Cross-linked Matrix Research Articles

Composite Hydrogel Model of Cartilage Predicts Its Load-Bearing Ability

Articular cartilage is a load-bearing tissue found in animal and human joints. It is a composite gel-like material in which a fibrous collagen network encapsulates large proteoglycan assemblies that imbibe fluid and “inflate” the network. Here we describe a composite hydrogel consisting of a cross-linked polyvinyl alcohol matrix filled with poly(acrylic acid) microparticles that mimics functional properties and biomechanical behavior of cartilage. The swelling and mechanical behaviors of this biomimetic model system are strikingly similar to that of human cartilage. The development of synthetic composite gel-based articular cartilage analog suggests new avenues to explore material properties, and their change in disease and degeneration, as well as novel strategies for developing composite tissue-engineered cartilage constructs for regenerative medicine applications.

Fabrication of bioactive hydroxyapatite/silk fibroin/gelatin cross-linked nanocomposite for biomedical application

Hydroxyapatite/Silk fibroin/Gelatin (HSG) composite is a promising artificial bone graft material, which mimics the properties of the natural extracellular matrix components that meet the current need for bone tissue engineering. In this study, HSG composite in different ratios (40:60:0, 40:50:10, 40:40:20, 40:30:30 and 40:20:40) were prepared using in-situ co-precipitation method. Here, glutaraldehyde was used as a chemical cross-linking agent to improve interactions and control degradation of the composite. The formation of carbonated hydroxyapatite on the cross-linked polymer matrix was evidenced from the optical analysis. The influence of the gelatin content on crystallinity, crystallite size and morphology of the composite were confirmed by XRD and FESEM spectroscopic techniques. The Physico-chemical properties of the composites such as in-vitro biodegradation, swelling ratio and biomineralization were evaluated by treating it with simulated body fluid. Cell viability of the nanocomposite was tested with MG-63 cell lines, which emphasized the biocompatibility of the composites. Moreover, all-composite exhibits good antibacterial ability against Staphylococcus aureus and Pseudomonas aeruginosa. Finally, HSG (40:30:30) composite with a swelling ratio of 69.30 ± 0.42% (day 15) and biodegradation of 18.51 ± 0.53% (day 15) reveals maximum cell viability (87.27 ± 0.62%) and significant antibacterial property indicating a potential candidate for orthopaedic application.

Pore-size dependence and slow relaxation of hydrogel friction on smooth surfaces

Hydrogels consist of a cross-linked polymer matrix imbibed with a solvent such as water at volume fractions that can exceed 90%. They are important in many scientific and engineering applications due to their tunable physiochemical properties, biocompatibility, and ultralow friction. Their multiphase structure leads to a complex interfacial rheology, yet a detailed, microscopic understanding of hydrogel friction is still emerging. Using a custom-built tribometer, here we identify three distinct regimes of frictional behavior for polyacrylic acid (PAA), polyacrylamide (PAAm), and agarose hydrogel spheres on smooth surfaces. We find that at low velocities, friction is controlled by hydrodynamic flow through the porous hydrogel network and is inversely proportional to the characteristic pore size. At high velocities, a mesoscopic, lubricating liquid film forms between the gel and surface that obeys elastohydrodynamic theory. Between these regimes, the frictional force decreases by an order of magnitude and displays slow relaxation over several minutes. Our results can be interpreted as an interfacial shear thinning of the polymers with an increasing relaxation time due to the confinement of entanglements. This transition can be tuned by varying the solvent salt concentration, solvent viscosity, and sliding geometry at the interface.

