Additive manufacturing of flexible bio-ceramic scaffolds

摘要

Introduction: Current bio-ceramic scaffolds are limited due to their brittleness and rigidity for shaping during implantation. In this work, additive manufacturing techniques have been explored with calcium polyphosphate (CPP) to print a flexible biodegradable scaffold that allows for conformability to the skeletal system's complex geometries. To date, extensive research has been conducted in manufacturing CPP bone tissue scaffolding, including dimensional analysis of cylindrical implants. Flexible scaffold designs, however, require a new analysis of manufacturability for complex features, such as overhanging bridges and the minimization of wall thickness. Materials and Methods: Proof of concept testing was performed on a stereolithography (SLA) type machine (3D Systems Viper SI2). Adapted chain mail designs were fabricated in which links are interconnected to form sheets or strips. Design features, such as link thickness and spacing, were varied to investigate effects on curvature. The chain mail was then fabricated from biodegradable CPP using powder deposition additive manufacturing, as described in previous work. The layer-by-layer additive manufacturing process was performed using a modified ZPrinter 310 Plus from ZCorp. The CPP powder was mixed with a polyvinyl alcohol binder and an aqueous solvent (Zb60) was injected to successive layers according to the chain mail CAD model. The formed "green" part was de-powdered from the print bed and annealed to first burn-off the binder, and then sinter the powder together using a two-step patented annealing process. Results and Discussion: To develop conformable interlocking chain links, a design study was conducted to understand curvatures resulting from varying link dimensions and spacing. Wall thickness was adjusted in 0.1 mm increments matching the resolution of the additive manufacturing step due to the CPP particle size. The expansion during the 3D printing was measured horizontally and vertically, as a function of wall thickness. Likewise, the contraction and deformation was measured during the secondary sintering stage. The tolerances of the expansion, contraction, and deformations are integral in the chain mail design so that individual links do not fuse the bio-ceramic together. Left: chain mail design, isotropic view. Right: Single chain mail link printed in CPP, top view. Conclusion: A novel design study was conducted to develop new flexible ceramic scaffolds. A dimensional analysis was conducted to understand the tolerances expected for each manufacturing step. Future work will test the chain mail structure to determine its mechanical strength and biodegradation characteristics.