejected from the injection mold. The angles should be at least 1° on an untextured surface and 3° on a textured one to properly let the components loose without prying. For applications that require a tight mating area, position the zero-draft area as close to the mating portion as possible rather than a complete surface.
4. Add a Radius Wherever Possible
Sharp corners on any injection molded part are challenging to form because they trap air. The most secure solution to this problem is to design them out. A radius also extends to a draft angle, aiding in smooth transitions and ensuring you can remove the part from the mold.
5. Always Design Resin Flow From Thick to Thin Sections
Thicker sections are needed for structure and strength. Because molten resin loses pressure and temperature as it continues to flow through the mold, it must first cover the thicker sections before moving on to the thinner areas.
6. Determine Which Molding Defects Are Acceptable
Injection molding defects are to be expected during the process. For example, sinks caused by bosses designed into the backside may occur on thicker sections, whereas adding structure to the part by strengthening the ribs may increase the possibility of visual defects. While advanced molding conditions can reduce some of these defects, they cannot eliminate them. As a workaround, determine which defects are acceptable and which are not, and then design around them.
7. Reduce Strengthening Rib Sizes As Much As Possible
Rib strengthening plays an essential role, but having too large of a feature can cause complications. Therefore, each rib must meet three primary design criteria: base thickness, rib height, and overall thickness.
First, the rib base must be structured at 60% or less of the wall thickness to reduce a sink mark on the surface. Second, the rib height should be as low as possible (at least less than three times the part thickness) to avoid getting stuck in the mold. Lastly, the overall thickness should be less than the rib base, which is connected to the designed draft angle.
8. Avoid Tooling Undercuts
An undercut in an injection molding tool occurs when the device’s opening and closing prevent the formation of a feature. A lifter and slide are recommended to form the component rather than complicated shapes. Therefore, it is best to maintain simplicity because they can create complex structures while still allowing the part to be removed.
9. Design for Manufacturing and Error Proofing
Most injection molded products are intended to be part of more extensive manufacturing. Use coordinates or datums when designing to ensure that each one is assembled the same way every time. Moreover, remember that huge businesses require manufacturing-ready designs, and minimizing error potential should be a part of every configuration.
10. Use Rapid Prototyping To Immediately Detect Problems
Rapid prototyping can help improve your design, manufacturing, and secondary processes. It can also detect early design flaws in a model that you might overlook. You can choose one from many rapid prototyping options, including metal 3D printing, digital light processing, CNC machining, binder jetting, rapid injection molding, and laminated object manufacturing.
ProMed for Your Injection Molding Needs
ProMed uses cutting-edge technology, relies on a highly experienced technical team, and uses a creative system to give our customers dependable, high-quality, and cost-effective service options for their production needs! We also specialize in small, finely crafted silicone and plastic components that can be implanted for short or long periods, with or without drug-releasing agents.
Contact us today to learn more about ProMed’s molding solutions and services! You can also request a quote now.
ProMed Pharma announces a preclinical rat study to assess pharmacokinetics of a novel long-acting contraceptive implant
Bioresorbable implant aims to address key unmet needs for
family planning at an affordable price in low and middle
income (LMIC) settings
PLYMOUTH, MINNESOTA, UNITED STATES, April 19, 2022
/EINPresswire.com/ — ProMed Pharma is pleased to
announce the initiation of preclinical evaluation of a novel
fully resorbable contraceptive implant. The implant,
developed in a project funded by the Bill & Melinda Gates
Foundation, aims to address key unmet needs for family
planning at an affordable price in low and middle income
(LMIC) settings.
Commercially available contraceptive implants, while safe
and highly effective, require removal by trained health care
providers any time the user wants to discontinue the
method, including when pregnancy is desired, or when the
implant reaches the end of its effectiveness. This
requirement imposes a strain on resources in LMIC
settings.
The implant being developed by ProMed is specifically designed to address the needs of LMIC settings. • First, it aims to expand women’s contraceptive options by providing 18 months of contraception by long-term release of levonogestrel. This duration fills the gap between that offered by existing injectables and longer-acting methods such as non-erodible implants. • Second, the implant is fully biodegradable, eliminating the need for women to return to medical clinics for removal at the end of the period of effectiveness. • Finally, the implant, which comprises a levonogestrel-releasing outer sheath surrounding a drug-free polymer core, is designed to retain sufficient mechanical integrity to allow removal if or when desired. Removability is important to respond to women’s needs, such as in cases where pregnancy is desired prior to exhaustion of the contraceptive.
