Low Crosslinking Research Articles

Qualitative and quantitative evaluation of epoxy systems by Fourier transform infrared spectroscopy and the flexibilizing effect of mercaptans.

Epoxy systems are widely applied as adhesives in the aerospace industry. They have excellent adhesion properties, however, being thermosetting, epoxy systems show fracture brittleness characteristics. Polysulfide and polymercaptans are good options to increase the flexibility of the epoxy adhesive. Thermal analysis techniques are generally used to evaluate the curing degree of epoxy systems. In most cases, when infrared (IR) analysis is used, it is employed qualitatively. This paper presents the reaction study of a DGEBA epoxy prepolymer with diethylenetriamine (DETA) and linear and branched dodecyl mercaptans as flexibilizers. Conversion data and curing time were assessed qualitatively and quantitatively by Fourier Transform Infrared Spectroscopy (FT-IR) in the medium infrared region (MIR) and in the near infrared region, using near infrared reflectance accessory (NIRA). NIRA methodology showed satisfactory results, with errors between 3 and 7%, especially in samples with lower amine contents. Mechanical tests confirmed the flexibilization of the cured epoxy system by the addition of mercaptans, indicating a lower crosslinking degree in the matrix. Young's modulus (E) significantly decreased from 2017 MPa to 578 MPa with the addition of approximately 20 wt% of normal dodecyl mercaptan to the epoxy system.

Wagyu–Angus cross improves meat tenderness compared to Angus cattle but unaffected by mild protein restriction during late gestation

For the spring-calving beef herds, late gestation coincides with winter and early spring, when cows are dependent on feed supplements with low quality hay, which is hard to meet their nutrient requirements. However, the effects of deficiencies of metabolizable protein intake during late gestation on offspring beef quality are unclear. Wagyu cattle have excellent marbling, and insemination with Wagyu vs Angus semen is a practical option for beef producers to improve beef quality. To test, Angus cows (621 ± 73 kg) were selected and randomly separated into two groups. Each group was inseminated with either Angus or Wagyu semen. During the last 90 days of gestation, cows in each group were further separated and received either a low protein diet (85% of the NRC metabolizable protein requirement), which was a low quality hay-based diet common in northwestern region of the U.S., or an adequate protein diet (108% NRC requirement). All progeny was managed together and harvested at a final BW of 576.5 ± 16.6 kg. Wagyu-sired offspring had higher marbling scores and quality grades than Angus (P < 0.01). Protein supplementation did not affect Slice Shear Force (SSF) in either breeds (P = 0.60). However, Wagyu-sired cattle had lower SSF than Angus-sired (P < 0.01). In addition, Wagyu-sired cattle had higher intramuscular fat (P < 0.05) and total collagen content (P < 0.05), but Angus-sired had greater mature collagen cross-links, as shown by higher contents of Pyridinoline (P < 0.01) and Ehrlich Chromogen (P < 0.01). Consistently, the mRNA expression of enzymes catalyzing collagen cross-linking was higher in Angus-sired offspring, including Plod 1 (P < 0.05), Plod 2 (P = 0.08), and P4Hα 2 (P < 0.01). In conclusion, Wagyu-sired cattle had greater tenderness and marbling score compared to Angus-sired, which was associated with lower collagen cross-links. Feeding mature grass hay-based diet with relatively low protein content during late gestation had no major effect on beef quality of subsequent cattle.

Programmable self-foldable films for origami-based manufacturing

Manufacturing of three-dimensional structures of millimeter and sub-millimeter sizes is required in emerging applications in microelectronics, packaging, and particle entrapment. This paper presents a manufacturing method for three-dimensional polyhedral structures at such scales enabled by programmable, self-foldable polymer films. The manufacturing method starts with a three-dimensional target shape and uses origami design to generate the outline and fold pattern of a planar film that can be folded towards the target shape. Double-exposure photolithography is employed to pattern a polymer film based on the generated geometry along with stiff faces of high crosslinking density and flexible folds of low crosslinking density. During the development step of the photolithography process, the folds absorb the developer solution from one side, creating a concentration gradient across their thickness. The non-uniformly absorbed developer in the folds is evaporated when the film is heated, causing non-uniform strains across their thickness and enabling self-folding. It is experimentally determined that the fold angles exhibited by the folds are directly proportional to the ratio between their width along the folding direction and the film thickness, which enables programming of the folding response through modulation of the fold dimensions. Different structures are fabricated to demonstrate the effectiveness of the developed manufacturing method.

