Geometric and Inertial Properties of the Pig Head and Brain in an Anatomical Coordinate System.

Porcine models in injury biomechanics research often involve measuring head or brain kinematics. Translation of data from porcine models to other biomechanical models requires geometric and inertial properties of the pig head and brain, and a translationally relevant anatomical coordinate system (ACS). In this study, the head and brain mass, center of mass (CoM), and mass moments of inertia (MoI) were characterized, and an ACS was proposed for the pre-adolescent domestic pig. Density-calibrated computed tomography scans were obtained for the heads of eleven Large White × Landrace pigs (18-48 kg) and were segmented. An ACS with a porcine-equivalent Frankfort plane was defined using externally palpable landmarks (right/left frontal process of the zygomatic bone and zygomatic process of the frontal bone). The head and brain constituted 7.80 ± 0.79% and 0.33 ± 0.08% of the body mass, respectively. The head and brain CoMs were primarily ventral and caudal to the ACS origin, respectively. The mean head and brain principal MoI (in the ACS with origin at respective CoM) ranged from 61.7 to 109.7 kg cm2, and 0.2 to 0.6 kg cm2, respectively. These data may aid the comparison of head and brain kinematics/kinetics data and the translation between porcine and human injury models.

Printability and Cell Viability in Bioprinting Alginate Dialdehyde-Gelatin Scaffolds.

Three-dimensional (3D) bioprinting is a promising technique used to fabricate scaffolds from hydrogels with living cells. However, the printability of hydrogels in bioprinting has not been adequately studied. The aim of this study was to quantitatively characterize the printability and cell viability of alginate dialdehyde (ADA)-gelatin (Gel) hydrogels for bioprinting. ADA-Gel hydrogels of various concentrations were synthesized and characterized using Fourier transform infrared spectroscopy, along with rheological tests for measuring storage and loss moduli. Scaffolds (with an area of 11 × 11 mm) of 1, 2, and 13 layers were fabricated from ADA-Gel hydrogels using a 3D-bioplotter under printing conditions with and without the use of cross-linker, respectively, at room temperature and at 4 °C. Scaffolds were then quantitatively assessed in terms of the minimum printing pressure, quality of strands and pores, and structural integrity, which were combined together for the characterization of ADA-Gel printability. For the assessment of cell viability, scaffolds were bioprinted from ADA-Gel hydrogels with human umbilical vein endothelial cells (HUVECs) and rat Schwann cells and were then examined at day 7 with live/dead assay. HUVECs and Schwann cells were used as models to demonstrate biocompatibility for potential angiogenesis and nerve repair applications, respectively. Our results illustrated that ADA-Gel hydrogels with a loss tangent (ratio of loss modulus over storage modulus) between 0.24 and 0.28 could be printed in cross-linker with the best printability featured by uniform strands, square pores, and good structural integrity. Additionally, our results revealed that ADA-Gel hydrogels with an appropriate printability could maintain cell viability over 7 days. Combined together, this study presents a novel method to characterize the printability of hydrogels in bioprinting and illustrates that ADA-Gel hydrogels can be synthesized and bioprinted with good printability and cell viability, thus demonstrating their suitability for bioprinting scaffolds in tissue engineering applications.

Cortical porosity assessment in the distal radius: A comparison of HR-pQCT measures with Synchrotron-Radiation micro-CT-based measures.

OBJECTIVE: To determine the agreement between cortical porosity derived from high resolution peripheral quantitative computed tomography (HR-pQCT) (via standard threshold, mean density and density inhomogeneity methods) and synchrotron radiation micro-CT (SR-µCT) derived porosity at the distal radius. METHODS: We scanned 10 cadaveric radii (mean donor age: 79, SD 11 years) at the standard distal region using HR-pQCT and SR-µCT at voxel sizes of 82 µm and 17.7 µm, respectively. Common cortical regions were delineated for each specimen in both imaging modalities. HR-pQCT images were analyzed for cortical porosity using the following methods: Standard threshold, mean density, and density inhomogeneity (via recommended and optimized equations). We assessed agreement in porosity measures between HR-pQCT methods and SR-µCT by reporting predicted variance from linear regression and mean bias with limits of agreement (LOA). RESULTS: The standard threshold and mean density methods predicted 85% and 89% of variance and indicated underestimation (mean bias -9.1%, LOA -15.9% to -2.2%) and overestimation (10.4%, 4.6% to 16.2%) of porosity, respectively. The density inhomogeneity method with recommended equation predicted 89% of variance and mean bias of 14.9% (-4.3 to 34.2) with systematic over-estimation of porosity in more porous specimens. The density inhomogeneity method with optimized equation predicted 91% of variance without bias (0.0%, -5.3 to 5.2). CONCLUSION: HR-pQCT imaged porosity assessed with the density inhomogeneity method with optimized equation indicated the best agreement with SR-µCT derived porosity.