PDB111 A COMPARATIVE EFFECTIVENESS RESEARCH STUDY OF A NATIVE TYPE I COLLAGEN MATRIX PLUS POLYHEXAMETHYLENE BIGUANIDE ANTIMICROBIAL AND A CRYOPRESERVED CADAVERIC SKIN ALLOGRAFT FOR USE IN DIABETIC FOOT ULCERS - A NON-INFERIORITY ANALYSIS

Real-world effectiveness was evaluated in a large patient population at 189 US treatment facilities comparing a purified native cross-linked extracellular matrix plus polyhexamethylene biguanide antimicrobial barrier (PCMP) and a cryopreserved cadaveric skin allograft (CCSA) for use in diabetic foot ulcers (DFUs). Electronic medical records were the source of these retrospective data. Treatment records collected from 2011-2019 on 945 patients (1,032 DFUs) were analyzed. Exclusion criteria were lack of baseline wound measurements or follow-up visits. Evaluations were performed on 314 PCMP patients (349 DFUs), and 631 CCSA patients (683 DFUs). Treatment cohorts were well matched. Baseline, mean areas were 6.2 and 7.8 cm2, mean depths were 4.0 and 3.5 mm, and median durations were 9.3 and 7.0 months, for PCMP and CCSA respectively. The median number of treatment applications was 2.0 in both groups, and the mean interval between treatment applications was 14.4 vs 24.1 days for PCMP and CCSA respectively. A Cox proportional hazards regression analysis (Cox) that adjusted for ulcer size, depth, and duration was used to compute frequency and probability of wound closure. The PCMP vs CCSA frequencies of wound closure were comparable at all study timepoints including week 4 (11 vs 10%), 8 (25 vs 24%), and 12 (36 vs 37%) respectively (p=0.20). PCMP demonstrated a comparable probability of wound healing vs CCSA treatment (Hazard Ratio=0.89 [95% CI: 0.75, 1.06]; p=0.20). In a Non-Inferiority (NI) analysis, PCMB demonstrated equivalence to CCSA when tested at a clinical margin of 20% (p=0.03). These real-world data demonstrate that PCMP vs CCSA showed comparable wound closure outcomes when used in DFUs. The NI design allows a valid conclusion of statistically significant equivalence between PCMP and CCSA at the clinical margin tested. These findings may inform wound care treatment algorithms and have meaningful clinical and health care economic implications.

Flexible Piezoelectric 0–3 PZT-PDMS Thin Film for Tactile Sensing

In this paper, Lead Zirconate-Titanate (PZT)/Poly-dimethylsiloxane (PDMS) based composite is fabricated and characterized for its potential application as a flexible piezoelectric material. Thin films of the composite are prepared by dispersing different volume percentage of PZT particles in cross-linked PDMS matrix. Corona poling of the films is performed to increase the piezoelectric charge constant. X-ray diffraction results indicate that poling aligns the randomly oriented ferroelectric domains in the PZT particles along the poling axis. Piezoelectric voltage response and piezoelectric charge constant values before and after the poling show the improvement in piezoelectricity due to poling. The piezoelectric charge constant, d33 and magnitude of relative permittivity of the films increase and flexibility of the films decrease with the increase of PZT particle volume percentage in the composite. Results show that for 28 v% PZT composite poled film a d33 of 78.33 pC/N was achieved with a Young’s modulus of around 10 MPa and magnitude of relative permittivity of 10. The film demonstrates effectiveness for tactile sensing by generating charges across the film proportional to the finger pressure applied on them. The easy fabrication process makes the composite a promising candidate to build flexible low cost tactile sensing devices.

NIR-light-induced thermoset shape memory polyurethane composites with self-healing and recyclable functionalities

