Biocompatibility Evaluation of Medical Dressings: ISO 10993 Testing Framework, Methods, and Applicat

Biocompatibility evaluation of medical dressings is the systematic assessment of whether wound-contact materials are safe for their intended use on intact, breached, or compromised skin over the expected contact duration. Built on the risk-based framework of the ISO 10993 series of standards, this evaluation combines in vitro cytotoxicity, sensitization, irritation testing, and chemical characterization to identify and control biological hazards before products reach patients. This article explains the classification logic, required endpoints, laboratory methods, and practical considerations for compliant biocompatibility assessment of medical dressings.

Technical Overview

Medical dressings represent one of the largest categories of wound care devices, ranging from simple absorbent gauze to advanced hydrocolloids, foams, alginates, hydrogels, antimicrobial dressings, and biologically derived matrices. Because these products are applied directly to wound beds that are frequently breached, inflamed, and highly permeable, the risk of local and systemic adverse biological reactions is significantly elevated compared with devices contacting intact skin. Biocompatibility evaluation therefore forms a core element of the safety demonstration for any medical dressing.

The evaluation follows the risk-based framework defined in ISO 10993-1:2018 (Biological evaluation of medical devices — Part 1: Evaluation and testing within a risk management process), which is harmonized in China as the GB/T 16886.1 standard and in Europe as EN ISO 10993-1 under the Medical Device Regulation. Rather than prescribing a fixed test list for all products, the standard requires manufacturers to classify the device by nature of body contact and contact duration, then select the relevant biological endpoints and justify any waived tests through a documented scientific rationale.

Classification by Nature of Body Contact

Most dressings are classified as surface medical devices. Common categories include:

• Surface devices contacting intact skin, such as adhesive borders, fixation tapes, and elastic bandages
• Surface devices contacting breached or compromised skin, including dressings applied to venous ulcers, diabetic foot ulcers, pressure injuries, burns, donor sites, and post-surgical wounds
• Surface devices contacting mucous membranes or breached mucosa, such as oral, nasal, or urological wound care products
• Implantable wound matrices, including certain bioresorbable scaffolds and regenerative skin substitutes, which fall under the implant category with additional endpoints

Classification by Contact Duration

ISO 10993-1 defines three exposure categories that directly determine the endpoint matrix:

• Limited contact: up to 24 hours, typical of single-use island dressings and wound closure strips
• Prolonged contact: more than 24 hours up to 30 days, which covers the majority of advanced dressings that remain in place for one to seven days but are used repeatedly over a treatment course
• Long-term contact: exceeding 30 days, applicable to slowly resorbing or permanent wound matrices

For a typical surface dressing contacting breached skin for prolonged durations, the primary mandatory endpoints are cytotoxicity, sensitization, and irritation or intracutaneous reactivity, supplemented by material-mediated pyrogenicity, acute systemic toxicity, and case-by-case assessments such as subacute toxicity, genotoxicity, and hemocompatibility. Chemical characterization and toxicological risk assessment, performed under ISO 10993-18 and ISO 10993-17 respectively, increasingly serve as the scientific foundation for the entire evaluation and for justifying test reductions.

Testing Samples

All biocompatibility testing must be performed on the medical dressing in its final finished form, incorporating the final materials, manufacturing processes, sterilization method, and packaging. Prototype or pre-sterilization samples may generate misleading results because sterilization (ethylene oxide, gamma or electron-beam irradiation, steam) can introduce residuals or alter material extractables. Test samples are typically divided into direct-test articles and extracts prepared under ISO 10993-12.

Traditional and Basic Dressings

Absorbent cotton gauze, nonwoven swabs, adhesive plasters, island dressings, elastic and tubular bandages, and wound closure strips. These products usually have well-characterized material histories, which often supports a streamlined evaluation based on documented equivalence and targeted testing.

