ASTM F981-23

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F981 − 04 (Reapproved 2016) F981 − 23
Standard Practice for
Assessment of Compatibility of Biomaterials for Surgical
Implants with Respect to Effect of Materials on Muscle and
Insertion into BoneMuscle and Bone Tissue Responses to
Long-Term Implantable Materials Used in Medical Devices
This standard is issued under the fixed designation F981; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice provides a series of experimental protocols for biological assays of tissue reaction to nonabsorbable biomaterials
for surgical guidelines for biological assessment of tissue responses to nonabsorbable for medical device implants. It assesses the
effects of the material on animal tissue in which it is implanted. that is implanted intramuscularly or intraosseously. The
experimental protocol is not designed to provide a comprehensive assessment of the systemic toxicity, immune response,
carcinogenicity, teratogenicity, or mutagenicity of the material since other standards deal with address these issues. It applies only
to materials with projected applications in humans where the materials will reside in bone or soft skeletal muscle tissue in excess
of 30 days and will remain unabsorbed. It is recommended that short-term assays, according to Practice days. F763, first be
performed. Applications in other organ systems or tissues may be inappropriate and are therefore excluded. Control materials will
consist of are well recognized with a well-characterized long-term response and can include metals and any one of the metal alloys
in SpecificationsSpecification F67, F75, F90, F136, F138, or F562, high purity dense aluminum oxide as described in Specification
F603, ultra high molecular weight polyethylene as stated in Specification F648, or USP polyethylene negative control.
1.2 This practice is a combination of Practice F361 and Practice F469. The purpose, basic procedure, and method of evaluation
of each type of material are similar; therefore, they have been combined.
1.2 The values stated in SI units units, including units officially accepted for use with SI, are to be regarded as standard. No other
unitssystems of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This practice is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee F04.16
on Biocompatibility Test Methods.
Current edition approved April 1, 2016Sept. 1, 2023. Published June 2016September 2023. Originally approved in 1986. Last previous edition approved in 20102016 as
F981 – 04 (2016).(2010). DOI: 10.1520/F0981-04R16.10.1520/F0981-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F981 − 23
2. Referenced Documents
2.1 ASTM Standards:
F67 Specification for Unalloyed Titanium, for Surgical Implant Applications (UNS R50250, UNS R50400, UNS R50550, UNS
R50700)
F75 Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants (UNS
R30075)
F86 Practice for Surface Preparation and Marking of Metallic Surgical Implants
F90 Specification for Wrought Cobalt-20Chromium-15Tungsten-10Nickel Alloy for Surgical Implant Applications (UNS
R30605)
F136 Specification for Wrought Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for Surgical Implant
Applications (UNS R56401)
F138 Specification for Wrought 18Chromium-14Nickel-2.5Molybdenum Stainless Steel Bar and Wire for Surgical Implants
(UNS S31673)
F361 Practice for Assessment of Compatibility of Metallic Materials for Surgical Implants with Respect to Effect of Materials
on Tissue (Withdrawn 1987)
F469 Practice for Assessment of Compatibility of Nonporous Polymeric Materials for Surgical Implants with Regard to Effect
of Materials on Tissue (Withdrawn 1986)
F562 Specification for Wrought 35Cobalt-35Nickel-20Chromium-10Molybdenum Alloy for Surgical Implant Applications
(UNS R30035)
F603 Specification for High-Purity Dense Aluminum Oxide for Medical Application
F648 Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants
F763 Practice for Short-Term Intramuscular Screening of Implantable Medical Device Materials
2.2 ISO Standard:
ISO 10993-6 Biological Evaluation of Medical Devices—Part 6: Tests for Local Effects After Implantation
3. Summary of Practice
3.1 This practice describes the preparation of implants, the number of implants and test hosts, test sites, exposure schedule, implant
sterilization techniques, animal models, test sites, assessment time points (that is, short-term and long-term), implant cleaning and
sterilization prior to implantation, implantation method, and methods of implant retrieval and tissue examination of each test site.
site for skeletal muscle and bone implantation. Histological criteria for evaluating tissue reaction are provided.
