Titanium (Ti) internal fixation devices used in maxillofacial traumatology and orthognathic surgery, are disadvantageous since they restrict growth and require a second intervention for removal. PLGA (polyglycolide-co-polylactide) internal fixation devices are being used for such applications but frequently elicit adverse tissue responses (ATRs).
ATRs are thought to originate from physiological and chemical processes deriving from the wound healing response and involve a foreign body reaction. Fustrated phagocytosis signals the fibroblast to encapsulate the implant with collagen, isolating it from the surrounding tissue vascularisation. Therefore, the isolation of the PLGA implant by a thick fibrous capsule may restrict the diffusion of acidic degraded polymer constituents away from the implant site possibly exaggerating the ATRs.
Surface roughness has been shown to be an effective way of controlling fibrous capsule thickness around Ti implants. Topography from Ti replicated on PLGA has also been shown to control cell behavior in vitro. We therefore hypothesised that replicating surface topography identical to Ti implants onto PLGA will reduce the fibrous capsule thickness and allow diffusion of acidic polymer degradation products.
To test this hypothesis three commercially available Ti surfaces (average roughness values 3.3, 0.8 and 0.2 µm) were replicated using a novel solvent casting technique onto PLGA films. The film surface was characterized by profilometry, contact angle measurement, scanning electron microscopy, and degradation mechanism was investigated over 12 weeks in vitro. Fibroblast cell response to both Ti and PLGA materials was quantified comparing cell adhesion, cell proliferation and gene expression on each material surface after 7 days.
The surface topography from each titanium implant was successfully replicated onto PLGA. The contact angle measurement of the PLGA (40o) was significantly higher than Ti (<20o) but remained in the hydrophilic range. PLGA surface topography did not change over 6 weeks. However, PLGA lost mass without volume change, which associated with maximum pH reduction to 6.8 after 8 weeks of incubation.
Cell behavior on PLGA was similar to Ti except that there was a delay in cell spreading and proliferation on the PLGA. Cell adhesion to both Ti and PLGA was greatest on the rougher surface. Gene expression of wound healing genes showed distinct differences between Ti and PLGA as well as topography.
This study confirms that surface topography can control cell behavior, but provides evidence that the underlying chemistry has also its effect on cell function and gene expression.
The study was funded by the AO Foundation Startup Grant Program S-08-43O; Straumann AG, Basel, Switzerland, for implant material.; Synthes AG, Chur, Switzerland, for implant material.