Zhibing Zhang

Biocomposites prepared by alkaline phosphatase mediated mineralization of alginate microbeads

This study set out to develop a biomimetic scaffold by incorporating osteoinductive hydroxyapatite (HA) particles into a porous alginate gel matrix via a cell-friendly pathway. Two types of alginate/calcium phosphate (Alg/CP) composites were prepared through alkaline phosphatase (ALP) mediated mineralization and counter-diffusion precipitation. Structural characteristics were analyzed by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Thermal stability and mineral content were studied by means of thermogravimetric (TG) analysis. X-ray diffraction (XRD) and Rietveld refinement showed the presence of bone-like hydroxyapatite. Our studies suggested that the gradual nature of enzymatic process together with alginate matrices provide regulation of nanocrystalline hydroxyapatite formation. The ALP-mediated mineralization process has great advantages over counter-diffusion precipitation, providing homogenous mineral distributions, smaller crystal sizes, and increased apparent Youngs moduli, which creates a better structure for bone defect repair scaffolds.

Viscoelastic properties of mineralized alginate hydrogel beads

Alginate hydrogels have applications in biomedicine, ranging from delivery of cells and growth factors to wound management aids. However, they are mechanically soft and have shown little potential for the use in bone tissue engineering. Here, the viscoelastic properties of alginate hydrogel beads mineralized with calcium phosphate, both by a counter-diffusion (CD) and an enzymatic approach, are characterized by a micro-manipulation technique and mathematical modeling. Fabricated hydrogel materials have low mineral content (below 3xa0% of the total hydrogel mass, which corresponds to mineral content of up to 60xa0% of the dry mass) and low dry mass content (<5xa0%). For all samples compression and hold (relaxation after compression) data was collected and analyzed. The apparent Young’s modulus of the mineralized beads was estimated by the Hertz model (compression data) and was shown to increase up to threefold upon mineralization. The enzymatically mineralized beads showed higher apparent Young’s modulus compared to the ones mineralized by CD, even though the mineral content of the former was lower. Full compression–relaxation force–time profiles were analyzed using viscoelastic model. From this analysis, infinite and instantaneous Young’s moduli were determined. Similarly, enzymatic mineralized beads, showed higher instantaneous and infinite Young’s modulus, even if the degree of mineralization is lower then that achieved for CD method. This leads to the conclusion that both the degree of mineralization and the spatial distribution of mineral are important for the mechanical performance of the composite beads, which is in analogy to highly structured mineralized tissues found in many organisms.

An injectable scaffold based on crosslinked hyaluronic acid gel for tissue regeneration

Injectable scaffolds have great potential in specialised applications in regenerative medicine. In this study, hyaluronic acid hydrogels (HAGs) were prepared by crosslinking hyaluronic acid (HA) with 1,4-butanediol diglycidyl ether (BDDE). Applications of HAG as an injectable scaffold for regenerating functional tissues were proposed by matching its viscoelastic properties with those of biological tissues. The effect of BDDE concentration on different properties of HAGs was explored. Swelling properties, cross-sectional morphology, and BDDE residues of the resulting gels were investigated. Rheological properties of different HAGs were measured by monitoring their storage modulus (G′) and loss modulus (G′′) and compared with those of biological tissues. It was shown that HAGs (BDDE from 0.4 vol% to 1.0 vol%) possess great water absorbing capability with swelling ratios ranging from 99.7 to 78.9. The higher the concentration of the crosslinker used, the more rigid the resulting hydrogel, subsequently the lower the swelling ratio would be and the higher the G′ and G′′ values as well. Similar viscoelastic behaviors were found between HAGs and biological tissues, such as epidermis, dermis, articular cartilage and tooth germ. SEM revealed that HAG obtained at 0.4 vol% BDDE had pore diameters ranging from a few microns to around 100 μm with a high degree of interconnectivity. The feasibility of this HAG, as an injectable scaffold, to regenerate cartilage and dentin–pulp complex was then demonstrated using a preliminary subcutaneous microenvironment. The current study could be a reference to take account of how a crosslinked HA gel should be chosen for specific tissue regeneration.

Contact mechanics of the human finger pad under compressive loads

The coefficient of friction of most solid objects is independent of the applied normal force because of surface roughness. This behaviour is observed for a finger pad except at long contact times (greater than 10 s) against smooth impermeable surfaces such as glass when the coefficient increases with decreasing normal force by about a factor of five for the load range investigated here. This is clearly an advantage for some precision manipulation and grip tasks. Such normal force dependence is characteristic of smooth curved elastic bodies. It has been argued that the occlusion of moisture in the form of sweat plasticises the surface topographical features and their increased compliance allows flattening under an applied normal force, so that the surfaces of the fingerprint ridges are effectively smooth. While the normal force dependence of the friction is consistent with the theory of elastic frictional contacts, the gross deformation behaviour is not and, for commonly reported values of the Youngs modulus of stratum corneum, the deformation of the ridges should be negligible compared with the gross deformation of the finger pad even when fully occluded. This paper describes the development of a contact mechanics model that resolves these inconsistencies and is validated against experimental data.