Advanced Moisture-Balancing Dressings

Hydrocolloid sheets, amorphous and sheet hydrogels, polyurethane foams, transparent adhesive films, calcium alginate fibers, carboxymethylcellulose gelling fibers, soft silicone contact layers, and superabsorbent dressings. These multicomponent constructions contain polymers, adhesives, plasticizers, and crosslinking agents, all of which are potential sources of leachables requiring characterization.

Antimicrobial-Impregnated Dressings

Dressings incorporating elemental or ionic silver, medical-grade honey, cadexomer or povidone-iodine, polyhexamethylene biguanide (PHMB), zinc, or copper. Because the antimicrobial agent is intentionally released into the wound environment, both the device material and the active constituent must be addressed in the biological safety assessment.

Biologically Derived and Combination Dressings

Collagen, chitosan, alginate-collagen blends, amniotic and chorionic membranes, decellularized dermal matrices, and dressings loaded with growth factors or drugs. These may require additional evaluation of degradation behavior, immunological effects, and, for animal- or human-derived materials, viral and transmissible spongiform encephalopathy safety.

Sample Extraction Parameters

Extraction is performed with a polar medium (such as physiological saline or culture medium) and, where the material contains nonpolar components, a nonpolar medium (such as sesame oil). Standard extraction ratios follow ISO 10993-12, commonly 6 cm2 of surface area per milliliter for materials up to 0.5 mm thick and 3 cm2 per milliliter for thicker materials, or 0.1 to 0.2 g of material per milliliter when surface area cannot be defined. Standard conditions include 37°C for 72 hours for simulated-use extraction, with exaggerated conditions such as 50°C for 72 hours, 70°C for 24 hours, or 121°C for 1 hour applied when scientifically justified.

Testing Items

Based on the ISO 10993-1 endpoint matrix, the following biological endpoints are relevant to medical dressings, selected according to contact type and duration:

• Cytotoxicity (ISO 10993-5) — mandatory for essentially all dressings
• Sensitization (ISO 10993-10) — mandatory for all skin-contacting and wound-contacting dressings
• Irritation or intracutaneous reactivity (ISO 10993-23) — mandatory for dressings contacting breached skin and mucosa
• Material-mediated pyrogenicity — required for prolonged-contact wound dressings
• Acute systemic toxicity (ISO 10993-11) — typically required for prolonged contact with breached skin
• Subacute and subchronic toxicity — case-by-case, driven by leachable burden and wound severity
• Genotoxicity (ISO 10993-3) — case-by-case, for novel polymers, antimicrobial actives, or materials with positive chemical screening results
• Hemocompatibility (ISO 10993-4) — relevant where dressings absorb blood or contact bleeding wounds, including hemolysis and complement activation
• Implantation (ISO 10993-6) — applicable to implantable or resorbable wound matrices
• Chronic toxicity and carcinogenicity — generally not required for surface dressings but may apply to long-term implantable matrices

Chemical Characterization

Chemical characterization under ISO 10993-18 identifies and quantifies extractables and leachables, including residual monomers, oligomers, antioxidants, plasticizers, adhesive components, vulcanization accelerators, degradation products, sterilant residuals such as ethylene oxide and ethylene chlorohydrin, and elemental impurities such as heavy metals. Techniques include gas chromatography-mass spectrometry for volatile and semivolatile organics, high-performance liquid chromatography-mass spectrometry for nonvolatile organics, inductively coupled plasma-mass spectrometry for elemental analysis, and headspace gas chromatography for residual solvents and sterilants.

Toxicological Risk Assessment

Under ISO 10993-17, the concentrations of identified leachables are converted into estimated patient doses using the wound surface area, extraction yield, and expected frequency and duration of use. These doses are compared with tolerable intake values derived from available toxicological data or threshold of toxicological concern (TTC) approaches to calculate margins of safety. A well-documented risk assessment can justify waiving specific animal tests, consistent with the 3Rs principles of replacement, reduction, and refinement.