To endow thermoset shape memory polymers with self-healing and recyclable functionalities is highly desirable. In this study, we fabricated Diels-Alder crosslinked polyurethane/functionalized reduced graphene oxide composites (DAPU-FRGOs) through in situ polymerization. The incorporated FRGO with urethane chains could achieve good compatibility with the DAPU matrix, forming physical and chemical crosslinking structures in the composite. And the most effective improvements of mechanical, thermal stability, crystallization-triggered, and photothermal effect were achieved for the DAPU/FRGO2 composite with 2 wt% FRGO. Owing to the outstanding crystallization-induced and photo-thermal effects of FRGO and the thermal reversible behavior of Diels-Alder bonds, the DAPU-FRGO2 composite showed rapid shape memory (<10 s, shape-fixity and recovery ratios were 92.3% and 94.1%, respectively) and self-healing (<120 s, healing efficiencies for tensile strength and elongation at break were 89.3% and 90.4%, respectively) under near-infrared light. Meanwhile, the DAPU-FRGO2 composite exhibited good repeatability of self-healing and shape-memory functionalities, and its shape memory parameters and healing efficiencies were maintained above 92% and 85% after three-cycles, respectively. Further recycling test demonstrated that the mechanical properties of the recycled DAPU-FRGO2 composite could be recovered to more than 82% of the original sample. This work provides a heuristic perspective for designing durable light-responsive thermoset shape memory composite materials.

Nanostructured Polymer Monoliths for Biomedical Delivery Applications.

Drug delivery systems are designed to control the release rate and location of therapeutic agents in the body to achieve enhanced drug efficacy and to mitigate adverse side effects. In particular, drug-releasing implants provide sustained and localized release. We report nanostructured polymer monoliths synthesized by polymerization-induced microphase separation (PIMS) as potential implantable delivery devices. As a model system, free poly(ethylene oxide) homopolymers were incorporated into the nanoscopic poly(ethylene oxide) domains contained within a cross-linked polystyrene matrix. The in vitro release of these poly(ethylene oxide) molecules from monoliths was investigated as a function of poly(ethylene oxide) loading and molar mass as well as the molar mass and weight fraction of poly(ethylene oxide) macro-chain transfer agent used in the PIMS process for forming the monoliths. We also developed nanostructured microneedles targeting efficient and long-term transdermal drug delivery by combining PIMS and microfabrication techniques. Finally, given the prominence of poly(lactide) in drug delivery devices, the degradation rate of microphase-separated poly(lactide) in PIMS monoliths was evaluated and compared with bulk poly(lactide).

Facile synthesis of hierarchical Na2Fe(SO4)2@rGO/C as high-voltage cathode for energy density-enhanced sodium-ion batteries

Abstract Fe-based sulfates are ideal cathode candidates for sodium-ion batteries (SIBs) owing to their high operating voltage and low cost but suffer from the nature of poor power performance. Herein, a hierarchical porous Na2Fe(SO4)2@reduced graphene oxide/carbon dot (Na2Fe(SO4)2@rGO/C) with low carbon content (4.12 wt%) was synthesized via a facile homogeneous strategy benefiting for engineering application, which delivers excellent sodium storage performance (high voltage plateau of 3.75 V, 85 mAh g−1 and 330 Wh kg−1 at 0.05 C; 5805 W kg−1 at 10 C) and high Na+ diffusion coefficient (1.19 × 10−12 cm2 s−1). Moreover, the midpoint voltage of assembled full cell could reach 3.0 V. The electron transfer and reaction kinetics are effectively boosted since the nanoscale Na2Fe(SO4)2 is supported by a robust cross-linked carbon matrix with rGO sheets and carbon dots. The slight rGO sheets sufficiently enhance the electron transfer like a current collecter and restrain the aggregation, as well as ensure smooth ion channels. Meanwhile, the carbon dots in the whole space connect with Na2Fe(SO4)2 and help rGO to promote the conductivity of the electrode. Ex-situ X-ray powder diffraction and X-ray photoelectron spectrometry analysis confirm the high reversibility of this sodiation/desodiation process.

Preparation of Nanoscale Semi-IPNs with an Interconnected Microporous Structure via Cationic Polymerization of Bio-Based Tung Oil in a Homogeneous Solution of Poly(ε-caprolactone).

