Abstract
Tissue engineered bone scaffolds are potential alternatives to bone allografts and autografts. Porous scaffolds based on triply periodic minimal surfaces (TPMS) are good candidates for tissue growth because they offer high surface-to-volume ratio, have tailorable stiffness, and can be easily fabricated by additive manufacturing. However, the range of TPMS scaffold types is extensive, and it is not yet clear which type provides the fastest cell or tissue growth while being sufficiently stiff to act as a bone graft. Nor is there currently an established methodology for TPMS bone scaffold design which can be quickly adopted by medical designers or biologists designing implants. In this study, we examine six TPMS scaffold types for use as tissue growth scaffolds and propose a general methodology to optimise their geometry. At the macro-scale, the optimisation routine ensures a scaffold stiffness within suitable limits for bone, while at the micro-scale it maximises the cell growth rate. The optimisation procedure also ensures the scaffold pores are of sufficient diameter to allow oxygen and nutrient delivery via capillaries. Of the examined TPMS structures, the Lidinoid and Split P cell types provide the greatest cell growth rates and are therefore the best candidates for bone scaffolds.
Highlights
Standard procedures for the repair of critical bone defects or fractures are bone allografts, where the graft is from a donor, and autografts, where it is from the patient
Calculating the maximum pore size limit based on the diffusion of oxygen and nutrients from capillaries was essential, as it ensured that the entire porous network could be filled with cells, allowing for a fair comparison between different triply periodic minimal surfaces (TPMS) scaffold types
The current paper demonstrates the design of optimal TPMS-based bone growth scaffolds combining computational analysis and a simple graphical framework which could be adopted by medical designers or biologists designing implants
Summary
Standard procedures for the repair of critical bone defects or fractures are bone allografts, where the graft is from a donor, and autografts, where it is from the patient The latter option is generally preferable as it presents a lower risk of tissue rejection and disease transmission (Zimmermann and Moghaddam 2011). There are several drawbacks to these processes: limited material availability, long surgical operation time (as bone is removed re-implanted), blood loss and pain, as well as potential complications at the donor site (Wang and Yeung 2017). Synthetic graft materials such as calcium phosphate (CaP), tricalcium phosphate (TCP) and hydroxyapatite possess mechanical properties similar to those of the organic part of bone, making them a possible alternative. Additive manufacturing (AM) enables accurate control of the scaffold geometry and microstructure, which potentially results in scaffolds with superior pore interconnectivity and improved mechanical properties relative to those created using traditional methods (Jariwala et al 2015)
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