Animal Liver Hemostasis Test – Preclinical Evaluation of Hemostatic Medical Devices

The animal liver hemostasis test is a widely used preclinical performance model for evaluating the hemostatic efficacy of medical devices such as dressings, sponges, powders, and tissue sealants. Because the liver is a highly vascularized parenchymal organ that produces diffuse, difficult-to-control bleeding, it provides a stringent and clinically relevant challenge for quantifying time to hemostasis and blood loss. Accredited third-party laboratories routinely conduct this testing to support design verification, regulatory submissions, and product development for hemostatic devices worldwide.

Technical Overview

The animal liver hemostasis test is an established preclinical evaluation method used to measure how effectively a hemostatic product arrests active parenchymal bleeding. The liver is deliberately chosen as the target organ because it is densely vascularized, lacks compressible anatomy, and produces diffuse bleeding from cut parenchymal surfaces where individual vessels cannot be easily ligated. These characteristics make hepatic bleeding one of the most demanding hemostatic challenges in both surgery and trauma care.

Porcine liver is the most commonly used model tissue because its anatomy, blood flow characteristics, and parenchymal structure closely resemble those of the human liver. The test typically quantifies objective endpoints such as time to hemostasis (TTH), total blood loss, hemostasis success rate, and the incidence of rebleeding. Depending on the study objective, testing may be performed ex vivo using perfused or heparinized fresh liver specimens, or in vivo using anesthetized animals with standardized hepatic injuries under approved ethical protocols.

Testing is generally conducted in accredited third-party laboratories operating under Good Laboratory Practice (GLP) or quality management systems aligned with ISO/IEC 17025, and the overall biological evaluation strategy is framed within the risk-based approach of the ISO 10993 series and its Chinese counterpart, the GB/T 16886 series. Results support design verification and validation, regulatory submissions to authorities such as the FDA, EU notified bodies under the MDR, and the NMPA, as well as scientific publication and competitive benchmarking.

Testing Samples

Hemostatic Dressings and Gauzes

Woven and nonwoven dressings, including mineral-based products containing kaolin or zeolite, chitosan-based dressings, and standard gauze comparators. These samples are evaluated for their ability to promote rapid clot formation on a actively bleeding hepatic wound surface.

Hemostatic Sponges and Matrices

Absorbable gelatin sponges, collagen-based matrices, oxidized regenerated cellulose products, and starch or polysaccharide-derived sponges. These materials are applied directly to standardized liver wounds to assess structural integrity, absorption behavior, and hemostatic performance.

Powders, Granules, and Particulate Agents

Particulate hemostatic agents such as microporous polysaccharide hemospheres, mineral powders, and plant-derived or synthetic granules. Particle adherence, dispersion behavior, and efficacy against diffuse parenchymal ooze are key observation points.

Tissue Adhesives, Sealants, and Combination Products

Fibrin sealants, synthetic hydrogels, cyanoacrylate-based products, thrombin-containing combination products, and hemostatic devices with drug or biologic components. These samples are tested for sealing performance, gelation time, and adhesion to wet bleeding tissue.

Controls and Comparative Articles

Each study typically includes a negative control (no treatment or standard gauze compression) and, where appropriate, a predicate or commercially available comparator product to establish relative performance benchmarks for statistical comparison.

Testing Items

The animal liver hemostasis test report typically covers the following evaluation endpoints:

• Time to hemostasis (TTH), recorded from wound creation or product application until bleeding completely ceases
• Total blood loss, measured gravimetrically by weighing absorbed gauze or collecting shed blood over a defined observation period
• Hemostasis success rate, defined as the percentage of wounds achieving stable hemostasis within a preset time limit (commonly 3 to 10 minutes)
• Rebleeding incidence, assessed after initial hemostasis, often following gentle irrigation or a standardized observation window
• Product handling characteristics, including flexibility, conformability, adherence to tissue, and ease of removal
• Macroscopic tissue reaction, such as residue, discoloration, or adhesion at the application site
• Comparative performance against control and predicate articles using appropriate statistical methods

Testing Methods

Ex Vivo Perfused Liver Model

Fresh porcine or bovine liver is obtained from an abattoir and perfused with heparinized blood, saline, or blood substitute at controlled physiological pressure and flow rate. A standardized wound, such as a cylindrical punch defect, scalpel incision, or partial resection, is created on the liver surface to induce consistent bleeding. The test article is applied according to the manufacturer's instructions for use, and timing begins immediately. This model offers high reproducibility, high throughput, and reduced animal usage while still capturing the dynamics of parenchymal bleeding.

