Congde Qiao

Electrospun N‐Substituted Polyurethane Membranes with Self‐Healing Ability for Self‐Cleaning and Oil/Water Separation

Membranes with special functionalities, such as self-cleaning, especially those for oil/water separation, have attracted much attention due to their wide applications. However, they are difficult to recycle and reuse after being damaged. Herein, we put forward a new N-substituted polyurethane membrane concept with self-healing ability to address this challenge. The membrane obtained by electrospinning has a self-cleaning surface with an excellent self-healing ability. Importantly, by tuning the membrane composition, the membrane exhibits different wettability for effective separation of oil/water mixtures and water-in-oil emulsions, whilst still displaying a self-healing ability and durability against damage. To the best of our knowledge, this is the first report to demonstrate a self-healing membrane for oil/water separation, which provides the fundamental research for the development of advanced oil/water separation materials.

Effect of aggregation behavior of gelatin in aqueous solution on the grafting density of gelatin modified with glycidol

The effect of aggregation behavior of gelatin in aqueous solution on the grafting density of glycidol grafted gelatin polymers (GGG polymers) was investigated. The grafting density was measured using the Van Slyke method by calculating the conversion rate of free - NH(2) groups of gelatin. The conversion rate reached peak values at 6% and 14% of the gelatin aqueous solution. SEM micrographs displayed a series of structural transitions (i.e., spherical, spindle, butterfly, irregular and dendritic aggregates) at varying concentrations from 2% to 16% (w/w) at an interval of 2% (w/w). The spindle aggregates reappeared at the concentrations of 6% and 14%. Viscosity measurements indicated that the physicochemical properties of the gelatin solution had changed with increasing concentration. UV and CD analysis indicated that hydrophobic interactions competed with hydrogen bonding, and the random coils partly transformed to β-sheet structure by changing the concentration. Zeta potential and pH data confirmed the increasing electrostatic repulsion associated with increasing the hydrophobic region. XPS analysis revealed that the elemental composition of the gelatin particle surface changed with variation in the aggregate structure, determining the monotonic variation of the grafting density with increasing concentration. Results demonstrate that aggregation behavior of gelatin in aqueous solution plays a crucial role in deciding the grafting density of gelatin modified products.

Molecular interactions in gelatin/chitosan composite films

Gelatin and chitosan were mixed at different mass ratios in solution forms, and the rheological properties of these film-forming solutions, upon cooling, were studied. The results indicate that the significant interactions between gelatin and chitosan promote the formation of multiple complexes, reflected by an increase in the storage modulus of gelatin solution. Furthermore, these molecular interactions hinder the formation of gelatin networks, consequently decreasing the storage modulus of polymer gels. Both hydrogen bonds and electrostatic interactions are formed between gelatin and chitosan, as evidenced by the shift of the amide-II bands of polymers. X-ray patterns of composite films indicate that the contents of triple helices decrease with increasing chitosan content. Only one glass transition temperature (Tg) was observed in composite films with different composition ratios, and it decreases gradually with an increase in chitosan proportion, indicating that gelatin and chitosan have good miscibility and form a wide range of blends.

Microstructure transformation of PDMS-E grafted gelatin polymers induced by SDS and SDBS

Inorganic-organic hybrid materials with tunable chemical and physical properties were prepared from mono epoxy terminated polydimethylsiloxane (PDMS) macromonomer and gelatin for improving their flexibility and hydrophobicity. Sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) were used to enhance the compatibility of two polymers phases. Measurement of grafting density indicated that anionic surfactants played a crucial role in deciding the detailed microstructure of PDMS-E grafted gelatin (PGG) polymers in alkaline solution. The interaction between gelatin and SDS/SDBS was investigated by viscosity and SEM. Viscosity analysis showed a regular increase in SDS system and a steeper change in the case of SDBS. SEM micrographs displayed a series of structural transitions (spherical, spindle, irregular granular and spherical aggregates) with the increase of SDS concentration, but spindle and granular aggregates appeared alternately as varying SDBS concentrations. The results demonstrated that both the electrostatic and hydrophobic interactions between anionic surfactant and gelatin controlled the aggregate structure of gelatin-SDS/SDBS, which affected the compatibility between gelatin and PDMS. Thermal properties of PGG polymers had changed with the modification of polymer microstructure. The results above revealed that microstructure transformation of PGG polymers was determined by the compatibility of two polymers in anionic surfactant aqueous solution and the chemical nature of their monomers.

Synthesis of Biocompatible Gelatin-functionalised Graphene Nanosheets For Drug Delivery Applications

Gelatin-functionalised graphene nanosheets (gelatin-GNS) with good biocompatibility were successfully synthesised using gelatin as a reductant. Factors that affect the reduction of graphene oxide (GO), such as the ratio of gelatin to GO, pH, and temperature, were investigated to establish optimum reaction conditions. We found that GO was efficiently reduced by gelatin at a comparatively low temperature and a stable gelatin-GNS aqueous dispersion was formed. The as-obtained biocompatible gelatin-GNS displayed a high methotrexate (MTX) drug loading capacity and a good ability for controlled drug release. The pH-dependent release behaviour of MTX from MTX@gelatin-GNS showed that the release amount under acid conditions was much higher than that under neutral conditions, indicating a gelatin-mediated sustained release process.

