Review: the latest advances in biomedical applications of chitosan hydrogel as a powerful natural structure with eye-catching biological properties

Journal of Materials Science - Chitosan is one of the natural cationic polymers with unique properties such as non-toxicity, biodegradability, biocompatibility, environmentally friendly that has...     

Thermal-Disrupting Interface Mitigates Intercellular Cohesion Loss for Accurate Topical Antibacterial Therapy

Bacterial infections remain a leading threat to global health because of the misuse of antibiotics and the rise in drug-resistant pathogens. Although several strategies such as photothermal therapy and magneto-thermal therapy can suppress bacterial infections, excessive heat often damages host cells and lengthens the healing time. Here, a localized thermal managing strategy, thermal-disrupting interface induced mitigation (TRIM), is reported, to minimize intercellular cohesion loss for accurate antibacterial therapy. The TRIM dressing film is composed of alternative microscale arrangement of heat-responsive hydrogel regions and mechanical support regions, which enables the surface microtopography to have a significant effect on disrupting bacterial colonization upon infrared irradiation. The regulation of the interfacial contact to the attached skin confines the produced heat and minimizes the risk of skin damage during thermoablation. Quantitative mechanobiology studies demonstrate the TRIM dressing film with a critical dimension for surface features plays a critical role in maintaining intercellular cohesion of the epidermis during photothermal therapy. Finally, endowing wound dressing with the TRIM effect via in vivo studies in S. aureus infected mice demonstrates a promising strategy for mitigating the side effects of photothermal therapy against a wide spectrum of bacterial infections, promoting future biointerface design for antibacterial therapy.     

Controllable Synthesis of NiSe<Subscript>2</Subscript> Nanostructures via Hydrothermal Process for Photocatalytic and Solar Cell Applications

This paper reports on the synthesis of rice-like NiSe₂ nanoparticles via a simple hydrothermal method by employing [bis(2-hydoxyacetophenato)nickle(II)], [Ni(HAP)₂], as a novel nickel precursor. Effect of nickel source on morphology and size of nanostructures was also investigated. Moreover, the as-synthesized NiSe₂ nanostructures were utilized as the photocatalyst for the degradation of methylene blue (MB) and as the counter electrode in dye-sensitized solar cells. The results showed that structures size and morphology have salient effect on solar cells and using rice-like NiSe₂ nanoparticles leads to an increase in DSSCs efficiency compared to agglomerated sphere-like particles from 6.04 to 8.99?% (~49?% improvement).     

A fast dual boundary element method for 3D anisotropic crack problems

In the present paper a fast solver for dual boundary element analysis of 3D anisotropic crack problems is formulated, implemented and tested. The fast solver is based on the use of hierarchical matrices for the representation of the collocation matrix. The admissible low rank blocks are computed by adaptive cross approximation (ACA). The performance of ACA against the accuracy of the adopted computational scheme for the evaluation of the anisotropic kernels is investigated, focusing on the balance between the kernel representation accuracy and the accuracy required for ACA. The system solution is computed by a preconditioned GMRES and the preconditioner is built exploiting the hierarchical arithmetic and taking full advantage of the hierarchical format. The effectiveness of the proposed technique for anisotropic crack problems has been numerically demonstrated, highlighting the accuracy as well as the significant reduction in memory storage and analysis time. In particular, it has been numerically shown that the computational cost grows almost linearly with the number of degrees of freedom, obtaining up to solution speedups of order 10 for systems of order 10⁴. Moreover, the sensitivity of the performance of the numerical scheme to materials with different degrees of anisotropy has been assessed. Copyright © 2009 John Wiley & Sons, Ltd.     

BEM Implementation of the Energy Domain Integral for the Elastoplastic Analysis of 3D Fracture Problems

An Elastoplastic Dual Boundary Element Method (EPDBEM) for the evaluation of the J-integral in three-dimensional fracture problems is presented in this paper. The point-wise J-integral is evaluated along crack fronts using the Energy Domain Integral (EDI) methodology. The domain expression of the EDI is naturally compatible with the EPDBEM, allowing to embed the computation of the J-integral within the boundary element formulation in such a way that it only accounts for a small additional computational effort. The accuracy of the proposed formulation is demonstrated by solving problems with straight and curved crack fronts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of thiolated carboxymethyl chitosan-graft-cyclodextrin nanoparticles as a drug delivery vehicle for albendazole

