Photothermal liquid release from arrayed Au nanorod/hydrogel composites for chemical stimulation

Controlled photothermal actuation of liquid release is presented using periodically arrayed hydrogel columns in a macroporous silicon membrane. Thermo-responsive hydrogel is mixed with Gold (Au) nanorods, and surface plasmon-induced local heating by near-infrared (NIR) light is utilized as an actuation method. We adopted theoretical modeling, which treats the hydrogel as a poro-viscoelastic medium to understand the mechanical and liquid transport properties of the hydrogel. To demonstrate the feasibility of the liquid release control using NIR light, we first characterized the temperature response of Au nanorod embedded hydrogel in the silicon membrane using its optical transmission behavior to confirm the successful device fabrication. Next, the liquid release characteristics from the structure were studied using fluorescent imaging of fluorescein dye solution while pulsed NIR light was illuminated on the structure. We successfully demonstrate that the liquid release can be controlled using remote NIR illumination from the presented structure. Considering the periodically arrayed configuration with high spatial resolution, this will have a potential prospect for optically-addressable chemical release systems, which benefit retina prosthesis interfaces.

In Vitro Evaluation of Calcium Phosphate Bone Cement Composite Hydrogel Beads of Cross-Linked Gelatin-Alginate with Gentamicin-Impregnated Porous Scaffold

Calcium phosphate bone cement (CPC) is in the form of a paste, and its special advantage is that it can repair small and complex bone defects. In the case of open wounds, tissue debridement is necessary before tissue repair and the subsequent control of wound infection; therefore, CPC composite hydrogel beads containing antibiotics provide an excellent option to fill bone defects and deliver antibiotics locally for a long period. In this study, CPC was composited with the millimeter-sized spherical beads of cross-linked gelatin–alginate hydrogels at the different ratios of 0 (control), 12.5, 25, and 50 vol.%. The hydrogel was impregnated with gentamicin and characterized before compositing with CPC. The physicochemical properties, gentamicin release, antibacterial activity, biocompatibility, and mineralization of the CPC/hydrogel composites were characterized. The compressive strength of the CPC/hydrogel composites gradually decreased as the hydrogel content increased, and the compressive strength of composites containing gentamicin had the largest decrease. The working time and setting time of each group can be adjusted to 8 and 16 min, respectively, using a hardening solution to make the composite suitable for clinical use. The release of gentamicin before the hydrogel beads was composited with CPC varied greatly with immersion time. However, a stable controlled release effect was obtained in the CPC/gentamicin-impregnated hydrogel composite. The 50 vol.% hydrogel/CPC composite had the best antibacterial effect and no cytotoxicity but had reduced cell mineralization. Therefore, the optimal hydrogel beads content can be 25 vol.% to obtain a CPC/gentamicin-impregnated hydrogel composite with adequate strength, antibacterial activity, and bio-reactivity. This CPC/hydrogel containing gentamicin is expected to be used in clinical surgery in the future to accelerate bone regeneration and prevent prosthesis infection after surgery.