Keyong Tang

Dissolution and regeneration of collagen fibers using ionic liquid

Native skin collagen fibers were successfully dissolved in the ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), and regenerated in different precipitators. The observation by polarized optical microscopy showed that the crystal structure of collagen fibers had been destroyed by [BMIM]Cl during the heating. Temperature-dependent FTIR was applied to detect the structural change of collagen/[BMIM]Cl during dissolving. The structure of regenerated collagen was characterized by FTIR and XRD. It showed that the triple helical structure of collagen had been partly destroyed during the dissolution and regeneration. The film forming ability and the thermostability of the regenerated collagen was highly dependent on the precipitating treatment. The possible mechanisms of dissolving of collagen in [BMIM]Cl and the regeneration in the precipitators have been proposed. The collagen/cellulose composite with different forms (film, fiber, gel) can be successfully prepared by using [BMIM]Cl as medium.

Electrospinning and Crosslinking of COL/PVA Nanofiber-microsphere Containing Salicylic Acid for Drug Delivery

Porous nanofiber-microsphere mats of collagen (COL)/polyvinyl alcohol (PVA) containing salicylic acid (SA) as model drug were prepared by electrospinning for the assessment of drug delivery system. The electrospun fibrous mats were crosslinked by UV-radiation or glutaraldehyde to weaken the degree of drug burst release and morphology damage when meeting water. The morphology and chemical structures of COL/PVA-SA electrospun fibers were characterized by SEM and FTIR. The crosslinking of UV-radiation did not destroy the morphology of COL/PVA-SA electrospun fibers in the crosslinking process, however, the crosslinking of glutaraldehyde did it. In vitro release studies showed that COL/PVA-SA electrospun fibers efficiently controlled the release of drugs by the crosslinking of UV-radiation for 4 h. The transport mechanism that controlled the release of drugs from electrospun mats was Fickian diffusion.

Dissolution of natural polymers in ionic liquids: A review

Abstract Natural polymers are produced by living organisms, e.g. plants, animals, microorganisms. Natural polymer materials have gained increasing attention due to their high strength and stiffness combined with carbon neutral, biocompatibility, biodegradability, renewability and sustainability. However, due to the strong interand intra-molecular hydrogen bonds, many natural polymers are extremely difficult to be dissolved in water or traditional organic solvents. The processing difficulties tremendously limit the applications of natural polymers in many fields. Recently, using ionic liquids (ILs) as novel solvents to dissolve natural polymers has attracted increasing attention. ILs has been shown to be highly effective at dissolving some natural polymers to technically useful concentrations. In this article, the structure and basic properties of ILs are introduced; the recent progress is reviewed in the dissolution of several important natural polymers using ionic liquids, including cellulose, chitin and chitosan, wool keratin fibers, silk fibroin and collagen fibers. The dissolution mechanisms of natural polymers using ILs as solvents are analyzed. The structure and properties of native and regenerated natural polymers are discussed in details.

Nano-TiO2/collagen-chitosan porous scaffold for wound repairing

Collagen-Chitosan (COL-CS) porous scaffolds have been widely used as a dermal equivalent to induce fibroblasts infiltration and dermal regeneration. To improve the anti-bacterial properties, nano-TiO2 hydrosol was introduced into COL-CS scaffolds. TiO2/COL-CS porous scaffolds were fabricated through a freeze-drying process, and scanning electron microscopy (SEM) was employed to study the micro-structure of the scaffolds. Fourier transform infrared spectroscopy (FT-IR) was used to study the intermolecular interactions in the scaffolds. The swelling property, porosity, degradation, antibacterial behavior, red blood cell aggregation, and cytotoxicity of the composite were investigated. The results showed that the scaffold is good in permeability and it may provide a humid environment for wound repairing. The degradation in lysozyme solution for 4 weeks showed that porous scaffolds are good in stability, which may satisfy the wound coverage protection in the repairing period. An obvious inhibitory effect on Staphylococcus aureus of the porous scaffolds was found, and the red blood cells were easy to form clusters aggregation to stop bleeding. It was suggested that the TiO2/COL-CS composite scaffolds could be a promising candidate for wound repairing dressing.

Nanocomposite scaffold with enhanced stability by hydrogen bonds between collagen, polyvinyl pyrrolidone and titanium dioxide

In this study, three-dimensional (3D) nanocomposite scaffolds, as potential substrates for skin tissue engineering, were fabricated by freeze drying the mixture of type I collagen extracted from porcine skin and polyvinyl pyrrolidone (PVP)-coated titanium dioxide (TiO2) nanoparticles. This procedure was performed without any cross-linker or toxic reagents to generate porosity in the scaffold. Both morphology and thermal stability of the nanocomposite scaffold were examined. The swelling behavior, mechanical properties and hydrolytic degradation of the composite scaffolds were carefully investigated. Our results revealed that collagen, PVP and TiO2 are bonded together by four main hydrogen bonds, which is an essential action for the formation of nanocomposite scaffold. Using Coasts-Redfern model, we were able to calculate the thermal degradation apparent activation energy and demonstrated that the thermal stability of nanocomposites is dependent on amount of PVP incorporated. Furthermore, SEM images showed that the collagen fibers are wrapped and stabilized on scaffolds by PVP molecules, which improve the ultimate tensile strength (UTS). The UTS of PVP-contained scaffold is four times higher than that of scaffold without PVP, whereas ultimate percentage of elongation (UPE) is decreased, and PVP can enhance the degradation resistance.