Testing Methods

Cytotoxicity Testing (ISO 10993-5)

The extract (elution) method is the most widely applied approach: dressing extracts are applied to established mammalian cell lines such as mouse fibroblasts (L929 or Balb/3T3), and cell viability is measured after 24 to 72 hours of exposure, commonly using the MTT tetrazolium reduction assay. A cell viability of 70 percent or greater relative to the blank control indicates the sample is non-cytotoxic. Direct contact and agar diffusion (indirect contact) methods are alternatives when extract testing is inappropriate, for example for highly absorbent materials that swell during extraction.

Sensitization Testing (ISO 10993-10:2021)

The guinea pig maximization test (GPMT, Magnusson-Kligman method) remains the reference method for extract-based evaluation: animals receive intradermal induction with the test extract together with Freund's complete adjuvant, topical challenge is performed approximately two weeks later, and delayed-type hypersensitivity reactions are graded on a standardized erythema and edema scale. The murine local lymph node assay (LLNA) is a refined alternative that measures lymphocyte proliferation in draining lymph nodes and reduces animal burden. The Buehler test may be appropriate when the product's exposure route is exclusively topical.

Irritation and Intracutaneous Reactivity (ISO 10993-23:2021)

ISO 10993-23 consolidated skin, mucosal, and ocular irritation testing and introduced validated in vitro alternatives. For dressings, the intracutaneous reactivity test in rabbits remains common: polar and nonpolar extracts are injected intradermally, and sites are scored for erythema and edema at 24, 48, and 72 hours, with the combined score not exceeding established acceptance limits. Reconstructed human epidermis (RhE) models, such as those used for skin irritation and, in specific protocols, for intracutaneous reactivity screening, provide animal-free options recognized under the standard.

Acute Systemic Toxicity (ISO 10993-11)

Mice receive a single dose of the polar and nonpolar extracts by an appropriate route (intravenous or intraperitoneal for saline extracts, oral for oil extracts), and are observed for clinical signs, morbidity, and mortality over 72 hours, with body weight monitoring. The test detects systemically toxic leachables that could be absorbed through large or heavily exuding wounds.

Hemocompatibility (ISO 10993-4)

For blood-contacting applications, the hemolysis test assesses both direct contact hemolysis and extract-mediated (indirect) hemolysis using human or rabbit blood, with acceptance typically defined as a hemolysis rate below 5 percent, and preferably below 2 percent for high-performance materials. Complement activation markers such as C3a and SC5b-9 are evaluated when immune activation is a concern, particularly for large-surface-area or long-duration applications.

Genotoxicity Testing (ISO 10993-3:2014)

A standard battery comprises the bacterial reverse mutation assay (Ames test) and an in vitro mammalian chromosomal aberration or micronucleus assay, followed by an in vivo micronucleus assay if in vitro results are positive or inconclusive. The scope of genotoxicity testing is increasingly defined by the outcome of chemical characterization, in accordance with the ISO 10993-1 and ISO 10993-3 workflow.

Chemical Characterization Workflow (ISO 10993-18)

The workflow proceeds from material identification (for example, polymer confirmation by infrared spectroscopy) through targeted and non-targeted extraction studies, chromatographic and spectrometric analysis, compound identification against spectral libraries, quantification against an analytical evaluation threshold (AET) derived from the TTC, and finally reporting of unknown, tentatively identified, and confirmed compounds. Data are then transferred to the ISO 10993-17 toxicological risk assessment.

Applications

Regulatory Registration and Market Access

Biocompatibility evaluation reports support device registrations worldwide: Class II and Class III registrations in China under the GB/T 16886 framework, 510(k) and De Novo submissions in the United States referencing ISO 10993-1 and the associated FDA guidance on biocompatibility, and EU MDR technical documentation requiring a biological safety evaluation file aligned with EN ISO 10993-1. Submissions in Japan, South Korea, and other jurisdictions reference the same ISO framework, allowing a well-designed evaluation to serve multiple markets with appropriate local addenda. Testing should be performed by accredited third-party laboratories or facilities with validated ISO 17025 quality systems.