Spatially Controlled Permeability and Stiffness in Photopatterned Two-Stage Reactive Polymer Films for Enhanced CO2 Barrier and Mechanical Toughness

Controlling the microstructure of heterogeneous, polymer membranes used in gas barrier and gas separation technologies is challenging. Being able to control composite structures is beneficial to achieve an optimum combination of gas permeation and mechanical performance. In addition, unique properties such as anisotropy and confined transport can be controlled by tailoring the size and position of constituent materials. Two-stage reactive polymer (TSRP) networks are an emerging dual-cure polymer material for spatially varying cross-linking density via photopatterning. In this work a thiol–acrylate-based TSRP was used to investigate the effects of pattern geometry on CO₂ permeability and mechanical properties. Line and square patterns of alternating high and low cross-linking density, with characteristic dimension between 1 mm and 10 μm, were generated in TSRP membranes. Notably, synergistic enhanced barrier properties were observed for 10 μm square patterns of lower cross-linking density (or higher permeability) material exhibiting two confined dimensions compared to line gratings with only one confined dimension.

Investigating the performance of an organically cross-linked grafted copolymer gel under reservoir conditions for profile modifications in injection wells

The injection of cross-linked polymer gels to block high permeability zones and divert subsequent water/surfactant flooding to low permeability streaks to improve hydrocarbon production efficiency is commonly known as profile modification. Moreover, in a reservoir condition with high temperature, pH, and salinity, these cross-linked polymeric gels are unstable, leading to early syneresis. In this research work, poly(Acrylamide)-grafted-xanthan gum copolymer was synthesized by free radical polymerization using potassium persulfate as an initiator. Field-Emission Scanning Electron Microscopy and Fourier Transform Infrared spectroscopy characterize the grafted copolymer in this study. This grafted copolymer, which is soluble in water, was cross-linked with a low toxic organic cross-linker. The organic cross-linker is composed of hexamethylenetetramine (HMTA) and hydroquinone (HQ). The rheological examination and gelation conduct of this polymeric gel was analyzed using a bottle test. The experimental design in response surface method generated a second-order polynomial equation for the gelation time responses to the change in the reservoir parameters (salinity, pH, and temperature) and their interactions. The results exhibited that the response surface model can be applied successfully to analyze gelation time with the various reservoir parameters. Laboratory prepared sand pack flow experiment demonstrated a decent diverting capability of the grafted copolymer gel than commercially used polyacrylamide gels. Subsequently, this grafted copolymer gel can be suitable for profile modification jobs required for improving oil recovery from mature oil fields with high reservoir heterogeneities.

Multiplexed imaging mass spectrometry of the extracellular matrix using serial enzyme digests from formalin-fixed paraffin-embedded tissue sections.

We report a multiplexed imaging mass spectrometry method which spatially localizes and selectively accesses the extracellular matrix on formalin-fixed paraffin-embedded tissue sections. The extracellular matrix (ECM) consists of (1) fibrous proteins, post-translationally modified (PTM) via N- and O-linked glycosylation, as well as hydroxylation on prolines and lysines, and (2) glycosaminoglycan-decorated proteoglycans. Accessing all these components poses a unique analytical challenge. Conventional peptide analysis via trypsin inefficiently captures ECM peptides due to their low abundance, intra- and intermolecular cross-linking, and PTMs. In previous studies, we have developed matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) techniques to capture collagen peptides via collagenase type III digestion, both alone and after N-glycan removal via PNGaseF digest. However, in fibrotic tissues, the buildup of ECM components other than collagen-type proteins, including elastin and glycosaminoglycans, limits efficacy of any single enzyme to access the complex ECM. Here, we have developed a novel serial enzyme strategy to define the extracellular matrix, including PTMs, from a single tissue section for MALDI-IMS applications. Graphical Abstract.

