A material or medical device is considered biocompatible when it can perform its intended function in contact with the body without causing an unacceptable biological response. In practical terms, biocompatibility does not simply mean that a material is “non-toxic.”
Its suitability depends on how and where it contacts the body, how long that contact lasts, its composition and surface condition, and the condition of the finished device. Manufacturing processes and sterilization can also affect the final biological safety profile.
For medical devices, this distinction is important. A polymer with supporting biocompatibility data may be a suitable material candidate, but that data alone does not automatically establish the biocompatibility of the finished device.
Why Biocompatibility Matters in Medical Devices
Medical devices interact with the body in different ways. A skin-contacting device, blood-contacting component, catheter, surgical instrument, and long-term implant do not create the same biological exposure.
Depending on the application, relevant concerns may include cytotoxicity, sensitization, irritation, systemic toxicity, implantation effects, or other biological endpoints. The appropriate evaluation depends on the nature and duration of contact rather than on a universal list of tests.
Biocompatibility must also be considered alongside device function. A catheter material may require flexibility, chemical resistance, and suitable surface properties, while an implant may require mechanical stability, corrosion resistance, and appropriate long-term tissue interaction.
How Do Biocompatible Materials Interact With the Human Body?
When a material contacts biological tissue or fluids, interactions can begin at its surface. Proteins may adsorb to the material, cells may interact with that surface, and the body may initiate inflammatory or foreign-body responses.
The extent and clinical significance of these interactions depend on the material, surface characteristics, exposure location, duration, and intended function. Some materials are selected to minimize interaction, while others are designed to support a controlled interaction with tissue.
Materials can also change during use. Polymers may release constituents or degrade, metals may undergo corrosion, and surfaces may change over time. Biological performance therefore cannot be predicted from the material name alone.
What Determines Whether a Material Is Biocompatible?
Biocompatibility is application-specific. Several variables determine whether a material is suitable and what biological evidence may be needed.
Type of Body Contact
A medical device may contact intact skin, mucosal membranes, breached surfaces, circulating blood, tissue, bone, or other biological environments.
The nature of that contact affects the biological risks that need to be considered.
Contact Duration
A material used for brief contact does not necessarily require the same biological evaluation as one used repeatedly or for long-term implantation.
Contact type and duration are therefore important inputs when identifying relevant biological endpoints.
Material Composition and Additives
Two products made from the same base polymer may have different formulations. Colorants, stabilizers, plasticizers, fillers, and processing aids can change the material’s chemical profile.
Supplier documentation and existing biological data can support initial material assessment, but the specific formulation intended for the device still matters.
Manufacturing and Surface Condition
Injection molding, extrusion, machining, joining, cleaning, and other manufacturing operations can affect the finished component.
Surface changes, residues, manufacturing aids, or additional materials introduced during processing may need to be considered when they are relevant to biological safety.
Sterilization
Sterilization can alter the chemical or physical properties of some polymers. Compatibility with steam, ethylene oxide, radiation, or another selected method therefore needs to be considered during material selection rather than after the material has already been finalized.
Types of Biocompatible Materials Used in Medical Devices
Medical devices use polymers, elastomers, metals, ceramics, and other biomaterials. Selection depends on the required combination of biological, mechanical, chemical, manufacturing, and sterilization performance.
| Material family | Examples | Why they may be selected | Key considerations |
|---|---|---|---|
| Polymers | PP, PE, PC, PEEK | Moldability, chemical resistance, transparency, or high-performance properties depending on polymer | Grade, additives, processing, sterilization |
| Elastomers | TPU, silicone | Flexibility, resilience, sealing, or soft-contact applications | Formulation, processing route, chemical exposure, sterilization |
| Metals | Titanium, stainless steel, cobalt-chromium alloys | Strength, fatigue resistance, corrosion resistance | Surface condition, corrosion, long-term contact |
| Ceramics | Alumina, zirconia | Hardness, wear resistance, chemical stability | Brittleness, processing, application |
| Composite or bioactive materials | Application-specific systems | Combination of mechanical or biological functions | Degradation, tissue interaction, manufacturing method |
These examples describe general material-family characteristics rather than the suitability of a specific medical-grade material. Actual suitability depends on the grade, formulation, supplier documentation, manufacturing process, and intended device application.
Biocompatible Plastics and Elastomers
Plastics and elastomers are widely used in medical devices because different material families can provide combinations of rigidity, flexibility, transparency, chemical resistance, low friction, or high-temperature performance.
However, there is no single category of plastic or elastomer that is automatically biocompatible in every medical application.
| Material | Useful properties for medical devices | Manufacturing and application considerations |
|---|---|---|
| PP | Low density, chemical resistance, good processability | Grade-specific biological data and sterilization requirements should be reviewed |
| PE | Chemical resistance, toughness, range of available densities | Mechanical requirements and sterilization conditions vary by grade |
| PC | Transparency, toughness, dimensional stability | Processing conditions, chemical exposure, and sterilization method require consideration |
| PEEK | High mechanical, thermal, and chemical performance | Requires high processing temperatures and application-specific evaluation |
| TPU | Flexibility, abrasion resistance, elastomeric behavior | Moisture control, formulation, chemical exposure, and sterilization can matter |
| Silicone | Flexibility and elastomeric performance | Processing differs from thermoplastic molding, and suitability depends on formulation and application |
A medical-grade designation or supplier test report can provide useful screening information, but material selection also needs to consider molding behavior, chemical exposure, mechanical requirements, aging, sterilization, and documentation.
ISO 10993 and USP Class VI: What Is the Difference?
