Thermo-Responsive Poly(N-Isopropylacrylamide)-Cellulose Nanocrystals Hybrid Hydrogels for Wound Dressing

Abstract

Thermo-responsive hydrogels containing poly(N-isopropylacrylamide) (PNIPAAm), reinforced both with covalent and non-covalent interactions with cellulose nanocrystals (CNC), were synthesized via free-radical polymerization in the absence of any additional cross-linkers. The properties of PNIPAAm-CNC hybrid hydrogels were dependent on the amounts of incorporated CNC. The thermal stability of the hydrogels decreased with increasing CNC content. The rheological measurement indicated that the elastic and viscous moduli of hydrogels increased with the higher amounts of CNC addition, representing stronger mechanical properties of the hydrogels. Moreover, the hydrogel injection also supported the hypothesis that CNC reinforced the hydrogels; the increased CNC content exhibited higher structural integrity upon injection. The PNIPAAm-CNC hybrid hydrogels exhibited clear thermo-responsive behavior; the volume phase transition temperature (VPTT) was in the range of 36 to 39 • C, which is close to normal human body temperature. For wound dressing purposes, metronidazole, an antibiotic and antiprotozoal often used for skin infections, was used as a target drug to study drug-loading and the release properties of the hydrogels. The hydrogels showed a good drug-loading capacity at room temperature and a burst drug release, which was followed by slow and sustained release at 37 • C. These results suggested that newly developed drugs containing injectable hydrogels are promising materials for wound dressing.

The mechanism of adhesion and graft polymerization of a PNIPAAm thermoresponsive hydrogel to polypropylene meshes

“…This section sketches the main reactions involved in those processes, based on the analytical results carried out in the present study. More in detail, the general mechanism proposed for the hydrogel deposition to iPP fibres ( Figure 2) is similar to that reported in the literature for the grafting of PNIPAAm onto cellulose nanocrystals 33 . The major novelty of our approach relies on the need of create high density of reactive functional groups in the polypropylene fibres by applying controlled plasma discharge.…”

“…A value very similar to the typical low critical solution temperature (LCST) of PNIPAAm of about 32°C was found, being in this case 33.2 °C. Below the VPTT, the hydrogel is hydrophilic and swollen in water; in contrast, above the VPTT, it becomes hydrophobic and decrease in volume 33 . The bilayer system was found to be completely flexible, despite the highest weight PNIPAAm hydrogel (3.89  0.12 mg/cm 2 ) was employed for this step.…”

Poly(N-isopropylacrylamide)-Based Thermoresponsive Composite Hydrogels for Biomedical Applications

“…Superior mechanical performance is also crucial for wound dressing materials. To compensate for the inherent drawback of poor mechanical strength of PNIPAM hydrogels, Zubik et al used cellulose nanocrystals (CNCs) to hybrid with PNIPAM via a free radical polymerization to fabricate composite hydrogel properties [79]. CNCs have outstanding mechanical properties and they served as reinforcing agents to enhance the mechanical strength of the composite hydrogels by two mechanisms.…”

“…One is the covalent cross-link between PNIPAM and the hydroxyl groups of CNCs that reinforces the hydrogels in chemistry. The other is the hydrogen bonds between PNIPAM chains and CNCs that reinforce the hydrogels physically [79].…”

Plasmonic Retrofitting of Membrane Materials: Shifting from Self‐Regulation to On‐Command Control of Fluid Flow

“…SEM characterization shows the plasmonic nanocapsules evenly distributed throughout the surface of the membrane (Figure 3a). [36] In this regard, this durability renders these hybrid membranes ideal candidates for their implementation in dead-end filtration devices with enhanced backwashing efficiencies. Additionally, control experiments on the membrane integrity demonstrate the absence of particle leakage under direct and reverse flow conditions ( Figure S6, Supporting Information).…”