Functional composite hydrogels entrapping polydopamine hollow nanoparticles for highly efficient resistance of skin penetration and photoprotection

Living organisms tend to evolve various naturally photoprotective mechanisms to avoid photodamage. Among them, polydopamine (PDA) is an effective sunscreen, a mimic of melanin, which is the main functional component of the photoprotective system of human skin. However, the concerns of its dark color, skin penetration and photoprotective efficiency remain yet to be solved. Herein, we have constructed melanin-inspired nanocomposite hydrogels (CS-PDA_h-GP-HA) for photoprotection, in which PDA was prepared as hollow nanoparticles (PDA_h NPs) and entrapped in a physically cross-linked hydrogel (CS-GP-HA) formed by chitosan (CS) and hyaluronic acid (HA) using β-glycerophosphate (β-GP) as a modulator. The CS-PDA_h-GP-HA hydrogels exhibit a shear-thinning flow behavior with an elastic modulus of 300 Pa with the gel-sol transition temperature maintained at about 37 °C simply by adjusting the β-GP content in the hydrogels. The CS-PDA_h-GP-HA hydrogels also possess excellent resistance toward skin penetration. The photoprotective performances of CS-PDA_h-GP-HA hydrogels were evaluated by the determination of sun protection factor (SPF) and in vitro UVA protection efficacy (UVAPE) along with UV-Vis spectroscopy. Compared with the TiO₂ nanoparticles in CS-GP-HA hydrogel, the CS-PDA_h-GP-HA hydrogels show stronger shielding ability in both UVA and UVB regions. When protected by the CS-PDA_h-GP-HA hydrogels, the cell viability of NIH-3T3 fibroblasts increases to 96% while it was only 14% in the case of non-protecting group. These results suggest that the CS-PDA_h-GP-HA hydrogels could efficiently shield the UV irradiation and protect the skin from photodamage. This work introduces PDA-based nanocomposite hydrogels with safe, biocompatible and photoprotective properties, and provides a melanin-mimicking photoprotection system for the application in sunscreens.

Tuneable hydrogels of Caf1 protein fibers

Capsular antigen fraction 1 (Caf1) is a robust polymeric protein forming a protective layer around the bacterium Yersinia pestis. Occurring as ≈1 μm polymeric fibers, it shares its immunoglobulin-like fold with the majority of mammalian extracellular proteins such as fibronectin and this structural similarity suggests that this unusual polymer could form useful mimics of the extracellular matrix. Driven by the pressing need for reliable animal-free 3D cell culture environments, we showed previously that recombinant Caf1 produced in Escherichia coli can be engineered to include bioactive peptides, which influence cell behavior. Here, we demonstrate that through chemical crosslinking with a small palette of PEG-based crosslinkers, Caf1-based hydrogels can be prepared displaying a wide range of mechanical and morphological properties that were studied by rheology, compressive testing, SDS-PAGE and scanning electron microscopy. By varying the Caf1 protein concentration, viscoelasticity and stiffness (~11-2300 Pa) are reproducibly tunable to match natural and commercial 3D gels. Hydrogel porosity and swelling ratios were found to be defined by crosslinker architecture and concentration. Finally the hydrogels, which are 95-99% water, were shown to retain the high stability of the native Caf1 protein in a range of aqueous conditions, including extended immersion in cell culture media. The unusual Caf1 polymer thus offers the possibility of presenting bioactive protein subunits in a precisely tuneable hydrogel for use in cell culture and drug delivery applications.

Facile and cost-effective synthesis of glycogen-based conductive hydrogels with extremely flexible, excellent self-healing and tunable mechanical properties

In materials science and engineering, the designing of hydrogels with excellent self-healing and tunable mechanical properties is an inviting issue. In this study, we introduce the sacrificial bonds interactions in a hybrid hydrogel of natural and synthetic polymers, to give a hydrogel with autonomous self-healing ability and tunable mechanical properties. Glycogen, a natural polymer tends to strengthen the hydrogel while PVA, a synthetic polymer plays a critical role in the flexibility and stretchability of the hydrogel. Hydrogels were designed by the sacrificial non-covalent interactions with physical cross-linking of the polymer chains to the trivalent metal ions. Functional groups of the polymers interact with sacrificial hydrogen bonds with and with the metal ions, they interact through sacrificial coordination interactions with different strength, results tunable sacrificial bonds. Weaker sacrificial bonds rupture prior to the strong sacrificial bonds upon external loading, which dissipate the energy and endow the hydrogel with adjustable mechanical and self-healing properties. The tunable mechanical properties and excellent self-healing efficiency enlarge the application areas of the developed hydrogel in various fields.

Multivalent cations-triggered rapid shape memory sodium carboxymethyl cellulose/polyacrylamide hydrogels with tunable mechanical strength

A novel multivalent cations-triggered shape memory hydrogels were synthesized in a one-pot method, and interpenetrating double network was formed by chemically cross-linked polyacrylamide (PAM) network and physically cross-linked sodium carboxymethyl cellulose network. The temporary shape was fixed by complexation between a native biopolymer, sodium carboxymethyl cellulose (CMC), and transition metal ions, specifically Fe³⁺, Ag⁺, Al³⁺, Cu²⁺, Ni²⁺, and Mg²⁺. In particular, CMC-Fe³⁺ hydrogel exhibits excellent shape fixity ratio (95%). Therefore, we chose PAM/CMC_1.0-Fe³⁺ hydrogel as the model material and further investigated its shape recovery process. It was found that a wide range of molecules and anions could be applied to break off the temporary cross-links between CMC and Fe³⁺. The PAM/CMC composite hydrogels also exhibited excellent tunable mechanical properties. The mechanical properties of the composite hydrogel can be adjusted by changing the cross-linking densities. The presented strategy could enrich the construction as well as application of biopolymers based shape memory hydrogels.