The preclinical evaluation of the implants follows selection of four lead formulations combining levonogestrel with cost-effective, commercially available biopolymers that yield near-linear release without the need of a rate controlling membrane. The preclinical study will evaluate the pharmacokinetics of levonogestrel, establish duration of removability, and track length of biodegradation of the designs. The results will allow further narrowing of formulations for clinical evaluation.
Dr. James Arps, Director of Business Development at ProMed, noted “the implant designs have shown promising mechanical integrity and drug release profiles based on in vitro tests to date and have a form factor which is similar if not superior to other implants on the market.” The study will be carried on for a minimum of 6 months with the option of gathering drug release and polymer degradation data up to 1.5 years.
ProMed Pharma specializes in the molding and extrusion of drug-loaded silicones, thermoplastics, and bioresorbable materials, leveraging this expertise to manufacture long-term implants and combination devices under cGMP. Working with both established and early stage companies, we utilize robust manufacturing processes for controlled release of APIs utilizing a variety of materials. From clinical trial materials to commercial products, ProMed supports
pharmaceutical and medical device companies developing controlled release formulations including subcutaneous, orthopedic, cardiovacular, and ophthalmic implants, intravaginal rings, and steroid-eluting combination components. The company has facilities in Plymouth and Maple Grove, Minnesota. Please visit www.promedpharmallc.com for more information.
Injection molding and other medical manufacturing processes are often complex and peppered with potential pitfalls. Fortunately, nearly all of these potential issues can be resolved with a highly competent design. Achieving the best design the first time around is crucial as there is a lot at stake. If OEMs do not get the design right, product rejection rates will increase, productivity will decline, and a host of other issues will ensue – all negatively impacting the bottom line. Additionally, modifying a product or mold design during the production stage can be very costly – so it is worth the time to get the design phase right.
One approach used in medical manufacturing to ensure the best design is Design for Manufacturing, or DFM. This is the process of designing products for ease of manufacturing as well as creating a better, more cost-effective product. DFM is a vital product development step that looks to simplify and optimize the design to ensure high quality and efficiency during production.
One apThe DFM process should occur early in the design phase of any molding project and should engage key parties including designers, tool fabricators, raw material suppliers, manufacturers, and other stakeholders. The goal is to tap into the experience of each of these experts. The team will scrutinize the current design from many angles with the goal of identifying a more cost-effective solution that maintains excellent quality.
How does the DFM Process Add Value?
Simply stated, OEMs need to ensure the part is as easy to manufacture as possible. This will result in more efficient production, better quality, and lower cycle times. Below are some ways OEMs gain value from the Design for Manufacturing process.
· Save Significant Cost and Time: OEMs are often in a rush to get a new product to market so it is tempting to shorten – or even skip – the DFM process. However, it is important to keep in mind that changes to the design become exponentially more expensive and timely to implement as the product advances through the life cycle. A thorough DFM upfront will allow any optimizations to be made or issues to be resolved before the changes significantly impact the project timeline or budget.
· Optimize Functionality and Aesthetics: tooling for molding projects is often expensive to fabricate and costly to modify; thus, it is imperative to get the tool design right the first time. If the design is off even by a small margin, the product aesthetics and functionality will be altered. The DFM process often includes computer simulations of the design as well as rapid prototyping so the team can fully visualize the product. Oftentimes, these steps yield valuable insights and design optimizations that would have been lost if the DFM process was not performed – resulting in a more functional and aesthetically-pleasing product.
· Confirm Manufacturability: last but certainly not least, the DFM process ensures the part can be manufactured. This may seem obvious but there are many instances of products reaching production only to realize the part cannot actually be manufactured per its current design – costing OEMs valuable time, money, and resources
ProMed’s Approach to DFM
To avoid this situation, OEMS should team up with an experienced medical manufacturing partner, like ProMed, that has DFM expertise. ProMed’s design and manufacturing teams are integrated to allow manufacturability issues to be identified and addressed during the design process instead of after the tooling is fabricated – saving customers significant development time and cost as well as innumerable headaches. At ProMed, we works with our customers throughout the product life cycle, providing a cost-effective solution that meets the customer’s needs.
LSR is a versatile silicone that has a wide range of end-uses from medical devices to consumer goods to electronics to automotive. There are several types of LSR that can be manufactured such as medical, self-lubricating, conductive, flame-retardant, and radio opaque. The type of LSR produced is determined by the additives incorporated during the manufacturing process. Additionally, LSR is available in different grades, namely medical, food, and industrial. Given its versatility, it is not surprising that the worldwide demand for LSR continues to grow.