Nanoscale semi-interpenetrating polymer networks of bio-based poly(ε-caprolactone) (PCL) and polymerized tung oil have been prepared via in situ cationic polymerization and compatibilization in a homogeneous solution. This novel blending technique produced a nanoscale morphology of poly(ε-caprolactone) with average particle sizes as small as 100 nm dispersed in a cross-linked tung oil matrix for 20 and 30 wt % PCL blend compositions. In addition, the exothermic cationic polymerization of tung oil in the presence of the PCL homogeneous solution created a microporous morphology with open three-dimensional interconnected cluster structures. The porous morphology was found to be composition-dependent (the pore size and interconnectivity decreased with increasing PCL content in the blend). The values of the cross-link density and storage modulus in the glassy state for fully cured samples increased significantly and reached a maximum for the 20 wt % PCL blend. This simple, versatile, low-cost strategy for preparing nanoscale and interconnected three-dimensional cluster structures with a microporous morphology and desired properties should be widely applicable for new polymer systems.

Durability-enhanced vanadium dioxide thermochromic film for smart windows

Vanadium dioxide (VO2)–based thermochromic films are of great interest for energy-saving smart windows as they can dynamically change the solar transmittance as the ambient temperature changes. However, VO2 is thermodynamically unstable and could be easily oxidized by the oxygen and moisture in the ambient air. In this work, a durability-enhanced VO2 nanoparticle-polymer thermochromic film was proposed and fabricated using the blade coating method where the cross-linked and highly entangled poly(methyl methacrylate) (PMMA) chains with a molecular weight (~ 950,000) was adopted to block gas diffusion in the polymer matrix. It was shown that the developed VO2 nanoparticle film kept ~30% of its solar modulation ability after ~900 h of accelerated durability test in the aging environment with a temperature at 60 °C and ~95% relative humidity. This is ~4 times of the lifetime of the VO2 nanoparticles which are embedded in the non–cross-linked PMMA matrix with low molecular weight (~15,000). The cross-linked PMMA-VO2 film also showed a high luminous transmittance of ~50%, a high solar modulation ability of ~17%, and a low haze of ~11%. Our method provides an easy and effective strategy to improve the lifetime of VO2 nanoparticles, showing a promising pathway toward environmentally stable and easily scalable thermochromic films for energy-efficient smart windows.

Host response of different cross-linked hyaluronic acidcomposite gels and matrix metalloproteinase-9 expression

Host response of different cross-linked hyaluronic acidcomposite gels and matrix metalloproteinase-9 expression

Polylysine Enriched Matrices: A Promising Approach for Vascular Grafts

Cardiovascular diseases represent the leading cause of death in developed countries. Modern surgical methods show poor efficiency in the substitution of small-diameter arteries (<6 mm). Due to the difference in mechanical properties between the native artery and the substitute, the behavior of the vessel wall is a major cause of inefficient substitutions. The use of decellularized scaffolds has shown optimal prospects in different applications for regenerative medicine. The purpose of this work was to obtain polylysine-enriched vascular substitutes, derived from decellularized porcine femoral and carotid arteries. Polylysine acts as a matrix cross-linker, increasing the mechanical resistance of the scaffold with respect to decellularized vessels, without altering the native biocompatibility and hemocompatibility properties. The biological characterization showed an excellent biocompatibility, while mechanical tests displayed that the Young’s modulus of the polylysine-enriched matrix was comparable to native vessel. Burst pressure test demonstrated strengthening of the polylysine-enriched matrix, which can resist to higher pressures with respect to native vessel. Mechanical analyses also show that polylysine-enriched vessels presented minimal degradation compared to native. Concerning hemocompatibility, the performed analyses show that polylysine-enriched matrices increase coagulation time, with respect to commercial Dacron vascular substitutes. Based on these findings, polylysine-enriched decellularized vessels resulted in a promising approach for vascular substitution.