Abstract 17388: Loss of Bone Morphogenetic Protein 9 (BMP9) Limits Survival and Paradoxically Increases Collagen Abundance, but Limits Collagen Cross-Linking in a Murine Model of Acute Myocardial Infarction

Myocardial infarction (MI) is a major cause of heart failure (HF). HF is associated with adverse cardiac remodeling that is primarily driven by Transforming growth factor beta (TGFb1) mediated fibrosis and myocyte hypertrophy. We previously reported that loss of bone morphogenetic protein 9 (BMP9) promotes cardiac fibrosis in pressure-overload induced HF. No studies have explored a role for BMP9 in post MI cardiac remodeling. We hypothesize that loss of BMP9 may promote cardiac healing by stabilizing LV scar formation. To test this hypothesis, we subjected whole body BMP9 knockout (-/-) mice to left coronary artery ligation for two weeks followed by PV loop analysis and studied indices of cardiac remodeling. Compared to wild type (WT) controls BMP9-/- mice had significantly lower survival (83% vs 61%, p&lt;0.001, respectively) with a higher rate of cardiac rupture(15% vs 90%). Compared to WT controls, surviving BMP9-/- mice had higher LVEDP, reduced LV dP/dt, and higher lung weight. Compared to WT mice, BMP9-/- mice had significantly higher levels of Type I collagen (2 fold p&lt;0.05). Compared to WT mice, BMP9-/- mice had increased matrix metalloproteinases (MMP)-2 and MMP-9 (2.5 fold p&lt;0.05) activity levels in the LV. Treatment of cultured primary human cardiac fibroblasts with recombinant BMP9 attenuated TGFb1-mediated Type I collagen and MMP-9 protein expression. To assess collagen content and cross-linking, two-photon excitation fluorescence imaging was performed and identified an increase in collagen abundance, but a trend towards lower collagen cross-linking in the LV of BMP9-/- mice compared to WT mice 2 weeks after MI. Our central finding is that loss of BMP9 is associated with reduced survival, increased propensity towards cardiac rupture, and increased LV collagen abundance, but reduced collagen integrity in a murine model of acute MI. These identify a potentially important functional role for BMP9 in post-infarct cardiac remodeling.

Composite catalytic materials based on k-carrageenan and CaO used on the transesterification of soybean oil for the process of biodiesel obtention

Composite materials based on CaO obtained from egg shells and k-carrageenan, an anionic sulfated linear polysaccharide obtained from red seaweeds was used as an efficient, environmentally friendly heterogeneous catalyst for the transesterification of soybean oil with methanol at 60 °C.The different composite samples were produced through the dissolution of the biopolymer in an ionic liquid (IL) derived from imidazolium ion and by further addition of CaO. The samples were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) and Termogravimetry (TGA). The materials exhibit an internal structure consisting of meso and macropores which widen with the addition of small amounts of Hexamethylene diisocyanate (HMDI) that acts as a crosslinker. The composite materials present a similar thermal behaviour to k-carrageenan, without loss of stability.The catalytic activity of the prepared composite materials was evaluated in the transesterification reaction of soybean oil with methanol through catalytic runs in batch conditions. It was found that both CaO loading and polymer cross-linking affect the sorption capacity and the transport properties of the prepared catalytic materials, with best results obtained for the intermediate CaO concentration in membrane and a lower crosslinking degree.

Poly(methylvinylsiloxane)-Based High Internal Phase Emulsion-Templated Materials (polyHIPEs)-Preparation, Incorporation of Palladium, and Catalytic Properties.