4. Significance and Use
4.1 This practice covers a test protocol for comparing the local tissue response evoked by biomaterials, from which medical
implantable devices might ultimately be fabricated, with the local tissue response elicited by control materials currently accepted
for the fabrication of surgical devices. The materials may include metals (and metal alloys), dense aluminum oxide, and
polyethylene that are standardized on the basis of acceptable, well recognized, long-term response. is a guideline for short-term
and long-term assessment of skeletal muscle and bone tissue responses to long-term implant materials. For testing of final finished
medical devices, the test article for implantation shall be as for intended use, including packaging and sterilization. The tissue
responses to the test article are compared to the skeletal muscle and/or bone tissue response(s) elicited by control materials. The
controls consistently produce demonstrate known cellular reaction and wound healing to a degree that has been found to be
acceptable to the host.healing.
5. Test HostsAnimal Model and Sites
5.1 Rats Laboratory rats, Rattus norvegicus (acceptable strains such as Fischer 344), laboratory rabbits, Oryctolagus cuniculus
(strains such as New Zealand White rabbits,(NZW)), and other small laboratory animals may be used as test hosts for soft animal
models for skeletal muscle tissue implant response. It is suggested that the rats be age and sex matched. sex-matched. Rabbits or
larger animals may be used as test hosts for animal models for both skeletal muscle and bone implants. When larger animals such
as dogs, goats, or sheep are used, the decision should be based upon special considerations of the particular implant material or
study.study design (for example, duration, size of the implant).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th
Floor, New York, NY 10036, http://www.ansi.org.
F981 − 23
5.1.1 All animal studies shall be done in a facility approved by a nationally recognized organization and in accordance with all
appropriate regulations.
5.2 The sacro-spinalis,sacrospinalis, paralumbar, or gluteal muscles, and the femur or tibia can serve as the test site for implants.
However, the same site must be used for test and material sites for intramuscular and intraosseous implants, respectively. The
implantation of the control and the test article should be performed in parallel (during the same study) with the contralateral site
used for the control implants in all the animal species. study animals.
5.3 There For intraosseous implantation, there shall be a minimum of four animals at each sacrifice interval rabbits at each
assessment time point (for example, see 6.8) for a total of sixteen rabbits per study. For implantation in the skeletal muscle, there
shall be a minimum of three rabbits at each assessment time point (for example, see 6.8twelve animals per study. ) for a total of
twelve rabbits per study. Additional animals may be considered for longer study duration to account for potential losses in animal
numbers. If larger animals are used, in which a greater at least two animals shall be euthanized at each time point so that an
adequate number of implants may be placed, can be assessed (for example, see 6.5.3at least two animals shall be sacrificed ),
without compromising the well-being of study animals. If rats are used, at least ten rats at each time point shall be used to provide
an adequate number of implants at each time period.point. Additional animals should be considered to address systemic responses
(for example, per ISO 10993-11). If assessing systemic toxicity endpoints as part of the implantation study, it is essential that
separate groups of animals be used for test and control groups.
6. Implant Specimens
6.1 Fabrication—Each implant shall be made in a cylindrical shape with hemispherical ends (see 6.36.4 and 6.46.5 for sizes). If
the ends are not hemispherical, this shall be reported. justified in the report. Each implant shall be fabricated, finished, and its
surface cleaned in a manner appropriate for its projected application in human subjects in accordance with Practice F86. If the
specimens test articles are porous, the method of preparation of the porous specimens test article shall be representative of the
contemplated human implant applicationfinal finished medical device and shall yield a specimen test article with characteristic pore
size, pore volume, and pore interconnection diameter. The choice between using solid core specimens with porous coatings and
specimens that are porous throughout shall be a decision of the investigator, and shall be reported.justified in the report.
6.2 Reference metallic specimens shall be fabricated in accordance with 6.1 from materials such as the metal alloys in
SpecificationsSpecification F67, F75, F90, F138, or F562, ceramic in Specification F603, or polymers such as in Specification F648
polyethylene or USP Negative Control Plastic. If the test materials are porous, consideration should be given to using porous
specimensarticles for reference specimens.controls. Alternatively, nonporous reference specimenscontrols may be used. The choice
of reference controls shall be reported and justified.
