ASTM F1635-95

Standard Test Method for In Vitro Degradation Testing of Poly (L-lactic Acid) Resin and Fabricated Form for Surgical Implants

SCOPE
1.1 This test method covers poly(L-lactic acid) resin intended for use in surgical implants.  
1.2 The requirements of this test method apply to poly(Llactic acid) in various forms:  
1.2.1 Virgin polymer, or  
1.2.2 Any form fabricated from virgin polymer such as a semi-finished component of a finished product, a finished product, which may include packaged and sterilized implants, or a specially fabricated test specimen.

General Information

• Status: Historical
• Publication Date: 31-Dec-1999
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.15 - Material Test Methods

Relations

• Replaced By: ASTM F1635-95(2000) - Standard Test Method for In Vitro Degradation Testing of Poly (L-lactic Acid) Resin and Fabricated Form for Surgical Implants
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3260-18 - Standard Test Method for Determining the Flexural Stiffness of Medical Textiles
• Effective Date: 01-Jan-2000
• Referred By: ASTM F1983-23 - Standard Practice for Assessment of Selected Tissue Effects of Absorbable Biomaterials for Implant Applications
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3225-17(2022) - Standard Guide for Characterization and Assessment of Vascular Graft Tissue Engineered Medical Products (TEMPs)
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3036-21 - Standard Guide for Testing Absorbable Stents
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3223-17 - Standard Guide for Characterization and Assessment of Tissue Engineered Medical Products (TEMPs) for Knee Meniscus Surgical Repair and/or Reconstruction
• Effective Date: 01-Jan-2000
• Referred By: ASTM F2224-09(2020) - Standard Specification for High Purity Calcium Sulfate Hemihydrate or Dihydrate for Surgical Implants
• Effective Date: 01-Jan-2000
• Referred By: ASTM F561-19 - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3274-21 - Standard Guide for Testing and Characterization of Alginate Foam Scaffolds Used in Tissue-Engineered Medical Products (TEMPs)
• Effective Date: 01-Jan-2000
• Referred By: ASTM F3510-21 - Standard Guide for Characterizing Fiber-Based Constructs for Tissue-Engineered Medical Products
• Effective Date: 01-Jan-2000
• Referred By: ASTM F2150-19 - Standard Guide for Characterization and Testing of Biomaterial Scaffolds Used in Regenerative Medicine and Tissue-Engineered Medical Products
• Effective Date: 01-Jan-2000
• Referred By: ASTM F2027-16 - Standard Guide for Characterization and Testing of Raw or Starting Materials for Tissue-Engineered Medical Products
• Effective Date: 01-Jan-2000
• Referred By: ASTM F2502-17 - Standard Specification and Test Methods for Absorbable Plates and Screws for Internal Fixation Implants
• Effective Date: 01-Jan-2000

