Qiuran Jiang

Cytocompatible cross-linking of electrospun zein fibers for the development of water-stable tissue engineering scaffolds.

This paper reports a new method of cross-linking electrospun zein fibers using citric acid as a non-toxic cross-linker to enhance the water stability and cytocompatibility of zein fibers for tissue engineering and other medical applications. The electrospun structure has many advantages over other types of structures and protein-based biomaterials possess unique properties preferred for tissue engineering and other medical applications. However, ultrafine fiber matrices developed from proteins have poor mechanical properties and morphological stability in the aqueous environments required for medical applications. Efforts have been made to improve the water stability of electrospun protein scaffolds using cross-linking and other approaches, but the current methods have major limitations, such as cytotoxicity and low efficiency. In this research electrospun zein fibers were cross-linked with citric acid without using any toxic catalysts. The stability of the cross-linked fibers in phosphate-buffered saline and their ability to support the attachment, spreading and proliferation of mouse fibroblast cells were studied. The cross-linked electrospun fibers retained their ultrafine fibrous structure even after immersion in PBS at 37 degrees C for up to 15 days. Citric acid cross-linked electrospun zein scaffolds showed better attachment, spreading and proliferation of fibroblast cells than uncross-linked electrospun zein fibers, cross-linked zein films and electrospun polylactide fibers.

Crosslinking biopolymers for biomedical applications

Biomaterials made from proteins, polysaccharides, and synthetic biopolymers are preferred but lack the mechanical properties and stability in aqueous environments necessary for medical applications. Crosslinking improves the properties of the biomaterials, but most crosslinkers either cause undesirable changes to the functionality of the biopolymers or result in cytotoxicity. Glutaraldehyde, the most widely used crosslinking agent, is difficult to handle and contradictory views have been presented on the cytotoxicity of glutaraldehyde-crosslinked materials. Recently, poly(carboxylic acids) that can crosslink in both dry and wet conditions have been shown to provide the desired improvements in tensile properties, increase in stability under aqueous conditions, and also promote cell attachment and proliferation. Green chemicals and newer crosslinking approaches are necessary to obtain biopolymeric materials with properties desired for medical applications.

Novel 3D Electrospun Scaffolds with Fibers Oriented Randomly and Evenly in Three Dimensions to Closely Mimic the Unique Architectures of Extracellular Matrices in Soft Tissues: Fabrication and Mechanism Study

In this work, novel electrospun scaffolds with fibers oriented randomly and evenly in three dimensions (3D) including in the thickness direction were developed based on the principle of electrostatic repulsion. This unique structure is different from most electrospun scaffolds with fibers oriented mainly in one direction. The structure of novel 3D scaffolds could more closely mimic the 3D randomly oriented fibrous architectures in many native extracellular matrices (ECMs). The cell culture results of this study indicated that, instead of becoming flattened cells when cultured in conventional electrospun scaffolds, the cells cultured on novel 3D scaffolds could develop into stereoscopic topographies, which highly simulated in vivo 3D cellular morphologies and are believed to be of vital importance for cells to function and differentiate appropriately. Also, due to the randomly oriented fibrous structure, improvement of nearly 5 times in cell proliferation could be observed when comparing our 3D scaffolds with 2D counterparts after 7 days of cell culture, while most currently reported 3D scaffolds only showed 1.5- to 2.5-fold improvement for the similar comparison. One mechanism of this fabrication process has also been proposed and showed that the rapid delivery of electrons on the fibers was the crucial factor for formation of 3D architectures.

