Biocompatibility of steroid-HA delivery system using adult castrated rams as a model

The objective of this study was to analyze the fibrous tissue surrounding dihydrotestosterone (DHT loaded HA devices implanted subcutaneously (S/C) in adult castrated rams. The microcrystals of HA were prepared by following standard laboratory procedure. Housing, surgical implantation and bleeding procedure of all rams used in this study was conducted according to the NIH guideline and approval of UCUCA. A total of 11 rams were castrated by elastrator rings within a week after birth. At 7 months of age the animals were randomly divided into three groups. Group 1 rams (n = 4) were not treated and served as the control group. Rams in group 2 (n = 3) were implanted s.c. with two HA capsules (80 mg DHT/capsule). Each ram (n = 3) in group 3 was implanted with two empty HA capsules and served as a sham group. All animals were housed together throughout this study and water, high quality hay and grain were given ad libitum. The sterilized ceramics were inserted S/C through a single incision using standard aseptic surgical techniques. Gross, radiographic and histological examinations of the site of implantation did not show any untoward reactions during the entire investigation. Histopathological evaluation have revealed that all HA implants were encapsulated with hyaline fibrous tissue at the end of two weeks, and the degree of encapsulation increased with time. Results collected from this investigation showed that the passage of DHT through HA capsules started within 3 days after implantation. Furthermore, sustained delivery of DHT by means of HA devices at levels ranging between 1.4-3.3 ng/ml imposed continuous negative feedback on post-castration rise in serum LH and FSH secretion. Representative retrieved implants showed slight degradation of the implant (27% +/- 38) and increased erosion at the sharp edges with time was observed. Light and electron microscopic evaluation demonstrated that at the end of four weeks postimplantation, a well developed granulation tissue is seen surrounding the implants. The thin developing fibrous capsule infiltrated with macrophages and numerous small and large capillaries were observed. A well-developed fibrous capsule formed at 6 months postimplantation. Four different layers were observed: (i) the HA tissue layer contains macrophages, some mononuclear leukocytes, and fibroblasts indicative of the chronic inflammatory responses, (ii) the fibrous capsule layer is composed of longitudinally oriented fibroblasts and mature collagen fibers, (iii) the vascularization layer contains numerous large and small capillaries, and (iii) the outer side of the fibrous capsule predominately composed of adipose tissue. Data obtained from this study suggest that lack of vascularization at the immediate HA tissue layer and the fibrous capsule layer may function to retard the rapid release of DHT from the HA implants. This retardation of DHT release from HA implants by the formation of fibrous capsule is needed to compensate for the macropores formed during the biodegradation of the implants.