ISO 10993 and USP Class VI are both encountered when reviewing materials for medical applications, but they are not interchangeable.
ISO 10993 and Biological Evaluation
ISO 10993 is a series of standards addressing the biological evaluation of medical devices. ISO 10993-1 establishes the general framework for evaluating biological safety within a risk management process.
The sixth edition of ISO 10993-1 was published in 2025, and the FDA recorded partial recognition of this edition in 2026.
The framework is risk-based rather than a fixed testing checklist. Relevant biological endpoints depend on factors such as the device category, nature and duration of body contact, material composition, and available biological and chemical evidence.
Where USP Class VI Fits
USP Class VI is associated with biological reactivity testing of plastics and other polymeric materials under USP General Chapter <88>. Suppliers may provide USP Class VI data, ISO 10993-related data, or both as supporting information during material assessment.
However, supplier material data does not by itself establish the biological safety of a finished medical device.
| Consideration | ISO 10993 framework | USP Class VI data |
|---|---|---|
| Main purpose | Biological evaluation within medical device risk management | Defined biological reactivity testing |
| Device-specific context | Central to the evaluation | Limited |
| Supplier data may support material assessment | Yes | Yes |
| Replaces finished-device evaluation | No | No |
The relevant question is whether available evidence applies to the actual material formulation, manufacturing condition, and intended device use rather than whether the resin carries a particular designation alone.
How Is Medical Device Biocompatibility Evaluated?
Biocompatibility evaluation may use existing material information, chemical characterization, toxicological assessment, biological testing, and other evidence. The appropriate combination depends on the device and identified biological risks.
In Vitro Testing
In vitro methods evaluate biological responses outside a living organism. Cytotoxicity testing is a common example and can help determine whether a material or its extracts adversely affect cultured cells.
The value of a particular test depends on the biological endpoint being investigated and the overall evaluation strategy.
Chemical Characterization and Toxicological Assessment
Chemical characterization helps determine which constituents may be present in or released from a medical device. Toxicological assessment then evaluates whether exposure to those constituents presents a relevant biological risk.
These activities are addressed within ISO 10993-18 and ISO 10993-17, respectively. They can be particularly useful when evaluating materials, manufacturing changes, or potential device constituents.
When In Vivo Evaluation May Be Relevant
In vivo evidence may still be appropriate for certain biological questions when existing information, chemical characterization, and other evidence do not adequately address the relevant endpoint.
Implantation evaluation is one example for devices or materials where local tissue response after implantation is relevant. The need for such testing should follow the biological risk assessment rather than a universal test sequence.
Bioinert, Bioactive, and Biotolerant Materials
Biocompatible materials are sometimes described as bioinert, bioactive, or biotolerant according to how they interact with surrounding tissue. These terms describe different biological behaviors rather than universal safety classifications.
Their relevance depends on the application, particularly for implants and other tissue-contacting materials. They do not replace device-specific biological evaluation.
Choosing Biocompatible Materials for Medical Device Manufacturing
Material selection should begin with the intended use of the device rather than with a list of plastics labeled “medical grade” or “biocompatible.”
Important questions include:
- What tissue, fluid, or body surface will the device contact?
- How long and how frequently will contact occur?
- What mechanical properties are required?
- Will the material encounter drugs, lipids, disinfectants, cleaning agents, or other chemicals?
- Which sterilization method will be used?
- Can the material tolerate molding and required secondary operations?
- Are the formulation and material supply sufficiently controlled?
- What biological, regulatory, and traceability documentation is available?
These variables interact. A polymer with extensive biological data may still be unsuitable if it cannot withstand sterilization, chemical exposure, dimensional requirements, or the intended manufacturing process.
For injection molded components, medical device material selection should therefore consider biological requirements and manufacturing behavior before tooling and process development are finalized.
Why a Biocompatible Resin Does Not Automatically Mean a Biocompatible Finished Device
Biocompatibility data for a raw resin should not be treated as proof that the finished molded device has the same biological safety profile.
The manufacturing pathway may include:
Raw material → molding → secondary operations → cleaning → assembly → sterilization → finished device
These steps can introduce changes not represented by the original resin data. Colorants or additives can alter formulation, joining can introduce adhesives or other materials, manufacturing aids may leave residues, and sterilization can affect certain polymers.
Biological evaluation therefore needs to consider the finished device or establish why existing evidence remains applicable to it. A resin supported by ISO 10993-related or USP Class VI data can provide useful evidence during material selection, but it does not automatically qualify the finished molded device.
How Sterilization Can Affect Biocompatible Materials
A polymer that performs well before sterilization may not respond identically afterward. Depending on the polymer and process, sterilization can affect chemical structure, mechanical properties, appearance, or aging behavior.
Compatibility therefore needs to be evaluated for the intended material grade, device configuration, sterilization process, and expected life cycle. Biocompatibility and sterilization resistance are related material-selection considerations, but one should not be used as evidence for the other.
From Material Selection to Medical Device Manufacturing
Biocompatibility begins with material selection but also depends on the condition of the finished medical device. Formulation, molding, secondary operations, cleaning, assembly, and sterilization can influence that final condition.
For medical injection molding projects, SeaSkyMedical supports material selection, DFM, mold development, molding, and manufacturing process development. Early material review can help identify conflicts between biological requirements and manufacturing constraints before tooling is finalized, such as sterilization incompatibility, unsuitable additives, or processing requirements that do not fit the intended resin.
Final biological evaluation and regulatory requirements remain specific to the device, its contact conditions, intended market, and applicable regulatory pathway.
