Production of hard tissue scaffolds using three-dimensional printing method

Abstract

Synthesised bone replacement scaffolds provide the possibility to individually tailor properties, overcome limited donor availability and improve osteointegration. The aim of bone tissue engineering is to provide solutions to these problems by making available high quality transplants that can be supplied in larger quantities. In these applications both the internal and external geometry of the scaffold are very important since they have significant effect on mechanical properties, permeability and cell proliferation. Rapid Prototyping technologies allow the use of customised materials with predetermined and optimised geometries to be fabricated with good accuracy. This work investigates the ability of the 3D printing technology to manufacture intricate bone scaffold geometries from biocompatible calcium phosphate based materials. Initial investigations with the proprietary materials showed that predicted directional mechanical behaviour can be realised. Practical measurements investigating the directional mechanical properties of the manufactured samples showed trends identical with the results of the Finite Element Analysis (FEA). The ability of 3D Printing technology to fabricate tissue engineering scaffold geometries made of biocompatible calcium phosphate cements was also demonstrated in this work. Scaffolds were manufactured by printing aqueous sodium phosphate dibasic solution on the powder bed consisting of a homogeneous mixture of dicalcium phosphate and calcium hydroxide. The wet-chemical reaction of precipitation took place in the powder bed of the 3D Printer. Solid specimens were manufactured in order to measure the bulk compressive mechanical properties of the fabricated Calcium Phosphate Cement (CPC). The average elastic modulus for the so produced parts was 3.59 MPa, and the average compressive strength was 0.147 MPa. Sintering resulted in significantly increased compressive properties (E = 9.15 MPa, σy = 0.483 MPa), but it decreased the specific surface area of the material. As a result of sintering, the calcium phosphate cement decomposed to β-Tricalcium Phosphate (β-TCP) and Hydroxyapatite (HA) as confirmed by Thermogravimetric Analysis and Differential Thermal Analysis (TGA/DTA) as well as with X-Ray Diffraction (XRD). The obtained mechanical properties are not sufficient for high load bearing implants, where the required strength in ranging between 1.5 -150 MPa and compressive stiffness is above 10 MPa. However further post processing such as infiltration with biodegradable polymers may allow these structures to be used for scaffold applications