Thixotropic Hydrogels Composed of Self-Assembled Nanofibers of Double-Hydrophobic Elastin-Like Block Polypeptides

Physically crosslinked hydrogels with thixotropic properties attract considerable attention in the biomedical research field because their self-healing nature is useful in cell encapsulation, as injectable gels, and as bioinks for three-dimensional (3D) bioprinting. Here, we report the formation of thixotropic hydrogels containing nanofibers of double-hydrophobic elastin-like polypeptides (ELPs). The hydrogels are obtained with the double-hydrophobic ELPs at 0.5 wt%, the concentration of which is an order of magnitude lower than those for previously reported ELP hydrogels. Although the kinetics of hydrogel formation is slower for the double-hydrophobic ELP with a cell-binding sequence, the storage moduli G′ of mature hydrogels are similar regardless of the presence of a cell-binding sequence. Reversible gel–sol transitions are demonstrated in step-strain rheological measurements. The degree of recovery of the storage modulus G′ after the removal of high shear stress is improved by chemical crosslinking of nanofibers when intermolecular crosslinking is successful. This work would provide deeper insight into the structure–property relationships of the self-assembling polypeptides and a better design strategy for hydrogels with desired viscoelastic properties.

Camel Gelatin Composition, Properties, Production, and Applications

Gelatin is an important protein produced through partial hydrolysis of collagen from animal parts and byproducts such as cartilage, bones, tendons, and hides. The ability of gelatin to form a thermo-reversible gel at normal body temperature and high water content make it an exceptional food ingredient. A good quality gelatin is translucent, brittle, colorless (sometimes slightly yellow), bland in taste, and odorless. Gelatin has been found useful as stabilizer and filler in dairy products and other food industries. Recently, the global gelatin production net over 300,000 metric tons: 46% were from pigskin, 29.4% from bovine hides, 23.1% from bones, and 1.5% from other parts. Although camels have been recognized as source of meat and milk, utilization of camel bones and skins for gelatin production has not been fully explored. This chapter will discuss the processing of camel gelatin extraction.

Synthesis and Characterization of Silicate Gel by using Sol-gel Process: Experiments and DFT calculations

The synthesis of geopolymers requires the formation of an irreversible gel. This gel is produced by the sol-gel process using sodium silicate and hydrochloric acid reagents. On the one hand, the experimental study of the gelling reaction shows that for concentrations of hydrochloric acid varying between 0.5-2.0 mol/L and concentration of sodium silicate varying between 1.0-6.0 mol/L, three reaction products are obtained. The first product is a clear solution, the second product is a reversible gel, and the last product is an irreversible gel. The products obtained are characterized by SEM, X-Ray Diffraction, FTIR spectroscopy and EDS Spectroscopy techniques. The microstructural analyzes of the two gels revealed that these obtained solids are almost similar whereas the structural and elementary analyzes show that the silica content in the irreversible gel is higher than the silica content in the reversible gel. On the other hand, the theoretical study of the reactivity of gelling, defined via the conceptual density functional theory (CDFT) combined with functional B3LYP function with a 6-31G base (d). They are allowed us to define the global and local reactivity indexes of two reagents, sodium silicate and hydrochloric acid.

Poly[(N-acryloyl glycinamide)-co-(N-acryloyl l-alaninamide)] and Their Ability to Form Thermo-Responsive Hydrogels for Sustained Drug Delivery

In the presence of water, poly(N-acryloyl glycinamide) homopolymers form highly swollen hydrogels that undergo fast and reversible gel↔sol transitions on heating. According to the literature, the transition temperature depends on concentration and average molecular weight, and in the case of copolymers, composition and hydrophilic/hydrophobic character. In this article, we wish to introduce new copolymers made by free radical polymerization of mixtures of N-acryloyl glycinamide and of its analog optically active N-acryloyl l-alaninamide in various proportions. The N-acryloyl l-alaninamide monomer was selected in attempts to introduce hydrophobicity and chirality in addition to thermo-responsiveness of the Upper Critical Solubilization Temperature-type. The characterization of the resulting copolymers included solubility in solvents, dynamic viscosity in solution, Fourrier Transform Infrared, Nuclear Magnetic Resonance, and Circular Dichroism spectra. Gel→sol transition temperatures were determined in phosphate buffer (pH = 7.4, isotonic to 320 mOsm/dm3). The release characteristics of hydrophilic Methylene Blue and hydrophobic Risperidone entrapped in poly(N-acryloyl glycinamide) and in two copolymers containing 50 and 75% of alanine-based units, respectively, were compared. It was found that increasing the content in N-acryloyl-alaninamide-based units increased the gel→sol transition temperature, decreased the gel consistency, and increased the release rate of Risperidone, but not that of Methylene Blue, with respect to homo poly(N-acryloyl glycinamide). The increase observed in the case of Risperidone appeared to be related to the hydrophobicity generated by alanine residues.

Intelligent copolymers based on poly (N-isopropilacrylamide). Part ii: Grafts polysaccharide to obtain new biomaterials for biomedical and pharmacological applications

Biopolymers such as polysaccharides are compounds that have functional groups and they are very susceptible to be used in chemical modifications and also allows them to synthesizer of new copolymers (used as graft-like chains). Poly (N-Isopropylacrylamide) PNIPAm, is a thermosensitive synthetic polymer widely used in the preparation of intelligent gels for the biomedical field, but have some limitations in use as biodegradable matrix or scaffolds. In this research wered the synthesis and characterization of copolymers their PNIPAm grafted with the polysaccharides: chitosan (CS) or hyaluronic acid (HA), were performed to obtain new biodegradable and biocompatible biomaterials that conserve the intelligent character (thermosensitivity).The PNIPAm was in first chemically modified with 3-butenoic acid in order to generate carboxyl end groups on the graft-polymer chain (PNIPAm-co-COOH) which serve as anchor points and then covalently graft the polysaccharides. For the specific case of grafting with hyaluronic acid, it was necessary to perform a second modification using piperazine (PIP) and obtain the graft-polymers PNIPAm-co-COO-g-PIP. All this modification process was previously reported (Carrero et al, 2018). In this case, the polysaccharides used as grafts-like chains were: (1) chitosan oligomers obtained by acid degradation and (2) hyaluronic acid. The characterization of all copolymers obtained was follow by infrared spectroscopic (FT-IR); the differential scanning calorimetric (DSC) technique was used to determine the lower critical solution transition temperature (LCST), resulting in the range of 29-34 °C. Its morphology was studied using scanning electron microscopy (SEM), but previously was simulate an inject process, for the reversible gel character presented by these novel copolymers; resulting a high porosity and interconnection between pores (scaffold-like micrometric structures). Hemocompatibility assays were performed on agar/blood systems, showing non cytotoxicity. All these results give these graftcopolymers a high potentiality of use as scaffolds in tissue engineering and also for pharmacological applications.