Degradable and Thermosensitive Microgels with Tannic Acid as the Sole Cross-Linker

Effect of segmental motion on hydrolytic degradation of polyglycolide in electro-spun fiber mats

Recently, environmentally degradable polymers have received great attention from the perspective of sustaining the aquatic environment. To control the degradation behavior of solid polymer materials in an aqueous phase, it is crucial to better understand the thermal molecular motion of polymer chains in water. We herein focus on polyglycolide (PGA), which is one of the representative aliphatic polyesters that are hydrolytically degradable. Three kinds of fiber mats of PGA with different fiber diameters and comparable crystallinities were prepared using an electrospinning method. Our choice of fiber mats was because the ratio of the surface area, where the hydrolytic degradation starts to occur, to the volume was larger than that for the films. Dynamic mechanical analysis (DMA) enabled us to gain direct access to the dynamic glass transition temperature (Tgα) of PGA in the fiber mats both in dry gaseous nitrogen and liquid water. The Tgα value varied not only with the presence of water molecules, but also with the fiber diameter, or the specific surface area. The degradation behavior of PGA fiber mats was examined by immersing the samples in phosphate-buffered saline at various temperatures. When the segmental motion of PGA in the fiber mats was released, the apparent crystallinity of the mats increased, meaning that PGA amorphous chains were cleaved and thus partially eluted into the aqueous phase. It was also shown that partially cleaved chains crystallized.

Degradable PDA@PNIPAM-TA Nanocomposites for Temperature- and NIR light-Controlled Pesticide Release

Controlled pesticide delivery systems offer many distinctive advantages over conventional pesticide formulations. In this work, degradable poly(N-isopropylacrylamide) (PNIPAM)-tannic acid (TA) microgels and multifunctional PDA@PNIPAM-TA nanocomposites were prepared in a high-gravity rotating packed bed reactor (RPB) for smart pesticide delivery and release. The as-prepared microgels and nanocomposites showed reversible temperature-dependent swelling/deswelling behavior and irreversible pH-induced degradation. A dynamic contact angle test suggested that the introduction of TA and PDA into the PNIPAM matrix could enhance foliar adhesion and deposition efficiency. The nanocomposites were further used for the encapsulation and delivery of imidacloprid (IMI) to protect it from rapid photolysis and improve its pest-control efficiency. Their thermoresponsive behavior as well as pesticide loading capacity could be tuned by tailoring the PNIPAM-TA shell thickness, which could be varied by the NIPAM amount. The release rate of IMI from the core/shell nanocomposites was positively correlated with environmental temperature and near-infrared (NIR) light, which was adaptive to the positive temperature-dependent toxicity correlation of IMI and the increasing trend of pests under high temperature. The cumulative release of IMI was 23.5% at 25 °C, while it was 81.2% at 40 °C after 24 h of incubation, and the release rate was greatly enhanced under NIR irradiation. The results indicated that the facile control of pesticide release could be realized by regulating environmental conditions. This work also provides an idea for using high-gravity technology to conveniently construct a smart, effective, and environmentally friendly pesticide delivery system for sustainable crop protection.

Tough, Stretchable, and Thermoresponsive Smart Hydrogels

Self-healing, thermoresponsive hydrogels with a triple network (TN) were obtained by copolymerizing N-isopropyl acryl amide (NiPAAm) with polyvinyl alkohol (PVA) functionalized with methacrylic acid and N,N'-methylene bis(acryl amide) crosslinker in the presence of low amounts (<1 wt.%) of tannic acid (TA). The final gels were obtained by crystalizing the PVA in a freeze-thaw procedure. XRD, DCS, and SEM imaging indicate that the crystallinity is lower and the size of the PVA crystals is smaller at higher TA concentrations. A gel with 0.5 wt.% TA has an elongation at a break of 880% at a tension of 1.39 MPa. It has the best self-healing efficiency of 81% after cutting and losing the chemical network. Step-sweep strain experiments show that the gel has thixotropic properties, which are related to the TA/PVA part of the triple network. The low amount of TA leaves the gel with good thermal responsiveness (equilibrium swelling ratio of 13.3). Swelling-deswelling loop tests show enhanced dimensional robustness of the hydrogel, with a substantial constancy after two cycles.

Soft Self-Assembled Mechanoelectrical Transducer Films from Conductive Microgel Waterborne Dispersions

The present study aims in the developing of new soft transducers based on sophisticated stimuli-responsive microgels that exhibit spontaneous self-assembly forming cohesive films with conductive and mechanoelectrical properties. For that, oligo(ethylene glycol)-based stimuli-responsive microgels have been synthesized using bio-inspired catechol cross-linkers by one-step batch precipitation polymerization in aqueous media. Then, 3,4-ethylene dioxyyhiophene (EDOT) has been directly polymerized onto stimuli-responsive microgels using catechol groups as the unique dopant. PEDOT location is dependent on the cross-linking density of microgel particles and EDOT amount used. Moreover, the spontaneous cohesive film formation ability of the waterborne dispersion after evaporation at soft application temperature is demonstrated. The films obtained present conductivity and enhanced mechanoelectrical properties triggered by simple finger compression. Both properties are function of the cross-linking density of the microgel seed particles and PEDOT amount incorporated. In addition, to obtain maximum electrical potential generated and the possibility to amplify it, several films in series were demonstrated to be efficient. The present material can be a potential candidate for biomedical, cosmetic, and bioelectronic applications.

Aggressive strategies for regenerating intervertebral discs: stimulus-responsive composite hydrogels from single to multiscale delivery systems

As our research on the physiopathology of intervertebral disc degeneration (IVD degeneration, IVDD) has advanced and tissue engineering has rapidly evolved, cell-, biomolecule- and nucleic acid-based hydrogel grafting strategies have been widely investigated for their ability to overcome the harsh microenvironment of IVDD. However, such single delivery systems suffer from excessive external dimensions, difficult performance control, the need for surgical implantation, and difficulty in eliminating degradation products. Stimulus-responsive composite hydrogels have good biocompatibility and controllable mechanical properties and can undergo solution-gel phase transition under certain conditions. Their combination with ready-to-use particles to form a multiscale delivery system may be a breakthrough for regenerative IVD strategies. In this paper, we focus on summarizing the progress of research on the stimulus response mechanisms of regenerative IVD-related biomaterials and their design as macro-, micro- and nanoparticles. Finally, we discuss multi-scale delivery systems as bioinks for bio-3D printing technology for customizing personalized artificial IVDs, which promises to take IVD regenerative strategies to new heights.