- Posted in: Blog
- By Jim Reed
Medical device programs rely on materials that withstand sterilization, mechanical stress, and prolonged use. Medical-grade Liquid Silicone Rubber (LSR) fits that need well, and the injection molding method gives engineers a reliable way to shape it into tight-tolerance, biocompatible parts. This manufacturing approach delivers stable mechanical properties, consistent dimensions, and the material itself provides an exceptional level of resistance to degradation, even in demanding operating environments.
Its flexibility also supports micro-molding, multi-material builds, and complex geometries that are hard to achieve with other methods. These capabilities work hand in hand with precise tooling configurations and validated manufacturing controls, allowing teams to scale from early prototypes to full-scale output without sacrificing performance.
Before breaking down each stage of the molding procedure, it’s helpful to start with the elastomer itself and why LSR is such an effective choice for regulated uses.
Understanding LSR and its advantages over many other alternatives
LSR distinguishes itself from other elastomers through its unique composition and performance characteristics, making it a preferred choice for high-precision, biocompatible parts.
Its chemical structure, properties, and compatibility with automated injection molding give it advantages over other elastomers and manufacturing methods.
Material composition and chemistry
This material is a silicone-based polymer built on a siloxane backbone composed of silicon (Si), oxygen (O), carbon (C), and hydrogen (H). This structure gives the elastomer its thermal stability, chemical resistance, and long-term reliability. It comes in multiple grades — including standard, medical, medical implantable, optical, fluorosilicone, and self-lubricating — allowing engineers to match performance to the specific demands of the end product.
LSR is typically supplied as a two-component system in which Parts A and B are mixed at a 1:1 ratio and cured through platinum catalysis. Platinum-cured systems produce no residual by-products, which renders the cured material highly biocompatible and minimizes contamination risk. This is one reason platinum curing is preferred over peroxide systems, especially for regulated medical and drug-delivery devices.
Because this elastomer is reactive, proper storage and handling are key. Most formulations carry a shelf life of three to six months, and maintaining stable temperature conditions helps preserve consistency across manufacturing runs. A clear understanding of the chemistry and behavior supports predictable processing and reliable results during injection molding.
Key properties and performance advantages
Part of what makes LSR ideal for high-demand, regulated uses is its unique combination of traits:
- Patient-safe and chemically inert: Fully FDA-compliant and hypoallergenic, it is suitable for devices that contact skin, tissue, or fluids, reducing the risk of adverse reactions.
- Extreme environmental resilience: This elastomer maintains performance across a wide range of temperatures (-76°F to 356°F) and resists degradation from sterilization methods such as autoclaving, gamma irradiation, or chemical exposure.
- Versatile mechanical behavior: With durometers from 10 to 80, it can be soft and cushioning or firm and structural. It also serves as a reliable electrical insulator in sensitive assemblies.
This combination enables the manufacturing of durable, precise, and biocompatible devices that meet strict regulatory and functional demands.
LSR vs. alternative materials and processes
When evaluating options for precision devices, LSR consistently surpasses alternatives in chemical stability, biocompatibility, and mechanical performance, making it the preferred choice for certain critical components.
LSR vs. Thermoplastic Elastomers (TPE)
Selecting the right compound requires understanding the strengths and limitations of each option. LSR and TPE differ significantly in terms of biocompatibility, environmental performance, and manufacturing characteristics, making it crucial to match properties to the specific use.
- Compliance and safety: LSR is well-suited to medical applications and can withstand patient contact, while TPE is generally better suited for less sensitive product types.
- Operational stability: It also maintains dimensional stability, chemical resistance, and mechanical performance under extreme temperatures and repeated sterilization. TPE may soften, warp, or degrade in demanding environments.
- Production considerations: TPE can offer faster molding cycles and lower costs, which may be advantageous for high-volume, non-critical devices. LSR, however, ensures consistent performance, longevity, and regulatory compliance in demanding sectors.
Evaluating these factors side by side ensures that the choice supports both functional performance and regulatory requirements without compromise.
LSR vs. High Consistency Rubber (HCR)
Comparing LSR and High Consistency Rubber (HCR) highlights the distinct advantages each brings to precision molding.
- LSR excels in reproducibility, consistent output, automation, and cleanroom compatibility. Its low viscosity enables precision injection molding of intricate geometries, making it ideal for high-volume manufacturing of medical-grade and regulated devices.
- HCR provides a lower-cost option for larger pieces. Its higher viscosity and compatibility with compression molding make it well-suited for bulkier assemblies where volume and mechanical strength (e.g., tear resistance) are key; though, it sometimes requires more manual processing. Promed does have substantial experience, however, in converting transfer-molded HCR components to an injection-molded HCR process.
