New cross‐linkable poly[bis(octafluoropentoxy) phosphazene] biomaterials: Synthesis, surface characterization, bacterial adhesion, and plasma coagulation responses

Abstract

Biomaterial-associated microbial infection and thrombosis represent major issues to the success of long-term use of implantable blood-contacting medical devices. The development of new poly[bis(octafluoropentoxy) phosphazene (OFP) biomaterials provides new routes for combatting microbial infection and thrombosis. However, the limited mechanical properties of OFP to date render them unsuitable for application in medical devices and inhibit any attempts at subsequent surface topography modification. In this study, we synthesized cross-linkable OFPs (X-OFPs) with the different degrees of cross-linking in an effort to improve the mechanical properties. The results showed that the surface chemistry and surface topography of X-OFPs do not change significantly, but the surface mechanical stiffness increased after crosslinking. Atomic force microscopic phase images showed that the polymer phase separation structures changed due to cross-linking. Experiments with three bacterial strains: Staphylococcal epidermidis, Staphylococcal aureus, and Pseudomonas aeruginosa showed that bacterial adhesion was significantly decreased on the OFP and X-OFPs for both the pre-cross-linked and cross-linked as compared to polyurethane biomaterials. Furthermore, bacterial adhesions were lower on X-OFP surfaces than on precross-linked materials, suggesting that mechanical stiffness is an important parameter influencing bacterial adhesion. Blood plasma coagulation responses revealed longer coagulation times for OFP and X-OFP materials than on polyurethanes, indicating that the new cross-linked OFPs are resistant to plasma coagulation compared to currently used polyurethane biomaterials.

Inhibition of bacterial adhesion and biofilm formation by a textured fluorinated alkoxyphosphazene surface

“…The structures of OFP and X-OFPs were confirmed by 1 H and 31 P NMR spectroscopy using a Bruker AV-360 instrument operated at 360 and 145 MHz, respectively. These results have been published elsewhere [ 31 ].

Scheme 1 Synthesis route of X–OFP polymers and crosslinking reactions under UV.

…”

“…When two adjacent macroradicals annihilate by recombination, covalent bonds form between different polymer chains, forming the crosslinking. Our previous study shows that the crosslinking largely enhanced the mechanical strengths and the increase in stiffness further reduced bacterial adhesion [ 31 ]. This study focuses on the fabrication of textured X–OFP films using a variety of modified X-OFPs and bacterial responses to these new material surfaces.…”

“…A previous study showed that the elastic modulus of OFP measure by AFM nano-indentation technique was approximately 0.076 GPa and the introduction of crosslinking functional groups increased the modulus of materials after crosslinking, with the modulus of X–OFP 13.6 increasing to 0.171 GPa, about 2.25 times higher than OFP. Results also showed that the modulus increased with the density of crosslinking groups in X-OFPs [ 31 ]. In this study we found more pillar defects in textured OFP film surfaces than X-OFPs and the pillar yields increased with the crosslinking levels ( Fig.…”

“…OFP and X-OFPs were synthesized following the procedures which have been described elsewhere [ 30 , 32 ] and the general synthesis routes to OFP and X-OFPs can be found in our previous publication [ 31 ]. Briefly, synthesis was carried out by dropwise addition of NaOAP to a solution of poly (dichlorophosphazene) in THF.…”

“…In our most recent study we find that the crosslinking improved the mechanical properties of materials and made it feasible for shaped medical devices such as catheters, as well as permitting further surface topography modification. Furthermore, we found that the increase in material stiffness decreased the bacterial adhesion responses [ 31 ]. Extending from the previous findings, these results suggest that the combination of surface fluorocarbon chemistry, stiffness, and submicron topography modification in polyphosphazenes may significantly improve the resistance to microbial infection and largely increase the biocompatibility.…”