Poly(methylvinylsiloxane) (V3 polymer) obtained by kinetically controlled anionic ring-opening polymerization of 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane was cross-linked with various amounts of 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) in w/o high internal phase emulsions (HIPEs). PolyHIPEs thus prepared differed in the polymer cross-linking degree, which affected their porous morphology and total porosity. The obtained V3 polymer-based polyHIPEs were applied as matrices for the incorporation of Pd from the Pd(OAc)2 solution in tetrahydrofuran. This process involved the conversion of Si–H groups remaining in the polymer networks and resulted in the formation of crystalline, metallic Pd in the systems. Mean sizes of the generated Pd crystallites were lower in polyHIPEs of higher than in those of lower polymer cross-linking degrees and porosities (∼5 nm vs ∼8 nm, respectively). The Pd-containing polyHIPEs showed activity in catalytic hydrogenation of the triple carbon–carbon bond in phenylacetylene giving the unsaturated product, styrene with a selectivity of ca. 80%. To the best of our knowledge, this is the first work devoted to polysiloxane-based polyHIPEs with dispersed metallic particles.

Effects of the curing atmosphere on the structures and properties of polybenzoxazine films

The effects of four different curing atmospheres, i.e., static air, circulating air, nitrogen and vacuum, on the polymerization mechanism, chemical structure, hydrogen bonding, mechanical property, thermal property, water contact angle, etc., of the polybenzoxazine films were systematically studied. It was found that curing in air caused more oxidation and decomposition, generating more benzoquinones, carbonyl groups and iminium ions in the resultant polybenzoxazine films. Consequently, the films cured in air were less cross-linked, darker in color and more brittle. The films cured in static air (SA) showed tensile strength and elongation at break of 12.59 MPa and 2.16%, respectively, which were 61.24 MPa and 2.74% lower than those of the films cured in nitrogen (N2). Moreover, it was demonstrated that more intramolecular rigid –OH···N hydrogen bonding was formed in the films cured in air, which was believed to be the fundamental reason for the lower chemical cross-linking density and poorer toughness. Nevertheless, these films showed higher char yield due to the formation of more thermally stable groups in oxidation process. Further investigation on chemical structures, hydrogen bonding and water contact angles of the upper and lower surfaces of the films revealed that the upper surfaces were more inclined to be oxidized and decomposed during curing and more intramolecular hydrogen bonding (–OH···N HB) was formed on upper surfaces, which led to increased water contact angles.

Properties of extruded cross-linked waxy maize starches and their effects on extruded oat flour

The objectives of this study were to study the extrusion of cross-linked waxy maize starches (CLWMS) with different cross-linking levels and their function as a secondary ingredient in extruded oat flour (OF) formulations. CLWMS (18 %) and OF (82 %) were hydrated to 20 % moisture content and subjected to twin-screw extrusion at the screw speed of 350 rpm. Low cross-linking level of CLWMS (0.05 % sodium trimetaphosphate/sodium tripolyphosphate) in OF formulation increased the void fraction and reduced the breaking strength of extrudates. The low cross-linked starch was more resistant to breakdown and had a higher pasting viscosity than the unmodified starch. Higher cross-linking levels of CLWMS restricted swelling of starch granule and increased the resistant starch level of OF formulation but had very poor structural and textural properties. Varying the level of cross-linking offers an alternative way to manipulate the structural, textural and nutritional properties of extrudates in snack and cereal applications.

