Portland cement for bone tissue engineering: Effects of processing and metakaolin blends

Enhancement of oriented cement-bonded boards' properties through CO2 curing

This study investigates the effects of CO2 curing on oriented cement-bonded boards. The boards comprised 35% and 45% (by mass) of strand-type particles of Eucalyptus spp. (8 × 2 × 0.1 cm) and 65% and 55% (by mass) of early high-strength Portland cement. To fabricate the boards, three layers of strands were arranged perpendicular to the previous layer, aiming for a target density of 1250 kg/m3, and the dimensions of the boards were 40 × 40 × 1 cm. The oriented cement-bonded boards underwent three different curing conditions: control, CO2 curing for 6 h, and 12 h, followed by curing in a saturated environment until the 28th day. The results indicated that CO2 curing increased the CaCO3 content in the boards, particularly when the curing period was longer (12 h). The physical and mechanical performance of the CO2-cured boards surpassed that of the control boards, with the modulus of rupture (MOR) increasing by 80% (6 h) and 84% (12 h) compared to the control. Scanning electron microscope investigations revealed that CO2 curing produced a denser matrix, leading to an improved bond between the strands and the matrix, resulting in enhanced technical performance. Based on these findings, this study suggests that CO2 curing can enhance the physical and mechanical properties of oriented cement-bonded boards, and a longer curing time (12 h) yielded superior performance.

Effect of Polymers on Behavior of Ultra-High-Strength Concrete

The development of ultra-high-performance concrete (UHPC) is still practically limited due to the scarcity of robust mixture designs and sustainable sources of local constituent materials. This study investigates the engineering characteristics of Styrene Butadiene Rubber (SBR) polymeric fiber-reinforced UHPC with partial substitution of cement at 0, 5 and 20 wt.% with latex polymer under steam and air curing techniques. The compressive and tensile strengths along with capillary water absorption and sulfate resistance were measured to evaluate the mechanical and durability properties. Scanning Electron Microscopy (SEM) was carried out to explore the microstructure development and hydration products in the designed mixtures under different curing regimes. The results indicated that the mixtures incorporating 20 wt.% SBR polymer achieved superior compressive strength at later ages. Additionally, the tensile strength of the polymeric UHPC without steel fibers and with 20% polymers was enhanced by 50%, which promotes the development of novel UHPC mixtures in which steel fibers could be partially replaced by polymer, while enhancing the tensile properties.

Early Intervention in Ischemic Tissue with Oxygen Nanocarriers Enables Successful Implementation of Restorative Cell Therapies

Background

Tissue ischemia contributes to necrosis and infection. While angiogenic cell therapies have emerged as a promising strategy against ischemia, current approaches to cell therapies face multiple hurdles. Recent advances in nuclear reprogramming could potentially overcome some of these limitations. However, under severely ischemic conditions necrosis could outpace reprogramming-based repair. As such, adjunctive measures are required to maintain a minimum level of tissue viability/activity for optimal response to restorative interventions.

Methods

Here we explored the combined use of polymerized hemoglobin (PolyHb)-based oxygen nanocarriers with Tissue Nano-Transfection (TNT)-driven restoration to develop tissue preservation/repair strategies that could potentially be used as a first line of care. Random-pattern cutaneous flaps were created in a mouse model of ischemic injury. PolyHbs with high and low oxygen affinity were synthesized and injected into the tissue flap at various timepoints of ischemic injury. The degree of tissue preservation was evaluated in terms of perfusion, oxygenation, and resulting necrosis. TNT was then used to deploy reprogramming-based vasculogenic cell therapies to the flaps via nanochannels. Reprogramming/repair outcomes were evaluated in terms of vascularity and necrosis.

Results

Flaps treated with PolyHbs exhibited a gradual decrease in necrosis as a function of time-to-intervention, with low oxygen affinity PolyHb showing the best outcomes. TNT-based intervention of the flap in combination with PolyHb successfully curtailed advanced necrosis compared to flaps treated with only PolyHb or TNT alone.

