Alginic acid, a naturally occurring polysaccharide, in its granular form and without any post-modification was found to be an efficient, environmentally benign, easily recoverable and low-cost ...catalyst for the clean and rapid synthesis of 1,4-dihydropiridine derivatives (DHPs) just based on its polysaccharide architecture. The Hantzsch pseudo-four-component reaction of ethyl or methyl acetoacetate, ammonium acetate and different aldehydes is catalyzed by alginic acid efficiently under mild conditions to afford the desired products in high to quantitative yields and clean reaction profiles. Avoiding the use of any transition metal, the use of a one-pot and multi-component procedure for the synthesis of DHPs, the reusability of the catalyst and operational simplicity are important features of this methodology.
Poly(glycerol sebacate) (PGS) is a biodegradable and biocompatible polyester that is increasingly used in the biomedical field. Herein, a novel ternary poly(ε‐caprolactone)/gelatin/PGS ...(PCL/gelatin/PGS) blend nanofibers were designed and fabricated with a wide range of chemical compositions, mechanical properties, and modulated degradability levels. PGS blends with gelatin are commonly used for enhancing electrospinability but their low‐mechanical properties, lack of structural stability in an aqueous medium, and unmodulated degradation behavior limited their application. Blending PGS and gelatin with PCL could improve their properties in a ternary structure. In addition, considering ternary blends of PCL/gelatin/PGS, an enhancement of hydrophilicity due to the presence of gelatin in the system is expected, resulting in better biocompatibility and controlled biodegradation. By increasing the polymer concentration, voltage, and distance of the needle to the collector, the bead‐free electrospun nanofibers were obtained. The ternary blend nanofibers with an equal weight ratio of polymers, T33 (containing 33 wt% PGS, 33 wt% gelatin, and 33 wt% PCL), possess more than a 4‐fold increase in tensile strength (7 MPa) and 89‐fold increase in elongation at break (1760.6%) compared to gelatin/PGS binary nanofibers. In vitro studies on glioma cells showed well attachment and proliferation of C6 glioma cells. The obtained results demonstrated the potential of these scaffolds for nerve tissue engineering applications.
A number of different ionic aqueous polyurethane dispersions (PUDs) were synthesized based on NCO-terminated prepolymers. Two different anionic and cationic polyurethane samples were synthesized ...using dimethylol propionic acid and N-methyldiethanolamine emulsifiers, respectively. Then, proper amounts of PUDs and sodium alginate were mixed to obtain a number of aqueous polyurethane dispersions–sodium alginate (PUD/SA) elastomers. The chemical structure, thermal, morphological, thermo-mechanical and mechanical properties, and hydrophilicity content of the prepared samples were studied by FTIR, EDX, DSC, TGA, SEM, DMTA, tensile testing and contact angle techniques. The cationic polyurethanes and their blends with sodium alginate showed excellent miscibility and highly stretchable properties, while the samples containing anionic polyurethanes and alginate illustrated a poor compatibility and no significant miscibility. The morphology of alginate particles shifted from nanoparticles to microparticles by changing the nature of PUDs from cationic to anionic types. The final cationic elastomers not only showed better mechanical properties but also were formulated easier than anionic samples.
Using tissue engineering approaches is one of interesting strategies to repair cartilage injuries. This study reports the preparation of surface-modified electrospun polycaprolactone nanofibrous ...scaffolds with highly negatively-charged sulfated alginate as functional support for chondrogenic differentiation of mesenchymal stem cells. In this regard, polycaprolactone (PCL) nanofibers were fabricated by electrospinning, surface-activated by cold atmospheric plasma and further surface-modified with aqueous solutions of sulfated alginate. The scanning electron microscopy images showed the nanofibrous structure of electrospun PCL mats. The successful surface modification of PCL nanofibrous scaffolds with sulfated alginate was confirmed by the appearance of fingerprint region of mannuronic acid at 812 cm
−1
in attenuated total reflectance Fourier transform infrared spectroscopy spectra. The cytocompatibility of the nanofibrous scaffolds for mesenchymal stem cells (MSCs) was confirmed using MTT assay. Reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry for type 2 COLLAGEN marker were conducted to confirm the chondrogenic differentiation of seeded MSCs on the surface of scaffolds. The expression of type 2 COLLAGEN by RT-PCR and immunocytochemistry analyses confirmed the chondrogenic differentiation of MSCs. Our results showed that sulfated alginate surface-modified PCL nanofibrous scaffold as an appropriate substrate for cell attachment and growth could promote the MSCs differentiate to chondrocytes.