Eucommia ulmoides gum-based engineering materials: fascinating platforms for advanced applications

Eucommia ulmoides gum (EUG) exhibits good rubber–plastic duality and great application potential in biomedicine, textiles, aerospace, and other fields. The extraction methods of EUG include mechanical (high-temperature cooking), alkali extraction, solvent, microbial (enzymatic hydrolysis), and comprehensive methods. However, the complicated preparation process and high cost of EUG greatly limit its application. EUG is composed mainly of trans-isoprene, and the high crystallinity of EUG at room temperature showing rigid plastics is due to the relatively regular and short identity period of its molecular chain. Through regulating the ratio of the three-phase structure of EUG (regular crystal region, completely irregular amorphous region, and intermediate region of transition pattern between the crystallized and amorphous regions), it exhibits rubber elasticity at room temperature. The application of EUG is closely related to its crystallinity and cross-linking degree. The double-bond modification of EUG by physical or chemical method can regulate its crystalline structure and cross-linking structure, so that EUG engineering materials that meet the performance requirements of multiple fields can be obtained. EUG with zero cross-linking degree is linear thermoplastic material, which is usually used in artificial limb, medical composite scaffold, composites denture soft lining, and modified plastic. EUG with low cross-linking degree is thermoelastic material, which is frequently used in the preparation of shape memory material, interfacial compatibilizer, and composite film. EUG with critical cross-linking degree is rubber-type material, which is regularly used in elastomer, self-healing material, and modified rubber. In this article, the extraction technology of EUG and its pros and cons and the structure and properties of EUG and their corresponding material states in the past 10 years were systematically discussed. The research progress of engineering materials in different states was introduced, and the effect of modification on the structure and properties of EUG was discussed. The future development direction of the materials was prospected.

Modular Chitosan-Based Adsorbents for Tunable Uptake of Sulfate from Water.

The context of this study responds to the need for sorbent technology development to address the controlled removal of inorganic sulfate (SO42−) from saline water and the promising potential of chitosan as a carrier system for organosulfates in pharmaceutical and nutraceutical applications. This study aims to address the controlled removal of sulfate using chitosan as a sustainable biopolymer platform, where a modular synthetic approach was used for chitosan bead preparation that displays tunable sulfate uptake. The beads were prepared via phase-inversion synthesis, followed by cross-linking with glutaraldehyde, and impregnation of Ca2+ ions. The sulfate adsorption properties of the beads were studied at pH 5 and variable sulfate levels (50–1000 ppm), where beads with low cross-linking showed moderate sulfate uptake (35 mg/g), while cross-linked beads imbibed with Ca2+ had greater sulfate adsorption (140 mg/g). Bead stability, adsorption properties, and the point-of-zero charge (PZC) from 6.5 to 6.8 were found to depend on the cross-linking ratio and the presence of Ca2+. The beads were regenerated over multiple adsorption-desorption cycles to demonstrate the favorable uptake properties and bead stability. This study contributes to the development of chitosan-based adsorbent technology via a modular materials design strategy for the controlled removal of sulfate. The results of this study are relevant to diverse pharmaceutical and nutraceutical applications that range from the controlled removal of dextran sulfate from water to the controlled release of chondroitin sulfate.

Biobased furan-based epoxy/TiO2 nanocomposites for the preparation of coatings with improved chemical resistance

Biobased, solvent-free thermosetting coating systems are developed from epoxidized hydroxymethylfuran (BOMF) crosslinked with methyl nadic anhydride (MNA) filled with TiO2 nanoparticles. The effect of 1 to 5 wt% of TiO2 on the curing behavior of the resin and the overall performance of the resulting coatings is studied by means of rheological, thermal, mechanical, morphological, and chemical resistance tests. TiO2 particles shift the curing reaction to higher temperatures and reduce the reaction enthalpy, resulting in lower crosslinking degrees and glass transition temperatures. The resins are applied as tinplate coatings, exhibiting optimal adhesion to the metal substrate (5A according to ASTM D3359), and performing well in pencil hardness tests (9H and 7H in gouge and scratch hardness, respectively). Morphological characterization highlights homogeneous distribution of TiO2 nanoparticles even at the highest loading. Finally, the chemical resistance of the coatings to ethanol and acetic acid solutions used as simulants is significantly enhanced by the addition of TiO2, resulting in an efficient protection of the tinplate from corrosion. Overall, these results demonstrate that the proposed furan-based thermosets show potential for use as coatings.