Conclusions

These results indicate that PolyHb and TNT technologies could potentially be synergistically deployed and used as early intervention measures to combat severe tissue ischemia.

Bioactive and biodegradable silica biomaterial for bone regeneration

Biosilica, a biocompatible, natural inorganic polymer that is formed by an enzymatic, silicatein-mediated reaction in siliceous sponges to build up their inorganic skeleton, has been shown to be morphogenetically active and to induce mineralization of human osteoblast-like cells (SaOS-2) in vitro. In the present study, we prepared beads (microspheres) by encapsulation of β-tricalcium phosphate [β-TCP], either alone (control) or supplemented with silica or silicatein, into the biodegradable copolymer poly(d,l-lactide-co-glycolide) [PLGA]. Under the conditions used, ≈5% β-TCP, ≈9% silica, and 0.32μg/mg of silicatein were entrapped into the PLGA microspheres (diameter≈800μm). Determination of the biocompatibility of the β-TCP microspheres, supplemented with silica or silicatein, revealed no toxicity in the MTT based cell viability assay using SaOS-2 cells. The adherence of SaOS-2 cells to the surface of silica-containing microspheres was higher than for microspheres, containing only β-TCP. In addition, the silica-containing β-TCP microspheres and even more pronounced, a 1:1 mixture of microspheres containing β-TCP and silica, and β-TCP and silicatein, were found to strongly enhance the mineral deposition by SaOS-2 cells. Using these microspheres, first animal experiments with silica/biosilica were performed in female, adult New Zealand White rabbits to study the effect of the inorganic polymer on bone regeneration in vivo. The microspheres were implanted into 5mm thick holes, drilled into the femur of the animals, applying a bilateral comparison study design (3 test groups with 4-8 animals each). The control implant on one of the two hind legs contained microspheres with only β-TCP, while the test implant on the corresponding leg consisted either of microspheres containing β-TCP and silica, or a 1:1 mixture of microspheres, supplemented with β-TCP and silica, and β-TCP and silicatein. The results revealed that tissue/bone sections of silica containing implants and implants, composed of a 1:1 mixture of silica-containing microspheres and silicatein-containing microspheres, show an enhanced regeneration of bone tissue around the microspheres, compared to the control implants containing only β-TCP. The formation of new bone induced by the microspheres is also evident from measurements of the stiffness/reduced Young's modulus of the regenerated bone tissue. The reduced Young's modulus of the regenerating bone tissue around the implants was markedly higher for the silica-containing microspheres (1.1MPa), and even more for the 1:1 mixture of the silica- and silicatein-containing microspheres (1.4MPa), compared to the β-TCP microsphere controls (0.4MPa). We propose that based on their morphogenetic activity on bone-forming cells in vitro and the results of the animal experiments presented here, silica/biosilica-based scaffolds are promising materials for bone repair/regeneration.

Reinforced Portland cement porous scaffolds for load-bearing bone tissue engineering applications

Modified Portland cement porous scaffolds with suitable characteristics for load-bearing bone tissue engineering applications were manufactured by combining the particulate leaching and foaming methods. Non-crosslinked polydimethylsiloxane was evaluated as a potential reinforcing material. The scaffolds presented average porosities between 70 and 80% with mean pore sizes ranging from 300 μm up to 5.0 mm. Non-reinforced scaffolds presented compressive strengths and elastic modulus values of 2.6 and 245 MPa, respectively, whereas reinforced scaffolds exhibited 4.2 and 443 MPa, respectively, an increase of ∼62 and 80%. Portland cement scaffolds supported human osteoblast-like cell adhesion, spreading, and propagation (t = 1-28 days). Cell metabolism and alkaline phosphatase activity were found to be enhanced at longer culture intervals (t ≥ 14 days). These results suggest the possibility of obtaining strong and biocompatible scaffolds for bone repair applications from inexpensive, yet technologically advanced materials such as Portland cement.