Chemical and photochemical DNA "gears" reversibly control stiffness, shape-memory, self-healing and controlled release properties of polyacrylamide hydrogels

A new class of stimuli-responsive DNA-based polyacrylamide hydrogels is described. They consist of glucosamine-boronate ester-crosslinked polyacrylamide chains being cooperatively bridged by stimuli-responsive nucleic acids. The triggered closure and dissociation of the stimuli-responsive units lead to switchable stiffness properties of the hydrogel. One hydrogel includes glucosamine-boronate esters and K⁺-ion-stabilized G-quadruplex units as cooperative crosslinkers. The hydrogel bridged by the two motifs reveals high stiffness, whereas the separation of the G-quadruplex bridges by 18-crown-6-ether yields a low stiffness hydrogel. By cyclic treatment of the hydrogel with K⁺-ions and 18-crown-6-ether, it is reversibly cycled between high and low stiffness states. The second system involves a photo-responsive hydrogel that reveals light-induced switchable stiffness functions. The polyacrylamide chains are cooperatively crosslinked by glucosamine-boronate esters and duplex nucleic acid bridges stabilized by trans-azobenzene intercalator units. The resulting hydrogel reveals high stiffness. Photoisomerization of the trans-azobenzene units to the cis-azobenzene states results in the separation of the duplex nucleic acid bridges and the formation of a low stiffness hydrogel. The control over the stiffness properties of the hydrogel matrices by means of K⁺-ions/crown ether or photoisomerizable trans-azobenzene/cis-azobenzene units is used to develop shape-memory, self-healing, and controlled drug-release hydrogel materials.

Controlled drug delivery of ciprofloxacin from ultrasonic hydrogel

Ciprofloxacin is an antibacterial fluoroquinolone that stops the DNA synthesis, after penetration into the bacterial cells. This drug is applied in the curing of bacterial infections, as well as in antibiotics to treat urinary infections in women, infectious diarrhea and typhoid fever. The objective of the present work is to study controlled release of ciprofloxacin by hydrogel prepared by ultrasound. For this, first the swelling properties of hydrogel and then the absorption of drug were evaluated. The swollen hydrogel was dried in oven (50°C) and was ready for release experiments. During release, the loaded powder of the hydrogel was added to a buffer solution of pH 7.4, similar to human body condition. Then drug concentration was measured using a UV-visible (UV-Vis) spectrophotometer and a calibration curve. The results showed that the hydrogel is sensitive to pH, which makes it a good candidate for ciprofloxacin delivery in intestine. In addition, it was shown that the drug absorption is proportional with the swelling content of the hydrogel and the drug concentration in the loading process. The chemical structure and morphology of the hydrogels and loaded drug were characterized using Fourier transform infrared, UV-Vis, scanning electronic microscopy and thermal gravimetric analysis spectroscopy. According to the results presented here, acrylic-based hydrogels can be used in biomedical fields, especially for controlled drug release.

Photo-crosslinking hyaluronan-heparin hybrid hydrogels for BMP-2 sustained delivery

A series of hyaluronan-heparin (HA-HP) hybrid hydrogels with an HP mass content from 1% to 10% were constructed by photo-crosslinking for the sustained delivery of growth factors (GFs) in soft tissue engineering. Glycidyl methacrylated HA (HAGMA) and glycidyl methacrylated HP (HPGMA) at a substitution degree of 33% and 17%, respectively, by 1H nucleic magnetic resonance (1H NMR) were synthesized and then used for gelation under ultraviolet radiation, followed by various characterizations, including elemental analysis, scanning electron microscopy (SEM), water swelling test, rheological analysis, and bone morphogenetic protein-2 (BMP-2) loading and delivery. The actual contents of HPGMA in HA-HP hydrogels were almost the same as their feeding ratios, indicative of a complete reaction by photo-crosslinking. The incorporation of HP into HA network gently influenced the morphology, water swelling property and rheological properties of hydrogels, but at 10% HP, it doubly increased the BMP-2 loading capacity to 65 ng/mg, alleviated the BMP-2 burst release to 40% within the initial 4 days and prolonged the BMP-2 sustained delivery to over 28 days. These results revealed that the long-term sustained delivery of BMP-2 from HA hydrogel could be achieved by conjugating HP into the crosslinked network with a controllable content.

Functional nucleic acid-based hydrogels for bioanalytical and biomedical applications

Hydrogels are crosslinked hydrophilic polymers that can absorb a large amount of water. By their hydrophilic, biocompatible and highly tunable nature, hydrogels can be tailored for applications in bioanalysis and biomedicine. Of particular interest are DNA-based hydrogels owing to the unique features of nucleic acids. Since the discovery of the DNA double helical structure, interest in DNA has expanded beyond its genetic role to applications in nanotechnology and materials science. In particular, DNA-based hydrogels present such remarkable features as stability, flexibility, precise programmability, stimuli-responsive DNA conformations, facile synthesis and modification. Moreover, functional nucleic acids (FNAs) have allowed the construction of hydrogels based on aptamers, DNAzymes, i-motif nanostructures, siRNAs and CpG oligodeoxynucleotides to provide additional molecular recognition, catalytic activities and therapeutic potential, making them key players in biological analysis and biomedical applications. To date, a variety of applications have been demonstrated with FNA-based hydrogels, including biosensing, environmental analysis, controlled drug release, cell adhesion and targeted cancer therapy. In this review, we focus on advances in the development of FNA-based hydrogels, which have fully incorporated both the unique features of FNAs and DNA-based hydrogels. We first introduce different strategies for constructing DNA-based hydrogels. Subsequently, various types of FNAs and the most recent developments of FNA-based hydrogels for bioanalytical and biomedical applications are described with some selected examples. Finally, the review provides an insight into the remaining challenges and future perspectives of FNA-based hydrogels.