Encapsulation of health-promoting ingredients: applications in foodstuffs

Abstract Many nutritional experts and food scientists are interested in developing functional foods containing bioactive agents and many of these health-promoting ingredients may benefit from nano/micro-encapsulation technology. Encapsulation has been proven useful to improve the physical and the chemical stability of bioactive agents, as well as their bioavailability and efficacy, enabling their incorporation into a wide range of formulations aimed to functional food production. There are several reviews concerning nano/micro-encapsulation techniques, but none are focused on the incorporation of the bioactive agents into food matrices. The aim of this paper was to investigate the development of microencapsulated food, taking into account the different bioactive ingredients, the variety of processes, techniques and coating materials that can be used for this purpose.

Effect of zinc oxide film morphologies on the formation of Shewanella putrefaciens biofilm

Zinc oxide (ZnO) films were prepared on aluminum substrate by a hydrothermal method to investigate the effect of their surface characteristics, including morphology and hydrophobicity, on the corresponding antibiofilm performance. The surface characteristics of the prepared ZnO films were examined by a comprehensive range of methodologies, suggesting that films of distinctive surface morphologies were successfully formed. Subsequently, their antibiofilm activities, using Shewanella putrefaciens as a model bacterium, were assessed. Surface measurements confirmed that the ZnO films equipped with a nanoscopic needlelike surface feature are more hydrophobic than those possessing densely packed microflakes. The reduced number of live cells and presence of biofilm, confirmed by optical and electron microscopy results, suggest that the former films possess an excellent antibiofilm performance. It is believed that the engineered nanoscopic needle feature might penetrate the cell membrane when they are in contact, allowing the effective substance of ZnO antibacterial ingredients to diffuse into the embedded bacteria. Furthermore, such surface characteristics might perturb the integrity of the cell membrane causing the intracellular substance is leaked from the cells. As such, the combinatorial effects of nanoscopic feature resulted in an inhibited growth of S. putrefaciens biofilm on ZnO film.

Novel polystyrene sulfonate–silica microspheres as a carrier of a water soluble inorganic salt (KCl) for its sustained release, via a dual-release mechanism

Herein we describe a novel type of organic–inorganic composite solid microsphere, comprised of polystyrene sulfonate and silica (PSS–SiO2), which has been synthesised from polystyrene sulfonic acid and tetraethyl orthosilicate. The microsphere can (i) encapsulate a low molar mass ( 48 hours) of the salt from the microspheres to an aqueous environment, which has hitherto not been possible. We propose a novel dual-release mechanism of the salt from the microspheres, which leads to the sustained release, and therefore has potential applicability for the controlled and prolonged release of other actives.

Biomechanical properties of human T cells in the process of activation based on diametric compression by micromanipulation

A crucial step in enabling adoptive T cell therapy is the isolation of antigen (Ag)-specific CD8+ T lymphocytes. Mechanical changes that accompany CD8+ T lymphocyte activation and migration from circulating blood across endothelial cells into target tissue, may be used as parameters for microfluidic sorting of activated CD8+ T cells. CD8+ T cells were activated in vitro using anti-CD3 for a total of 4 days, and samples of cells were mechanically tested on day 0 prior to activation and on day 2 and 4 post-activation using a micromanipulation technique. The diameter of activated CD8+ T cells was significantly larger than resting cells suggesting that activation was accompanied by an increase in cell volume. While the Youngs modulus value as determined by the force versus displacement data up to a nominal deformation of 10% decreased after activation, this may be due to the activation causing a weakening of the cell membrane and cytoskeleton. However, nominal rupture tension determined by compressing single cells to large deformations until rupture, decreased from day 0 to day 2, and then recovered on day 4 post-activation. This may be related to the mechanical properties of the cell nucleus. These novel data show unique biomechanical changes of activated CD8+ T cells which may be further exploited for the development of new microfluidic cell separation systems.

Coating of sodium percarbonate particles using water soluble materials in a fluidised bed to achieve delayed release in aqueous environment

Abstract Three coating materials, namely sodium sulphate, 1.6R and 2.35R sodium silicate, were respectively used to coat sodium percarbonate (SPC) particles in a fluidised bed coater to achieve its delayed release in aqueous environment. The size of SPC particles was measured using image analysis. The thickness and porosity of the shell materials were analysed using scanning electron microscopy (SEM) and helium pycnometry respectively. The rates of SPC release from uncoated and the coated particles were measured using an iodide molybdate titration method coupled with UV-vis spectrometry. The results indicate that sodium sulphate coating with an average thickness of 53 ± 9 μm only reduced the release rate of SPC as no delayed release was observed. In contrast, sodium silicate coating generated a significant delayed release. 1.6R sodium silicate coating with a thickness of 109 ± 8 μm delayed the release of SPC by approximate 60 s under a static condition. At the same condition, 2.35R sodium silicate coating with a thickness of 71 ± 10 μm delayed the release by approximately 7 min. When the coated SPC particles immersed in water were shaken using an orbital shaker at 150 rpm, the delayed time was reduced by 50% in comparison with the static condition. The 1.6R sodium silicate shell in solid phase transformed to gel-like structure during dissolution and the hydrodynamic forces generated in the shaker accelerated its dissolution. However, there was no significant change of 2.35R sodium silicate shell when the capsules were immersed in water under the static condition, and they broke into pieces in the shaker. For both 1.6R and 2.35R sodium silicate, the further increase in shell thickness increased their shell porosity, which facilitated the water penetration and thus resulted in no significant benefit to additional delay. Moreover, the thermal stability of SPC after coating was slightly improved and the flowability did not change significantly. This study demonstrates that a significant delay in release of SPC can be achieved using 2.35R sodium silicate as a coating material.