LSR has excellent properties, such as a low viscosity and low shrink rate, that make it a great choice for silicone injection molding and the manufacturing of complex products and intricate parts. One of the benefits of LSR is that it cures faster than most other rubber materials; additionally, due to the highly automated nature of silicone injection molding and the potential for 24/7 manufacturing, high volumes of LSR products can be produced in a short period of time – adding to its popularity.
A key benefit of LSR’s lower viscosity is that it is easier to mix additives into. Additives that can readily be incorporated into a batch of LSR include colorants, desiccants, barium, and pharmaceuticals such as hormones or steroids. For these reasons, LSR is a great option for medical devices such as combination products. The low viscosity of LSR and the temperatures needed to vulcanize LSR are usually low enough that significant degradation of compounded substances, like Active Pharmaceutical Ingredients (APIs) that are used in combination products, can be avoided.
While LSR has many attractive properties, its biocompatibility is outstanding. LSR has demonstrated superb compatibility with human tissue and body fluids, and is resistant to bacteria growth. Medical grades of LSR are temperature resistance and can easily sterilize, which makes them compatible with various medical devices and accessories such as implantable devices, liquid feeding bottles, dialysis filters, and oxygen mask instruments.
Looking for a proven and reliable medical manufacturing partner for your next silicone injection molding project?
Contact the professionals at ProMed to learn more about our range of medical manufacturing solutions and the various silicone materials we utilize.
There are many factors to consider when designing a molded product for the healthcare sector. Below is an example of a DFM checklist that lists key design consideration for an injection molding project. These are topics that OEMs should discuss with their medical manufacturing partner to ensure each of these items is considered in the product design. This is not a comprehensive list but these are some of the most common design parameters that will help ensure a robust design and a successfully molded product. The DFM checklist for your project can be customized to meet the specifics of your application. Visit our website for more medical manufacturing design considerations regarding material selection and part functionality.
· Simplification:
Can the product size or geometry be simplified or standardized?
Can complex features such as undercuts or sharp corners be simplified or removed?
Are all specified tolerances necessary, and which dimensions/tolerances are critical?
· Part thickness:
Can the part be made to have a uniform thickness throughout?
Check for thick areas of the part that could result in sinks and voids
Check for thin areas of the part that could result non-fill
· Part Draft:
Does sufficient draft exist? Is draft in the right direction and location for a good parting line?
If texture is being used, is there enough draft to release the part?
· Gate location:
Can the gate be located in a thick area of the part?
Will the gate seal at the right time?
Are multiple gates needed?
· Material considerations:
Will the material have flow concerns such as excessive shear?
If the resin does not flow well, are long or thin flow lengths needed?
Is the fiber orientation correct?
· Operating conditions to consider:
Maximum pressure during filling and packing
Clamp force profile
Fill pattern – is there a potential for material solidification, voids, or hot spots?
Temperature profile
Venting temperature – is there a potential for air traps?
· Defects:
Consider the potential for flash, weld lines, sink marks, short shots, burn marks, shrinkage, warpage, etc.
· Tooling: potential for tool integrity concerns such as thin steel?
About ProMed
ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. Over time, we broadened our product offerings to include assembly, micro-molding of highly engineered plastics, and combination products. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.
ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.
We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:
· Automated Silicone Injection Molding
· Multi-cavity tooling
· Micro molds and micro molding
· Servo-controlled de-molding capabilities
· Insert molds, overmolds, and automation integration
· Transfer molding
· Compression molding
Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next silicone injection molding project.
MediSilicone injection molding is a cost-effective manufacturing solution that many OEMs rely on for high-quality, efficient production. This method of manufacturing is very common within the medical sector and has several benefits compared to other molding processes. For example, silicone injection molding is a good choice for a wide range of part sizes, materials, and colors – including highly intricate and complex parts. This method produces products that are virtually identical from part to part which provides excellent brand consistency and part reliability during high volume runs, which is especially crucial for products used in the medical industry. The high reproducibility of silicone injection molding also allows for production to be scaled up to very large volumes, resulting in low costs per unit.
Common Silicones for Injection Molding: LSR and HCR
Silicone elastomers have long been a popular material for silicone injection molding due to their highly desirable mechanical and physical properties. Silicones have excellent durability, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, a wide temperature range, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for implants due to its excellent biocompatibility.
