Nanofibrous Foams of Poly(3-hydroxybutyrate)/Cellulose Nanocrystal Composite Fabricated Using Nonsolvent-Induced Phase Separation.

In this study, we fabricated nanofibrous foams of neat poly(3-hydroxybutyrate) (PHB) and PHB/cellulose nanocrystal (CNC) nanocomposite using nonsolvent-induced phase separation (NIPS) followed by solvent extraction. Two different nonsolvents, tetrahydrofuran (THF) and 1,4-dioxane (Diox), in combination with the solvent, chloroform (CF), were used for NIPS. The parameters of NIPS-derived crystallization kinetics were calculated using Avrami analysis of time-dependent infrared spectral measurements. The lower viscosity and poorer PHB affinity of THF than those of Diox resulted in rapid crystallization and gelation rate, which in turn resulted in higher strength of the foam. The mechanical reinforcement by the incorporation of CNCs was achieved for the composite foam prepared in Diox/CF but not in THF/CF, owing to the relatively better dispersion of the CNCs in Diox than that in THF. A rapid rate of NIPS-derived crystallization and gelation was achieved in THF/CF with the incorporation of CNCs, indicating the effective crystal nucleation of CNCs. However, the presence of CNCs deaccelerated the crystallization in Diox/CF, indicating that the inhibition effect of PHB mobility became more dominant than the nucleation effect of CNCs; this was because the CNC dispersion became more homogeneous in Diox/CF. In vitro cell viability assays exhibited excellent cytocompatibility of the foams, thereby showing potential for use in biomedical applications.

Porous Poly(3-hydroxybutyrate) Scaffolds Prepared by Non-Solvent-Induced Phase Separation for Tissue Engineering.

Highly porous poly(3-hydroxybutyrate) (PHB) scaffolds were fabricated using non-solvent-induced phase separation with chloroform as the solvent and tetrahydrofuran as the non-solvent. The microporosity, nanofiber morphology, and mechanical strength of the scaffolds were adjusted by varying the fabrication parameters, such as the polymer concentration and solvent composition. The influence of these parameters on the structure and morphology of PHB organogels and scaffolds was elucidated using small-angle neutron scattering and scanning electron microscopy. The organogels and scaffolds in this study have a complex hierarchical structure, extending over a wide range of length scales. In vitro viability assays were performed using the human keratinocyte cell line (HaCaT), and all PHB scaffolds demonstrated the excellent cell viability. Microporosity had the greatest impact on HaCaT cell proliferation on PHB scaffolds, which was determined after a 3-day incubation period with scaffolds of different morphologies and mechanical properties. The superior cell viability and the controlled scaffold properties and morphologies suggested PHB scaffolds fabricated by non-solvent-induced phase separation using chloroform and tetrahydrofuran as promising biomaterials for the applications of tissue engineering, particularly of epidermal engineering. Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s13233-020-8109-x.

Double-Network Hydrogel Films Based on Cellulose Derivatives and κ-Carrageenan with Enhanced Mechanical Strength and Superabsorbent Properties.

Covalently crosslinked sodium carboxymethyl cellulose (CMC)-hydroxyethyl cellulose (HEC) hydrogel films were prepared using citric acid (CA) as the crosslinking agent. Thereafter, the physically crosslinked κ-carrageenan (κ-CG) polymer was introduced into the CMC-HEC hydrogel structure, yielding κ-CG/CMC-HEC double network (DN) hydrogels. The κ-CG physical network provided sacrificial bonding, which effectively dissipated the stretching energy, resulting in an increase in the tensile modulus, tensile strength, and fracture energy of the DN hydrogels by 459%, 305%, and 398%, respectively, compared with those of the CMC-HEC single network (SN) hydrogel. The dried hydrogels exhibited excellent water absorbency with a maximum water-absorption capacity of 66 g/g in distilled water. Compared with the dried covalent SN gel, the dried DN hydrogels exhibited enhanced absorbency under load, attributed to their improved mechanical properties. The water-absorption capacities and kinetics were dependent on the size of the dried gel and the pH of the water.

Chitosan-reinforced PHB hydrogel and aerogel monoliths fabricated by phase separation with the solvent-exchange method.

