Self-assembling tripeptide forming water-bound channels and hydrogels

D-Ser(tBu)-L-Phe-L-Trp is described as a self-assembling tripeptide that yields nanofibrillar hydrogels at physiological conditions (phosphate buffer at pH 7.4). The peptide is characterized by several spectroscopic methods, such as circular dichroism and fluorescence, oscillatory rheometry, and transmission electron microscopy. Single-crystal X-ray diffraction reveals supramolecular packing into water-bound channels and allows the visualization of the intermolecular interactions holding together peptide stacks.     

A short oxazolidine-2-one containing peptide forms supramolecular hydrogels under controlled conditions

Low-molecular-weight hydrogels are made of a small percentage of small organic molecules dispersed in an aqueous medium, which may aggregate in several manners using different methods. However, often the organic gelator in water has poor solubility, so the addition of a solubilising agent is required. In the case of acidic gelators, this mainly consists of the addition of a strong base, that is sodium hydroxide, that deprotonates the acidic moiety, so the gelator molecules become more soluble and tend to assemble into micelles, forming a dispersion. Some gelators, however, are sensitive to the harsh pH and get hydrolysed. This is the case of some molecules presenting carbamates in their features, like Fmoc-protected or oxazolidinone-containing peptides. In this paper, we present a valid alternative to sodium hydroxide, by dissolving a tripeptide containing an oxazolidinone moiety in a phosphate buffer (PB) medium at pH 7.4. The results obtained with the NaOH dissolution are compared with the ones with PB, as both methods present advantages and drawbacks. The use of NaOH produces transparent but weak hydrogels, as it exposes the gelator to harsh conditions that end up in its partial hydrolysis, which is more pronounced at high concentrations (≥10 mM). Using PB to dissolve the gelator, this problem is completely avoided as no hydrolysis product has been detected in the hydrogels, which are very stiff although more opaque. By tuning the preparation conditions, we can obtain a wide variety of hydrogels, with the properties required by the final application.     

Superabsorbent hydrogel composite made of cellulose nanofibrils and chitosan-graft-poly(acrylic acid)

Superabsorbent hydrogel composites based on cellulose nanofibrils and chitosan-graft-poly(acrylic acid) copolymer were developed in this work. The FTIR data showed that the copolymerization and the composite formation reaction were successfully performed. In addition, the XRD pattern indicated that the nanofibrils crystallinity was as high as 90%. A 2⁴⁻¹ fractional factorial design was employed to evaluate the effect of acrylic acid/chitosan molar ratio, crosslinker, initiator, and filler in the swelling capacity of hydrogel composites. By the analysis of variance (ANOVA), including F-test and P-values, it was found that the crosslinker and filler correspond to 40% and 30% of the evaluated response, respectively. The addition of nanofibrils provided faster equilibrium conditions as well as improved the swelling capacity in ca. 100 units, from 381 to 486. SEM images showed that the addition of nanofibrils into the hydrogel matrix increased the averaged-dimension of porous. Finally, the composites showed responsive behavior in relation to pH and salt solution. Such characteristics make these smart materials suitable for several technological applications.     

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler¹ in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m²/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO₂ conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO₂ drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm³), high specific surface area (350 - 500 m²/g) and pore volume (3 - 7 cm³/g for pore sizes less than 150 nm).     

Development of a simple coarse-grained DNA model for analysis of oligonucleotide complex formation

In this paper, we develop a coarse-grained nucleotide model for the purpose of simulating large-scale aptamer-based hydrogel network formation in future research. In the model, each nucleotide is represented by a single interaction site containing sugar, phosphate and base. Discontinuous molecular dynamics (DMD) simulations are performed to simulate formation and denaturation of oligonucleotide duplexes as a function of temperature. The simulated melting temperatures of oligonucleotide duplexes are calculated in simulations of systems with different sequences, lengths and concentrations of oligonucleotides, and compared to data from the OligoAnalyzer tool. The denaturation of oligonucleotide triplexes containing a hybridised structure of three different oligonucleotides is analysed using both simulations and experiments. The nucleotide model is found to be a good predictor of the oligonucleotide’s hybridised state for both duplexes and triplexes. This coarse-grained model has wide ranging applications in the development or optimisation of DNA-based technologies including DNA origami, DNA-enabled hydrogels and DNA-based biosensors.     