Silicone elastomers are primarily available in two forms for medical manufacturing: Liquid Silicone Rubber (LSR) and High Consistency Rubber (HCR). LSR and HCR are both used in medical manufacturing. While HCR and LSR have several similarities, viscosity is a key differentiator and often impacts the decision on which material is utilized for a given silicone injection molding project. The following provides an overview of both elastomers and when each should be utilized.
What is Liquid Silicone Rubber (LSR)?
Liquid Silicone Rubber (LSR) is a platinum-cured elastomer. LSR is a newer silicone technology and starts out as a 2-part liquid that cures into a solid form when mixed. LSR generally comes in buckets and has a longer shelf life than HCR.
LSR is a versatile silicone that has a wide range of end-uses from medical devices to consumer goods to electronics to automotive. There are several types of LSR that can be manufactured such as medical, self-lubricating, conductive, flame-retardant, and radio opaque. The type of LSR produced is determined by the additives incorporated during the manufacturing process. Additionally, LSR is available in different grades, namely medical, food, and industrial. Given its versatility, it is not surprising that the worldwide demand for LSR continues to grow.
LSR has excellent properties, such as a low viscosity and low shrink rate, that make it a great choice for silicone injection molding and the manufacturing of complex products and intricate parts. One of the benefits of LSR is that it cures faster than most other rubber materials; additionally, due to the highly automated nature of silicone injection molding and the potential for 24/7 manufacturing, high volumes of LSR products can be produced in a short period of time – adding to its popularity.
A key benefit of LSR’s lower viscosity is that it is easier to mix additives into. Additives that can readily be incorporated into a batch of LSR include colorants, desiccants, barium, and pharmaceuticals such as hormones or steroids. For these reasons, LSR is a great option for medical devices such as combination products. The low viscosity of LSR and the temperatures needed to vulcanize LSR are usually low enough that significant degradation of compounded substances, like Active Pharmaceutical Ingredients (APIs) that are used in combination products, can be avoided.
While LSR has many attractive properties, its biocompatibility is outstanding. LSR has demonstrated superb compatibility with human tissue and body fluids, and is resistant to bacteria growth. Medical grades of LSR are temperature resistance and can easily sterilize, which makes them compatible with various medical devices and accessories such as implantable devices, liquid feeding bottles, dialysis filters, and oxygen mask instruments.
Looking for a provenand reliable medical manufacturing partner for your next silicone injection molding project?
Contact the professionals at ProMed to learn more about our range of medical manufacturing solutions and the various silicone materials we utilize.
Another common elastomer for silicone injection molding is High-Consistency Rubber, or HCR. It should be noted that the terms HCR and HTV, which stands for High Temperature Vulcanization, are often used interchangeably and refer to the same silicone material; for the purpose of this article, we will use the acronym HCR.
HCR is a type of silicone elastomer comprised of long polymer chains with a very high molecular weight. It is cured at high temperatures with a platinum catalyst or peroxides. HCR is known for its gummy consistency that is similar to peanut butter, and mostly comes in partially vulcanized sheets.
HCR has many desirable properties such as excellent aging resistance, thermal stability, electrical properties, mechanical strength, elongation, and hardness. For these reasons, HCR is a good material for a broad range of applications within medical manufacturing. Due to its higher viscosity compared to other elastomers such as LSR, HCR is typically processed using compression and transfer molding methods, but is also utilized for silicone injection molding projects.
HCR takes longer to cure than many other molding materials. A longer cure time results in a longer silicone injection molding cycle time. To improve project economics, HCR molds often have a large number of
cavities in order to accommodate the longer cycles and still achieve the desired production volume for each cycle – resulting in a more cost-effective solution on a per unit basis.
Which Silicone is Best for My Injection Molding Project?
Medical device OEMs often face a tough decision: should we use HCR or LSR for our silicone injection molding project? For companies already using HCR to manufacture medical components, it may make sense to continue using this elastomer especially since the initial capital equipment costs have already been made. For new product development, however, LSR is often the best choice given the lower capital costs and labor associated with processing this silicone. Due to its lower cost and versatility with formulations, companies often prefer LSR over HCR – but the decision should be made on a case-by-case basis. This is why it is important to team up with an experienced partner, such as ProMed, who will guide you through the selection process to ensure the right material is chosen for your silicone injection molding project.
About ProMed
ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. Over time, we broadened our product offerings to include assembly, micro-molding of highly engineered plastics, and combination products. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.
ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.