Effect of salt on the coil-helix transition of gelatin at early stages: Optical rotation, rheology and DSC studies

The influence of the concentration and type of salt on the physical gelation of gelatin at early stages was explored by polarimeter, rheometer and differential scanning calorimetry (DSC). With the increase of salt concentration, both the triple helix content and the storage modulus of gelatin increased slightly and then decreased in CaCl2 solutions, whereas they decreased monotonically in NaCl and CrCl3 solutions. The addition of CaCl2 at low concentrations facilitated the coil-helix transition of gelatin, which could be significantly inhibited by high salt concentrations. The melting temperature of gels was nearly unchanged with varying salt concentration, but the melting enthalpy decreased monotonically with salt addition. This result indicates that salt additions mainly affect the nucleation of triple helices, but had minor effect on its growth. In addition, the coil-helix transition of gelatin in salt solutions at early stages could be treated successfully by an equation of first order kinetics.

Synthesis and Characterization of Reduced Graphene Oxide/Gelatin Composite Films

Reduced graphene oxide (RGO) was fabricated using gelatin as a reductant, and it could be stably dispersed in gelatin solution without aggregation. A series of RGO/gelatin composite films with various RGO contents were prepared by a solution-casting method. The structure and thermal properties of the RGO/gelatin composite films were characterized by UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). The addition of RGO enhances the degree of crosslinking of gelatin films and decreases the swelling ability of the gelatin films in water, indicating that RGO/gelatin composite films have a better wet stability than gelatin films. The glass transition temperature () of gelatin films is also increased with the incorporation of RGO. The presence of RGO slightly increases the degradation temperature of gelatin films due to the very low content of RGO in the composite films. Since gelatin is a natural and nontoxic biomacromolecule, the RGO/gelatin composite films are expected to have potential applications in the biomedical field.

Stimuli-Responsive Films Based on N-Substituted Polyurethane with Different Alkyl Length

N-Alkyl-substituted polyurethanes with different alkyl chain lengths were prepared from the corresponding bromoalkane (1-bromooctane, 1-bromotetradecane, and 1-bromooctadecane) and polyurethane consisting of poly(propylene glycol) (PPG), 4,4′-diphenylmethane diisocyanate, and 1,4-butanediol. The synthesised materials were characterised by 1H NMR and FTIR spectroscopy and the degrees of substitution were discussed by changing the reaction conditions. Differential scanning calorimetry and X-ray diffraction were used to characterise the thermal properties and crystalline state. Microphase-separated nanostructures, with hard segments (nanofibre-like) embedded into amorphous PPG soft segments, are observed by atomic force microscopy and scanning electron microscopy. A reversible behaviour of the films was revealed by contact angle measurement. Stimuli-responsive films were realised by solvent vapour annealing and heat treatment, and exhibited a reversible switching in surface wettability with a remarkable change in the water contact angle of 21°.

Effect of sorbitol content on microstructure and thermal properties of chitosan films

In this work, the influence of sorbitol content on the microstructure and thermal properties of chitosan films was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). It showed that the addition of sorbitol weakened the hydrogen bonding between chitosan molecules as well as the electrostatic interactions existed in chitosan films. Structural analysis revealed that a small amount of sorbitol (~10 wt%) could facilitate the crystallization of chitosan, whereas it was seriously hindered at high content of sorbitol (~50 wt%). The thermal behavior of composite films indicated that the sorbitol addition did not reduce the thermal stability of polymer films. When the sorbitol content rose to above 30 wt%, phase separation may occur and two glass transitions presented in composite films. The lower temperature transition was associated with the glass-rubber transition of sorbitol-rich phase, and the higher one was related to chitosan-rich phase. These results implied that the microstructure as well as properties of the plasticized chitosan films can be controlled by adding sorbitol, which is important for their usage as packaging materials.

Electrostatic and hydrophobic controlled self-assembly of PDMS-E grafted gelatin for self-cleaning application

Understanding the assembly mechanisms of supramolecular architectures in nature is essential for the design and synthesis of novel biomaterials. In the work, self-assembly of gelatin-mono epoxy terminated polydimethylsiloxane polymer (PGG) controlled by electrostatic and hydrophobic interactions between gelatin and sodium dodecyl sulfate (SDS) was investigated in suit. Confocal laser scanning microscopy, circular dichroism spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were conducted to reveal the structure evolution of PGG at a molecular level with the increment of SDS concentration, including micro-sized sphere, core-shell and multi-layer structure. Notably, the multi-layer structure was formed from the large contribution of antiparallel β-sheets on the boundary and new hydrophobic aggregation driven by higher monomer conversions. The delicate supramolecular architectures preliminarily present excellent anti-water, anti-contamination and anti-radiation properties in the surface of skin. The excellent self-cleaning function of PGG indicates potential application in biomaterials.