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Freeze-FRESH: A 3D Printing Technique to Produce Biomaterial Scaffolds with Hierarchical Porosity.

ABSTRACT: Tissues are organized in hierarchical structures comprised of nanoscale, microscale, and macroscale features. Incorporating hierarchical structures into biomaterial scaffolds may enable better resemblance of native tissue structures and improve cell interaction, but it is challenging to produce such scaffolds using a single conventional scaffold production technique. We developed the Freeze-FRESH (FF) technique that combines FRESH 3D printing (3DP) and freeze-casting to produce 3D printed scaffolds with microscale pores in the struts. FF scaffolds were produced by extrusion 3DP using a support bath at room temperature, followed by freezing and lyophilization, then the FF scaffolds were recovered from the bath and crosslinked. The FF scaffolds had a hierarchical pore structure from the combination of microscale pores throughout the scaffold struts and macroscale pores in the printed design, while control scaffolds had only macroscale pores. FF scaffolds frozen at -20 °C and -80 °C had similar pore sizes, due to freezing in the support bath. The -20 °C and -80 °C FF scaffolds had porous struts with 63.55% ± 2.59% and 56.72% ± 13.17% strut porosity, respectively, while control scaffolds had a strut porosity of 3.15% ± 2.20%. The -20 °C and -80 °C FF scaffolds were softer than control scaffolds: they had pore wall stiffness of 0.17 ± 0.06 MPa and 0.23 ± 0.05 MPa, respectively, compared to 1.31 ± 0.39 MPa for the control. The FF scaffolds had increased resilience in bending compared with control. FF scaffolds supported MDA-MB-231 cell growth and had significantly greater cell numbers than control scaffolds. Cells formed clusters on the porous struts of FF scaffolds and had similar morphologies as the freeze cast scaffolds. The FF technique successfully introduced microscale porosity into the 3DP scaffold struts to produce hierarchical pore structures that enhanced MDA-MB-231 growth.

SUBMITTER: Wang Z

PROVIDER: S-EPMC7013579 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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Freeze-FRESH: A 3D Printing Technique to Produce Biomaterial Scaffolds with Hierarchical Porosity.

Wang Zi Z Florczyk Stephen J SJ

Materials (Basel, Switzerland) 20200112 2

Tissues are organized in hierarchical structures comprised of nanoscale, microscale, and macroscale features. Incorporating hierarchical structures into biomaterial scaffolds may enable better resemblance of native tissue structures and improve cell interaction, but it is challenging to produce such scaffolds using a single conventional scaffold production technique. We developed the Freeze-FRESH (FF) technique that combines FRESH 3D printing (3DP) and freeze-casting to produce 3D printed scaffo ...[more]

PMID: 31940933

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Project description: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.

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Freeze-FRESH: A 3D Printing Technique to Produce Biomaterial Scaffolds with Hierarchical Porosity.

Publications

Freeze-FRESH: A 3D Printing Technique to Produce Biomaterial Scaffolds with Hierarchical Porosity.

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