Materials for medical device prototypes: USP Class VI, ISO 10993 and what the standards actually mean

If you are developing a medical device, at some point someone will ask whether your prototype material is USP Class VI or ISO 10993 tested. The answer matters, but so does understanding what those designations actually cover, because they are not interchangeable, and specifying the wrong one for your application can create problems further down the regulatory pathway.

This article explains what USP Class VI and ISO 10993 mean in practical terms, how they differ, when each is relevant, and which materials are available at Prototype Projects for programmes that require biocompatibility credentials.

Why prototype material choice matters for regulated development

In early-stage prototyping, material choice is often driven by process, availability and cost. That is entirely appropriate when a part is being made to check geometry or evaluate form.

The situation changes when parts are intended to come into contact with the body, even temporarily – or when a programme follows a regulated development pathway in which the materials used in testing need to be documented and justified. In those cases, using a material without biocompatibility credentials at the prototype stage can create a gap in the development record that is difficult to close retrospectively.

It also affects what the test data actually tells you. A functional evaluation carried out on a standard resin prototype can answer questions about geometry, mechanism and user interaction, but it can’t tell you how the device will behave in contact with tissue or fluid, because the material properties are different. If patient contact is part of the intended use, you need the right material in the prototype at the point where that contact is being evaluated.

The earlier material selection is considered in the development process, the less likely it is to become a programme delay.

USP Class VI: what it means and what it does not

USP Class VI is a biological reactivity standard published by the United States Pharmacopeia. It is one of six classes in the USP plastics testing framework, and Class VI is the most stringent – requiring a material to pass three tests carried out in vivo:

• Systemic Injection Test: assessing acute systemic toxicity when an extract of the material is injected into mice
• Intracutaneous Test: assessing local tissue reaction when an extract is injected into rabbit skin
• Implantation Test: assessing tissue reaction to a sample implanted in rabbit muscle for 5 days

A material that passes all three tests can be described as USP Class VI compliant for the specific conditions under which it was tested – typically a defined temperature range and extraction solvent.

What USP Class VI does not mean

USP Class VI is a useful baseline and is widely referenced in medical device development, but it has limitations that are worth understanding.

It does not mean a material is approved for any specific medical application. USP Class VI is a material-level designation, not a device-level approval. A device using USP Class VI materials still requires its own regulatory assessment.

It does not cover all biocompatibility endpoints. The three USP Class VI tests are a subset of the full biocompatibility test matrix. They do not include genotoxicity, carcinogenicity, reproductive toxicity, or degradation product assessment, among others.

It is not equivalent to ISO 10993 compliance. The two frameworks have some overlap, but ISO 10993 is broader in scope and is the standard most commonly referenced in the context of the EU Medical Device Regulation (MDR) and FDA 510(k) submissions.

For many prototype applications – particularly where parts require limited, short-term contact with the body during evaluation – USP Class VI-capable material is an appropriate choice and a credible starting point for the biocompatibility assessment. For applications closer to clinical use, the ISO 10993 framework is likely to be more relevant.

ISO 10993: the broader biocompatibility framework

ISO 10993 is a series of international standards covering the biological evaluation of medical devices. It is the framework referenced by the EU MDR, the FDA, and most other major regulatory bodies when assessing a device’s biocompatibility.

Rather than a single pass/fail test, ISO 10993 is a risk-based framework. ISO 10993-1 sets out the overall principles and provides a matrix of recommended tests based on the nature and duration of body contact:

• Surface contact: skin, mucosal membrane, or breached/compromised surface
• External communicating: indirect contact with blood path, tissue or bone
• Implant: contact with tissue, bone or blood

Contact duration is also categorised: limited (under 24 hours), prolonged (24 hours to 30 days), and permanent (over 30 days).

The test endpoints covered across the ISO 10993 series include cytotoxicity, sensitisation, irritation, systemic toxicity, genotoxicity, implantation, haemocompatibility, carcinogenicity, reproductive toxicity, and degradation. Not all endpoints are required for every device – the assessment is based on the specific contact type and duration, and a thorough biological evaluation report is used to justify the selection of tests.

What this means in practice for prototyping

For most prototype applications, a full ISO 10993 evaluation is not required at the early development stage. What matters is that the material used has a credible biocompatibility profile that supports the intended use and is consistent with the regulatory pathway being followed.