Design Verification and Development

During product development, biocompatibility screening guides material selection, adhesive formulation, sterilization method validation, and antimicrobial loading levels. Early screening cytotoxicity and extractable profiling shorten development cycles by identifying problematic leachables before full evaluation is initiated.

Change Control and Re-evaluation

A documented change control process must determine when re-evaluation is triggered. Common triggers include:

• Change of raw material supplier, polymer grade, or adhesive formulation
• Change of sterilization method or dose
• Change of manufacturing site, curing conditions, or cleaning agents
• Change of primary packaging that may migrate into the dressing
• Extension of the intended use, contact duration, or wound type

Justification of Testing Reduction

The ISO 10993-1:2018 framework explicitly allows biological tests to be omitted when a documented scientific rationale demonstrates equivalence to a clinically established material, supported by chemical characterization data, literature evidence, and clinical history. This approach reduces animal use and accelerates time to market while maintaining patient safety.

FAQ

What is the minimum set of biocompatibility tests for a wound dressing contacting breached skin for up to seven days per application?

For a surface device with prolonged contact, the core tests are cytotoxicity (ISO 10993-5), sensitization (ISO 10993-10), and irritation or intracutaneous reactivity (ISO 10993-23). Because the cumulative contact over a wound treatment episode typically exceeds 24 hours, acute systemic toxicity and material-mediated pyrogenicity are usually added, together with chemical characterization and toxicological risk assessment. Additional endpoints such as genotoxicity or subacute toxicity are selected case by case based on the leachable profile.

Are antimicrobial dressings such as silver-containing products evaluated differently?

Yes. The antimicrobial agent is an intentional released constituent, so the evaluation must characterize the released active substance, its concentration in wound fluid, and its toxicological profile. Silver and other actives frequently require hemocompatibility assessment, and in some cases genotoxicity data on the released agent, in addition to the standard endpoints applied to the dressing matrix.

Can animal testing be reduced or avoided?

Yes. Validated in vitro methods, including reconstructed human epidermis models under ISO 10993-23 and the local lymph node assay as a refinement, reduce animal use. In addition, a robust chemical characterization and toxicological risk assessment can justify waiving certain animal studies entirely, provided the rationale is documented in the biological evaluation file.

What extraction conditions should be used for dressings?

The default simulated-use condition is 37°C for 72 hours with both polar and nonpolar media where relevant. Exaggerated conditions, such as 50°C for 72 hours, 70°C for 24 hours, or 121°C for 1 hour, are applied when the intent is to maximize leachable recovery for characterization or when justified by the clinical exposure scenario, always with an explanation of why the condition does not degrade the material unrealistically.

What is the difference between ISO 10993 and GB/T 16886?

GB/T 16886 is the Chinese national adoption of the ISO 10993 series and shares essentially identical technical content. Device registrations in China accept test reports generated under GB/T 16886 from accredited third-party laboratories, and data packages built on ISO 10993 are generally transferable to the Chinese framework with appropriate documentation of laboratory accreditation and test method alignment.

How long does a complete biocompatibility evaluation take?

Indicative laboratory timelines are two to four weeks for cytotoxicity, six to eight weeks for sensitization studies, three to four weeks for intracutaneous reactivity and acute systemic toxicity, and six to twelve weeks for chemical characterization and toxicological risk assessment depending on complexity. A complete evaluation file for a new dressing, including planning, testing, assessment, and documentation, typically requires three to six months.

Does a dressing with documented material equivalence still need testing?

Potentially not. If the material, manufacturing process, sterilization, and intended use are equivalent to a predicate with established clinical safety, and supporting chemical data confirm equivalent extractables, the biological evaluation may conclude that additional testing is unnecessary. The justification must be explicit, documented, and reviewed within the manufacturer's risk management system.