Design and manufacturing proposal of porous bone scaffolds, based on parametric triply periodic minimal surfaces and 3D hydrogel bioprinting.

Abstract

Tissue engineering is a discipline with the aim of regenerating or replacing organs and tissues affected by degenerative diseases or deep injuries. To achieve this, it combines different biomaterials, manufacturing techniques and biochemical factors. In this sense, the creation of scaffolds as a method of cell guidance, attracts the attention of many studies, since, due to their assistance in the healing process, tissue growth can be faster and with a faithful reproduction of the original organ anatomy. Focusing on a more specific area, it appears the demand to develop porous scaffolds for bone regeneration, which require certain characteristics, such as a minimum pore size of 150µm, a porosity gradient to imitate distinct sections of the bone (10% for the cortex, to 80 90% for the inner part), and interconnectivity to create channels for nutrients and blood vessels. This is how a need arises to design a structure with minimal curvature, using a biomaterial that supports high cell viability (> 90%), and an effective seeding ratio, that allows cells to distribute uniformly throughout the entire scaffold. Hence, this work presents solutions for the limitations involved in the combination of a complex geometry design, and its manufacture with biocompatible materials such as hydrogels. After a review of the literature, a proposal is introduced, covering three major areas; obtaining a parametric model of the periodic minimum triple surfaces (TPMS) to facilitate the simulation of the bone, the delimitation of a protocol for 3D extrusion bioprinting, and finally, the selection and aggregation of biomaterials and methodologies to fabricate the complete scaffold. The results show that the use of the TPMS allows to design a geometry that really resembles the shape of the bone, additionally, its approach with a parametric method (using Weierstrass equation and an integration domain) gives rise to an efficient characterization in terms of computational costs, since it facilitates the use of B-splines and NURBS for isogeometric analysis, making it easier to verify that the designed scaffold meets the required characteristics. On the other hand, the scopes of having a protocol for bioprinting lie in a comprehensive study of the printing variables such as extrusion pressure and speed, together with the intrinsic properties of the material like viscosity and gelation time, ending with a method to quantify the resolution obtained. In that way, having a well characterized geometry and process, allows manufacturing to be manipulated by means of instructions, as Gcodes, and the incorporation of other support materials for rapid extrusion without neglecting viability, and in some way, surpassing the obstacles of generating TPMS with hydrogels