Tannin-immobilized cellulose hydrogel fabricated by a homogeneous reaction as a potential adsorbent for removing cationic organic dye from aqueous solution

Tannin-immobilized cellulose (CT) hydrogels were successfully fabricated by homogeneous immobilization and crosslinking reaction via a simple method. The structures and properties of hydrogels were characterized by SEM and mechanical test. Methlyene Blue (MB) was selected as a cationic dye model, and the adsorption ability of CT hydrogel was evaluated. Tannins immobilized acted as adsorbent sites which combined MB by electrostatic attraction, resulting in the attractive adsorption ability of CT hydrogel. Adsorption kinetics could be better described by the pseudo-second-order model, and the absorption behaviors were in agreement with a Langmuir isotherm. The adsorption-desorption cycle of CT hydrogel was repeated six times without significant loss of adsorption capacity. In this work, both tannin immobilization and hydrogel formation were achieved simultaneously by a facile homogeneous reaction, providing a new pathway to fabricate tannin-immobilized materials for water treatment.

A unique high mechanical strength dialdehyde microfibrillated cellulose/gelatin composite hydrogel with a giant network structure

Microfibrillated cellulose (MFC) with diameters less than 100 nm and a three-dimensional network structure was produced through high-pressure homogenization. MFC was surface modified by periodate to prepare dialdehyde microfibrillated cellulose (DAMFC). DAMFC/gelatin composite hydrogel was prepared by mixing DAMFC with gelatin solution. A Schiff base was formed through the reaction between the aldehyde groups of DAMFC and amino groups of gelatin; therefore, a giant three-dimensional network structure was formed in the composite hydrogel. Since the nano reinforcing agent DAMFC was covalently bonded to the matrix gelatin, the load could be efficiently transferred through the giant network, therefore, the composite hydrogel presented extremely high mechanical properties. The compression strength of DAMFC/gelatin 25/75 (wt/wt) hydrogel dramatically increased to 1.63 MPa, 41 times that of the pure gelatin. Morphology observation revealed that the pore size of the composite hydrogel could be regulated by the DAMFC oxidation level. The composite scaffold demonstrated a good swelling capacity and could successfully maintain its shape in buffer solution. It should be noted that the giant network is different from the double network or fiber reinforced hydrogel. The present work shows that by forming a giant network structure through chemical crosslinking with the reinforcing agent itself, an extremely high mechanical strength composite hydrogel could be obtained.

Efficient removal of anionic dye (Congo red) by dialdehyde microfibrillated cellulose/chitosan composite film with significantly improved stability in dye solution

A novel composite film with efficient removal of anionic dye (Congo red) was developed using chitosan and dialdehyde microfibrillated cellulose nano fibrils. Microfibrillated cellulose with three dimensional network structure was prepared from microcrystalline cellulose by high-pressure homogenization. Then it was surface modified by periodate to prepare dialdehyde microfibrillated cellulose (DAMFC). DAMFC/chitosan composite films were prepared by solvent-casting. During the compounding of DAMFC with chitosan, a Schiff base was formed through the reaction between the aldehyde groups of DAMFC and amino groups of chitosan. A giant network structure was therefore formed. The addition of DAMFC resulted in remarkably increased adsorption capacity of the chitosan material as well as drastically improved stability in dye solution. The adsorption performance was investigated with respect to pH, temperature, contact time, and the initial dye concentration. The possible adsorption mechanism was proposed. Various isotherm models have been used to fit the data, and kinetic parameters were evaluated.

Compatibility and properties of biodegradable blend films with gelatin and poly(vinyl alcohol)

The blend films with gelatin and poly(vinyl alcohol) (PVA) were prepared by a solution casting method. The compatibility between gelatin and PVA in the blend films was investigated. The transmittance, Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), thermogravimetry analysis (TG), and differential scanning calorimetry (DSC) were employed to characterize the resultant blend films. According to optic result, the opacity of the blend film at the ratio of 20/80 (w/w, Gel to PVA) was the lowest, indicating the best compatibility between Gel and PVA at the ratio. The results of IR, XRD, DSC, and TG revealed an intensive interaction and good compatibility between them in the blend film at the ratio. The mechanical properties and solubility showed that PVA content in the blend films obviously affected the elongation at break and solubility. The mechanical properties and water resistance of gelatin film may be improved by the introduction of PVA.

Electrospinning and rheological behavior of poly (vinyl alcohol)/collagen blended solutions

Poly(vinyl alcohol)/collagen (PVA/COL) micro-nanofibers were successfully prepared by electrospinning process. Water, green, and non-toxic was used as the solvent. The electrospun mats consisted of micro-nanoscale fibers with mean diameter ranging from approximately 363 nm to 179 nm. It was observed that the mean diameters of PVA/COL electrospun fibers decreased with increasing collagen content. The effects of PVA/COL blending ratio on the rheological behavior of PVA/COL blended solutions were investigated by rotate rheometer. It was found that PVA/COL blended solutions behaved as Non-Newtonian fluids. With increasing collagen content, the Non-Newtonian index (n) of PVA/COL blended solutions decreased. Meanwhile, a linear relationship was found between the Non-Newtonian index (n) and the mean diameters of the PVA/COL micronanofibers. The chemical structures of PVA/COL electrospun fibers were also characterized by FTIR.