Cold-crystallizing erythritol-polyelectrolyte: Scaling up reliable long-term heat storage material

Renewable energy usage would benefit from efficient and high-capacity long-term heat storage material. However, these types of material solutions still lack reliable and durable operation on bulk level. Previously, we showed that cold-crystallizing material (CCM), which consists of erythritol in cross-linked polymer matrix, stored heat for a long-term period in a milligram scale by supercooling stably and preventing undesired crystallization during storage. Crystallization of CCM can be triggered efficiently by re-heating the material (i.e. cold-crystallization). Supercooling and cold-crystallization are stochastic phenomena which manifest in a way that the properties in bulk scale often deviate from the microscale. In this work, we scale up CCM to a bulk size of 160 g, and analyze its supercooling and crystallization characteristics for long-term heat storage. In order to identify the impact of the scale-up on the tested compositions and to discover optimal storage conditions, CCM samples are maintained in storage mode at constant temperature between 0 and 10 °C and up to 97 days. To this end, the thermal chamber measurement procedure estimates the heat release of CCM samples based on the measured temperature data and the one-dimensional transient heat conduction model. Results indicate that the heat release in cold-crystallization is over 70% of the melting heat. This heat can be stored without reduction for at least 97 days, demonstrating the reliable performance of long-term heat storage. Analysing the thermal properties of CCM compositions indicates a maximum volumetric storage capacity of 250 MJ/m3 and excellent properties for further heat storage applications.

Determining the Role of Extracellular Matrix Compliance on Facial Morphogenesis

We have previously found that collagen 4 and laminin are thinner in regions of the frontonasal process undergoing growth, suggesting tissue compliance may contribute to regulation of facial morphogenesis. Lysyl oxidase (LOX) initiates enzymatic crosslinking of collagen and elastin. Crosslinking in extracellular matrix fibrils increases tissue stiffness and may constrain growth in certain directions while allowing cells to exert forces required for directional growth. Our goal was to examine the distribution of lysyl oxidase in the frontonasal process (FNP) of chick embryos during growth and fusion of the palate. At Hamburger and Hamilton stage 22, LOX is present in the ectodermal basement membrane along the FNP, but at stage 26 it is present primarily in the basement membrane lining the nasal pits. LOX is also present in the lateral edges of the mesenchyme of the FNP at stage 22, but is more present in the medial and caudal mesenchyme at stage 26. These results mirror the distribution of collagen 4 and laminin, where more crosslinking was observed in regions resisting growth (like the nasal pits) and in regions where cellular forces may be generated to direct growth (ectodermal basement membrane). We next prevented initiation of crosslinking with a small‐molecule from Lathyrus odoratus, beta‐aminoproprionitrile (BAPN), which permanently binds to LOX. Ingestion of L. odoratus causes osteolathyrism, a musculoskeletal degenerative disease, and researchers have found that BAPN administered in high concentrations to embryos causes skeletal and craniofacial deformities. We found that microinjections of BAPN in the caudo‐lateral edge of the FNP at low concentrations (50, 75, and 100 ng/uL) caused mild truncation of the FNP without affecting LOX localization or increasing cell apoptosis (via TUNEL staining). Together, these results provide preliminary evidence that tissue compliance may play an important role in facial morphogenesis. Future work will utilize a LOX RNAi vector to further examine the role of extracellular matrix crosslinking on palate growth and fusion.Support or Funding InformationFunding was provided by: CIHR, and NIH, NIDCR R21‐DE028198

Heterogeneous Diffusion of Polystyrene Nanoparticles through an Alginate Matrix: The Role of Cross-linking and Particle Size.

Most bacteria in natural and engineered environments grow and exist in biofilms. Recent investigations have shown that nanoparticles (NPs) interact with environmental biofilms, but these interactions are still not well characterized. Extracellular polymeric substances (EPS) are polymers secreted by bacteria to establish the functional and structural integrity of biofilms, and EPS porosity is a major contributor to NP access to and diffusion in biofilms. We used a synergistic combination of total internal reflection fluorescence microscopy and image correlation spectroscopy to monitor and map diffusion of fluorescent NPs in alginate yielding a detailed picture of the heterogeneous structure and connectivity of pores within a model EPS polymer. Using different sizes (20, 100, and 200 nm) of carboxylated polystyrene NPs, we examined how NP diffusive behaviors change as a result of calcium-induced cross-linking of the alginate matrix. This study reveals that cross-linking decreases NP diffusion coefficients and pore accessibility in an NP size-dependent manner and that NP movement through alginate matrices is anisotropic and heterogeneous. These results on heterogeneous and size-dependent movement within biofilms have important implications for future studies and simulations of NP-biofilm interactions.