A new strategy for the synthesis of thiolated carboxymethyl chitosan-g-cyclodextrin nanoparticles by an ionic-gelation method is presented. The synthetic approach was based on the utilization of 1,6-hexamethylene diisocyanate during cyclodextrin grafting onto carboxymethyl chitosan. The use of the 1,6-hexamethylene diisocyanate resulted in reactions between cyclodextrin and active sites at the C₆-position of chitosan, and preserved amino groups of chitosan for subsequent reactions with thioglycolic acid, as the thiolating agent, and tripolyphosphate, as the gelling counterion. Various methods such as scanning electron microscopy, rheology and in vitro release studies were employed to exhibit significant features of the nanoparticles for mucosal albendazole delivery applications. It was found that the thiolated carboxymethyl chitosan-g-cyclodextrin nanoparticles prepared using an aqueous solution containing 1 wt% of tripolyphosphate and having 115.65 (μmol/g polymer) of grafted thiol groups show both the highest mucoadhesive properties and the highest albendazole entrapment efficiency. The latter was confirmed theoretically by calculating the enthalpy of mixing of albendazole in the above thiolated chitosan polymer.     

Boundary element analysis of flat cracked panels with adhesively bonded patches

Adhesively bonded patch repairs for cracked finite sheets are analysed by the boundary element method. The interaction between the plate and the patch on a repaired sheet is modelled as a distribution of forces which include in-plane, out-of-plane and two moment body forces. The coupled boundary integral formulations of shear deformable plate (Mindlin theory) and two-dimensional plane stress elasticity are presented. Stress intensity factors, three for the bending problem and two for the membrane problem, are evaluated from crack opening displacements. Several examples are presented to demonstrate the accuracy and efficiency of the proposed method. Comparison with two-dimensional solutions demonstrate the significance of the bending loads on the stress intensity factors.     

Differences between Human and Mouse IgM Fc Receptor (FcµR)

Both non-immune “natural” and antigen-induced “immune” IgM are important for protection against pathogens and for regulation of immune responses to self-antigens. Since the bona fide IgM Fc receptor (FcµR) was identified in humans by a functional cloning strategy in 2009, the roles of FcµR in these IgM effector functions have begun to be explored. In this short essay, we describe the differences between human and mouse FcµRs in terms of their identification processes, cellular distributions and ligand binding activities with emphasis on our recent findings from the mutational analysis of human FcµR. We have identified at least three sites of human FcµR, i.e., Asn66 in the CDR2, Lys79 to Arg83 in the DE loop and Asn109 in the CDR3, responsible for its constitutive IgM-ligand binding. Results of computational structural modeling analysis are consistent with these mutational data and a model of the ligand binding, Ig-like domain of human FcµR is proposed. Serendipitously, substitution of Glu41 and Met42 in the CDR1 of human FcµR with mouse equivalents Gln and Leu, either single or more prominently in combination, enhances both the receptor expression and IgM binding. These findings would help in the future development of preventive and therapeutic interventions targeting FcµR.     

THE ANALYSIS OF MECHANICALLY FASTENED REPAIRS AND LAP JOINTS

Abstract— A new Dual Boundary Element formulation is presented, which allows for the analysis of mechanically fastened repairs and lap joints. The method requires only the boundaries of the problem to be discretized and the fasteners location is simply defined by a set of internal points.
The technique enables the evaluation of fastener forces, sheet stresses and the stress intensity factors which are important parameters for a Damage Tolerance assessment.
Examples of applications to repair designs and to a lap joint are presented to demonstrate the robustness of the new formulation that is proposed in this paper.     

Dual boundary element analysis of cracked plates: singularity subtraction technique

The present paper is concerned with the formulation of the singularity subtraction technique in the dual boundary element analysis of the mixed-mode deformation of general homogeneous cracked plates.The equations of the dual boundary element method are the displacement and the traction boundary integral equations. When the displacement equation is applied on one of the crack surfaces and the traction equation is applied on the other, general mixed-mode crack problems can be solved in a single region boundary element formulation, with both crack surfaces discretized with discontinuous quadratic boundary elements.The singularity subtraction technique is a regularization procedure that uses a singular particular solution of the crack problem to introduce the stress intensity factors as additional problem unknowns. The single-region boundary element analysis of a general crack problem restricts the availability of singular particular solutions, valid in the global domain of the problem. A modelling strategy, that considers an automatic partition of the problem domain in near-tip and far-tip field regions, is proposed to overcome this difficulty. After the application of the singularity subtraction technique in the near-tip field regions, regularized locally with the singular term of the Williams' eigenexpansion, continuity is restored with equilibrium and compatibility conditions imposed along the interface boundaries. The accuracy and efficiency of the singularity subtraction technique make this formulation ideal for the study of crack growth problems under mixed-mode conditions.