We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:
· Automated Silicone Injection Molding
· Multi-cavity tooling
· Micro molds and micro molding
· Servo-controlled de-molding capabilities
· Insert molds, overmolds, and automation integration
· Transfer molding
· Compression molding
Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next silicone injection molding project.
When it comes to material selection, the medical industry is one of the most demanding sectors. Materials employed within healthcare must be durable enough to withstand harsh conditions, resistant to degradation, and, of course, compatible with the human body. Most materials are unable to tolerate medical environments; fortunately, the medical industry can rely on silicones for essential, life-saving devices and products.
Why the Medical Industry Uses Silicones
Silicones have long been a popular material for medical devices and medical device components due to their durability, ease of molding by many methods, wide temperature range, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for implants. Additionally, medical-grade silicones, such as Liquid Silicone Rubber (LSR), have undergone stringent purity and biocompatibility testing that make them suitable for short and long-term usage.
Silicone has a unique molecular structure, namely its silicon-oxygen backbone, that results in several excellent properties. The following is a deeper dive into some of these properties, and why the medical industry uses silicones.
Superior Biocompatibility: medical devices and products often come in contact with the human body – either externally on a patient’s skin or internally as an implant that contacts tissue and fluids. Materials utilized in these applications are subject to rigorous and extensive biocompatibility testing and must comply with stringent regulations. Simply put, medical grade silicones are unmatched in their biocompatibility, making silicones an excellent option for the medical industry.
Withstands Sterilization: medical grade material must be able to withstand sterilization in order to minimize contaminants and the risk of infections. Devices and products made of medical grade silicone are easily sterilized and resist bacteria growth. In fact, medical grade silicones are often processed in special facilities called cleanrooms that reduce the potential for contamination. For example, all of ProMed’s manufacturing facilities are equipped with certified class 10,000 / ISO Class 7 cleanrooms, demonstrating a strong commitment to quality.
Chemical Resistance: silicones are resistant to water and many other chemicals. For example, LSR is chemically inert and its biocompatibility is unparalleled, making LSR a great option for medical devices, implantables, and other healthcare applications.
Ease of Processing: silicones utilized by the medical industry are easily processed via a variety of manufacturing methods. The 3 most common molding techniques are injection molding, transfer molding, and compression molding. Due to the high volumes required for many medical devices and products, injection molding is often the most cost-effective solution.
Conductivity: many materials degrade when exposed to electrical and other environmental stresses over time, however, this is not the case for silicones. Silicones are naturally nonconductive, and are often used in high-voltage and electrical equipment due to its electrical resistance and ability to act as an insulator. However, some medical applications require conductive silicone, which allows electric current to flow through the silicone product. Silicones are able to be formulated as necessary to meet the requisite conductivity demands.
Superb Stability: silicone is known for its resistance to UV, weather, and other environmental conditions that tend to age materials, leading to a high level of stability and long-life span for silicone products. These characteristics are critical for a number of medical devices such as implantables.
Wide Temperature Range: compared to other materials, silicones, such as LSR, have excellent thermal stability. These blends are able to withstand high temperatures without deforming or melting. As for low temperatures, LSR maintains its flexibility and does not become brittle and vulnerable to breaking like thermoplastic elastomers.
ProMed Pharma’s Capabilities
ProMed Pharma is a leading contract manufacturer of polymer-based drug releasing molded dosage forms and combination device components, such as drug-eluting products. Working with both established and early-stage medical device and pharmaceutical companies, we develop robust manufacturing processes and platforms for extended drug release from a variety of materials, including silicones and thermoplastics.
We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.
ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics – including Liquid Silicone Rubber (LSR) that is an excellent option for drug-eluting medical products! We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All have certified class 10,000 / ISO Class 7 cleanrooms.
Contact ProMed today at 763-331-3800 to discuss your next medical molding project.
For medical device OEMs, the design phase is when a general concept and a list of requirements becomes a detailed plan for creating a potentially life-saving product. While there are several fabrication methods available for making medical devices, injection molding continues to be the dominant method. Its advantages of low price per part, high production volumes, compatibility with many different FDA-approved materials, and its ability to maintain tight tolerances, produces consistent results.
Injection molding is a supremely flexible process, but there are a few constraints and requirements that need to be incorporated into the design of any parts made by that process. For medical injection molded parts in particular, we’ve identified the five most important of these design considerations, which we’ve listed below along with our advice for part design success.
Part Function: What is it Supposed to Do?
All five of these design considerations are interrelated—design choices in one area constrain your options in the other four—but the primary driver of the part design process is ultimately the intended end-use of the medical injection molded part.