Impact of pea protein isolate in partial substitution of milk protein concentrate on the microstructural, rheological, and sensory properties of bacteriologically acidified feta‐type cheese

The aim of this work is to study the impact of pea protein isolate (PPI) on the microstructural, textural, and rheological properties of bacteriologically acidified feta (BAF) cheese fortified with milk protein concentrate (MPC) during 30 days of storage. Various blends of MPC and PPI were mixed at levels of 12:0%, 10:2%, 9:3%, 8:4%, 7:5%, 6:6% (w/v dry basis), respectively. The results showed that substitution of MPC by PPI led to reduction G′ (storage modulus) and G″ (loss modulus), but the gain firmness, springiness, and gumminess were observed during the storage. Low PPI supplements (2% and 3%) did not have adverse effects on the sensory and textural characteristics. The images of microstructure indicated the homogenous and denser protein matrix networks, it was due to good cross-linked protein matrix. However, a weak structure and more open network were observed at higher concentration of PPI (5% and 6%). Practical applications These days, there is a rapid increase in demand for legume proteins. Moreover, pea protein has a great potential so as to use in the food formulations as a substitution of animal proteins. For this purpose, PPI was used at different rates for producing BAF cheese fortified with MPC. The results showed that adding PPI and MPC changed the physicochemical properties of cheese samples and MPC could be replaced with 3% PPI in BAF cheese without the undesirable effects on the sensory and textural properties.

Remodeling of Cross-bridges Controls Peptidoglycan Cross-linking Levels in Bacterial Cell Walls.

Cell walls are barriers found in almost all known bacterial cells. These structures establish a controlled interface between the external environment and vital cellular components. A primary component of cell wall is a highly cross-linked matrix called peptidoglycan (PG). PG cross-linking, carried out by transglycosylases and transpeptidases, is necessary for proper cell wall assembly. Transpeptidases, targets of β-lactam antibiotics, stitch together two neighboring PG stem peptides (acyl-donor and acyl-acceptor strands). We recently described a novel class of cellular PG probes that were processed exclusively as acyl-donor strands. Herein, we have accessed the other half of the transpeptidase reaction by developing probes that are processed exclusively as acyl-acceptor strands. The critical nature of the cross-bridge on the PG peptide was demonstrated in live bacterial cells, and surprising promiscuity in cross-bridge primary sequence was found in various bacterial species. Additionally, acyl-acceptor probes provided insight into how chemical remodeling of the PG cross-bridge (e.g., amidation) can modulate cross-linking levels, thus establishing a physiological role of PG structural variations. Together, the acyl-donor and -acceptor probes will provide a versatile platform to interrogate PG cross-linking in physiologically relevant settings.

Elevated intracellular copper contributes a unique role to kidney fibrosis by lysyl oxidase mediated matrix crosslinking

Copper ions play various roles in mammalian cells, presumably due to their involvement in different enzymatic reactions. Some studies indicated that serum copper correlates with fibrosis in organs, such as liver and lung. However, the mechanism is unknown. Here, we explored the role of copper in kidney fibrosis development and possible underlying mechanisms. We found that copper transporter 1 (CTR1) expression was increased in the kidney tissues in two fibrosis models and in patients with kidney fibrosis. Similar results were also found in renal tubular epithelial cells and fibroblast cells treated with transforming growth factor beta (TGF-β). Mechanistically, the upregulation of CTR1 required Smads-dependent TGF-β signaling pathway and Smad3 directly binded to the promoter of CTR1 in renal fibroblast cells using chromatin immunoprecipitation. Elevated CTR1 induced increase of copper intracellular influx. The elevated intracellular copper ions activated lysyl oxidase (LOX) to enhance the crosslinking of collagen and elastin, which then promoted kidney fibrosis. Reducing intracellular copper accumulation by knocking down CTR1 ameliorated kidney fibrosis in unilateral ureteral obstruction induced renal fibrosis model and renal fibroblast cells stimulated by TGF-β. Treatment with copper chelator tetrathiomolybdate (TM) also alleviated renal fibrosis in vivo and in vitro. In conclusion, intracellular copper accumulation plays a unique role to kidney fibrosis by activating LOX mediated collagen and elastin crosslinking. Inhibition of intracellular copper overload may be a potential portal to alleviate kidney fibrosis.

