Abstract
3D printed scaffolds can be used, for example, in medical applications for simulating body tissues or for manufacturing prostheses. However, it is difficult to print porous structures of specific porosity and pore size values with fused deposition modelling (FDM) technology. The present paper provides a methodology to design porous structures to be printed. First, a model is defined with some theoretical parallel planes, which are bounded within a geometrical figure, for example a disk. Each plane has randomly distributed points on it. Then, the points are joined with lines. Finally, the lines are given a certain volume and the structure is obtained. The porosity of the structure depends on three geometrical variables: the distance between parallel layers, the number of columns on each layer and the radius of the columns. In order to obtain mathematical models to relate the variables with three responses, the porosity, the mean of pore diameter and the variance of pore diameter of the structures, design of experiments with three-level factorial analysis was used. Finally, multiobjective optimization was carried out by means of the desirability function method. In order to favour fixation of the structures by osseointegration, porosity range between 0.5 and 0.75, mean of pore size between 0.1 and 0.3 mm, and variance of pore size between 0.000 and 0.010 mm2 were selected. Results showed that the optimal solution consists of a structure with a height between layers of 0.72 mm, 3.65 points per mm2 and a radius of 0.15 mm. It was observed that, given fixed height and radius values, the three responses decrease with the number of points per surface unit. The increase of the radius of the columns implies the decrease of the porosity and of the mean of pore size. The decrease of the height between layers leads to a sharper decrease of both the porosity and the mean of pore size. In order to compare calculated and experimental values, scaffolds were printed in polylactic acid (PLA) with FDM technology. Porosity and pore size were measured with X-ray tomography. Average value of measured porosity was 0.594, while calculated porosity was 0.537. Average value of measured mean of pore size was 0.372 mm, while calculated value was 0.434 mm. Average value of variance of pore size was 0.048 mm2, higher than the calculated one of 0.008 mm2. In addition, both round and elongated pores were observed in the printed structures. The current methodology allows designing structures with different requirements for porosity and pore size. In addition, it can be applied to other responses. It will be very useful in medical applications such as the simulation of body tissues or the manufacture of prostheses.
Highlights
Many new applications have arisen as a result of recent advances in 3D printing techniques.For example, printed parts are used for manufacturing space instrumentation, for both prototypes and flying parts [1], for manufacturing cost-effective parts in the sports industry or for developing new Materials 2018, 11, 1532; doi:10.3390/ma11091532 www.mdpi.com/journal/materialsMaterials 2018, 11, 1532 protective structures for vehicles in the automotive industry [2]. 3D printing has many different medical applications, such as bioprinting tissues and organs, building vascularized organs, the manufacture of customized implants, prostheses and models for surgical preparation, among others [3]
In order to compare calculated and experimental values, scaffolds were printed in polylactic acid (PLA) with fused deposition modelling (FDM) technology
Technology are its easiness of use and the fact that it allows printing a wide range of materials, as long as they can be extruded, for example plastic materials such as acrylonitrile butadiene styrene (ABS)
Summary
Many new applications have arisen as a result of recent advances in 3D printing techniques.For example, printed parts are used for manufacturing space instrumentation, for both prototypes and flying parts [1], for manufacturing cost-effective parts in the sports industry or for developing new Materials 2018, 11, 1532; doi:10.3390/ma11091532 www.mdpi.com/journal/materialsMaterials 2018, 11, 1532 protective structures for vehicles in the automotive industry [2]. 3D printing has many different medical applications, such as bioprinting tissues and organs, building vascularized organs, the manufacture of customized implants, prostheses and models for surgical preparation, among others [3]. Many new applications have arisen as a result of recent advances in 3D printing techniques. Printed parts are used for manufacturing space instrumentation, for both prototypes and flying parts [1], for manufacturing cost-effective parts in the sports industry or for developing new Materials 2018, 11, 1532; doi:10.3390/ma11091532 www.mdpi.com/journal/materials. 3D printing has many different medical applications, such as bioprinting tissues and organs, building vascularized organs, the manufacture of customized implants, prostheses and models for surgical preparation, among others [3]. It is more cost-effective than other additive manufacturing techniques, and its lead times are short. It does not provide high dimensional precision, layer steps are usually observed on the part’s surface, causing the surfaces not to be smooth
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