Enzymatically Cross-Linked Sodium Caseinate as Techno-Functional Ingredient in Acid-Induced Milk Gels

Sodium caseinate is widely used as techno-functional ingredient in food processing. However, no studies are currently available on applications of enzymatically cross-linked sodium caseinate although such a modification might have a potential to improve its techno-functional properties and thus reduce the amount of protein necessary to achieve the desired product properties. In the present study, aqueous sodium caseinate solutions were cross-linked by microbial transglutaminase to different extents and subsequently spray-dried. These powders were either redissolved in water or added to reconstituted skim milk to compare acid-induced gels from sodium caseinate solutions to gels from milk with added sodium caseinate. Gelation induced by glucono-δ-lactone was studied using time-based oscillation rheology. The maximum storage modulus (G′MAX) of sodium caseinate gels increased with increasing cross-linking extent, whereas enriched milk gels showed a peak in G′MAX at moderate cross-linking extents. Heat treatment of the enriched milk shifted the highest G′MAX to an even lower cross-linking extent. The results show that constituents of complex food matrices as well as processing routes affect the techno-functional properties of modified food proteins such as cross-linked caseins. It was possible to reduce the amount of added protein from 10 to 7.5 g/kg when cross-linked sodium caseinate was used while obtaining milk gels with similar G′MAX and forced syneresis. Future studies should elaborate ways to further improve the properties of cross-linked sodium caseinate to allow for an even greater reduction in protein enrichment.

Mitigation of Physical Aging with Mixed Matrix Membranes Based on Cross-Linked PIM-1 Fillers and PIM-1.

A low cross-link density (LCD) network-PIM-1, which offers high compatibility with the polymer of intrinsic microporosity PIM-1, is synthesized by a modified PIM-1 polycondensation that combines both a tetrafluoro- and an octafluoro-monomer. To maximize the advantages of utilizing such cross-linked PIM-1 fillers in PIM-1-based mixed matrix membranes (MMMs), a grafting route is used to decorate the LCD-network-PIM-1 (dispersed phase) with PIM-1 chains, to further enhance compatibility with the PIM-1 matrix. Mixed-gas CO2/CH4 (1:1, v/v) separation results over 160 days of membrane aging confirm the success of a relatively short (24 h) grafting reaction in improving the initial CO2 separation performance, as well as hindering the aging of PIM-1/grafted-LCD-network-PIM-1 MMMs. For MMMs based on a 24 h grafting route, all the gas separation data surpass the 2008 Robeson upper bound by a significant margin, and the 160-day aged membranes show only 29% reduction from the initial CO2 permeability, which is substantially less than the equivalent losses of nearly 70% and 48% for PIM-1 and traditionally fabricated MMMs counterparts, respectively. These results demonstrate the potential of network-PIM components for obtaining much more stable gas separation performance over extended periods of time.

In-depth investigation on the factors affecting the performance of high oil-absorption resin by response surface method

A series of high oil-absorption resins with low cross-linking degree were synthesized by suspension polymerization using stearyl methacrylate (SMA), 2-Ethylhexyl methacrylate (EHMA), and styrene (St) as monomers. Response surface methodology (RSM) with central composite design (CCD) was also applied to determine the optimal parameters that are mainly known to affect their synthesis. Thus, the effects of the monomer mass ratio (EHMA:SMA), the rigid monomer (St) dosage, the porous agent (acetone) dosage, and their pairwise interaction on the resin's oil-absorption capacity were analyzed, highlighting PSES-R 2 as the resin with the optimum performance. The pure oil-absorption rates of PSES-R 2 for gasoline, diesel, and kerosene were 11.19 g·g −1 , 16.25 g·g −1 , and 14.84 g·g −1 , respectively, while the oil removal rates from oily wastewater were 98.82%, 65.11%, and 99.63%, respectively. • A series of high oil-absorption resins with low cross-linking degree were synthesized by suspension polymerization. • The optimal parameters were determined by response surface methodology (RSM) with central composite design. • The optimized sample PSES-R 2 exhibited the excellent oil-absorption performance.

