Abstract
A biphasic calcium phosphate with submicron needle-shaped surface topography combined with a novel polyethylene glycol/polylactic acid triblock copolymer binder (BCP-EP) was investigated in this study. This study aims to evaluate the composition, degradation mechanism and bioactivity of BCP-EP in vitro, and its in vivo performance as an autograft bone graft (ABG) extender in a rabbit Posterolateral Fusion (PLF) model. The characterization of BCP-EP and its in vitro degradation products showed that the binder hydrolyses rapidly into lactic acid, lactide oligomers and unaltered PEG (polyethylene glycol) without altering the BCP granules and their characteristic submicron needle-shaped surface topography. The bioactivity of BCP-EP after immersion in SBF revealed a progressive surface mineralization. In vivo, BCP-EP was assessed in a rabbit PLF model by radiography, manual palpation, histology and histomorphometry up to 12 weeks post-implantation. Twenty skeletally mature New Zealand (NZ) White Rabbits underwent single-level intertransverse process PLF surgery at L4/5 using (1) autologous bone graft (ABG) alone or (2) by mixing in a 1:1 ratio with BCP-EP (BCP-EP/ABG). After 3 days of implantation, histology showed the BCP granules were in direct contact with tissues and cells. After 12 weeks, material resorption and mature bone formation were observed, which resulted in solid fusion between the two transverse processes, following all assessment methods. BCP-EP/ABG showed comparable fusion rates with ABG at 12 weeks, and no graft migration or adverse reaction were noted at the implantation site nor in distant organs.
Highlights
The biphasic calcium phosphate with submicron needle-shaped surface topography (BCP) investigated in this study has previously been demonstrated to be a promising solution for predictable spine fusion, circumventing the disadvantages of the gold standard autologous bone graft (ABG), i.e., limited availability, donor site morbidity, patient complications such as pain, secondary site infections, and subsequent risks of revision surgery [1,2,3,4]
The X-ray Diffractometry (XRD) spectrum of the BCP granules extracted from BCP-EP showed the presence of beta-tricalcium phosphate (TCP) and hydroxyapatite (HA) phases
1H-Nuclear Magnetic Resonance (1H-NMR) and Fourier-Transform Infrared Spectroscopy (FT-IR) analysis of the LEOL 400 extracted from BCP-EP shown in Figures 1 and 2 confirmed the identity and composition of the polymer (PLA-PEGPLA)
Summary
The biphasic calcium phosphate with submicron needle-shaped surface topography (BCP) investigated in this study has previously been demonstrated to be a promising solution for predictable spine fusion, circumventing the disadvantages of the gold standard autologous bone graft (ABG), i.e., limited availability, donor site morbidity, patient complications such as pain, secondary site infections, and subsequent risks of revision surgery [1,2,3,4]. The first clinical case series reported successful fusion rates 12 months post-surgery near 97% (94 out of 97 levels) in the lumbar fusion cohort of 52 patients, and 93.8% (75 out of 80 levels) in the cervical fusion cohort of 25 patients [9]. The mechanism underlying these outcomes is associated with the needle-shaped submicron surface topography of BCP, which promotes the differentiation of macrophages, key players in the bone-biomaterial response, towards an anti-inflammatory M2 phenotype which has been associated with a favorable pro-healing mechanism [9,10,11,12,13]. The submicron needle-shaped surface topography feature of BCP is, pivotal for predictable fusion and should be preserved when designing bone graft formulations suitable for the end-users
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