55. Evaluation of Poly(styrene-b-isobutylene-b-styrene) (SIBS) as an Alternative to Silicone for Biomaterial Applications

PURPOSE: Silicone - namely poly(dimethylsiloxane) (PDMS) - has numerous applications in surgery, ranging from hydrocephalus shunts and gastric bands to craniofacial prostheses and breast implants. Despite its widespread use, PDMS can induce a strong foreign body response with fibrous encapsulation that can lead to pain, discomfort and implantable device failure. Poly(styrene-block-isobutylene-block-styrene) (SIBS) is a silicon-deficient elastomer clinically used in ocular and vascular implants. Although SIBS has demonstrated excellent biocompatibility in these applications, we lack understanding of the foreign body response induced by SIBS in more immunological active tissues. Here, we compare the physicochemical properties of SIBS with those of PDMS and evaluate the biocompatibility of both biomaterials using in vitro macrophage and fibroblast cell culture models. METHODS: We first performed tensile testing, profilometry and contact angle goniometry to characterize the stiffness, roughness and wettability of SIBS and PDMS. Then, we differentiated THP-1 cell line monocytes into macrophages, cultured them on these biomaterials and assessed their phenotype using quantitative reverse transcription polymerase chain reaction for expression of inflammatory, anti-inflammatory and fibrotic genes. To study how SIBS and PDMS can indirectly influence fibroblast phenotype and contractility via macrophages, we treated fibroblast cultures on tissue culture polystyrene (TCPS) and in collagen gels with SIBS-/PDMS-macrophage conditioned media. Results. Both biomaterials demonstrated comparable physicochemical properties (data not shown). Expression of CXCL8, TNF and TGFB1 genes were significantly different for macrophages, while fibroblasts displayed a more pronounced senescence-associated secretory phenotype and were less contractile when exposed to SIBS-macrophage conditioned media. CONCLUSIONS: Although SIBS was globally similar to PDMS in terms of physical properties, it did however biologically stimulate macrophages to drive fibroblasts towards a more senescent phenotype, suggesting that SIBS might induce less fibrosis than PDMS and could thus be a favorable biomaterial substitute for silicone.