Soft liquid metal nanoparticles achieve reduced crystal nucleation and ultrarapid rewarming for human bone marrow stromal cell and blood vessel cryopreservation.

High warming rates during cryopreservation are crucial and essential for successful vitrification. However, realizing a faster warming rate in low-concentration cryoprotective agents appears to be challenging for conventional warming process through convective heat transfer. Herein, we developed a liquid metal (LM) nanosystem that can act as a spatial source to significantly enhance the warming rates with near-infrared laser irradiation during the warming process. The synthetic Pluronic F127-liquid metal nanoparticles (PLM NPs) displayed multiple performances with uniform particle size, superior photothermal conversion efficiency (52%), repeatable photothermal stability, and low cytotoxicity. Particularly, it is more difficult for the liquid PLM NPs with less surface free energy to form crystal nucleation than other solid NPs such as gold and Fe3O4, which is beneficial for the cooling process during cryopreservation. The viability of human bone marrow-derived mesenchymal stem cells postcryopreservation reached 78±3%, which is threefold higher than that obtained by the conventional warming method (25±6%). Additionally, the cells postcryopreservation maintained their normal attachment, proliferation, surface marker expression, and intact multilineage differentiation properties. Moreover, the results of mouse tails including blood vessel cryopreservation showed a relatively improved intact structure when using PLM NP rewarming compared with the results of conventional warming. The new LM nanosystem provides a universal platform for cryopreservation that is expected to have potential for widespread applications including bioengineering, cell-based medicine, and clinical translation. STATEMENT OF SIGNIFICANCE: In this study, we fabricated soft liquid metal nanoparticles with high photothermal conversion efficiency, repeatable photothermal stability, and low cytotoxicity. Particularly, soft liquid metal nanoparticles with less surface free energy and suppression effects of ice formation were first introduced to mediate cryopreservation. Superior ice-crystallization inhibition is achieved as a result of less crystal nucleation and ultrarapid rewarming during the freezing and warming processes of cryopreservation, respectively. Collectively, cryopreservation of human bone marrow stromal cells (HBMSCs) and mouse tails including blood vessels can be successfully performed using this new nanoplatform, showing great potential in the application of soft nanoparticles in cryopreservation.

Light- and temperature-responsive liposomes incorporating cinnamoyl Pluronic F127.

Light- and temperature-responsive liposomes were prepared by immobilizing cinnamoyl Pluronic F127 (CP F127) on the surface of egg phosphatidylcholine liposomes. CP F127 was prepared by a condensation reaction, and the molar ratio of cinnamoyl group to Pluronic F127 was calculated to be 1:1.4 on (1)H NMR spectrum. The cinnamoyl group of CP F127 was readily dimerized under the irradiation of a UV light (254 nm, 6 W). CP F127 decreased the absolute value of the zeta potential of liposome possibly because it can shift the hydrodynamic plane away from the liposome surface. The size of liposome decorated with CP F127, measured on a dynamic light scattering machine and observed on a TEM, was larger than that of bare liposome. The liposome bearing CP F127 seemed to fuse and aggregate each other. The liposome released calcein, a fluorescence dye, in response to a UV irradiation, possibly because the photo-dimerization of cinnamoyl group perturbs the liposomal membrane. Moreover, the liposome released the dye in response to a temperature change, possible due to the phase transition of Pluronic F127 layer on the liposomal surface or the hydrophobic interaction of the polymer with liposomal membrane.

Terminal sterilization of alginate hydrogels: efficacy and impact on mechanical properties.

Terminal, or postprocessing, sterilization of composite biomaterials is crucial for their use in wound healing and tissue-engineered devices. Recent research has focused on optimizing traditional biomaterial formulations to create better products for commercial and academic use which incorporate hydrophobic compounds or secondary gel networks. To use a hydrogel in a clinical setting, terminal sterilization is necessary to ensure patient safety. Lyophilization, gamma-irradiation, and ethylene oxide treatment all have negative consequences when applied to alginate scaffolds for clinical use. Here, we aim to find alternative terminal sterilization methods for alginate and alginate-based composite hydrogels which maintain the structure of composite alginate networks for use in biomedical applications. A thorough investigation of the effect of common sterilization methods on swollen alginate-based hydrogels has not been reported and therefore, this work examines autoclaving, ethanol washing, and ultraviolet light as sterilization techniques for alginate and alginate/Pluronic® F68 composite hydrogels. Preservation of structural integrity is evaluated using shear rheology and analysis of water retention, and efficacy of sterilization is determined via bacterial persistence within the hydrogel. Results indicate that ethanol sterilization is the best method of those investigated because ethanol washing results in minimal effects on mechanical properties and water retention and eliminates bacterial persistence. Furthermore, this study suggests that ethanol treatment is an efficacious method for terminally sterilizing interpenetrating networks or other composite hydrogel systems.

Formulation and in vitro characterization of an in situ gelable, photo-polymerizable Pluronic hydrogel suitable for injection.

Utilizing the existence of a sufficiently long induction period during photo-polymerization, defined as the time required to initiate macroscopic gelation after UV irradiation, we propose a new injection method of making a photo-polymerized hydrogel made of thermo-sensitive di-acrylated Pluronic F 127 (DA-PF 127). First, the photo-polymerization of DA-PF 127 solution at the molecular level is initiated by UV irradiation, and this solution is injected into a target site by macroscopic gelation before it becomes viscous. This method can overcome the problems of the existing methods to make an injectable and stable hydrogel by photo-polymerization, reducing the potential damage to normal tissue around the injection site due to direct UV exposure, and the requirement of special equipment for UV crosslinking after injection. By controlling photo-polymerization variables, we found the condition for making an injectable system, where the induction time is equal to or longer than the UV irradiation time. The feasibility of the proposed method was demonstrated in vitro, and the enhanced stability of the produced hydrogels by photo-polymerization was verified. We also characterized the cytotoxicity of the present method using cell cultures and cell encapsulation with the present method, and found minimal cytotoxicity.