Design of a UCST Polymer with Strong Hydrogen Bonds and Reactive Moieties for Facile Polymer-Protein Hybridization

Introducing UCST onto Chitosan for a Simple and Effective Single-Phase Extraction

Upper critical solution temperature (UCST) polymers undergo their own collapsed structures to show thermoresponsive functions favoring controlled release systems, cell adhesion, including separation process, etc. Although the copolymerization of UCST monomers with other vinyl monomers containing a pendant group is a good way to introduce additional functions, uncertain UCST performance as well as extensive bio-related properties are always the points to be considered. To accomplish this, the present work proposes the application of polysaccharides, i.e., chitosan (CS), as the biopolymer backbone to conjugate with functional molecules and UCST polymers. The use of chain transfer agents, e.g., mercaptoacetic acid, in radical polymerization with UCST poly(methacrylamide) (PMAAm) via the CS/NHS (N-hydroxysuccinimide) complex allows the simple water-based modification. The further conjugation of mouse anti-LipL32 IgG monoclonal antibody (anti-LipL32 mAb) onto CS-PMAAm (CS-PMAAm-Ab) enables a selective binding of recombinant LipL32 (rLipL32) antigen (Ag) in the solution. The CS-PMAAm obtained not only shows the cloud point in the range of 10-30 °C but also the extraction of rLipL32 because of CS-PMAAm-Ab-Ag aggregation. The present work demonstrates how CS expresses UCST with additional antibody conjugated is feasible for a simple and effective Ag single-phase extraction.

Thermo-Responsive Hydrogels Coupled with Photothermal Agents for Biomedical Applications

Intelligent hydrogels are materials with abilities to change their chemical nature or physical structure in response to external stimuli showing promising potential in multitudinous applications. Especially, photo-thermo coupled responsive hydrogels that are prepared by encapsulating photothermal agents into thermo-responsive hydrogel matrix exhibit more attractive advantages in biomedical applications owing to their spatiotemporal control and precise therapy. This work summarizes the latest progress of the photo-thermo coupled responsive hydrogel in biomedical applications. Three major elements of the photo-thermo coupled responsive hydrogel, i.e., thermo-responsive hydrogel matrix, photothermal agents, and construction methods are introduced. Furthermore, the recent developments of these hydrogels for biomedical applications are described with some selected examples. Finally, the challenges and future perspectives for photo-thermo coupled responsive hydrogels are outlined.

Synergistic Approaches in the Design and Applications of UCST Polymers

This review summarizes recent progress in the synergistic design strategy for thermoresponsive polymers possessing an upper critical solution temperature (UCST) in aqueous systems. To achieve precise control of the responsive behavior of the UCST polymers, their molecular design can benefit from a synergistic effect of hydrogen bonding with other interactions or modification of the chemical structures. The combination of UCST behavior with other stimuli-responsive properties of the polymers may yield new functional materials with potential applications such as sensors, actuators, and controlled release devices. The advances in this area provide insight or inspiration into the understanding and design of functional UCST polymers for a wide range of applications.

H-bond-type thermo-responsive schizophrenic copolymers: The phase transition correlation with their parent polymers and the improved protein co-assembly ability

Schizophrenic copolymers are one type of the popular smart polymers that show invertible colloidal structures in response to temperature stimulus. However, the lack of principles to predict the phase transition temperature of a schizophrenic copolymer from its corresponding parent thermo-responsive polymers limits their development. Additionally, studies on their applications remain scarce. Herein, a series of schizophrenic copolymers were synthesized by polymerization of a RAFT-made polymer precursor poly(acrylamide-co-N-acryloxysuccinimide-co-acrylic acid) (P(AAm-co-NAS-co-AAc)) with the mixture of N-isopropylmethacrylamide (NIPAm) and acrylamide (AAm) in varying molar ratios. In aqueous solution, the block P(AAm-co-NAS-co-AAc) and the block poly(NIPAm-co-AAm) exhibited upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The schizophrenic copolymers featured either UCST-LCST, LCST-UCST, or only LCST thermo-responsive transition. A preliminary correlation of phase transition between the schizophrenic copolymers and their parent polymers was summarized. Furthermore, the co-assembly of the schizophrenic copolymers and proteins were conducted and the kinetics of protein loading and protein activity were investigated, which showed that the schizophrenic copolymers were efficient platforms for protein co-assembly with ultra-high protein loading while preserving the protein bioactivities. Additionally, all the materials were non-toxic towards NIH 3T3 and MCF-7 cells. This work offers the prospects of the schizophrenic polymers in soft colloidal and assembly systems, particularly in guiding the design of new materials and their use in biomedical applications.

Poly(N-acryloyl glycinamide-co-N-acryloxysuccinimide) Nanoparticles: Tunable Thermo-Responsiveness and Improved Bio-Interfacial Adhesion for Cell Function Regulation

Poly(N-acryloyl glycinamide) (PNAGA) can form high-strength hydrogen bonds (H-bonds) through the dual amide motifs in the side chain, allowing the polymer to exhibit gelation behavior and an upper critical solution temperature (UCST) property. These features make PNAGA a candidate platform for biomedical devices. However, most applications focused on PNAGA hydrogels, while few focused on PNAGA nanoparticles. Improving the UCST tunability and bio-interfacial adhesion of the PNAGA nanoparticles may expand their applications in biomedical fields. To address the issues, we established a reactive H-bond-type P(NAGA-co-NAS) copolymer via reversible addition-fragmentation chain transfer polymerization of NAGA and N-acryloxysuccinimide (NAS) monomers. The UCST behaviors and the bio-interfacial adhesion toward the proteins and cells along with the potential application of the copolymer nanoparticles were investigated in detail. Taking advantage of the enhanced H-bonding and reactivity, the copolymer exhibited a tunable UCST in a broad temperature range, showing thermo-reversible transition between nanoparticles (PNPs) and soluble chains; the PNPs efficiently bonded proteins into nano-biohybrids while keeping the secondary structure of the protein, and more importantly, they also exhibited good adhesion ability to the cell membrane and significantly inhibited cell-specific propagation. These features suggest broad prospects for the P(NAGA-co-NAS) nanoparticles in the fields of biosensors, protein delivery, cell surface decoration, and cell-specific function regulation.