Despite numerous applications of nanofibrous alginate (Alg) mat, its facile fabrication via electrospinning is still challenging. The low alginate content compared to the carrier polymer and ...existence of impurities are the main drawbacks of existing approaches. The purpose of this research is both to study and improve alginate electrospinnability by focusing on the effect of inter- and intramolecular hydrogen bonding. Based on hard and soft acids and bases (HSAB) theory, the Na+ cations (carboxylate counter-cation) were substituted with a harder acid, Li+ cation, to increase the strength of ionic interaction and decrease the density of hydrogen bonding. Viscosity and electrical conductivity measurements as well as FTIR and 1H NMR revealed a lower intramolecular hydrogen bonding density in Li-Alg. SEM images showed improvement of alginate electrospinnability for Li-Alg compared to the salts of Na-Alg and K-Alg. This study sheds more light on underlying reasons hindering alginate electrospinning and introduces a simple method for fabrication of nanofibers with high alginate content.
Abstract
Owing to the similarity of hydrogels to cartilage extracellular matrix, they have been extensively utilized in the chondral lesions. Moreover, their tunable administration properties are ...desirable for reducing injuries in lesion sites. Generally, injectable hydrogels are mechanically weak, requiring some modifications for being used as a cell carrier in place of articular cartilage. In this study, a combination of
β
-cyclodextrin-grafted alginate (Alg-
β
-CD) and pluronic-amine with multiple physical crosslinking was used for the first time. Supramolecular interactions, including electrostatic forces, host-guest interaction, and hydrophobic interaction with increasing temperature maintain injectability of hydrogels while these interactions boost mechanical properties to the extent that shear modulus surpassed 40 kPa. Vacant
β
-CD cavities in conjunction with gel network were exploited for kartogenin (KGN) loading. All groups had gel time of less than one minute and gel temperature was 28 °C. No toxic effect of hydrogels on encapsulated cells was observed. While the optimum combination of polymers provided a sustainable release for KGN, it also extended the
in vitro
degradation time of hydrogels from six days to two weeks. KGN facilitated encapsulated mesenchymal stem cells differentiation towards chondrocytes. Taken together, the synthesized hydrogel proved to be a promising candidate for being utilized in cartilage regeneration.
•We showed that different stereochemistries of a material can influence its biocompatibility.•Regioselectivity of sulfate groups significantly affect the biocompatibility of the alginate.•Sulfated ...alginate was found as a more biocompatible material than neat alginate.•Sulfated alginate is an appropriate coating candidate to use in islet microencapsulation.