ProMed’s dual capability allows for selecting LSR (10 to 80 durometer) or HCR (20 to 80 durometer) based on complexity, functional requirements, and scale, ensuring every project achieves optimal performance, reliability, and efficiency.
The injection molding process: From tooling to production
The injection molding process begins with precise tooling engineering and extends through each stage of manufacturing to ensure high-quality, reliable devices.
Understanding the essential steps, methods, and potential challenges is critical for consistent results. This includes anticipating defects and implementing effective troubleshooting strategies.
Tooling design, process steps, and production methods
Tooling engineering is a cornerstone of successful silicone injection molding. Mold fabrication requires appropriate design, precision manufacturing, and correct mold material selection to resist wear over high-volume runs. Critical features include flashless construction, minimal runners, thin walls, appropriate venting, and the correct geometry and part design to facilitate smooth release from the production mold.
Two common tooling options exist:
- Aluminum: Offers cost-effective, fast-turnaround solutions for small volumes. Ideal for prototyping, low- to mid-volume runs, and iterative design adjustments due to its shorter fabrication time, lower cost, and speed to produce.
- Steel: Provides superior durability, suited for high-volume manufacturing but with longer lead times. Best for long production runs requiring consistent dimensional accuracy, high wear resistance, and minimal maintenance over extended tool useful lives.
The injection molding procedure itself follows five key steps: preparation, machine setup, injection, curing, and demolding. Advanced capabilities, such as micro-molding and multi-shot production, further enhance precision, efficiency, and device performance.
Exploring the five-phase molding cycle
Each phase of the LSR molding cycle contributes to producing precise, high-quality components. Material preparation begins with accurately metering the two-part system to ensure the proper mix ratio. Machine setup establishes the correct temperature, pressure, and cycle parameters tailored to each part’s geometry, ensuring repeatable performance.
During injection, the mixed compound flows through the cold runner system into heated mold cavities. Platinum curing transforms the liquid silicone into a solid elastomer, with precise control of time and temperature to achieve complete cross-linking without degradation.
Finally, demolding takes advantage of LSR’s flexibility to release finished components, either manually or via automated systems. Parts then move to secondary operations or final inspection, maintaining consistency, dimensional accuracy, and regulatory compliance across every production run.
Common challenges, defects, and troubleshooting
Even with careful planning and tooling, challenges can arise during silicone injection molding. Common defects include incomplete filling, warping, or flash formation. Maintaining precise control over temperature, pressure, and flow is essential to mitigate these issues.
Routine inspection and testing are critical to ensure consistency. Adjusting parameters to account for the LSR raw material’s inherent lot-to-lot variability helps avoid defects and improve reproducibility. Persistent issues may require revising the mold configuration or modifying injection parameters to restore optimal performance.
Design guidelines, quality standards, and testing requirements
Success in injection molding starts with understanding the key engineering principles, standards, and testing requirements. Following best practices in device and mold engineering ensures that every unit meets or exceeds industry expectations. Thoughtful choices, combined with a robust management system, provide a solid foundation for consistently high results.
Thorough testing throughout manufacturing verifies reliability, performance, and safety. By confirming that devices function as intended under real-world conditions, manufacturers can minimize defects, reduce waste, and ensure long-term durability.
Best practices and quality management systems
High-performing results begin with thoughtful engineering:
- Consider wall thickness, surface finish, angles, and depth of undercuts to ensure ideal moldability and consistent output.
- Choose the appropriate durometer and grade for LSR and HCR to achieve desired mechanical properties and durability.
- Maintain specified tolerances for both molds and unit-to-unit variation to guarantee consistent performance across runs. Plan ahead for tolerance changes related to normal routine wear to maximize the life of the tool’s ability to produce quality product.
ProMed’s management system emphasizes structured collaboration, careful planning, and validated procedures. Regular inspections and scientifically controlled molding practices help maintain consistency, minimize defects, and deliver reliable devices every time.
Industries, applications, and practical program considerations
LSR injection molding serves a wide range of industries, each with unique requirements for precision, performance, and regulatory compliance. Being aware of how this method applies across sectors — from medical devices and pharmaceuticals to aerospace, automotive, and consumer products — helps frame its versatility and value.
Program planning also requires attention to practical considerations, including economic factors and nuances. Early evaluation of these elements can optimize efficiency, reduce costs, and ensure consistent, high-performing outcomes.
Key industries, applications, and economic considerations
ProMed specializes in silicone injection molding for industries where reliability and precision are critical. Their expertise supports medical, pharmaceutical, and aerospace/security spaces.
Economic considerations are central to program planning:
- Tooling investment – evaluate the break-even point between aluminum and steel molds for cost efficiency.
- Per-unit cost drivers – account for factors such as size, grade, volume, and cycle time.
- Volume considerations – assess the benefits of single-cavity versus multi-cavity tooling to match needs.
