Alterations in gap junction connexin43/connexin45 ratio mediate a transition from quiescence to excitation in a mathematical model of the myometrium

The smooth muscle cells of the uterus contract in unison during delivery. These cells achieve coordinated activity via electrical connections called gap junctions which consist of aggregated connexin proteins such as connexin43 and connexin45. The density of gap junctions governs the excitability of the myometrium (among other factors). An increase in gap junction density occurs immediately prior to parturition. We extend a mathematical model of the myometrium by incorporating the voltage-dependence of gap junctions that has been demonstrated in the experimental literature. Two functional subtypes exist, corresponding to systems with predominantly connexin43 and predominantly connexin45, respectively. Our simulation results indicate that the gap junction protein connexin45 acts as a negative modulator of uterine excitability, and hence, activity. A network with a higher proportion of connexin45 relative to connexin43 is unable to excite every cell. Connexin45 has much more rapid gating kinetics than connexin43 which we show limits the maximum duration of a local burst of activity. We propose that this effect regulates the degree of synchronous excitation attained during a contraction. Our results support the hypothesis that as labour approaches, connexin45 is downregulated to allow action potentials to spread more readily through the myometrium.     

Bioactive borosilicate glass scaffolds: improvement on the strength of glass-based scaffolds for tissue engineering

Three-dimensional macroporous scaffolds with the pore size of 200-500 mum were fabricated by replication method using bioactive borosilicate glass from Na(2)O-K(2)O-MgO-CaO-SiO(2)-P(2)O(5)-B(2)O(3) system. The effects of the strength of the strut in reticulated scaffold, as well as the geometrical parameter of the scaffold on the strength of reticulated scaffold were investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) results show that the solidified glass struts in the reticulated scaffold could be obtained through a sufficient vicious flow of glass, during the fabrication. By increasing the solid content in slurries, from which the scaffold was made, the load-bearing units of the reticulated scaffold switch from struts to the walls between the pores, and the compressive strength dramatically climbs higher than the theoretical strength calculated by Gibson model. In particular, the compressive strength of the reticulated scaffold, as high as approximately 10 MPa with the porosity of approximately 70%, is close to the reported compressive values of human cancellous bone. This indicates the bioactive borosilicate glass-based scaffold is a promising candidate for bone tissue engineering.     

Toward modulating the architecture of hydrogel scaffolds: curtains versus channels

The design, development and evaluation of biomaterials that can sustain life or restore a certain body function, is a very important and rapidly expanding field in materials science. A key issue in the development of biomaterials is the design of a material that mimics the natural environment of cells. In the present work, we have therefore developed hydrogel materials that contain both a protein (gelatin) and a glycosaminoglycan (chondroitin sulphate) component. To enable a permanent crosslinking, gelatin and chondroitin sulphate were first chemically modified using methacrylic anhydride. Hydrogels containing modified gelatin (gel-MOD) and/or chondroitin sulphate (CS-MOD) were cryogenically treated as optimised earlier for gel-MOD based hydrogels (Van Vlierberghe et al., Biomacromolecules 8:331–337, 2007). The cryogenic treatment leads to tubular pores for gel-MOD based systems. For CS-MOD based hydrogels and hydrogels containing both gel-MOD and CS-MOD, a curtain-like architecture (i.e. parallel plates) was observed, depending on the applied CS-MOD concentration. In our opinion, this is the first paper in which such well-defined scaffold architectures have been obtained without using rapid prototyping techniques.     

Bioactive glass scaffolds for bone tissue engineering: state of the art and future perspectives

The repair and regeneration of large bone defects resulting from disease or trauma remains a significant clinical challenge. Bioactive glass has appealing characteristics as a scaffold material for bone tissue engineering, but the application of glass scaffolds for the repair of load-bearing bone defects is often limited by their low mechanical strength and fracture toughness. This paper provides an overview of recent developments in the fabrication and mechanical properties of bioactive glass scaffolds. The review reveals the fact that mechanical strength is not a real limiting factor in the use of bioactive glass scaffolds for bone repair, an observation not often recognized by most researchers and clinicians. Scaffolds with compressive strengths comparable to those of trabecular and cortical bones have been produced by a variety of methods. The current limitations of bioactive glass scaffolds include their low fracture toughness (low resistance to fracture) and limited mechanical reliability, which have so far received little attention. Future research directions should include the development of strong and tough bioactive glass scaffolds, and their evaluation in unloaded and load-bearing bone defects in animal models.     

Mapping irreversible electrochemical processes on the nanoscale: ionic phenomena in li ion conductive glass ceramics

A scanning probe microscopy approach for mapping local irreversible electrochemical processes based on detection of bias-induced frequency shifts of cantilevers in contact with the electrochemically active surface is demonstrated. Using Li ion conductive glass ceramic as a model, we demonstrate near unity transference numbers for ionic transport and establish detection limits for current-based and strain-based detection. The tip-induced electrochemical process is shown to be a first-order transformation and nucleation potential is close to the Li-metal reduction potential. Spatial variability of the nucleation bias is explored and linked to the local phase composition. These studies both provide insight into nanoscale ionic phenomena in practical Li-ion electrolyte and also open pathways for probing irreversible electrochemical, bias-induced, and thermal transformations in nanoscale systems.     

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.     

