The development of a novel cold isostatic pressing and gelling protocol for a calcium polyphosphate-based local delivery system in osteomyelitis therapy

Abstract

Event Abstract Back to Event The development of a novel cold isostatic pressing and gelling protocol for a calcium polyphosphate-based local delivery system in osteomyelitis therapy Patricia Comeau1 and Mark Filiaggi1, 2 1 Dalhousie University, School of Biomedical Engineering, Canada 2 Dalhousie University, Department of Applied Oral Sciences, Canada Introduction: In comparison with traditional pelleting techniques, cold isostatic pressing (CIP) significantly increases the complexity of device geometry possible and may allow for the design of a local delivery device better suited for osteomyelitis therapy. For example, manipulating the shape of the device will not only impact how well the dead space is filled following debridement of the infected tissue, but also directly influence the therapeutic release rate and tissue response in wound healing[1],[2]. The main objectives of this study were to reproducibly form vancomycin (VCM) loaded calcium polyphosphate (CPP) beads using a novel CIP and gelling protocol, and to determine the impact of strontium doping on bead degradation and VCM release. It was hypothesized that strontium doping would delay bead degradation and VCM release in vitro. Materials and Methods: xSrO-CPP glass powder (x=0, 10 mol%) was first mixed with distilled water (dH2O) at a ratio of 150mg CPP: 0.0602mL dH2O: 7.5mg VCM (or 0mg for blanks)[3]. The resulting paste was then transferred into disk molds and gelled at 37°C under high humidity for 2h. After drying for 48h the gelled glass disks were milled to obtain <45µm powders. Approximately 85mg of this powder was next placed in bead molds prior to vacuum bagging and placing in the CIP chamber at 113MPa for 5 min (Avure Technologies). The final beads were subsequently gelled under high humidity at 37⁰C for 3h before drying for a minimum of 24h. SEM images of the mounted and Au/Pd sputter coated beads (n=1), under intact and sectioned conditions, were obtained using a Hitachi S-4700 (15kV, at 30X and 80X magnification). The average of four bead diameter measurements was reported per bead prior to (d1) and after gelling (d2). Macro images of the freshly prepared beads were also captured with a Nikon D3100 camera. For in vitro elution studies, the beads were added to 15mL polypropylene tubes containing 15mL of 0.1M TBS and rotated at roughly 30⁰ at a speed of 30rpm (one bead per tube, n=6). At set time points over a span of three weeks, 7mL of elution media was removed for measurement of VCM using UV/Vis (280nm) as well as calcium, strontium, and phosphorus ion release using ICP-OES (317.933, 407.771, 213.677nm, respectively). A fresh 7mL of 0.1M TBS was then added to each bead to maintain the elution volume. Data was analyzed with one- or two-way analysis of variance and a post-hoc pairwise Tukey analysis (Minitab15.0, p=0.05). Results and Discussion: Bead shape and diameter uniformity were not significantly influenced by either strontium doping or VCM loading of the CPP glass (Fig 1). VCM loading significantly reduced CPP bead degradation and ion release in vitro over 3 weeks (Fig 2). In contrast, strontium doping only had a brief impact on CPP bead degradation with reduced ion release from blank beads and greater VCM release from VCM-loaded beads in first 24h of study. Conclusion: Therapeutically-loaded CPP beads were successfully and reproducibly fabricated using a novel CIP and gelling protocol. Unexpected and novel to our CPP-based local delivery system was the apparent improvement in bead structural stability in vitro observed upon loading the CPP with VCM. The largely insignificant impact on degradation upon doping CPP with 10mol% strontium was also unexpected. Altogether this study provides early support for the combinatorial fabrication approach of a CPP bead-based local delivery system for osteomyelitis therapy. We are grateful to the Institute for Research in Materials for assistance with SEM imaging and to the Natural Sciences and Engineering Research Council for funding of this project.