For short-term, limited surface contact – a handheld device, a wearable monitor, a disposable diagnostic component – a material with relevant ISO 10993 test data covering cytotoxicity, sensitisation, irritation and acute systemic toxicity provides a reasonable basis for evaluation at the prototype stage.

Materials available at Prototype Projects with biocompatibility credentials

Accura ClearVue – SLA 3D printing

Accura ClearVue is a clear, rigid SLA resin that is USP Class VI capable. It is humidity- and moisture-stable, durable and strong, and produces parts with a smooth surface finish suitable for patient contact evaluation models.

It is suitable for prototype parts requiring limited contact with the body – drug delivery device components, device housings that will contact skin, transparent assemblies for fluid visualisation and similar applications.

Parts produced for patient contact use are handled, cleaned and packaged to a strict in-house protocol. No post-processing operations – sanding, lacquering, painting – can be carried out on USP Class VI parts, as these would compromise the surface and potentially the biocompatibility status. This is worth considering at the design stage: the part will be used as-printed and as-cleaned, so surface finish expectations need to be set accordingly.

BIO – Micro 3D Printing

BIO is a biocompatible resin for micro 3D printing that has passed six ISO 10993 biocompatibility tests:

ISO Standard	Test
ISO 10993-10 / -12 / -2	Skin Irritation Test
ISO 10993-10 / -12 / -2	Skin Sensitisation Test
ISO 10993-4	In Vitro Hemolytic Test
ISO 10993-11 / -12 / -2	Pyrogen Test
ISO 10993-5 / -12	In Vitro Cytotoxicity Test
ISO 10993-11 / -12 / -2	Acute Systemic Toxicity Test

BIO can be sterilised and is suitable for non-implantable medical applications. It is a rigid material (84 Shore D, tensile strength 56 MPa) with low water absorption (0.69% over 24 hours) and a heat deflection temperature of 85.7°C.

It is particularly relevant for small, detailed components – drug delivery device parts, surgical instrument details, diagnostic device features – where the feature resolution of micro 3D printing (down to 0.1 mm) is needed alongside biocompatibility credentials.

PEEK – CNC Machining

PEEK (polyether ether ketone) is a high-performance thermoplastic widely used in medical devices, surgical instruments and implantable components. It is inherently biocompatible, has excellent chemical resistance, a continuous use temperature above 250°C, and low moisture absorption.

For prototype parts that need to represent a PEEK production component – or where the functional testing environment demands PEEK’s material properties – CNC machining is the route. PEEK machines well and can be held to tight tolerances.

Stainless Steel 316 – CNC Machining

Stainless steel 316 is the standard specification for medical instrument components requiring corrosion resistance. Its molybdenum content gives it improved resistance to chloride corrosion compared to 316L and standard 304, making it appropriate for components that will be exposed to cleaning agents or sterilisation processes.

Choosing between USP Class VI and ISO 10993 tested materials

The two are not directly comparable, and the right choice depends on the application and the regulatory context.

As a general guide:

• For early-stage ergonomic and fit evaluation with no body contact: standard prototyping materials are appropriate
• For prototype parts requiring limited skin or mucosal contact during evaluation: USP Class VI capable material (Accura ClearVue) is a reasonable starting point
• For small components where non-implantable biocompatibility is a requirement and ISO 10993 test data is needed: BIO resin via micro 3D printing
• For functional test components in a material that will represent the production device: PEEK or stainless steel 316 via CNC machining

If your programme is following a specific regulatory pathway – EU MDR, FDA 510(k), or similar – it is worth discussing material selection with your regulatory affairs lead before placing an order, to ensure the materials used in prototype testing are consistent with the biological evaluation strategy for the device.

A practical note on documentation

When biocompatible or USP Class VI materials are specified, it is worth requesting the relevant material datasheet and test documentation at the quoting stage. At Prototype Projects, material datasheets for Accura ClearVue and BIO are available for download on our materials pages. If your programme requires additional documentation – batch records, certificates of conformance – raise this before the order is placed.

Ready to start your project?

Material selection for medical device prototypes is one of the decisions where getting specialist input early saves time later. Our team is used to working through these questions at the quoting stage.

Call us on 01763 249760, email office@prototypeprojects.com, or request a quote.