Solid-state supercritical CO2 foaming of PCL and PCL-HA nano-composite: Effect of composition, thermal history and foaming process on foam pore structure

In this work we investigated the solid-state supercritical CO₂ (scCO₂) foaming of poly(?-caprolactone) (PCL), a semi-crystalline, biodegradable polyester, and PCL loaded with 5 wt% of hydroxyapatite (HA) nano-particles.In order to investigate the effect of the thermal history and eventual residue of the crystalline phase on the pore structure of the foams, samples were subjected to three different cooling protocols from the melt, and subsequently foamed by using scCO₂ as blowing agent. The foaming process was performed in the 37-40 °C temperature range, melting point of PCL being 60 °C. The saturation pressure, in the range from 10 to 20 MPa, and the foaming time, from 2 to 900 s, were modulated in order to control the final morphology, porosity and pore structure of the foams and, possibly, to amplify the original differences among the different samples.The results of this study demonstrated that by the scCO₂ foaming it was possible to produce PCL and PCL-HA foams with homogeneous morphologies at relatively low temperatures. Furthermore, by the appropriate combination of materials properties and foaming parameters, we prepared foams with porosities in the 55-85% range, mean pore size from 40 to 250 μm and pore density from 10⁵ to 10⁸ pore/cm³. Finally, we also proposed a two-step depressurization foaming process for the design of bi-modal and highly interconnected foams suitable as scaffolds for tissue engineering.     

Porous β-Ca2SiO4 ceramic scaffolds for bone tissue engineering: In vitro and in vivo characterization

The biodegradable ceramic scaffolds with desirable pore size, porosity and mechanical properties play a crucial role in bone tissue engineering and bone transplantation. A novel porous β-dicalcium silicate (β-Ca₂SiO₄) ceramic scaffold was prepared by sintering the green body consisting of CaCO₃ and SiO₂ at 1300 °C, which generated interconnected pore network with proper pore size of about 300 μm and high compressive strength (28.13±5.37–10.36±0.83 MPa) following the porosity from 53.54±5.37% to 71.44±0.83%. Porous β-Ca₂SiO₄ ceramic scaffolds displayed a good biocompatibility, since human osteoblast-like MG-63 cells and goat bone mesenchymal stem cells (BMSCs) proliferated continuously on the scaffolds after 7 d culture. The porous β-Ca₂SiO₄ ceramic scaffolds revealed well apatite-forming ability when incubated in the simulated body fluid (SBF). According to the histological test, the degradation of porous β-Ca₂SiO₄ ceramic scaffolds and the new bone tissue generation in vivo were observed following 9 weeks implantation in nude mice. These results suggested that the porous β-Ca₂SiO₄ ceramic scaffolds could be potentially applied in bone tissue engineering.     

Topological interlocking and damage mechanisms in periodic Ti2AlC-Al building block composites

Ceramic Ti₂AlC building blocks of 4 × 1.24 × 1.24 mm³ size were prepared by injection molding and assembled to brick-and-mortar structures with tetragonal, monoclinic and triclinic unit cells. The single building blocks were bonded with an Al-loaded polysiloxane adhesive, which was afterwards pyrolized. Afterwards the 3D-assemblies were infiltrated with an Al-melt to fabricate dense 0–3 ceramic-metal composites. The influence of the unit cell of the resulting Ti₂AlC-Al composites was investigated regarding the mechanical properties and damage mechanisms in bending tests. The developed near-net shape fabrication process shows great potential to manufacture structured ceramic-metal composites with high toughness and complex shape. Due to their ductile behavior scaffold applications are possible. The calculated initial fracture toughness of monolithic Ti₂AlC could be improved from 5.0 MPa m^0.5 to 14.5 MPa m^0.5 for the monoclinic assembly and 14.7 MPa m^0.5 for the triclinic assembly, corresponding to an increase of 191%.     

