SummaryThis experiment describes resorption rate, light and electron microscopic appearance of the implant site, and tissue distribution and route of elimination of radioactivity from carbon-labelled polylactic acid implants. Fifty-six rats received abdominal implants and were serially sacrificed at 28, 56, 84, 112, 140, 154, and 168 days. Urine and fecal output was measured for radioactivity, along with implant site and several tissues at the time of sacrifice. Tissue distribution of activity was negligible. Resorption rate of the implant was linear with 63.2% remaining after 168 days. Elimination of radioactivity was via respiration, approximately 29.4% by this route. Histologically, the implant was invaded rapidly along septa1 defects or slowly on broad fronts. Invading cells were characterized either by large double-walled vacuoles or by large accumulations of mitochondria and microvesicles adjacent to the implant surface. The long duration of this type of implant may be an important consideration in surgical applications.

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Changes in osseous tissue after injury were studied in monkeys with the use of thermogravimetric analysis (TGA) and mechanical strength measurements. An exponential relationship was found to exist between strength and weight loss for repair tissues 3 to 8 weeks old. The quantitative techniques investigated seem promising for the improved characterization of mineralized tissue.