Micro-Structured Patches for Dermal Regeneration Obtained via Electrophoretic Replica Deposition

Artificial substrates supporting the healing of skin wounds require specific structural and chemical architectures that promote a recapitulation of the complexity of the native organ. Bottom-up fabrication technologies are emerging as effective strategies to fine tune biochemical, morphological, and structural features intended for regenerative applications. Here, we proposed an electrophoretic replica deposition (EPrD) approach to realize chitosan three-dimensional structures specifically designed to treat patients with serious cutaneous damages or losses. The EPrD process has been optimized to consistently obtain random porosity vs. hierarchical lattice structures, showing mechanical properties in the range of skin tissue (E = 0.2–20 MPa). The obtained patches were tested in vivo via a one-stage grafting procedure in a full thickness skin wound rat model. Chitosan patches showed no adverse reactions throughout the experimental period (14 days). Hair follicles and sebaceous glands were observed in histological sections, indicating the regeneration of a thin epidermal layer with more skin appendages. Immunohistochemistry results demonstrated that keratin 10 was mostly expressed in basal and suprabasal layers, like normal skin, in structures with random porosity and with smaller lattice structures. The obtained results show the potential of EPrD to innovate the design of artificial substrates in skin healing therapies.

Variant Porosity Pebble Bed Reactor Core Thermal Hydraulic Simulation

Spherical fuel elements are distributed randomly in the pebble bed reactor core and helium flow through the pebble bed to remove nuclear reaction heat. Pebble bed reactor core is usually treated as a uniform porous media flow in thermal hydraulic research. However the porosity distribution is nonuniform and the porosity near the wall increase sharply. A new random model is developed in this paper to investigate thermal hydraulic characteristics of pebble bed reactor core. Porosity assumption is based on porosity measurement of other research. Porosity simulation is divided into three parts according to the distance from wall. In the center of core, porosity is assumed to obey normal distribution, where average porosity is from the experimental relation based on statistical results. The mean and standard deviation of porosity distribution near the wall will increase because of the wall effect, where the distance from the wall is about three times of fuel ball’s diameter. The third part is zone from three times to five times of ball’s diameter departed from the wall. The wall effect of this zone is between center and the wall zone. Based on above assumption, a random porosity simulation is completed to apply in this research. COMSOL Multiphysics 3.5a software is used in this research. COMSOL Multiphysics are a calculation platform using proven Finite Elements Methods (FEM). In this research, Brinkman equation for porous media flow is applied in the simulation. Non-thermal Balance model is used in local heat transfer research between gas and pebble bed. A geometry model is built to simulate HTR-10. Temperature profile of variant porosity is gained from stationary analysis and comparison with uniform porosity is also discussed in the paper. For transient analysis, four cases simulation is carried out in the research. Case 1 and 2 simulate heat transfer phenomena with forced cooling system and with passive cooling system after reactor shut down. Way-Wigner-curve is used in Case 1 and Case 2 to simulate decay heat in the calculation. Case 3 and Case 4 simulate ATWS phenomena with natural convection and without natural convection system when blower is trip off in normal operation. Simulation results also are compared with some ATWS experiments and some discussion is done in the paper. From the results, it can be seen that random porosity will affect temperature distribution near the wall and make outlet temperature non-uniform greatly. The maximum temperature of variant porosity is much greater than the maximum temperature of uniform porosity at the same condition. Transient analyses of variant model show that passive cooling system can remove residual heat even in accident conditions when the blower trip off whether reactor shut down or not and the analyses results correspond substantially with experimental results. In general, variant porosity should be considered in the thermal hydraulic research of pebble bed reactor core. Variant porosity model can provide good prediction of heat transfer phenomena than uniform porosity model. Especially it can explain some transient analysis results.

Strong Biomimetic Hydroxyapatite Scaffolds

Despite extensive efforts in the development of fabrication methods to prepare porous ceramic scaffolds for osseous tissue regeneration, all porous materials have a fundamental limitation- the inherent lack of strength associated with porosity. Shells (nacre), tooth and bone are frequently used as examples for how nature achieves strong and tough materials made out of weak components. So, the unresolved engineering dilemma is how to create a scaffold that is both porous and strong. The objective of this study was to mimic the architecture of natural materials in order to create a new generation of strong hydroxyapatite-based porous scaffolds. The porous inorganic scaffolds were fabricated by the controlled freezing of water-based hydroxyapatite (HA) slurries. The scaffolds obtained by this process have a lamellar architecture that exhibits similarities with the meso- and micro- structure of the inorganic component of nacre. Compressive strengths of 20 MPa were measured for lamellar scaffolds with densities of 32%, significantly better than for the HA with random porosity. In addition, the lamellar materials exhibit gradual fracture unlike conventional porous HA scaffolds. These biomimetic scaffolds could be the basis for a new generation of porous and composite biomaterials.