Structural interaction of semi-interpenetrating polymer network polyurethane/styrene acrylonitrile latex particles

A series of novel structured latex particles with semi-interpenetrating polymer network (IPN) of glassy styrene-acrylonitrile copolymer (SAN) cores and rubbery polyurethane (PU) shells were synthesized to improve damping property. The inverted core/shell synthesis method (rubbery part first, then the glassy part) was applied to control morphology of core/shell latex particles. The glass transition temperature and mechanical property of the obtained semi-IPN were characterized by DMA and UTM, respectively. The effect of composition on the mechanical properties of core/shell latex IPN particles was studied. It was found that the core/shell latex particles with high crosslinking density are more miscible than those with low crosslinking density. Additionally, the improved tensile strength and elongation were observed. Therefore, the crosslinking efficiency of PU plays an important role in governing phase miscibility in core/shell latex IPN particles.

Dual Cross-linked HHA Hydrogel Supplies and Regulates MΦ2 for Synergistic Improvement of Immunocompromise and Impaired Angiogenesis to Enhance Diabetic Chronic Wound Healing.

Immunocompromise and impaired angiogenesis of diabetes lead to chronic inflammation when wounds occur, which is the primary reason for the long-term incurable nature of diabetic chronic wounds. Herein, a high-molecular-weight hyaluronic acid (HHA) hydrogel is developed to supply and regulate M2 phenotype macrophages (MΦ2) for synergistic improvement of immunocompromise and impaired angiogenesis. MΦ2 are seeded on the Cu-HHA/PVA hydrogels prepared by Cu2+ cross-linking of low degree and physical cross-linking (one freeze-thaw cycle and unique lyophilization) to form Cu-HHA/PVA@MΦ2 hydrogels. The Cu-HHA/PVA@MΦ2 hydrogel can directly supply the MΦ2 in the wound site, maintain the consistent phenotype of loaded MΦ2, and transform the M1 phenotype macrophages (MΦ1) in the wound bed to MΦ2 by HHA. Furthermore, Cu2+ could be released from the hydrogels to further stimulate angiogenesis, thus accelerating the wound-healing phase transition from inflammation to proliferation and remodeling. The average wound area after the 0.5Cu-HHA/PVA@MΦ2 (ionic cross-linking degree 0.5%) treatment was much smaller than that of other diabetic groups at day 12 and close to that of the wild nondiabetic control group. Therefore, this facile hydrogel strategy with multiple modulation mechanisms of immunocompromise and angiogenesis may act as a safe and effective treatment strategy for a diabetic chronic wound.

Crosslinking of Chitosan with Dialdehyde Chitosan as a New Approach for Biomedical Applications.

Materials based on natural high molecular compounds are particularly interesting for biomedical applications. It is known that the cross-linking agent used for preparation of biomacromolecule-based materials is as important as used biopolymer. Therefore, natural cross-linkers containing reactive carbonyl groups are of great interest especially for modifying properties of natural polysaccharides. One of the most popular cross-linking agents is glutaraldehyde. Nevertheless, the unreacted particles can be released from the cross-linked material and cause cytotoxic effects. This can be eliminated when using a cross-linker based e.g., on polysaccharides. This article describes quick and efficient synthesis of dialdehyde chitosan (DACS) and its application for the preparation of chitosan films. Materials obtained with different amount of DACS were fully characterized in terms of structure and surface morphology. Thermal and mechanical properties as well as hydrophilic character were also examined. The results obtained were compared with the materials obtained by cross-linking chitosan with low molecular weight glutaraldehyde and high molecular weight cross-linking agent based on polysaccharide–dialdehyde starch. Toxicity of all obtained materials was tested using the Microtox® test. It has been shown that due to better mechanical, thermal and surface properties as well as lower toxicity, dialdehyde chitosan is a very promising crosslinking agent.