ASTM F1635-95(2000)
(Test Method)Standard Test Method for In Vitro Degradation Testing of Poly (L-lactic Acid) Resin and Fabricated Form for Surgical Implants
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.
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Designation: F 1635 – 95 (Reapproved 2000)
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 3. Summary of Test Method
1.1 This test method covers poly(L-lactic acid) resin in- 3.1 Samples of poly(L-lactic acid) resin, semi-finished com-
tended for use in surgical implants. ponents, finished surgical implants, or specially designed test
1.2 The requirements of this test method apply to poly(L- specimens fabricated from poly(L-lactic acid) resin are placed
lactic acid) in various forms: in buffered saline solution at physiologic temperatures.
1.2.1 Virgin polymer, or Samples are periodically removed and tested for various
1.2.2 Any form fabricated from virgin polymer such as a material or mechanical properties at specified intervals (typi-
semi-finished component of a finished product, a finished cally 1, 3, 6, 12, 26, 52 and 104 weeks).
product, which may include packaged and sterilized implants,
4. Significance and Use
or a specially fabricated test specimen.
4.1 This test method is intended to help assess the biodeg-
2. Referenced Documents
radation rates and changes in material or structural properties,
2.1 ASTM Standards: or both, of poly(L-lactic acid) materials used in surgical
D 638 Test Method for Tensile Properties of Plastics implants.
D 671 Test Method for Flexural Fatigue of Plastics by 4.2 This test method may not be appropriate for all types of
Constant-Amplitude-of-Force implant applications. The user is cautioned to consider the
D 695 Test Method for Compressive Properties of Rigid appropriateness of the test method in view of the materials
Plastics being tested and their potential application.
D 747 Test Method for Apparent Bending Modulus of 4.3 The application of mechanical loading or other forms of
Plastics by Means of a Cantilever Beam energy to the specimens during aging may significantly alter
D 790 Test Method for Flexural Properties of Unreinforced (that is, increase) the rate at which properties change. This
and Reinforced Plastics and Electrical Insulating Materi- needs to be considered when comparing in vitro behavior with
als that expected/observed at an in vivo site.
D 882 Test Method for Tensile Properties of Thin Plastic
2 5. Apparatus
Sheeting
D 1708 Test Method for Tensile Properties of Plastics by 5.1 Physiologic Soaking Solution—A phosphate-buffered
saline (PBS) solution shall be used. The pH of the solution
Use of Microtensile Specimens
D 1822 Test Method for Tensile-Impact Energy to Break shall be maintained at 7.4 6 0.2 (see X1.3). The ionic
concentration should be in the physiological range (for ex-
Plastics and Electrical Insulating Materials
D 2857 Test Method for Dilute Solution Viscosity of Poly- ample, a solution that contains 0.1 M phosphate buffer and 0.1
M NaCl would be appropriate). The solution:specimen mass
mers
F 1251 Terminology Relating to Polymeric Biomaterials in ratio shall be as high as practical. Although there is some
experience with ratios as low as 20:1, the experimenter is
Medical and Surgical Devices
cautioned that at lower ratios (that is, less buffering capacity)
the solution pH may change more quickly. In accordance with
This test method is under the jurisdiction of ASTM Committee F04 on Medical
9.1.3 and X1.4, aging/testing is to be terminated once solution
and Surgical Materials and Devicesand is the direct responsibility of Subcommittee
temperature or pH are allowed to drift outside of the specified
F04.15 on Material Test Methods.
ranges. Higher solution:specimen ratios (that is, 100:1) will
Current edition approved Nov. 10, 1995. Published January 1996.
Annual Book of ASTM Standards, Vol 08.01.
facilitate maintenance of stable aging conditions.
Annual Book of ASTM Standards, Vol 08.02.
Annual Book of ASTM Standards, Vol 13.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 1635
5.1.1 Over the course of the study it may be possible to 8.1.1 Test samples, in either resin or fabricated form, shall
adjust solution pH and ionic concentration through the addition be weighed to a precision of 0.1 % of the total sample weight
of individual solution constituents; however, it is preferable to prior to placement in the physiological solution. Samples shall
exchange the test solution completely when it nears the limits be dried to a constant weight before initial weighing (see Note
of acceptability. Refer to X1.5 for additional information. 2 and Note X1.8). Drying conditions, including final relative
5.1.2 Other physiologic solutions, such as bovine serum, humidity (if applicable), shall be reported and may include the
may be substituted provided the solution is properly buffered. use of a desiccator, partial vacuum or elevated temperatures
An anti-microbial additive should be used to inhibit the growth (see Note 3).
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.
solution loss by evaporation. NOTE 3—Elevated temperatures may be used to assist drying of the
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
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