Category: Manufacturing and Bioprocessing
Purpose: The goal of this study is to investigate how modification of 3D printed calcium phosphate cement scaffolds can enhance their ability to regenerate bone upon implantation into defect sites. Specifically, the method of mineralization and treatment after mineralization can impact the surface morphology of the scaffolds, potentially impacting the ability of cells to adhere to the scaffolds and begin the regenerative processes of resorbing the scaffold and producing new bone. Additionally, a gene therapy capability can be granted to the scaffolds by incorporating reagents that can transfect local cells with genes of interest. The resulting gene-activated matrices can assist with the regeneration of bone by inducing production of regenerative growth factors over an extended period. This technique circumvents stability and dose issues that similar protein-based approaches must face, the release of transfection reagents can be controlled with release systems such as nanoparticles and diffusion from the scaffold itself.
Methods: Cylindrical scaffolds 7.5mm in width and 1mm in height were printed from a calcium phosphate cement in an oil-based carrier fluid. The scaffolds were then mineralized via immersion in water or exposure to water vapor in a highly humid environment for 3 days. Some vapor-mineralized scaffolds were then immersed in water or simulated body fluid for an additional 3 days. The resulting scaffolds were pre-incubated in complete DMEM growth medium for 24 hours, then seeded with HEK 293T cells and allowed to incubate for 4 hours. The scaffolds were then fixed, dehydrated, and imaged with scanning electron microscopy.
Results: The differently treated scaffolds showed differing surface morphology, with the “water only” scaffolds having the highest apparent surface roughness while the “vapor only” scaffolds have the lowest. Cells appeared to adhere to all scaffolds, though the number of cells adhered was so low that relative adherence could not be accurately quantified. The “water only” scaffolds showed large cracks throughout the strands of the scaffold, whereas the other scaffolds did not.
Conclusion: The data shown here demonstrate the morphological differences in scaffold surface upon differing mineralization and post-treatment protocols. These crystal structures may impact the adherence of cells by having differing surface roughness. Importantly, a surface roughness was able to be induced on scaffolds mineralized with vapor. This could grant better adherence while also avoiding the cracking in the scaffold seen with water mineralization that could lead to reduced strength of the scaffold. Future work will investigate sequential mineralization to induce sequential release of transfecting reagents to create a scaffold with high surface roughness, high mechanical strength, and gene therapy capabilities.
Timothy Acri– Graduate Student, University of Iowa, Iowa City, Iowa
Jaidev Chakka– Post-Doctorate Researcher, University of Iowa, Iowa City, Iowa
Satheesh Elangovan– Professor, College of Dentistry, University of Iowa, Iowa City, Iowa
Aliasger Salem– Professor, College of Pharmacy, University of Iowa, Iowa City, Iowa