Soft actuators have recently been widely studied due to their significant advantages including light weight, continuous deformability, high environment adaptability, and safe human−robot interactions. In this study, we designed electrically responsive poly(sodium 4-vinylbenzenesulfonate/2hydroxyethylmethacrylate/acrylamide) (P(VBS/HEMA/AAm)) and poly(sodium 4-vinylbenzenesulfonate/2-hydroxyethyl methacrylate/acrylic acid) (P(VBS/HEMA/AAc)) hydrogels. A series of P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels were prepared by adjusting the monomer composition and crosslinking density to systemically analyze various factors affecting the actuation of hydrogels under an electric field. All hydrogels exhibited more than 65% gel fraction and a high equilibrium water content (EWC) of more than 90%. The EWC of hydrogels gradually increased with decreasing cross-linker content and was also influenced by the monomer composition. The mechanical properties of hydrogels were proportional to the cross-linking density. Particularly, hydrogels showed bending deformation even at low voltages below 10 V, and the electrically responsive bending actuation of hydrogels can be modulated by cross-linking density, monomer composition, applied voltage, ion strength of the electrolyte solution, and geometrical parameters of the hydrogel. By controlling these factors, hydrogels showed a fast response with a bending of more than 100°within a minute. In addition, hydrogels did not show significant cytotoxicity in a biocompatibility test and exhibited more than 84% cell viability. These results indicate that P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels with fast response properties even under a low electric field have the potential to be used in a wide range of soft actuator applications.
Recently, photodynamic therapy (PDT) has been intensively investigated as a useful modality for the treatment of various cancers. In addition, near infrared (NIR) photothermal therapy (PTT) using gold nanocarriers has attracted particular interest as a hyperthermia strategy. In this study, gold nanorod (AuNR)-photosensitizer conjugates with glutathione-sensitive linkages were designed for PDT and PTT. Several kinds of AuNRs with different aspect ratios were synthesized and modified with FA-conjugated block copolymers (FA-PEG-P(Asp)-DHLA) and Chlorin e6 (Ce6) as a photosensitizer. The surface-modified AuNRs showed excellent stability and solubility in aqueous solution. In particular, FA-PEG-P(Asp)-DHLA-AuNR100-SS-Ce6 with a 3.84 aspect ratio exhibited strong photothermal effects, enhanced singlet oxygen generation, and marked phototoxicity. Based on these results, we suggest that AuNR-photosensitizer conjugates with glutathione-sensitive linkages have potential application in PDT/PTT for effective clinical treatment of various cancers.
Although photodynamic therapy (PDT) is an effective, minimally invasive therapeutic modality with advantages in highly localized and specific tumor treatments, large and deep-seated cancers within the body cannot be successfully treated due to low transparency to visible light. To improve the therapeutic efficiency of tumor treatment in deep tissue and reduce the side effects in normal tissue, this study developed a near-infrared (NIR)-triggered upconversion nanoparticle (UCNP)-based photosensitizer (PS) carrier as a new theranostics system. The NaYF4:Yb/Er UCNPs were synthesized by a hydrothermal method, producing nanoparticles of a uniformly small size (≈20 nm) and crystalline morphology of the hexagonal phase. These UCNPs were modified with folic acid-conjugated biocompatible block copolymers through a bidentate dihydrolipoic acid linker. The polymer modified hexagonal phase UCNPs (FA-PEAH-UCNPs) showed an improved dispersibility in the aqueous solution and strong NIR-to-vis upconversion fluorescence. The hydrophobic PS, pheophorbide a (Pha), was then conjugated to the stable vectors. Moreover, these UCNP-based Pha carriers containing tumor targeting folic acid ligands exhibited the significantly enhanced cellular uptake efficiency as well as PDT treatment efficiency. These results suggested that this system could extend the excitation wavelength of PDT to the NIR region and effectively improve therapeutic efficiency of PSs.
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