The in vitro response of human osteoblasts to polyetheretherketone (PEEK) substrates compared to commercially pure titanium.

Polyetheretherketone (PEEK) is used as an alternative to titanium in medical devices. Previous in vitro studies examining PEEK have differed in their choice of polymer variant [PEEK or carbon-fiber reinforced PEEK (CFR-PEEK)], source of polymer (some of which are no longer available or for implantation) and cell type. While all studies demonstrated favorable cytocompatibility of the PEEK material, no studies are available which reflect the current state of the art of the material. Here, we use different forms of the only implantable grade PEEK available. These are compared with commercially pure titanium (cpTi) Grade 1 using a human primary osteoblast model. Sample materials were presented as industrially relevant surfaces. Machined or injection molded PEEK and CFR-PEEK were evaluated along with polished (Ra=0.200microm) and rough (Ra=0.554microm) cpTi. Osteoblast adhesion at 4h on injection molded variants of PEEK (Ra=0.095microm) and CFR-PEEK (Ra=0.350microm) material was comparable to titanium. Machined variants of PEEK (Ra=0.902microm) and CFR-PEEK (Ra=1.106microm) materials were significantly less. Proliferation at 48h determined by [(3)H]-thymidine incorporation was the greatest on the smoothest of all materials, the injection molded unfilled PEEK, which was significantly higher than the rough titanium control. The machined unfilled PEEK had the lowest DNA synthesis. RT-PCR for alkaline phosphatase, Type I collagen and osteocalcin normalized to glyceraldehyde-3-phosphate dehydrogenase revealed different patterns of mRNA levels. High mRNA levels for Type I collagen showed that CFR-PEEK stimulated osteoblast differentiation, whilst injection molded unfilled PEEK was less differentiated. Machined unfilled PEEK had comparable message levels of bone matrix proteins as rough titanium. All material variants permitted a degree of mineralization. Scanning electron microscopy at 3 days and 2 weeks in differentiation medium showed that human osteoblasts were well spread on all the different substrates. The varied response reported here at different time points during the study suggests that material formulation (unfilled PEEK or CFR-PEEK), subjection to industrial processing, surface roughness and topography may all influence the cellular response of osteoblasts to PEEK. Thus, differences in human osteoblast responses were found to the various samples of PEEK, but implantable grade PEEK, in general, was comparable in vitro to the bone forming capacity of rough titanium.

Porcine collagen crosslinking, degradation and its capability for fibroblast adhesion and proliferation.

Porcine dermal collagen permanently crosslinked with hexamethylene diisocyanate was investigated for its suitability as a dermal tissue engineering matrix. It was found that the chemically crosslinked collagen had far fewer free lysine groups per collagen molecule than did the uncrosslinked matrix. The ability of the matrix to support human primary fibroblast outgrowth from explants was compared for matrices that had been presoaked in various solutions, including fibroblast media, cysteine and phosphate buffered saline (PBS). It was found that superior cell outgrowth was obtained after soaking with fibroblast media and PBS. The fibroblast attachment properties of the matrix were compared against tissue culture plastic and PET. The collagen matrix showed the least amount of cell retention compared to the other to matrices, however, the general trends were similar for all three scaffolds. Longer term cultures on the collagen showed fibroblasts covering the matrix stacking up on each other and bridging natural hair follicles. However, it was also observed that the fibroblasts were not able to penetrate into the matrix structure. This was believed to result from the chemical crosslinking, as shown by the resistance of the matrix to degradation by collagenases.