Calculation of stresses on 3D scaffolds fabricated using extrusion-based bioprinting using a semi-analytical approach.

The scaffold is essential to tissue engineering. In particular, the mechanical property of scaffolds has a significant impact on the success rate of regeneration. While numerous techniques exist for measuring mechanical properties, Compression test, three-point bending test, and nano-indentation test are the most common. Nevertheless, the mechanical property of porous structures cannot be accurately measured by previous testing methods. Combining superposition principles with the Flamant solution, this study developed semi-analytical solutions. Through compression testing and FEM simulation, the semi-analytical solution was fully validated. The solution can calculate not only the maximum stress of layer-by-layer construction of complex 3D scaffolds, but also the maximum load-bearing capacity if the mechanical property of the material is known.

Biomechanical model of cells probing the myosin-II-independent mechanosensing mechanism.

Mechanosensing of cells to extracellular matrix (ECM) is highly active and plays a crucial role in various physiological processes. Growing numbers of studies provide evidence that cell sensitivity to ECM stiffness is a complex stress-strain feedback process. However, the mechanisms that rule this process are still not fully known. Here, an alternative mechanosensing scheme of cells, which is different from the previous myosin-II-based mechanisms, is proposed by employing the tension in cortical cytoskeletons (CSKs) as a force module to probe the substrate. The molecular mechanotransduction from cortical CSKs, through actin filaments and focal adhesions, and finally to the substrate, is mechanically modeled to scale the dynamic traction forces of cells. The developed model captures the characteristic spread of cells with respect to ECM stiffness whereby the spread is fully developed on a stiff substrate but not on a soft one. Furthermore, durotactic migration of cells on an elastic-gradient substrate is successfully modeled by the current method. The cells are concluded to migrate, actuated by the polarized traction forces from the stiffness gradient of the substrate and the stiffness matching between cells and substrate. Finally, the cells are proposed to actively target the preferred substrate by following a rule of mechanical matching between cells and substrate. This study provides a theoretical tool to advance our knowledge regarding the passive mechanical properties and the active sensing of cells, and further promotes the discovery of mechanosensing mechanisms as well as the material design for embryonic development and tissue homeostasis.

Current Advances in 3D Bioprinting Technology and Its Applications for Tissue Engineering.

Three-dimensional (3D) bioprinting technology has emerged as a powerful biofabrication platform for tissue engineering because of its ability to engineer living cells and biomaterial-based 3D objects. Over the last few decades, droplet-based, extrusion-based, and laser-assisted bioprinters have been developed to fulfill certain requirements in terms of resolution, cell viability, cell density, etc. Simultaneously, various bio-inks based on natural-synthetic biomaterials have been developed and applied for successful tissue regeneration. To engineer more realistic artificial tissues/organs, mixtures of bio-inks with various recipes have also been developed. Taken together, this review describes the fundamental characteristics of the existing bioprinters and bio-inks that have been currently developed, followed by their advantages and disadvantages. Finally, various tissue engineering applications using 3D bioprinting are briefly introduced.

Fabrication of a Polycaprolactone/Alginate Bipartite Hybrid Scaffold for Osteochondral Tissue Using a Three-Dimensional Bioprinting System.

Osteochondral defects, including damage to both the articular cartilage and the subchondral bone, are challenging to repair. Although many technological advancements have been made in recent years, there are technical difficulties in the engineering of cartilage and bone layers, simultaneously. Moreover, there is a great need for a valuable in vitro platform enabling the assessment of osteochondral tissues to reduce pre-operative risk. Three-dimensional (3D) bioprinting systems may be a promising approach for fabricating human tissues and organs. Here, we aimed to develop a polycaprolactone (PCL)/alginate bipartite hybrid scaffold using a multihead 3D bioprinting system. The hybrid scaffold was composed of PCL, which could improve the mechanical properties of the construct, and alginate, encapsulating progenitor cells that could differentiate into cartilage and bone. To differentiate the bipartite hybrid scaffold into osteochondral tissue, a polydimethylsiloxane coculture system for osteochondral tissue (PCSOT) was designed and developed. Based on evaluation of the biological performance of the novel hybrid scaffold, the PCL/alginate bipartite scaffold was successfully fabricated; importantly, our findings suggest that this PCSOT system may be applicable as an in vitro platform for osteochondral tissue engineering.

Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty - A simulation study.

BACKGROUND: We studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations. METHODS: Using a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion. FINDINGS: Change in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level. INTERPRETATION: 135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.