Understanding cell-extracellular matrix interactions for topology-guided tissue regeneration

Tissues are made up of cells and the extracellular matrix (ECM) which surrounds them. These cells and tissues are actively adaptable to enduring significant stress that occurs in daily life. This astonishing mechanical stress develops due to the interaction between the live cells and the non-living ECM. Cells in the matrix microenvironment can sense the signals and forces produced and initiate a signaling cascade that plays a crucial role in the body’s normal functioning and influences various properties of the native cells, including growth, proliferation, and differentiation. However, the matrix’s characteristic features also impact the repair and regeneration of the damaged tissues. The current study reviewed how the cell-ECM interaction regulates cellular behavior and physicochemical properties. Herein, we have described the response of cells to mechanical stresses, the importance of substrate stiffness and geometry in tissue regeneration, and the development of scaffolds to mimic the nature of native ECM in 3D for tissue engineering applications has also been discussed. Finally, the study summarizes the conclusions and promising prospects based on the cell-ECM interplay.     

Numerical study on the abrasive wear of screw flights considering the scaffolding near the bustle pipe zone in a COREX shaft furnace

Scaffolding near the bustle pipe zone is a common problem in the operation of the COREX shaft furnace. To study the asymmetrical abrasive wear of screw flights in the presence of scaffolding, a three-dimensional COREX shaft furnace model with two representative locations of scaffolding is established based on the Discrete Element Method. Two different structures of the screw are investigated and the abrasive wear is calculated using Archard wear equation. The results show that the maximum abrasive wear of the screw flights occurs on the opposite side of the scaffold. The abrasive wear of screw flights is greater when the scaffold is located directly above the middle of two adjacent screws than above a certain screw. The abrasive wear of equidistant screw flights is about twice the modified screw under the same scaffold condition. The findings of this study provide a theoretical basis for the optimization of the COREX shaft furnace.     

Effects of the methyl methacrylate addition,polymerization temperature and time on the MBG@PMMA core-shell structure and its application as addition in electrospun composite fiber bioscaffold

Mesoporous bioactive glass (MBG) possesses a high specific surface area and excellent biocompatibility making it a promising biomaterial. In the present study, poly(methyl methacrylate) (PMMA) was coated on MBG to obtain a MBG@PMMA core-shell structure to further expand the potential applications of MBG. Changes in the MMA to MBG ratio, polymerization temperature and time were investigated to determine their effects on the core-shell structure. The as-prepared core-shell powders were evaluated using scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy to determine the optimal core-shell structure for electrospinning application. Electrospun composite fiber scaffolds prepared by adding MBG with or without an optimized PMMA shell were examined through microstructural observation, mechanical testing, Raman spectroscopy, and in vitro bioactivity evaluation. Experimental results showed that optimized MBG@PMMA core-shell powder was prepared using MMA: MBG = 3: 1, with polymerization at 70 °C for 4 h. The spherical core-shell powder exhibited a relatively smooth surface and the flake- or cotton-like shell structure was beneficial to electrospinning. Electrospun composite fiber scaffold prepared using MBG@PMMA powder exhibited superior mechanical performance and excellent biocompatibility compared to its shell-less MBG counterpart.     

The effect of filler content on mechanical properties and cell response of elastomeric PGS/apatite foam scaffolds

Poly(glycerol sebacate) (PGS) is a novel polymeric material intended for applications in tissue engineering (TE). This study involves synthesizing the PGS prepolymer (pPGS) and subsequent manufacturing of porous PGS-based scaffolds with an addition of hydroxyapatite (HAp) by means of thermally induced phase separation followed by thermal cross-linking and salt-leaching (TIPS-TCL-SL). The study aims to investigate the effect of the apatite filler content on properties and morphology of porous PGS/HAp scaffolds. The emphasis is put on the mechanical behavior of the material characterized by means of compression tests and dynamic thermal mechanical analysis (DMTA). In addition to the reference polymer scaffold, the composites with filler contents of 10, 20 and 30 wt% have been examined. Our research revealed that the HAp content does not affect the mechanical properties in a directly proportional manner. The 30 wt% addition of HAp resulted in frayed structure and decrease in the mechanical parameters in comparison to other tested specimens. On the other hand, an addition of 10% did not sufficiently boost the properties. Therefore, a 20% addition of HAp was concluded to have superior mechanical properties in comparison to other analyzed specimens. A similar relationship results from the DMTA studies. Moreover, the strain sweep and frequency sweep tests confirmed the stability of the mechanical parameters in various conditions, as well as the elastomeric nature of the materials. Finally, the material did not exhibit cytotoxicity against standard L929 fibroblasts and cells readily populated the scaffolds.