INVESTIGATION OF THE EFFECTS OF DESIGN AND PROCESS PARAMETERS ON THE MECHANICAL PROPERTIES OF BIODEGRADABLE BONE SCAFFOLDS, FABRICATED USING PNEUMATIC MICROEXTRUSION PROCESS

Pneumatic micro-extrusion (PME) is a direct-write additive manufacturing process, which has emerged as a robust, high-resolution method for the fabrication of a broad spectrum of biological tissues and organs. In the PME process, a high-pressure flow is injected into a cartridge, 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, maintained at 120 degrees C. The flow pressure was set to 550 kPa. Laminar molten PCL flow was deposited on a glass surface (steadily and uniformly kept at 45 degrees C), using a 200 mu m 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 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 mu m with 25 mu m increments. Finally, infill density was set at four levels in the range of 0.20-0.35 with 5% increments. As a result, 16 experimental runs were characterized, each replicated four 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.