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 1635 – 95
Standard Test Method for
In Vitro Degradation Testing of Poly (L-lactic Acid) Resin
and Fabricated Form for Surgical Implants
This standard is issued under the fixed designation F 1635; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope specimens fabricated from poly(L-lactic acid) resin are placed
in buffered saline solution at physiologic temperatures.
1.1 This test method covers poly(L-lactic acid) resin in-
Samples are periodically removed and tested for various
tended for use in surgical implants.
material or mechanical properties at specified intervals (typi-
1.2 The requirements of this test method apply to poly(L-
cally 1, 3, 6, 12, 26, 52 and 104 weeks).
lactic acid) in various forms:
1.2.1 Virgin polymer, or
4. Significance and Use
1.2.2 Any form fabricated from virgin polymer such as a
4.1 This test method is intended to help assess the biodeg-
semi-finished component of a finished product, a finished
radation rates and changes in material or structural properties,
product, which may include packaged and sterilized implants,
or both, of poly(L-lactic acid) materials used in surgical
or a specially fabricated test specimen.
implants.
2. Referenced Documents 4.2 This test method may not be appropriate for all types of
implant applications. The user is cautioned to consider the
2.1 ASTM Standards:
appropriateness of the test method in view of the materials
D 638 Test Method for Tensile Properties of Plastics
being tested and their potential application.
D 671 Test Method for Flexural Fatigue of Plastics by
4.3 The application of mechanical loading or other forms of
Constant-Amplitude-of-Force
energy to the specimens during aging may significantly alter
D 695 Test Method for Compressive Properties of Rigid
(that is, increase) the rate at which properties change. This
Plastics
needs to be considered when comparing in vitro behavior with
D 747 Test Method for Apparent Bending Modulus of
that expected/observed at an in vivo site.
Plastics by Means of a Cantilever Beam
D 790 Test Method for Flexural Properties of Unreinforced
5. Apparatus
and Reinforced Plastics and Electrical Insulating Materi-
2 5.1 Physiologic Soaking Solution—A phosphate-buffered
als
saline (PBS) solution shall be used. The pH of the solution
D 882 Test Method for Tensile Properties of Thin Plastic
2 shall be maintained at 7.4 6 0.2 (see X1.3). The ionic
Sheeting
concentration should be in the physiological range (for ex-
D 1708 Test Method for Tensile Properties of Plastics by
2 ample, a solution that contains 0.1 M phosphate buffer and 0.1
Use of Microtensile Specimens
M NaCl would be appropriate). The solution:specimen mass
D 1822 Test Method for Tensile-Impact Energy to Break
2 ratio shall be as high as practical. Although there is some
Plastics and Electrical Insulating Materials
experience with ratios as low as 20:1, the experimenter is
D 2857 Test Method for Dilute Solution Viscosity of Poly-
cautioned that at lower ratios (that is, less buffering capacity)
mers
the solution pH may change more quickly. In accordance with
F 1251 Terminology Relating to Polymeric Biomaterials in
9.1.3 and X1.4, aging/testing is to be terminated once solution
Medical and Surgical Devices
temperature or pH are allowed to drift outside of the specified
3. Summary of Test Method ranges. Higher solution:specimen ratios (that is, 100:1) will
facilitate maintenance of stable aging conditions.
3.1 Samples of poly(L-lactic acid) resin, semi-finished com-
5.1.1 Over the course of the study it may be possible to
ponents, finished surgical implants, or specially designed test
adjust solution pH and ionic concentration through the addition
of individual solution constituents; however, it is preferable to
This test method is under the jurisdiction of ASTM Committee F-4 on Medical
exchange the test solution completely when it nears the limits
and Surgical Materials and Devices and is the direct responsibility of Subcommittee
of acceptability. Refer to X1.5 for additional information.
F04.15 on Material Test Methods.
Current edition approved Nov. 10, 1995. Published January 1996.
5.1.2 Other physiologic solutions, such as bovine serum,
Annual Book of ASTM Standards, Vol 08.01.
may be substituted provided the solution is properly buffered.
Annual Book of ASTM Standards, Vol 08.02.
4 An anti-microbial additive should be used to inhibit the growth
Annual Book of ASTM Standards, Vol 13.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 1635
of microorganisms in the solution during the test period. 8.1.2 Test samples shall be fully immersed in the physi-
Paragraph X1.6 provides additional information. The appropri- ological solution for a specified period of time (for example, 1
ate MSDS should always be consulted concerning toxicity, safe week, 2 weeks, etc.).
use, and disposal of such additives. 8.1.3 Upon completion of the specified time period, each
5.2 Sample Container—A self-contained, inert container sample shall be removed and dried to a constant weight (see
(bottle, jar, vial, etc.) capable of holding the test sample and the Note 2 and Note X1.8). The weight shall be recorded to a
required volume of physiologic soaking solution (see X1.7). precision of 0.1 % of the original total sample weight.
Multiple samples may be stored in the same container provided
NOTE 2—Drying to a constant weight may be quantified as less than
that suitable sample separation is maintained to allow fluid
0.1 % weight change over a period of 48 h, or less than 0.05 % change in
access to each sample surface and to preclude sample-to-
24 h if the balance used is capable of such precision. Paragraph X1.8
sample contact. Each container must be sealable against
provides additional information.
NOTE 3—Elevated temperatures may be used to assist drying of the
solution loss by evaporation.
sample provided that the temperature used does not induce material or
5.3 Constant Temperature Bath or Oven—An aqueous bath
chemical changes in the sample. The drying conditions used for the
or heated air oven capable of maintaining the samples and
samples prior to aging and for the samples retrieved at each test interval
containers at physiologic temperatures, 37 6 2°C, for the
shall be identical. The actual drying conditions used are to be reported.
specified testing periods.
8.1.4 After weighing, the samples shall not be returned to
5.4 pH Meter—A pH metering device sensitive in the
the physiological solution and shall be retired from the study.
physiological range (pH 6 to pH 8).
8.2 Test B, Molecular Weight:
5.5 Balance—A calibrated weighing device capable of mea-
8.2.1 Determine the inherent viscosity (logarithmic viscos-
suring the weight of a sample to a precision of 0.1 % of its
ity number) of representative samples in chloroform at 25°C
initial weight. A balance having precision to 0.05 % or 0.01 %
using Test Method D 2857 prior to placement of samples in the
will facilitate establishment of an appropriate specimen drying
physiological solution. Dilution ratio in g/mL shall be reported.
period.
8.2.2 Test samples shall be fully immersed in the physi-
5.6 Other—Additional equipment as deemed appropriate by
ological solution for the specified period of time (for example,
the specific test method.
1 week, 3 weeks, 52 weeks, etc.).
6. Sampling 8.2.3 Samples shall be removed at each specified time
period throughout the duration of the test, dried as in 8.1.1, and
6.1 Weight Loss—A minimum of three samples shall be
tested for inherent viscosity as above.
tested per time period.
8.3 Test C, Mechanical Testing:
6.2 Molecular Weight—A minimum of three samples shall
8.3.1 Determine the appropriate mechanical properties of
be tested per time period.
representative samples of resin or fabricated forms using
6.3 Mechanical and Other Testing—A minimum of three
tensile, compressive, torque, bending or other appropriate
samples shall be tested per time period.
mechanical tests prior to placement of the samples in the
NOTE 1—Statistical significance may require more than the minimum
physiological solution (time zero). Relevant ASTM test meth-
number of samples to be tested.
ods may include one or more of the following:
6.4 Solution Temperature and pH—Soaking solutions shall
Test Method D 638
be tested on a periodic basis throughout the test duration. The
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