Long-term inflammatory response to liquid injectable silicone, cartilage, and silicone sheet.

[OBJECTIVES/HYPOTHESIS] To show and compare the long-term inflammatory responses to subdermal microdroplet injections of 1,000 centistoke (cS) and 5,000 cS liquid injectable silicone (LIS), and to assess the applicability of insulin pen as an alternative LIS delivery device in an animal model.

[STUDY DESIGN] Animal study.

[METHODS] Eighteen healthy adult Sprague-Dawley rats were used. Two graft recipient sites and four injection sites were prepared on each rat's back for: 1) autogenous auricular cartilage graft; 2) silicone sheet; 3) 1,000 cS LIS injection with insulin syringe; 4) 1,000 cS LIS injection with insulin pen; 5) 5,000 cS LIS injection with insulin syringe; and 6) 5,000 cS LIS injection with insulin pen. The animals were followed up for 6 months, and skin biopsies were examined for the evaluation of LIS microdroplets in situ and the degree of inflammatory tissue response. Immunohistochemistry was used for the examination of macrophages and the density of microvessels.

[RESULTS] Biopsies from 17 animals were assessed. There was no statistically significant difference among the groups in terms of the number of lymphocytes (P = 0.081), macrophages (P = 0.857), and neutrophils (P = 0.995), the degree of vascular proliferation (P = 0.698), and the mean LIS microdroplet diameter (P = 0.540). Grossly, there was no sign of granuloma formation in any of the specimens.

[CONCLUSION] There is a low-grade, well-tolerated long-term inflammatory response to microdroplet injections of 1,000 cS and 5,000 cS LIS that is comparable to autogenous cartilage graft in rats. Standard dose delivery devices such as insulin pens can be used for controlled LIS injections.

[LEVEL OF EVIDENCE] N/A.