Materials are a critical component of medical device design and performance. The materials used in devices that interact with the human body have a direct impact on patient safety, device efficacy, and overall functionality. Selecting the right materials is key to mitigating risk and meeting regulatory requirements.
This article covers the key considerations and criteria for selecting materials for medical device applications. With this foundational understanding, companies can systematically evaluate tradeoffs between candidate materials and make informed selections aligned with device goals.
Regulatory and Compliance Considerations
The selection of medical device materials must take into account relevant regulatory requirements and standards that ensure safety, effectiveness, and performance. Meeting these requirements is crucial for regulatory approval and market access.
FDA and ISO Standards
In the US, the FDA provides guidance on material biocompatibility, sterilization, and testing via documents such as the Blue Book Memoranda and international standards like ISO 10993.
Additionally, the FDA provides direction on materials characterization and validation through frameworks like the Quality System Regulation (QSR). Staying current with the latest applicable standards and guidelines can inform material selection decisions.
Biocompatibility Requirements
Biocompatibility refers to the ability of a material to perform safely with an appropriate host response when used for its intended purpose. ISO 10993 and FDA guidance provide a risk-based approach to assessing biocompatibility through tests like cytotoxicity, sensitization, irritation, systemic toxicity, and more. The results help determine a material’s appropriate level of body contact from limited (external devices) to extended (implants).
Sterilization Compatibility
Most medical devices require sterilization to prevent infection. Common methods like steam autoclaving, gamma irradiation, and ethylene oxide can degrade polymers and embrittle device components. Additionally, these methods can leave harmful residues if the materials are not compatible. Testing materials under the intended sterilization approach identifies possible physical or chemical changes that could impact safety and function.
Adhering to the latest standards, demonstrating biocompatibility, and verifying sterilization compatibility allow for the selection of safe, effective medical device materials that can meet regulatory approvals.
Key Material Properties for Medical Devices
The desired functionality and performance requirements of a medical device guide the selection of materials with suitable properties. Depending on the application, different characteristics take priority.
Mechanical Properties
Medical devices often experience mechanical forces during implantation, use, and removal. Important mechanical properties include strength, hardness, elasticity, fatigue resistance, and wear resistance. For example, materials for orthopedic implants need high fracture toughness and fatigue strength.
Thermal Properties
Some devices generate or are exposed to heat, requiring materials with properties like thermal conductivity, heat capacity, and coefficient of thermal expansion. Devices with electronics need materials that resist thermal degradation and ensure heat dissipation.
Chemical Resistance
Body environments contain water, enzymes, proteins, and other chemicals that could interact with device materials. Factors like corrosion resistance, hydrolytic stability, and bio-inertness ensure stable performance.
Surface Properties
The surface finish, roughness, porosity, and coatings influence biological interactions, friction and wear, corrosion, and other material behaviors. Surface treatments can tailor these behaviors for the application.
Electrical Properties
Electronic devices require materials with tailored electrical conductivity, resistance, dielectric strength, and permittivity. Insulative coatings prevent current leakage and ensure patient safety.
The clinical use environment determines the priority properties to characterize during material selection for medical devices. Ongoing verification testing continues to validate these properties during development.
Common Materials Used in Medical Devices
Medical devices leverage a wide range of materials, both conventional and advanced, to meet application requirements. Metals, polymers, ceramics, and composites each offer unique advantages.
Metals
Metals like stainless steel, titanium, and cobalt-chrome are common in devices needing high strength, fracture resistance, and durability over repeated loading. Stainless steel offers corrosion resistance, while titanium and cobalt-chrome have enhanced biocompatibility for implants.
Polymers
Polymers like silicone, polyurethane, PEEK, and UHMWPE are essential for flexible devices and soft tissue applications. Silicone excels in biocompatibility and temperature resistance. Polyurethanes exhibit durability, elasticity, and biostability. PEEK matches bone strength and enables radiolucency. UHMWPE resists wear in load-bearing implants.
Ceramics and Glasses
Bioceramics like alumina, zirconia, and bioactive glasses support hard tissue repairs through their strength, corrosion resistance, and bone-bonding ability. Alumina and zirconia excel in orthopedic applications. Bioactive glasses integrate with bone through controlled dissolution and hydroxyapatite formation.
Composites and Hybrid Materials
Reinforced polymer composites combine the biocompatibility of polymers with the strength of fillers like fibers or particulates. Coatings and surface treatments alter interfacial properties. Emerging hybrid materials like polymer-metal and polymer-ceramic composites aim to mimic natural tissues with graded interfaces.
Traditional and advanced materials each carry distinct advantages that inventive device designers can leverage through composites and hybrids.
Material Selection Process
Selecting the optimal materials for a medical device is a systematic, multi-step procedure that balances performance, safety, and cost.
Defining the Device’s Functional Requirements
The first step is understanding the design goals, intended uses, operating environments, and performance metrics like mechanical properties, maximal temperatures, and expected lifetime. This sets materials performance targets.
Identifying the Material Properties Needed
With desired functionality defined, critical material properties that align with performance goals, environments, and safety factors can be identified. Property targets are defined through standards, device benchmarks, and literature review.
Screening and Comparing Candidate Materials
A broad list of material classes and specific candidates matching required properties gets compiled through databases and prior knowledge, then screened by characteristics like biocompatibility, sterilization resilience, manufacturability, and availability. A weighted decision matrix compares remaining candidates against priorities to identify the optimal choice(s).
Conducting Detailed Material Testing and Validation
Experimental characterization quantitatively verifies the selected material’s critical properties over a range of test conditions, durations, and sterilization methods. Testing validates subsequent processing steps and device performance over the intended lifetime.
Considering Manufacturing and Supply Chain Factors
Material selections account for reliable sourcing, lead times, processing implications, machinability, and costs associated with the chosen material to ensure manufacturability and quality while controlling expenses.
The material selection process balances performance, safety, and quality requirements with technical and business considerations to aid medical device development. With sound materials science guiding design decisions, the healthcare improvements promised by cutting-edge medical devices can fully materialize.
Need help with material selection for your medical device? Contact DeviceLab today to ensure your choices meet regulatory standards and enhance performance. Let’s turn your vision into reality!