Are you designing a device meant to remain implanted in a patient for several years, or is the part a knob or button on a monitoring device or life-supporting equipment? Perhaps it’s a patient connected device that is disposable? Each of those uses implies specific operating temperatures, chemical exposure, and applied stresses over the lifetime of a product. Everything from material choice to the shape of the part is determined by this, so having a well-defined list of requirements at the beginning of the design process will not only help your team, but also assist your medical injection molding contract manufacturer with their DFM review and subsequent mold design.
Will the Part Need to be Repeatedly Sterilized or will it be Disposable?
Single-use products meant to be incinerated give you more leeway with material choice than those that will need to repeatedly withstand the abuse from the sterilization method(s) chosen. Devices that will be steam sterilized will need to be made out of materials that not only have a high melting temperature, but are also highly resistant to both heat and hydrolysis. On the other hand, ethylene oxide (EtO) sterilization requires excellent chemical resistance. UV, gamma, and e-beam methods limit your choices to other materials. Finally, only a handful of niche materials are suitable for devices which could potentially be sterilized by multiple methods over their lifetime.
What will it be Made of?
From liquid silicone rubber (LSR) and thermoplastic elastomers (TPEs) to polysulfone and PEEK, the choices of rubbers and resins are almost endless. With that wide selection of materials come wide ranges of durometers, opacities, biocompatibilities, lubricities, and resistances to heat, steam, radiation, chemicals, tearing, and wear.
With overmolding, design engineers aren’t restricted to just one material. A stiff thermoplastic component can be overmolded with soft silicone rubber grip, a popular combination for the product to be mechanically strong yet comfortable to hold.
How Easy is the Part to Actually Mold?
In order to consistently make high quality parts without exorbitantly expensive revisions, your part design needs to incorporate features such as adequate draft angles, consistent wall thicknesses, and generous radii for perpendicular features such as walls, bosses, and ribs.
Furthermore, for parts made with thermoplastics, really thick walls should be eliminated via core-outs. This not only helps prevent sink marks and warping, but also reduces the cost per part since less cycle time is required to fill and cool large volumes, not to mention the material cost savings from the reduction in resin used to pack the mold.
Price of the Finished Part
Ultimately, medical injection molded parts must be price competitive with competing products already on the market, and affordable enough to provide compelling value over the lifetime of the product.
Closely tied to the price per part, is the production volume expected for the tooling. If you are making millions of parts with a single mold, it’s easier to justify more expensive mold materials (like hardened steel) and features like hot runners for thermoplastic molds and cold decks for LSR. Multi-cavity molds may require a larger upfront investment, but also pay for themselves in the long run due to time and material savings.
Having processed many medical injection molded parts from initial concept to finished product, ProMed’s medical device design expertise can help your engineering team avoid common pitfalls, improve your product, and ensure consistent, high quality results.
From surgical instrument handles and catheters, to drug-eluting implants and stents, different jobs require different devices to be made. Different devices in turn, require different fabrication processes. In this article, we’ll discuss five different molding processes within our expertise here at ProMed, and explain the niches that each of them fill.
Silicone Injection Molding
Liquid Injection Molding (LIM) is a process in which liquid silicone rubber (LSR) is injected into a heated mold under pressure, completely filling the cavity before curing into a solid part which is then ejected from the mold. This process is virtually identical to the injection molding of thermoplastic polymers, except for the fact that LSR is a thermoset polymer. This means that the mold must be heated (not cooled as with thermoplastic resins) so that the mold permanently cures the silicone in a process called vulcanization. Once cured, the part will not melt back into a liquid. This flipping of temperature zones also means that LIM utilizes “cold decks”, not “hot runners” in order to conserve material and reduce cycle times.
Injection molding is a natural fit for making medical devices out of silicone because LSR’s low viscosity allows the mold cavities to be filled quicker and at lower pressures. LIM’s short molding cycles produce cost-effective parts in medium- or high-volume production runs, making it a popular choice for our OEM customers.
Transfer molding
Transfer molding is a process that’s similar to injection molding, and uses many of the same elements: a heated mold cavity, sprue channels, and an external actuator that pushes the molten material into the mold. In transfer molding, an open chamber (called the pot) is filled with the material to be molded (which can start as either a solid or liquid). Then, a plunger pushes on this material and squeezes it into the mold, which is connected to the pot via channels.
Transfer molding typically uses higher pressures than injection molding does to fill the mold. Another difference is the fact that the mold casting material may begin the process as a solid, in contrast to both LIM and thermoplastic injection molding.
