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For many years, stainless steel, cobalt-chromium, and titanium alloys have been the primary biomaterials used for load-bearing applications. However, as the need for structural materials in temporary implant applications has grown, materials that provide short-term structural support and can be reabsorbed into the body after healing are being sought. Since traditional metallic biomaterials are typically biocompatible but not biodegradable, the potential for magnesium-based alloys in biomedical applications has gained more interest. This paper summarizes the history and current status of magnesium as a bioabsorbable implant material. Also discussed is the development of a magnesium-zinc-calcium alloy that demonstrates promising degradation behavior. Harpreet S. Brar, Peter I. Martin, and Michele V. Manuel are with the

Magnesium has recently received an increased amount of interest due to its potential use in biodegradable implant applications. The rapid degradation of conventional Mg is, however, a major limitation that needs to be addressed in the design of these materials, along with consideration of toxicity in selection of alloying elements. In this study, five alloys in the Mg-xCa-ySr system (x = 0.5-7.0 wt %; y = 0.5-3.5 wt %) were prepared and characterized for their suitability as degradable orthopedic implant materials. The alloys were characterized using optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, degradation measurements in Hanks' solution at 37°C, compression testing, and in vitro cytotoxicity testing with a mouse osteoblastic cell line. The results indicate that the Mg-1.0Ca-0.5Sr alloy is the most promising alloy for orthopedic implant applications since it showed the lowest degradation rate in Hanks' solution (0.01 mL cm(-2) h(-1)) along with no significant toxicity to MC3T3-E1 osteoblasts and a compressive strength of 274 ± 4 MPa.

For this study, 66 patients with a preoperative diagnosis of unilateral primary inguinal hernia were randomized to undergo laparoscopic totally extra peritoneal (TEP), laparoscopic transabdominal (TAPP), or open inguinal hernia repair with polypropylene mesh (Lichtenstein type). Both the operative team caring for the patient postoperatively and the patient were blinded to the operative approach by placement of a large dressing covering the abdomen, which was not removed until postoperative day 3. The patients recorded their pain level on a visual analog pain scale daily. Medication usage also was recorded. All patients were seen at 7-day intervals until they returned to work. The patients were interviewed during their postoperative visits by an investigator blinded to the operative approach and questioned regarding their ability to return to work and their pain levels. The average number of lost work days in all the groups was 12, and there was no significant difference between the three groups (p = 0.074). The average operating time for the TAPP procedure was 59 min, less than the time required to complete either the TEP or the Lichtenstein approach, which had equivalent operative times (p = 0.027). The material cost was significantly lower for the Lichtenstein repair (1,200 dollars less) than for either of the laparoscopic approaches, a saving primarily related to consumable operating room supplies. The TEP repair costs were minimally higher than those for the TAPP repair (125 dollars more). No significant differences were noted in the postoperative pain scales, and the use of postoperative oral analgesics was equivalent. The higher operative costs noted for the laparoscopic hernia repairs were not offset by a shortened convalescence. Postoperative pain appears to be equivalent regardless of the operative approach chosen and is easily managed with oral analgesics.

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