Surface Bio-modified PEEK And Hydroxyapatite-coated Porous PEEK Scaffolds For Bone Defect Repair

The history of using biomaterials to repair damaged tissues goes back to prehistory.Ancient humans have understood how to use natural organic and inorganic materials such as bones,animal teeth and even wood to replace organs or parts of organs to improve their health.According to the literature,it has been more than 2600 years since the Etruscan civilization learned to use the mixture of animal teeth and gold to replace the missing teeth of patients.With the development of human society and technology,biomaterials are constantly updated,and their types and functions are more and more abundant.Gold is one of the earliest "biomaterials" used in ancient civilization.There is clear evidence that the intelligent Chinese and Roman People 2000 years ago have learned to use gold to repair damaged teeth.With the sharp increase in trauma,tumors,deformities,degeneration and aging population,the demand for surgical reconstruction materials is also increasing.The clinical treatment results show that autogenous bone transplantation is effective in repairing bone defects,but the complications and limited sources limiting its clinical use.Allogeneic bone grafts and xenograft bone materials have potential risks such as pathogen transmission and immune response.With the development of material technology,stainless steel and titanium alloys are widely used in orthopedics.When the artificial joint prostheses or plates were implanted into the bone defect or fracture area,these devices provide mechanical support and structural reinforcement,and the stress of the surrounding bone tissue is reduced due to the sharing of load.According to Wolff’s law,the "stress shielding" phenomenon of bone around metal implants has been valued.In order to reduce stress shielding and related bone loss around metal orthopedic implants,more compliant polymer composites have been studied.When the elastic modulus of the implant is equivalent to that of bone,the "isoelastic" prosthesis could be able to increase the stress load of bone,thus reduce the stress shielding,extend the lifespan of orthopaedic implants,avoid loosening,failure and bone loss.PEEK,as a member of polyaryletherketone(PEAK)polymer family,is widely used in orthopedics and spinal implants,and its "isoelastic" characteristics have been widely valued.PEEK has many advantages such as corrosion resistance,high temperature resistance,non-toxic and fatigue resistance.However,PEEK is a kind of hydrophobic bio inert material with poor bone integration ability,and PEEK material has a high melting point(about 340℃),which requires a relatively difficult manufacturing process.In this study,we focused on how to improve the surface bioactivity of PEEK,improve the ability of osseointegration,improve the surface morphology,how to prepare the HA coating and continuous porous structure to promote osteogenesis while maintaining good mechanical properties of PEEK.Section 1.Polyetheretherketone(PEEK),as the most promising implant material for orthopedics and dental applications,has bone-like stiffness,excellent fatigue resistance,X-ray transparency,and near absence of immune toxicity.However,due to biological inertness,its bone conduction and bone ingrowth performance is limited.The surface modification of PEEK is an option to overcome these shortcomings and retain most of its favorable properties,especially when an excellent osseointegration is desired.In this study,a simple reaction procedure was employed to bind the osteogenic growth peptide(OGP)on the surface of PEEK materials by covalently chemical grafting to construct a bioactive interface.The PEEK surface was activated by N,N’-Disuccinimidyl Carbonate(DSC)after hydroxylation,and then OGP was covalently grafted with amino group.The functionalized surface of PEEK samples were characterized by X-ray photoelectron spectroscopy(XPS),Fourier-transform infrared spectroscopy(FT-IR),water contact angle measurement and biological evaluation in vitro.OGP-functionalized PEEK surface significantly promoted the attachment,proliferation,alkaline phosphatase(ALP)activity and mineralization of pre-osteoblast cells(MC3T3-E1).The in vivo rat tibia implantation model is adopted and micro-CT analyses demonstrated that the OGP coating significantly promoted new bone formation around the samples.The in vitro and in vivo results reveal that the modification by covalent chemical functionalization with OGP on PEEK surface can augment new bone formation surrounding implants compared to bare PEEK.Section 2: In this section,a novel process has been demonstrated for the manufacture of Hydroxyapatite(HA)coated porous near spherical salt beads,which is able to produce porous Polyetheretherketone(PEEK)with HA coatings on the inner wall surface.Beads have been prepared through the Rolling granulation method using a flour-based paste.The process has been simple and shown to be repeatable.After thermal decomposition of the flour from the beads they contain a high fraction of interconnected porosity which allows water to penetrate them and accelerates the dissolution of the salt from the component.These beads used as a sacrificial porogens which carries the coating integrates into the contact surface during thesintering,and after dissolution of the salt,internal coatings are achieved.The resulting highly interconnected Hydroxyapatite coated scaffolds have possessed superior osseointegration in vivo without affecting the mechanical properties of the material matrix.In the studies,we have improved the shortcomings of PEEK materials in the following aspects: 1.OGP peptide was successfully grafted on the surface of PEEK by covalent bond,and favorable bioactivity and osteogenic interface were obtained,which could effectively improve the surface inertness of PEEK materials;2.Inspired by the traditional Chinese food Tangyuan and sesame glutinous rice balls,the spherical sodium chloride porogen and the spherical sodium chloride porogen with HA coating were prepared by rolling granulation method,and the porogen with high temperature resistance,low cost,safety and non toxicity was prepared successfully;3.The interconnected porous PEEK scaffolds and the porous PEEK scaffolds with HA coating were designed and prepared,which solved the problem of poor pore connectivity of the porous PEEK material,and also solved the difficulties in the preparation of porous PEEK surface coating layer.This provides a way for further clinical application of PEEK materials.