Whereas LIM is the preferred process for LSR, transfer molding (along with compression molding, explained below) is commonly used for a different type of silicone called high consistency rubber (HCR). HCR’s higher viscosity makes that particular silicone unsuitable for injection molding.
Compression molding
If the pot in the transfer molding process were removed, and the top half of the heated mold took the place of the plunger, the result would be compression molding. Unlike both injection molding and transfer molding where the molded material is forced into the cavity, compression molding forces the heated cavity onto the material.
Like transfer molding and LIM, thermoset elastomers like silicone are used as the molding material. The heat for the vulcanization is provided by the mold and usually a preheating of the material as well.
Suitable for high-volume production, compression molding excels at fabricating large parts at low cost and with less waste compared to other methods (as there is no runner system or gates to trim off). One disadvantage of compression molding is that the process doesn’t accommodate undercuts in the parts, as any undercuts make ejecting the cured part very difficult.
Insert Molding & Overmolding
Parts made by the three molding processes described above need not be a single material all the way through. It’s often very desirable to make a composite product which has a plastic or silicone layer molded over some or all of a piece of a different material. Silicone gripping surfaces on steel surgical instruments are just one example of such overmolding.
Creating overmolded parts is typically a two-shot (or more) process—essentially a separate molding process for each layer. OEMs must carefully check the material compatibility of the materials they wish to combine because not all combinations of elastomers, thermoplastics, and metals are possible. On the whole, though there are few obstacles, leaving the OEM’s design team’s creativity as the limiting factor.
Insert molding also involves combining premade parts with molded rubber or plastics, but is a one-shot process. This is because the inserts are usually metal parts like threaded studs, which are machined rather than molded.
Both overmolding and insert molding are great for joining parts to moldable materials without using adhesives or mechanical fasteners.
RTV Casting
The last molding process on our list is actually an indirect molding (i.e. casting) process, since it’s a method to make molds that then make the actual parts. With that aside, room temperature vulcanizing (RTV) silicone casting definitely deserves to be on any list of processes applicable to silicone molded medical devices.
A cost-effective way to produce small volumes of parts, RTV casting reproduces surface textures and other fine details. Furthermore, since silicones feature great chemical and heat resistance, RTV molds can be used to cast materials like low melting point metals (e.g. zinc and pewter), epoxies, waxes, and gypsum—all without needing a mold release agent.
The team at ProMed specializes in molding medical devices, including the five methods we touched on here. Whether you’re in the market for micro-molded implantable devices, or an RTV casting for new design concept, the professionals at ProMed have you covered.
Injection molding, a manufacturing method used for making everything from car parts to kids’ toys, is also utilized to make life-saving medical devices, including those inserted or implanted into patients’ bodies. Catheters, balloons, and feeding tubes are all made possible and affordable when biocompatible materials combine with injection molding.
As we have discussed before in an earlier article, the material of choice for implantable medical devices is often medical grade silicone. Its range of available durometers, extreme chemical inertness and biocompatibility, excellent tear and heat resistance make it ideal for parts that need to remain in the human body for extended periods of time.
Furthermore, the low viscosity of liquid silicone rubber (LSR) make that elastomer ideal for injection molding (and therefore mass producing) implantable medical devices, making life-saving advances in medical technology more affordable for patients.
But those advances don’t stop with opening up arteries or providing ports into and out of the body. Increasingly, injection molded implantable medical devices are being used to deliver steady, long-term doses of hormones, cancer drugs and other active pharmaceutical agents (APIs). Injection molding of medical devices is extending its impact into drug delivery.
Drug-eluting medical implants offer several advantages over both pills and injections when it comes to drug delivery. Perhaps the most important clinical benefit is the larger amount of time the API dose is within therapeutic window—the range of concentrations within the body low enough not to be toxic, but high enough to be effective. Both pills and injections produce API concentrations that rapidly rise and then exponentially decay as the body dilutes, metabolizes, and/or excretes the pharmaceutical compounds. By contrast, drug-eluting implants can slowly and steadily release the API at a controllable, optimal rate within the therapeutic window.
These implants are able to do so because the matrix of the device is loaded with the API before they are molded. Silicones, because of the relatively low temperatures at which they can be injection molded and vulcanized and their ability to be compounded with various APIs, are optimal for this application because the injection molding process is less likely to degrade the drug.
Molded medical implants can also provide site specific administration of a drug, and therefore achieve local concentrations of an API that would be above the therapeutic window if present systematically. This enables lower total doses, reduces side effects, and has a greater therapeutic effect.