Porous nanocellulose gels and foams: Breakthrough status in the development of scaffolds for tissue engineering

We report on the latest scientific advances related to the use of porous foams and gels prepared with cellulose nanofibrils (CNF) and nanocrystals (CNC) as well as bacterial nanocellulose (BNC) – collectively nanocelluloses – as biomedical materials for application in tissue regeneration. Interest in such applications stems from the lightweight and strong structures that can be efficiently produced from these nanocelluloses. Dried nanocellulose foams and gels, including xerogels, cryogels, and aerogels have been synthesized effortlessly using green, scalable, and cost-effective techniques. Methods to control structural features (e.g., porosity, morphology, and mechanical performance) and biological interactions (e.g., biocompatibility and biodegradability) are discussed in light of specific tissues of interest. The state-of-the-art in the field of nanocellulose-based scaffolds for tissue engineering is presented, covering physicochemical and biological properties relevant to these porous systems that promise groundbreaking advances. Specifically, these materials show excellent performance for in vitro cell culturing and in vivo implantation. We report on recent efforts related to BNC scaffolds used in animal and human implants, which furthermore support the viability of CNF- and CNC-based scaffolds in next-generation biomedical materials.     

Three-dimensional scaffolds: an in vitro strategy for the biomimetic modelling of in vivo tumour biology

Limitations associated with the study of cancer biology in vitro, including a lack of extracellular matrix, have prompted an interest in analysing the behaviour of tumour cells in a three-dimensional environment. Such model systems can be used to better understand malignancy and metastasis and a cancer’s response to therapies. We review the materials that have been used in such models to date, including their fabrication techniques and the results from their study in cancer. Despite the variety of materials available, obstacles remain to perfecting an in vitro model system and we outline some of the challenges yet to be overcome.     

3D-macroporous hybrid scaffolds for tissue engineering: Network design and mathematical modeling of the degradation kinetics

In the present study it is reported the synthesis, characterization and subsequent degradation performance of organic-inorganic hybrid systems chemically modified by bi-functional crosslinker (glutaraldehyde, GA). The hybrids were prepared by combining 70% poly (vinyl alcohol) and 30% bioactive glass (58SiO₂-33CaO-9P₂O₅, BaG) via sol-gel route using foaming-casting method producing different macroporous tri-dimensional scaffolds depending on the degree of network crosslinking. The in vitro degradation kinetics was evaluated by measuring the mass loss upon soaking into de-ionized water at 37 °C for up to 21 days and different mathematical models were tested. The PVA/BaG hybrids scaffolds properties “as-synthesized” and after the degradation process were extensively characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), mechanical compressing tests and X-ray Micro-computed Tomography analysis (μCT). The results have clearly shown the effectiveness of tailoring the PVA/BaG hybrids properties and degradation kinetics mechanisms by chemically engineering the structure at nano-order level using different concentrations of the crosslinker. Moreover, these hybrid crosslinked nanostructures have shown 3D hierarchical pore size with interconnected architecture within the range of 10-450 μm for potential use in the field of bone regenerative medicine.     

Rationalized method to enhance the chromium uptake in tanning process: role of Gallic acid

In the present study, a greener approach to tanning process based on Gallic acid (GA: Trihydroxybenzoic acid) assisted chrome tanning has been attempted. The exhaustion, the thermal stability, mechanical strength and organoleptic properties of tanned leather as well as the evaluation of eco-friendly characteristics were investigated. The microshrinkage, differential scanning calorimetric and thermo mechanical analyses show the shrinkage temperature, denaturation temperature and % elongation, respectively, of GA-chrome-tanned leather are more than that of chrome alone. Chrome exhaustion greater than 93 % has been achieved. This high exhaust aid offers fullness and softness to leather compared to chrome alone. The environmental impact assessment reveals that the developed high exhaust chrome tanning process is beneficial as significant reduction in total solids content (TSC) such as dissolved solids and suspended solids in the effluent is achieved when compared to tanning with chrome alone. The GA could bring about the enhancement of chromium(III) uptake, significant reduction in TSC resulting in improved environmental, economic and social positive impact.     

Development of electromagnetic shielding materials from the conductive blends of polyaniline and polyaniline-clay nanocomposite-EVA: Preparation and properties

Electromagnetic interference shielding composite materials were developed from the conductive blends of nanostructured polyaniline (PANI) and polyaniline-clay nanocomposite (PANICN) with ethylene vinyl acetate (EVA) as host matrix. Electrically conducting nanostructured PANI and PANICNs were prepared using amphiphilic dopants, 3-pentadecyl phenol 4-sulphonic acid (3-PDPSA) derived from cashew nut shell liquid, a low cost renewable resource based product and dodecyl benzene sulfonic acid (DBSA). Effects of type and quantity of conductive fillers on the electrical conductivity, mechanical properties, thermal stability, morphology and electromagnetic shielding efficiency were investigated. The presence of exfoliated nanoclay and interaction between the conductive filler–host matrix in conductive films containing PANICNs manifested from the measurement on rheological property. Films with conductive filler (～15% loading) showed a shielding effectiveness of ～40–80 dB at 8 GHz which makes these conducting composites potential candidate for the encapsulation as EMI shielding materials for electronic devices.     

Correction to: Influence of the nanocellulose raw material characteristics on the electrochemical and mechanical properties of conductive paper electrodes

Journal of Materials Science -