ProMed’s flexible approach ensures a smooth transition from prototype to full-scale output, minimizes waste, and maximizes tool life. Combined with rapid lead times and a robust supply chain, this approach delivers cost-effective, high-performing devices that meet demanding specifications.
Frequently asked questions:
1) What is the difference between LSR and HCR?
Liquid Silicone Rubber (LSR) is a two-part system designed for precision injection molding. Its low viscosity allows it to flow easily into complex molds, offering consistent reproducibility and tight tolerances. It is particularly suited for small or intricate devices where high accuracy is essential.
High Consistency Rubber (HCR) is a single-component, gum-like silicone processed primarily through compression or transfer molding. It is best for larger pieces or simpler geometries. ProMed provides both compounds, with LSR ranging from 10 to 80 durometer and HCR from 20 to 80 durometer, allowing engineers to select the ideal formulation for performance and engineering requirements.
2) How long does it take to get LSR injection-molded parts?
Lead times depend on tooling type and complexity. Aluminum tooling can typically be produced in one to two weeks, while steel tooling will require more time, especially with higher cavitation.
Once the tool is ready, sample units can be produced within days. ProMed’s integrated in-house capabilities streamline the workflow from approval to delivery, often completing full runs in 15 days or less, while maintaining precision, standards, and regulatory compliance.
3) Can LSR parts be sterilized?
Yes. This material is compatible with a wide range of sterilization methods commonly used in medical and pharmaceutical applications. Common options include steam autoclaving, ethylene oxide (EtO), gamma radiation, and electron beam (e-beam).
The elastomer maintains its dimensional integrity, biocompatibility, and bond strength throughout sterilization cycles. This makes it suitable for both short-term and long-term use in implantable, surgical, and diagnostic devices.
4) What testing is required for medical-grade LSR components?
Testing ensures safety, performance, and compliance with regulatory standards. Typical protocols for devices that include silicone components include dimensional testing, biocompatibility evaluation, physical testing, and sterilization validation.
ProMed’s production documentation ensures compliance with FDA and ISO 13485 standards and supports traceability for manufacturing and regulatory submissions.
5) Is LSR suitable for long-term implantable medical devices?
Yes. LSR is highly biocompatible, chemically stable, and resistant to degradation, making it an excellent choice for both short-term and long-term implantable devices.
Its ability to withstand sterilization and maintain mechanical integrity ensures reliability over extended periods. ProMed has extensive experience manufacturing implantable silicone devices, providing engineering, regulatory, and procedural support to meet exacting standards for patient safety and clinical use.
6) How do I choose between LSR and thermoplastic elastomers (TPE)?
LSR is ideal for implementations requiring biocompatibility, extreme temperature resistance (-76°F to 356°F, or -60°C to 180°C), chemical stability, long-term reliability, and sterilization compatibility. These properties make it a preferred choice for medical and regulated devices.
TPE may be selected for cost-sensitive deployments or when recyclability is a priority. ProMed assists engineers in evaluating performance, device engineering, and volume to determine the optimal formulation for each project.
7) What industries does ProMed serve?
ProMed specializes in highly regulated industries requiring precision, biocompatibility, and stringent management systems. Key sectors include medical devices (implantable, surgical, diagnostic), pharmaceutical and combination drug-device products, and aerospace or security & defense applications.
Each project leverages ProMed’s expertise in high-precision molding, validated procedures, and regulatory compliance.
8) Can LSR injection molding be used for prototyping?
Yes, and it allows engineers to validate configurations before committing to hard steel production tooling. ProMed uses low or even single cavity tools and 3D-printed molds to produce functional prototypes that replicate the final device’s fit, form, and performance.
This approach enables early testing of mechanical, thermal, and chemical properties. Engineers can refine configurations, optimize manufacturability, and reduce risk, accelerating time-to-market while ensuring regulatory requirements are met.
9) What are common defects, and how can they be prevented?
Common defects in silicone injection molding include flash, incomplete filling, poor adhesion, air entrapment, and dimensional variability. Prevention requires proper tool engineering, optimized injection parameters, adequate venting, and meticulous substrate surface preparation.
ProMed implements statistical control, rigorous inspection, and validated parameters to mitigate defects. Early identification and corrective actions, combined with consistent tooling and control, ensure high-performing, repeatable devices suitable for medical and other regulated sectors.
Conclusion
LSR molding produces durable, biocompatible devices engineered for precision, reliability, and regulatory compliance. Accurate tooling, strict adherence to industry standards, and advanced techniques, such as micro-molding, ensure consistent performance and long-term durability. Understanding engineering best practices, standards, and practical program considerations allows manufacturers to optimize every stage of output.
Partnering with ProMed provides expert guidance, proven procedures, and end-to-end support to bring high-performing silicone products from concept to scalable manufacturing. Contact us today to discuss how our capabilities can meet your needs.
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