6.3 To assess the impact of surgical procedure, sham controls may be helpful. If sham controls are used, the same implantation
procedure with the test or control should be used.
6.4 Suggested Sizes and Shapes of Implants for InsertionImplantation in Skeletal Muscle:
6.4.1 The implants shall be cylindrical in shape and may range from 1 mm to 6 mm in diameter and from 10 mm to 20 mm 20 mm
in length depending upon the relative size of the species under study.
6.4.2 The dimensions used shall be reported in accordance with 8.1.
6.4.3 Depending upon the particular device application, other sample shapes may be used. For instance, an investigator might wish
to test the biocompatibility of a new material for screws in the form of a screw. If an alternative specimen a medical device in its
final finished form. If an article with an alternative shape is used, this should be reported and justified in accordance with 8.1.
6.5 Sizes and Shapes of Implants for Insertion in Bone: Intraosseous Implantation:
6.5.1 Implant diameters for use in bone shall be approximately equal to the cortex thickness. shall be cylindrical in shape and the
dimension may range from 2 mm to 4 mm in diameter and from 6 mm to 12 mm in length depending upon the animal model used
in the study. Implant lengths shall allow them the test or control article to reside in onethe cortex and the medulla medullary cavity
without excessive protrusion beyond the periosteum. level of the periosteum.
F981 − 23
6.5.2 Depending upon the particular device application, other sample shapes that are anatomically compatible may be used.
6.5.3 The dimensions and shapes used shall be reported and justified in accordance with 8.1.
6.6 Number of Test and Control Implants:
6.5.1 In each rat, due to size, there may be two implants; one test and one control material implant.
6.6.1 In each rabbit, due to size, there may be six implants; four test and two control material implants.Selection of the animal
model and animal numbers in the study shall depend on body weight, anatomical location for implantation, and implant
characteristics (for example, size, configuration). Ten test and ten control material implants shall be assessed at each time point
and shall be from at least three different animals for skeletal muscle implantation and at least four different animals for intraosseous
implantation.
6.5.3 In larger animals, there may be twelve implants; eight test material and four control material implants.
6.5.4 In rabbits or larger animals, at least sixteen test materials and eight materials shall be tested at each time period.
6.7 Conditioning: Cleaning, Sterilization, and Conditioning (per device intended use):
6.7.1 Remove all surface contaminants with appropriate solvents cleaning agents and rinse all test and control implants in distilled
water prior to sterilization. It is recommended that the implant materials be processed and cleanedprocessed, cleaned, packaged,
and sterilized in the same way the final product will be.
6.6.2 Clean, package, and sterilize all implants in the same way as used for human implantation.
6.7.2 After final preparation and sterilization, handle the test and control implants with great care to ensure that they are not
scratched, damaged, or contaminated in any way prior to insertion. If there is device-specific preparation (for example, delivery
through a catheter) this should be included as a conditioning step prior to implantation.
6.7.3 Report all details of cleaning, sterilization, and conditioning in accordance with 8.1.
6.8 Implantation Period—Insert all implants into each animal at the same surgical session for implantation periods of 4, 12, 26,
and 52 weeks. Justification shall be provided for the selection of additional time points.
7. Procedure
7.1 All the procedures shall be performed using sterile techniques.
7.2 Implantation (Muscle):Intramuscular Implantation:
7.1.1 Place material implants in the paravertebral muscles in such a manner that they are directly in contact with muscle tissue.
7.2.1 Introduce material implants in larger animals by the technique of making an implantation site in the muscle directly inserting
the material intramuscularly or by using a hemostat to separate the muscle fibers. fibers creating an implantation site. Then insert
the implant into the site using plastic-tipped forceps or any tool that is nonabrasive to avoid damage to the implant.
7.2.2 Introduce material implants using sterile technique. Sterile disposable needles or hypodermic tubing and trochar may be used
to implant the material implants into the paravertebral muscles along the spine. In rats, insert amuscles. In rats and rabbits, insert
the negative control implant on one side of the spine and aand the test material implant on the other side. In rabbits, implant one
negative control material on each side of the spine and implant two test materials on each side of the spine. contralateral side. If
larger diameter specimens are us
...