A third benefit of drug delivery via an implantable device is much greater patient compliance. Since the implant can continually release the drug within the body for several months, there are no daily doses for the patient to forget.
Peering Beyond Silicone
Even as medical grade silicone finds wide use in drug-eluting implantable devices, an exciting new frontier is opening up: expanding beyond silicone into synthetic biodegradable polymers. Such polymers open the door to drug-eluting implants which slowly and safely dissolve away inside the patient’s body, releasing the loaded therapeutic as they do so. These implants don’t need to be removed at the end of the treatment period. Another benefit is the potential to slowly release difficult to deliver API’s, because the therapeutic is released as the polymer encasing the API particles dissolves away, much like an oral pill. This results in steady release rate over time even for these difficult molecules.
Although this new breed of drug-eluting implants won’t be made with silicone, they in all likelihood will still be made via injection molding. Although technical questions still remain—like which polymers in this class have low enough melting points to be molded without significantly degrading any compounded API—injection molding’s ability to produce high volumes at low price per part while at the same time maintaining tight dimensional tolerances, will surely play a key role in this new drug delivery technology.
High quality medical components—whether for implants, instruments, or IV bags—must be safe and durable, because lives literally depend on them. Low toxicity, high biocompatibility, chemical inertness, and the ability to repeatedly withstand sterilization environments (like gamma rays, steam, or EtO) are all requirements of the materials that long-life medical components are made of. The ability to safely reuse the same medical devices reduces the cost of medical care, while re-use procedures put in place protect not only the healthcare professional, but also the patient’s health and safety.
For disposable, single-use medical parts where repeated sterilization isn’t a requirement, the toxicity and biocompatibility requirements, however, still apply. In addition, those single-use parts must be cost-effective for the manufacturer and affordable for the consumer.
For both categories of medical components, plastics and elastomers (rubbers) are the materials of choice. Since medical grade thermoplastics (which harden when cooled down to near ambient temperature) and silicones (like LSR which permanently sets when heated) have a lot to offer designers of new molded medical components, we’ll be discussing them in this post.
Silicone: Safe and Versatile
Let’s begin with silicone, which has many chemical and mechanical properties well suited for medical molded components:
Very chemically inert: Medical grade silicone resists attack from disinfecting chemicals and biochemical interaction. Medical grade silicones have excellent biocompatibility.
Strong, flexible, and durable: Silicones have high tear and tensile strength, great elongation, and low compression set, even over a wide temperature range. They’re high elasticity and flexibility is a great match for applications such as feeding tubes and seals for peristaltic IV drug delivery pumps.
Sticky when it needs to be: Although silicone has a low surface energy (and is thus used in applications that need to repel liquids), there are formulations of Liquid Silicone Rubber (LSR) that are self-adhesive and can stick to other plastics without priming. Overmolding silicone to specific thermoplastics is a common occurrence for durable medical devices that need extra grip capabilities for the doctor/nurse.
Silicone is permeable and thus makes a great matrix for pharmaceutical delivery in drug-eluting implants.
Wide range of available durometers: from 0 Shore A to 80 Shore A. This customizability makes it great for applications like clinical and surgical instrument grips, gaskets and o-ring seals.
There’s a Great (Medical) Future in Plastics
All of these features are why medical grade silicones have been widely used for decades, and will continue to be considered, in spite of LSR’s higher cost compared to some other resins.
But they are not the only game in town when it comes to molded medical components. Thermoplastics are also popular choices, especially for niche use. With so many different polymers (and varying molecular weights of each polymer), this family of plastics exhibits a wide gamut of thermal, chemical, and mechanical properties. A few of these are worth mentioning here:
Polysulfone (PS): This thermoplastic elastomer (TPE) has excellent resistance to both hydrolysis and heat, and thus can be sterilized by steam and autoclaving. PS has great biocompatibility, and can be thermoformed by injection molding and extruding.
Polyether ether ketone (PEEK): PEEK maintains its excellent chemical resistance and mechanical stability at high temperatures (and thus can be sterilized by heat and disinfected by chemical agents). Like both silicone and PS, PEEK can be molded, albeit at very high temperatures (PEEK melts at about 343°C). Since PEEK resists biodegradation, it’s a good candidate for implantable medical devices.
Medical device OEM’s can choose from many polymers for their next innovative, life-saving product. Although silicones continue to dominate (particularly in implantable devices), some thermoplastics have long been chosen for use in healthcare.
