Discipline: Technology and Engineering
Subcategory: Materials Science
Charles Baker - Alabama State University
Co-Author(s): Derrick Dean, Alabama State University, Montgomery, AL; Hanxiao Huang, Alabama State University, Montgomery, AL
Three-dimensional printing is greatly utilized in the production of 3D scaffolds with precise control of pore geometry, size and distribution. However, we are still posed with several obstacles that must be overcome to print scaffolds with complex structures and properties that provide adhesion, growth and proliferation. These include: the need for a broader range of materials that can be used as inks/ bioinks in the 3-D printing process and understanding the link between pore structure and cell response. The objective of this work is to investigate the processing-structure-property relationships of 3-dimensional cellulose acetate scaffolds for orthopedic applications including bone, articular cartilage and ligaments. Cellulose acetate was combined with acetone to yield concentrations of 20, 25 and 30 wt%, respectively. Mesh samples (32 x 32 mm) with varying pore sizes were 3D printed utilizing an EnvisonTec 3D Bioplotter equipped with a low temperature printing head. Glycerol (Fisher Scientific) was used as a rheology modifier as needed. In this study, pore sizes ranging from 40 to 576 ?m were printed and all samples contained four layers. TA Instruments HR-2 rheometer was utilized to characterize the rheology of samples used as inks and to conduct mechanical testing on the printed scaffolds. Rheology of the inks were conducted using a Peltier plate fixture equipped with a 40mm parallel plate. Examination of the low shear rate behavior indicates that viscosity increases with concentration, with a significant increase from 20 to 25 %. It was observed that the presence of glycerol in the 25% sample does not affect the low frequency viscosity; however, it dramatically decreases the viscosity as the shear rate increases. According to Poisueille?s law, which describes the ink flow from the extruder, smaller needles lead to higher resolution structures; however, the flow rate and print time is longer. This would require a higher pressure being applied to offset solidification of the printed layer, making adhesion of subsequent layers more difficult. We discovered that controlling the viscosity with a rheology modifier and size helps to achieve smaller pore sizes. Rheological studies show addition of a rheology modifier enhances the shear thinning behavior of the inks and consequently their printability. This promotes the printing of scaffolds with smaller pore sizes that would be unachievable without its incorporation in the inks. These findings will broaden the range of pore sizes and porosity attainable in 3D printed tissue scaffolds and provide more control over the mechanical properties and cell response.
References: 1. S. J. Stanley, Porous scaffold design for tissue engineering, Nat Mater. 2005 Jul;4(7):518-24.; 2. Zhen Cao, Ce Dou, and Shiwu Dong, Scaffolding Biomaterials for Cartilage Regeneration, Journal of Nanomaterials, Volume 2014 (2014).
Funder Acknowledgement(s): This study was supported by a grant from NSF/CBET 1510479 and CMMI-1548571 awarded to Derrick Dean PhD, Professor of Biomedical Engineering, Alabama State University, Montgomery, AL 36101.
Faculty Advisor: Derrick Dean, firstname.lastname@example.org
Role: I assisted in the fabrication of samples, as well as, initiating the various tests. In addition, I performed analyses of the test results and collaborated with professors to determine future goals.