251. Additive manufactured Ti-6Al-4V/polyetheretherketone composite porous cage for interbody fusion: bone growth and biocompatibility evaluation in a porcine model

Abstract

BACKGROUND CONTEXT Several materials have been used to manufacture the cages, the most common being polyetheretherketone (PEEK) and titanium (Ti) alloy (Ti–6Al–4V). Each material has its advantages and disadvantages. PURPOSE The purpose is to utilize the advantages of each material in combination with additive manufacturing technology to develop a new porous Ti alloy/PEEK composite interbody cage. STUDY DESIGN/SETTING In vitro mechanical tests and cell biocompatibility study; in vivo posterior instrumented interbody fusion porcine model. PATIENT SAMPLE In vitro cell culture analysis for Porous Ti alloy/PEEK composite cages. In vivo animal study used 20 female pigs through an anterior intervertebral lumbar fusion and posterior pedicle screws augmentation. Each level was randomly implanted with one of five testing cages. OUTCOME MEASURES In vitro mechanical tests for shear strength of the interface layer. In vitro cell culture analysis for alkaline phosphatase (ALP) activity, ALP and osteocalcin mRNA expression for in vitro study. Micro–computed tomography (CT), back-scattered-electrons SEM (BSE-SEM) and histological analyses for in vivo study. METHODS In vitro and in vivo study compared 5 groups of cages. The first was a commercialized pure PEEK cage (group 1). The second was a Ti alloy/PEEK composite cage with nonporous Ti alloy end plates (group 2). The third, fourth, and fifth groups were composite cages with porosity of 40%, 60%, and 80% (groups 3, 4, and 5), respectively. Mechanical tests, alkaline phosphatase activity and mRNA expression, osteocalcin mRNA expression, SEM were performed for in vitro study. Micro–computed tomography (CT), back-scattered-electrons SEM (BSE-SEM) and histological analyses were performed for in vivo study. RESULTS The shear strength reached 33.4 MPa at the Ti alloy/PEEK interface. ALP activity and ALP mRNA expression were positively correlated with the porosity rate and peaked at 60% porosity. Micro-CT and BSE-SEM demonstrated that structures with high porosities, especially 60% and 80%, facilitated more bone formation inside the implant but not outside the implants. Histological analysis also showed that bone formation was better in Ti alloy groups than in the PEEK group. CONCLUSIONS In vitro cell culture showed higher porous structure exhibited superior bone growth. Micro-CT and histological analyses showed improved bone growth in high-porosity composite cage groups. Composite cage implant takes the biological advantages of Ti alloy porous end plates and the mechanical and radiographic advantages of PEEK central core to incorporate as a single implant suitable for intervertebral fusion. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.