The overarching goal of this research work is to fabricate biocompatible, porous bone tissue scaffolds, incorporating patient-derived bone marrow mesenchymal stem cells (hBMSCs), for the treatment of osseous fractures, defects, and diseases. In pursuit of this goal, the objective of the work is to investigate the influence of consequential scaffold design factors as well as pneumatic micro-extrusion (PME) process parameters (i.e., layer height, layer width, infill density, and print speed) on the mechanical properties of fabricated bone tissue scaffolds. This work tests the following hypothesis: biocompatible, porous bone tissue scaffolds with tunable functional properties are additively fabricated using the PME process.

PME is a direct-write additive manufacturing method, which has emerged as a robust, high-resolution process for the fabrication of a broad spectrum of biological tissues and organs. In the PME process, a high-pressure flow (typically, compressed air) is injected into a cartridge (barrel), which contains a bioink material, resulting in pressure-driven material deposition on a free surface via a converging conical micro-capillary. In this study, PCL powder was loaded into the cartridge (as received), maintained at 120 °C. To ensure steady-state and uniform material transport in the PME process, the loaded PCL was kept in the heated barrel for three hours prior to material deposition. The flow pressure was set to 550 kPa (supplied by an oilless, rust-free air compressor). Laminar molten PCL flow was deposited on a glass surface (steadily and uniformly kept at 45 °C), using a 200 μm nozzle. A porous, cylindrical scaffold was designed (honeycomb-filled), having a diameter and height of 10 mm and 3 mm, respectively.

To investigate the effects of the design and process parameters, a series of factorial experiments were designed and conducted where print speed was varied at four levels in the range of 0.30-0.45 mm/s with 0.05 mm/s increments. In addition, similarly, layer height and layer width were changed at four levels in the range of 125-200 μm with 25μm increments. Finally, infill density was set at four levels in the range of 20-35% with 5% increments. As a result, 16 experimental runs were characterized, each replicated five times. Of each of the PME-fabricated samples, an image was acquired (both horizontally and vertically) using a high-resolution CCD camera. Illumination was provided by an LED ring light (being of a brightness in the range of 30,000-40,000 Lux as well as a color temperature of 6000 K). Subsequently, the acquired images were analyzed using in-house digital image processing algorithms, forwarded with the aim to characterize both the diameter and the height of the fabricated bone scaffolds. The veracity of the image-based measurements was corroborated, using offline caliper measurements. Furthermore, the compression properties of the fabricated bone scaffolds were measured using a compression testing machine; the samples were subjected to a compression load, applied with a velocity of 0.08 mm/s. Overall, the results of this study pave the way for future investigation of PME-deposited PCL scaffolds with optimal mechanical and morphological properties for incorporation of hBMSCs toward the treatment of osseous fractures and defects.


Investigation of the Effects of Design and Process Parameters on the Mechanical Properties of Biodegradable Bone Scaffolds, Fabricated Using Pneumatic Microextrusion Process

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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