Polyurethane sponges were soaked in a 5 mg/ml solution of lead acetate, dried, and implanted subcutaneously in rats. Sponges soaked in distilled water were implanted as controls. The reaction to the sponges was studied from 5 h to 140 days after implantation, utilising sponge dry weight gain, rate of ingrowth of granulation tissue, histology and electron microscopy. Five hours after implantation, test sponges showed lead phosphate deposits in the central sponge zone and by one day the deposits stained positively for calcium. Transmission electron microscopy (TEM) showed needle-shaped crystals of hydroxyapatite. Ingrowth of granulation tissue into test sponges was delayed. Breakdown of the sponge matrix was observed in control sponges after 140 days. This model highlighted the physicochemical nature of the calcergic reaction, implicating fluid transudates/exudates in the initial stages.
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Hirsch et al. (1985) studied this question.