P11. Facile aqueous based method to improve mineralization onto PEEK

Abstract

BACKGROUND CONTEXT Spinal fusion is the standard surgical care for numerous pathologic conditions of the spine, including degenerative disc disease, spondylolisthesis, scoliosis, instability of the spine and spinal fractures. Poly(ether ether ketone) (PEEK), due to its properties of artifact free imaging, radiolucency, and an elastic modulus similar to cortical bone, has been the material of choice for interbody implants. While these advantages arise from the physical and mechanical properties of PEEK, its inert, hydrophobic surface and lack of functional groups which promote cell attachment and growth create the potential for poor surgical outcomes. The aforementioned negative material properties of PEEK may limit osseointegration of PEEK-based implants in clinical and pre-clinical settings leading to eventual poor spinal fusion. Thus, enchaining PEEK's biological properties by suitable surface modification strategies remain critical to expand its application in the clinic. The modification and derivatization of PEEK and PEEK-based spinal implant devices to improve osseointegration properties has been widely explored including physical surface modification and changes to the polymers surface properties. Methods to increase the surface area of PEEK such as laser or acid etching as well as salt crystal templating result in additional regions for bone growth. Chemical derivatization of PEEK adds cell binding functional groups including techniques to introduce sulfate, alcohol, polymers, or metallic layers. Both chemical and physical approaches have shown some clinical improvements but are challenging to scale-up or may damage the mechanical integrity of the PEEK materials. PURPOSE Determine if a covalent surface modification strategy could improve PEEK cell growth. Determine if modification of PEEK improved cell binding compared to unmodified PEEKStudy how modified PEEK's properties impact early and late phase markers of osseointegration. STUDY DESIGN/SETTING The study was designed to compare the ability of surface modified PEEK to support cell binding and growth compared to unmodified PEEK and positive control tissue culture polystyrene(TCPS). Cell binding was studied using scanning electron microscopy and dye membrane labeled cells. Early stage osteogenic proliferation was measured using alkaline phosphatase (ALP) staining. Mineralization, a late phase osteogenic marker, was studied via Alizarin red staining. OUTCOME MEASURES Cell growth: number of cell per image field and cell morphological assessmentALP staining: Colorimetric assessment of ALP substrate converted into product Alizarin red staining: Quantification of Alizarin red stain absorbed onto cell mineral deposits. METHODS PEEK discs were reacted with a arginine memetic compound and characterized to determine percent nitrogen incorporation using x-ray photoelectron spectroscopy and morphological assessment using scanning electron microscopy. Cell binding: C2C12 cells were labeled with a green fluorescent dye and incubated with PEEK, modified PEEK or TCPS. ALP Assay: C2C12 cells were stimulated with BMP2 supplemented media and incubated with PEEK, modified PEEK or TCPS ALP expression was evaluated after 72 hours. Mineralization assay: MC3T3 cells were stimulated with BMP2 supplemented media incubated with PEEK, modified PEEK or TCPS. Mineral deposits were stained with Alizarin red after 28 days. RESULTS Both ALP and Alizarin red assays showed our novel surface modification produced significant enhancement in osteoblastic activity. Measurement of absorbance related to ALP expression was significantly higher with modified PEEK samples (7463±722) compared to standard PEEK (3183±942), p=0.003. Similarly, quantification of alizarin red was significantly higher with modified PEEK samples (0.403±0.06) when compared to standard PEEK (0.057±0.02), p=0.001. Notably, there was no significant difference between modified PEEK samples and the tissue culture polystyrene with respect to either ALP or Alizarin red expression. Through the attachment of novel cell binding groups to the ketone repeat unit of the PEEK backbone, using mild aqueous based reaction conditions, we demonstrate through a series of cell-based experiments dramatically improved rates of cell adhesion and proliferation in vitro and vastly improved early (two times greater, p=0.003) and late stage markers of osteoblast maturation (almost seven times greater, p=0.001) late stage mineral deposition with results statistically equivalent to data acquired from positive tissue culture polystyrene. CONCLUSIONS An ideal strategy for the creation of next generation PEEK materials would render the material surface with functional groups that promote cell binding and growth using a process that is (a) solution based to evenly react at complex medical device surfaces while avoiding labor intensive material manipulation, (b) employs facile reaction conditions to avoid damaging material mechanical integrity, (c) utilizes materials that are non-toxic and covalently modify the surface. We have recently demonstrated dramatically improved rates of cell adhesion and proliferation in vitro and vastly improved markers of osteoblast maturation at both early and late time points. In vivo evaluation studies for changes to osseointegration to compare the novel surface modified PEEK to translational PEEK devices are being planned. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.