β-Cyclodextrin hydrogels as potential drug delivery systems

β-cyclodextrins (βCD) are cyclic oligosaccharides which have been widely employed for pharmaceutical applications. Discs of insoluble polymers were synthesized by crosslinking β-cyclodextrins with the reagent epichlorohydrin. In this work, the possibility of employing a polymer containing 60 ± 3% βCD for drug delivery of two antiinflammatory (naproxen and nabumetone) and two antifungal drugs (naftifine and terbinafine) has been investigated. The interaction of Naproxen with the polymers was evidenced by X-ray diffractometry, FTIR spectroscopy and differential thermal analysis. Drug release kinetics were carried out at physiological conditions of pH and temperature, and kinetic and diffusion constants were calculated by fitting 60% of the release profile according to the Korsmeyer-Peppas equation. Also, diffusion coefficients were calculated according to the simplified Higuchi model. The drug release followed a simple Fickian diffusion mechanism for all the model drugs. This study suggests that these hydrogel matrices are potentially suitable as sustained release systems.     

Modulation of hydrogel networks by metal ions

Self-assembling hydrogels are receiving great attention for both biomedical and technological applications. Self-assembly of protein/peptides as well as organic molecules is commonly induced in response to external triggers such as changes of temperature, concentration, or pH. An interesting strategy to modulate the morphology and mechanical properties of the gels implies the use of metal ions, where coordination bonds regulate the dynamic cross-linking in the construction of hydrogels, and coordination geometries, catalytic, and redox properties of metal ions play crucial roles. This review aims to discuss recent insights into the supramolecular assembly of hydrogels involving metal ions, with a focus on self-assembling peptides, as well as applications of metallogels in biomedical fields including tissue engineering, sensing, wound healing, and drug delivery.     

Optically activated and interrogated plasmonic hydrogels for applications in wound healing

We disclose the use of hybrid materials featuring Au/Ag core/shell nanorods in porous chitosan/polyvinyl alcohol scaffolds for applications in tissue engineering and wound healing. The combination of Au and Ag in a single construct provides synergistic opportunities for optical activation of functions as near infrared laser tissue bonding, and remote interrogation to return parameters of prognostic relevance in wound healing monitoring. In particular, the bimetallic component ensures optical tunability, enhanced shelf life and photothermal stability, serves as a reservoir of germicidal silver cations, and changes in near‐infrared and visible color according to the environmental level of oxidative stress. At the same time, the polymeric blend is ideal to bind connective tissue upon photothermal activation, and to support fabrication processes that provide high porosity, such as electrospinning, thus putting all the premises for cellular repopulation and antimicrobial protection.     

甘氨酸和赤藓糖醇胶饵对红火蚁工蚁的毒杀效果

前期研究发现甘氨酸和赤藓糖醇对红火蚁Solenopsis invicta Buren有较好的毒杀效果,为进一步挖掘这两种物质的实际应用价值,在室内测试了甘氨酸和赤藓糖醇不同浓度配比的水溶液及胶状饵剂对红火蚁工蚁的毒杀效果.结果显示,20％的配比为1∶3、3∶1的赤藓糖醇和甘氨酸溶液喂饲48 h红火蚁工蚁的死亡率分别为83.1％和84.93％,而72h后,死亡率分别为95.07％和95.21％,与取食茚虫威饵剂的工蚁死亡率(48 h:92.57％;72 h:100％)无显著差异.20％的配比为1∶3、3∶1的赤藓糖醇和甘氨酸水凝胶颗粒喂饲48 h红火蚁工蚁的死亡率分别为58.94％和55.05％,而72 h后,死亡率分别为85.11％和80.05％,显著低于取食茚虫威饵剂的工蚁死亡率(48 h:95.71％;72 h:99.59％).研究结果为进一步利用开发红火蚁环保型饵剂提供参考.     

Smart hydrogels for bioseparation

Smart hydrogels are hydrogels which alter their dimension (i.e., either swell or shrink) dramatically upon a small change in an environmental condition, such as temperature, pH, ionic strength, salt type, solvent, etc. Due to large changes in the swelling ratio, the smart hydrogels have been used widely in the separation of various molecules including proteins. Bioseparation using smart hydrogels is convenient, cost effective, and operable in mild conditions. The use of mild conditions during separation is critical for proteins which can be easily denatured or degraded. Smart hydrogels currently used in bioseparation and their limitations as well as improvements to be made are described here. This revised version was published online in July 2006 with corrections to the Cover Date.