The poly(3-hydroxybutyrate) (PHB) organogel monoliths were prepared by nonsolvent-induced phase separation (NIPS). The NIPS-derived organogels were solvent-exchanged with chitosan (CS) solution, resulting in the successful loading of CS into PHB hydrogel. With increasing the CS content, the as-prepared composite hydrogels became syringe injectable with excellent thixotropy due to the increase in the gel network's hydrophilicity. The hydrogels were successfully freeze-dried into PHB/CS composite aerogels, which exhibited remarkably improved compressive modulus/collapse strength of 1.6 MPa/159 kPa compared to 0.5 MPa/31 kPa for pure PHB aerogels. The effect of CS on gel crystallization and structure was also investigated. The amphiphilic PHB/CS hydrogels effectively entrapped both hydrophilic/cationic doxorubicin (DOX) and hydrophobic/anionic indomethacin (IDM). The drug release behavior depended on the charge interactions between drugs and CS. The accelerated DOX release in acidic condition from injected hydrogels owing to the charge repulsion shows potential for a controlled and localized cancer therapy.

Alginate-reinforced poly(3-hydroxybutyrate)/ poly(hydroxybutyrate-co-hydroxyvalerate) aerogel monoliths fabricated by phase separation as environmental floating adsorbents.

Poly(3-hydroxybutyrate) (PHB)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) aerogel monoliths were prepared via nonsolvent induced phase separation and then sequentially immersed in ethanol and sodium alginate (ALG) solutions. The resulting composite aerogels contained up to a 52 wt% fraction ALG, causing a remarkable increase in their compressive modulus and collapse strength from 0.3 MPa and 33 kPa to 4 MPa and 406 kPa, respectively, i.e., by 13/12 times. An increase in the ALG contents in the composite aerogels allowed them to effectively adsorb both water and soybean oil, according to pseudo-second-order adsorption kinetics. The highly porous composite aerogel acted as an efficient floating adsorbent for a cationic dye (i.e., methylene blue (MB)) in water. MB adsorption was found to be strongly dependent on ALG contents in the adsorbent, as well as operating parameters such as the initial concentration, pH, and temperature of MB solutions. MB adsorption is best described by the Langmuir isotherm and follows pseudo-second-order kinetics. Ca2+-crosslinking of ALG further increased compressive strength but significantly decreased MB adsorption capability following pseudo-first-order kinetics, implying a slow internal diffusion step for MB adsorption due to its tightened network structure relative to noncrosslinked adsorbents.

Chitosan-dipeptide hydrogels as potential anticancer drug delivery systems.

A novel chitosan-dipeptide hydrogel was fabricated through a combination of self-assembly of 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc-FF) and its electrostatic interaction with glycol chitosan (GCS). Hydrogel strength and stability depended on its composition. The highest gel strength was observed at a Fmoc-FF mass fraction (ϕFF) of 0.85, whereby the highest combined strength of the two interactions was achieved. As the ϕFF increased above 0.6, gel stability decreased in buffered solution at pH 7.46. The incorporation of doxorubicin (DOX) as a cationic model drug significantly increased the stability of the complex hydrogels. DOX-loaded hydrogels exhibited slow DOX release, probably due to the drug's strong binding to Fmoc-FF via electrostatic attraction and the high gel stability. These hydrogels also exhibited excellent thixotropic features that facilitated the development of injectable self-healing drug delivery systems. Notably, DOX release was significantly accelerated as the pH of the medium decreased from 7.46 to 5.5 and 4.0, possibly due to hydrogel components' protonation. The DOX-loaded hydrogel exhibited notable cytotoxicity against A549 human lung cancer cells, which suggests the newly developed hydrogel to be a promising candidate vehicle for the localized and controlled drug delivery in cancer therapy.

Nonsolvent-induced phase separation of poly(3-hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) blend as a facile platform to fabricate versatile nanofiber gels: Aero-, hydro-, and oleogels.

We demonstrated a strategy to prepare different types of 3-D nanofibrous polymeric gels, including hydro-, aero-, and oleogels by nonsolvent-induced phase separation (NIPS). NIPS-derived gel monoliths of poly(3-hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) blends were converted into hydrogels and aerogels by solvent exchange and freeze-drying, respectively. The high hydrophobicity and porosity of the nanofibrous PHB/PHBV aerogels enabled them to absorb various oils and swell to 20-30 times their own weight. The pseudo-second-order model was successfully used to describe the oil absorption behavior, and the obtained absorption rate constant increased with increasing PHBV content. The oil-swollen aerogels were highly elastic, thereby indicating that NIPS-derived aerogels are an excellent template for the fabrication of oleogels. With an increase in the PHBV ratio, the gels exhibited reduced modulus and collapse strength but increased collapse strain, thereby revealing higher ductility by compression. The rapid separation and re-binding of the liquid phase entrapped in the nanofiber network resulted in the unique thixotropic properties of the hydro- and oleogels. Indomethacin, a hydrophobic model drug, was successfully incorporated into injectable self-healing oleogels containing soybean oil and aerogels. These gels exhibited excellent cytocompatibility, and a better sustained drug release was observed for the oleogels compared to the aerogels.