In Vivo Hepatic Injury Model

For devices intended for surgical or trauma indications, studies may be performed in anesthetized swine, rabbits, or rodents under institutional animal ethics approval. Systemic heparinization is frequently administered to standardize the severity of the bleeding challenge. Standardized liver injuries, including lacerations, wedge resections, or punch biopsies, are created surgically, and the test article is applied under conditions simulating clinical use. This model allows evaluation of survival, hemodynamic stability, and rebleeding under realistic physiological circulation.

Wound Standardization and Application Protocol

Reproducibility depends on strict standardization of wound geometry, depth, and location. A defined compression force and application time are used when specified by the instructions for use, and observers blinded to sample identity record all endpoints to reduce bias. Ambient conditions, tissue temperature, and perfusion parameters are documented and controlled throughout the procedure.

Data Collection and Statistical Analysis

Time to hemostasis is recorded with a stopwatch or video timing system, and blood loss is determined gravimetrically. Data from replicate wounds and multiple animals are analyzed using appropriate statistical methods, such as t-tests, ANOVA, or Kaplan-Meier survival analysis of time-to-event data, to determine whether the test article demonstrates superiority or non-inferiority against the control.

Acceptance Criteria

Acceptance criteria are defined in the study protocol before testing begins. Typical criteria require the test article to achieve a statistically significant reduction in time to hemostasis or blood loss compared with the untreated or gauze-only control, together with a high stable hemostasis rate and no significant adverse tissue observations.

Applications

The animal liver hemostasis test serves multiple purposes across the medical device lifecycle:

• Design verification and validation for new hemostatic dressings, agents, and sealants during research and development
• Regulatory submission support for FDA 510(k) and PMA applications, EU MDR technical documentation, and NMPA registration dossiers
• Comparative benchmarking against predicate or competitor products to substantiate marketing claims
• Formulation optimization, such as screening material compositions, thicknesses, or active ingredient loadings
• Batch consistency evaluation and process change verification for manufacturers
• Scientific publication and presentation of preclinical efficacy evidence

Because hemostatic efficacy cannot be fully predicted by physical or chemical characterization alone, regulatory reviewers frequently expect objective in vivo or ex vivo performance data. The liver model remains one of the most widely accepted and cited approaches for generating this evidence in accredited third-party laboratories.

FAQ

Why is the liver used instead of other organs for hemostasis testing?

The liver produces simultaneous venous, arterial, and parenchymal bleeding from an organ that cannot be compressed or ligated vessel by vessel. This creates a worst-case, clinically relevant bleeding scenario that strongly differentiates the performance of hemostatic products.

Which animal species are most commonly used?

Pigs are the preferred large-animal model because porcine liver closely resembles human liver in size, vasculature, and coagulation physiology. Bovine liver is often used for ex vivo perfusion studies, while rabbits and rodents are used for smaller-scale in vivo screening under ethics approval.

What is the difference between ex vivo and in vivo testing?

Ex vivo testing uses harvested, perfused liver tissue and offers high reproducibility, lower cost, and reduced animal usage. In vivo testing in living, anesthetized animals evaluates performance under real circulation, coagulation feedback, and survival conditions, which is often required for regulatory submissions of trauma-indicated products.

Why is heparin sometimes administered during the test?

Heparinization suppresses the natural clotting cascade and standardizes the severity of the bleeding challenge, preventing spontaneous clotting from masking differences between products. It makes the model more stringent and discriminative, particularly for products claiming efficacy in anticoagulated or coagulopathic patients.

How is blood loss accurately measured?

Blood loss is most commonly determined gravimetrically: pre-weighed gauze and collection materials are weighed after the observation period, and the mass difference is converted to blood volume. Supplemental methods include collection cup measurement and photometric assessment of collected fluid.

How long does the test take and how many samples are needed?

Study duration depends on the model, number of test groups, and regulatory objective. Ex vivo perfusion studies may be completed within a few weeks, while in vivo GLP studies including protocol approval, animal preparation, and reporting typically require several weeks to a few months. Sample quantity is determined by statistical power analysis, usually involving multiple replicate wounds per product group.

Is this test mandatory for regulatory approval of hemostatic devices?

While requirements vary by jurisdiction and product classification, objective hemostatic efficacy data from an appropriate animal model is generally expected for clearance or approval of hemostatic dressings, agents, and sealants. The animal liver model is among the most frequently accepted methods for satisfying this expectation, alongside biocompatibility testing per the ISO 10993 and GB/T 16886 series.