Insights into the heparan sulphate-dependent externalisation of transglutaminase-2 (TG2) in glucose-stimulated proximal-like tubular epithelial cells

The extracellular matrix crosslinking enzyme transglutaminase 2 (TG2) is highly implicated in tissue fibrosis that precedes end-stage kidney failure. TG2 is unconventionally secreted through extracellular vesicles in a way that depends on heparan sulphate (HS) proteoglycan syndecan-4 (Sdc4), the deletion of which reduces experimental kidney fibrosis as a result of lower extracellular TG2 in the tubule-interstitium. Here we establish a model of TG2 externalisation in NRK-52E tubular epithelial cells subjected to glucose stress. HS-binding TG2 mutants had reduced extracellular TG2 in transfected NRK-52E, suggesting that TG2-externalisation depends on an intact TG2 heparin binding site. Inhibition of N-ethylmaleimide sensitive factor (NSF) vesicle-fusing ATPase, which was identified in the recently elucidated TG2 kidney membrane-interactome, led to significantly lower TG2-externalisation, thus validating the involvement of membrane fusion in TG2 secretion. As cyclin-G-associated kinase (GAK) had emerged as a further TG2-partner in the fibrotic kidney, we investigated whether glucose-induced TG2-externalisation was accompanied by TG2 phosphorylation in consensus sequences of cyclin-dependent kinase (CDK). Glucose stress led to intense TG2 phosphorylation in serine/threonine CDK-target. TG2 phosphorylation by tyrosine kinases was also increased by glucose. Although the precise role of glucose-induced TG2 phosphorylation is unknown, these novel data suggest that phosphorylation may be involved in TG2 membrane-trafficking.

Electrospinning of a Near Gel Resin To Produce Cross-Linked Fibrous Matrices.

Electrospun fibers and matrices have been researched for their utility in various fields; however, because of poor mechanical strength and loss of structural integrity, their commercial viability is limited. A near gel resin (nGR) of polystyrene (PS) was used in the present approach to fabricate cross-linked fibrous matrices of better mechanical strength and oil adsorption while retaining the structural integrity. Electrospinnability of nGR was assessed in bulk (i.e., in styrene monomer) and solution (i.e., in dimethyl formamide) forms with variations in formulation and electrospinning conditions. Ultimately, a uniform cross-linked fibrous matrix of PS was prepared using an oil-in-water emulsion, where the oil phase composed of a monomer (styrene), an initiator (benzoyl peroxide), and a cross-linker (divinylbenzene) was dispersed in a continuous phase of aqueous poly(vinyl alcohol) (PVA). The monomer conversion in the oil phase was carried out below the gel point, and the nGR of PS formed in dispersed droplets was electrospun to fabricate uniform fibrous matrices with the help of a template polymer, that is, PVA. The effect of various material and process parameters on the gelation behavior, electrospinnability, and fiber uniformity was studied and optimized to produce uniform core-sheath fibrous matrices of cross-linked PS. Postelectrospinning heat treatment of matrices was carried out to achieve complete monomer conversion and cross-linking. Fiber formation behavior of the emulsion was assessed using ionic and nonionic surfactants. The cross-link density of the matrices was optimized to achieve the desired structural morphology and dimensional stability. The process of fabrication of emulsion electrospun cross-linked fibers can be further extended to a variety of other monomers in order to enhance the suitability of fibrous matrices for many applications.