Type 1 diabetes, an autoimmune disease, is increasing in prevalence worldwide. Pancreatic islet encapsulation by biocompatible alginate hydrogels may be a promising cell-based therapy approach to control blood glucose levels in patients with type 1 diabetes. However, a substantial obstacle to this approach is the immune system’s reaction to the presence of a foreign body and fibrosis formation. In this study, we used three methods to synthesize three different constitutional isomers of sulfated alginate by sulfation of uronic acid residues of alginate. Next, we evaluated the effects of the different stereochemistries of these isomers on alginate biocompatibility. In addition, we assessed the immune system response to these isomers. The calcium sulfated alginate microcapsules were subcutaneously implanted into male Wistar rats. After 14 days, the samples were evaluated by histological and immunofluorescent analyses. The results showed considerable variations in biocompatibility of the islet-free microcapsules that contained the different stereochemistries. Next, we chose the best samples that mitigated fibrosis and used them as the third layer of three-layer microcapsules that contained pancreatic islets. These microcapsules were subsequently transplanted into the omental pouches of diabetic mice. Interestingly, the mice had reduced blood glucose levels for more than six weeks. Both the intraperitoneal glucose tolerance test (IP-GTT) and C-peptide analyses showed correct function of the transplanted islets in these diabetic mice at four and six weeks after transplantation, respectively. There was a significant reduction in collagen content around the transplanted microcapsules in both the method 1 (M1) and method 3 (M3) coated groups (sulfated alginates) compared with the alginate group.
Aqueous polyurethane dispersions (APUDs) are commodity synthetic polymers and have a broad range of well-known applications, nevertheless their possible use as a green catalyst or ionic solvent is ...yet unknown. Here, we demonstrate how a polyurethane dispersion facilitates the progress of the Cannizzaro reaction under very mild alkaline conditions. We introduce anionic polyurethane nanomicelles as an expeditious green polymer ionic solvent for the Cannizzaro reaction. The reusable and novel eco-friendly polymer solvent, excellent yields of the products, low reaction times and low reaction temperatures are the main advantages of this reaction.
Aqueous polyurethane dispersions (APUDs) are commodity synthetic polymers and have a broad range of well-known applications, nevertheless their possible use as a green catalyst or ionic solvent is ...yet unknown. Here, we demonstrate how a polyurethane dispersion facilitates the progress of the Cannizzaro reaction under very mild alkaline conditions. We introduce anionic polyurethane nanomicelles as an expeditious green polymer ionic solvent for the Cannizzaro reaction. The reusable and novel eco-friendly polymer solvent, excellent yields of the products, low reaction times and low reaction temperatures are the main advantages of this reaction.
The Cannizzaro reaction is performed under very mild alkaline conditions using anionic polyurethane nanomicelles as a novel reusable polymeric ionic solvent.
Wound healing remains a burdensome healthcare problem due to moisture loss and bacterial infection. Advanced hydrogel dressings can help to resolve these issues by assisting and accelerating ...regenerative processes such as cell migration and angiogenesis because of the similarities between their composition and structure with natural skin. In this study, we aimed to develop a keratin-based hydrogel dressing and investigate the impact of the delivery of LL-37 antimicrobial peptide using this hydrogel in treating full-thickness rat wounds. Therefore, oxidized (keratose) and reduced (kerateine) keratins were utilized to prepare 10% (w/v) hydrogels with different ratios of keratose and kerateine. The mechanical properties of these hydrogels with compressive modulus of 6–32 kPa and tan δ <1 render them suitable for wound healing applications. Also, sustained release of LL-37 from the keratin hydrogel was achieved, which can lead to superior wound healing. In vitro studies confirmed that LL-37 containing 25:75% of keratose/kerateine (L-KO25:KN75) would result in significant fibroblast proliferation (∼85% on day 7), adhesion (∼90 cells/HPF), and migration (73% scratch closure after 12 h and complete closure after 24 h). Also, L-KO25:KN75 is capable of eradicating both Gram-negative and Gram-positive bacteria after 18 h. According to in vivo assessment of L-KO25:KN75, wound closure at day 21 was >98% and microvessel density (>30 vessels/HPF at day 14) was significantly superior in comparison to other treatment groups. The mRNA expression of VEGF and IL-6 was also increased in the L-KO25:KN75-treated group and contributed to proper wound healing. Therefore, the LL-37-containing keratin hydrogel ameliorated wound closure, and also angiogenesis was enhanced as a result of LL-37 delivery. These results suggested that the L-KO25:KN75 hydrogel could be a sustainable substitute for skin tissue regeneration in medical applications.