Hollow nanoparticles from zein for potential medical applications

Hollow nanoparticles from corn storage protein zein, with average diameters as small as 65 nm and capable of loading a large amount of drug and penetrating into the cell cytoplasm, have been developed for potential drug delivery applications. As an important protein co-product of corn-based ethanol, zein is biocompatible and has been proved to be useful for medical applications through in vitro and in vivo evaluations. Zein can overcome the limitations of inorganic or metal nanoparticles that tend to accumulate in the organs and tissues and is therefore preferable for drug delivery applications. However, it has been observed that only small proteins and peptides are able to penetrate into cells and zein with a molecular weight of 14–44 kDa may not be able to enter into the cells. In this research, hollow zein nanoparticles have been developed and the potential of the hollow zein nanoparticles to load drugs and enter the cell cytoplasm was investigated. Hollow zein nanoparticles developed in this research were capable of loading as high as 369 mg g−1 of the drug metformin at an equilibrium concentration of 3 g L−1. Metformin in hollow zein nanoparticles showed a more sustained and controlled release profile than that in solid zein nanoparticles. Hollow zein nanoparticles were found to be able to enter the fibroblast cells 1 hour after incubation. The biocompatibility, nano-scale diameters, potential for loading a large amount of drugs and the ability to penetrate into cells make hollow zein nanoparticles ideal candidates for carrying various payloads for intracellular drug delivery.

Water-stable electrospun collagen fibers from a non-toxic solvent and crosslinking system

Cytocompatible and water-stable ultrafine collagen fibers were electrospun by dissolving collagen in a low corrosive ethanol-water solvent and crosslinked by citric acid (CA) with glycerol as the crosslinking extender. Conventional solvents used for electrospinning of collagen either cause denaturation or contain more than 50% salt potentially leading to poor mechanical properties and water stability of the scaffolds. Collagen scaffolds have to be modified by techniques, such as, crosslinking to overcome the limitations in strength and stability. However, the existing crosslinking methods are either cytotoxic or ineffective. In this research, a benign ethanol-water solvent system and an extender-aided CA crosslinking method were developed. The native collagen conformation was retained after electrospinning, and the dry/wet strengths and water stability of fibers were substantially enhanced after crosslinking. The crosslinked electrospun scaffolds could maintain their fibrous structure for up to 30 days in phosphate-buffered saline at 37°C. Cells exhibited better attachment and growth on the CA crosslinked collagen fibers than on the glutaraldehyde crosslinked scaffolds.

Biodegradable hollow zein nanoparticles for removal of reactive dyes from wastewater

In this study, biodegradable hollow zein nanoparticles with diameters less than 100 nm were developed to remove reactive dyes from simulated post-dyeing wastewater with remarkably high efficiency. Reactive dyes are widely used to color cellulosic materials, such as cotton and rayon. Wastewater from reactive dyeing process contains up to 50% dye and electrolytes with concentrations up to 100 g L(-1). Current methods to remove reactive dyes from wastewater are suffering from low adsorption capacities or low biodegradability of the sorbents. In this research, biodegradable zein nanoparticles showed high adsorption capacities for dyes. Hollow zein nanoparticles showed higher adsorption for Reactive Blue 19 than solid structures, and the adsorption amount increased as temperature decreased, pH decreased or initial dye concentration increased. At pH 6.5 and pH 9.0, increasing electrolyte concentration could improve dye adsorption significantly. Under simulated post-dyeing condition with 50.0 g L(-1) salt and pH 9.0, maximum adsorption of 1016.0 mg dye per gram zein nanoparticles could be obtained. The adsorption capacity was much higher than that of various biodegradable adsorbents developed to remove reactive dye. It is suggested that the hollow zein nanoparticles are good candidates to remove reactive dye immediately after dyeing process.

Water-Stable Electrospun Zein Fibers for Potential Drug Delivery

This paper reports the development of electrospun zein fibers with improved water stability and tensile strength for potential drug delivery. The low morphological stability in aqueous environment and poor mechanical properties in dry and wet states have restricted the applications of electrospun protein materials, though these materials possess a unique structure, special adsorption properties, biocompatibility and biodegradability. In this study, the electrospun zein fibers were modified by non-toxic citric acid crosslinking catalyzed by NaOH. An up to 183% enhancement in dry tensile strength and an up to 448% improvement in wet tensile strength were generated. The cross-linked fibers were able to maintain their fibrous structure for 15 days in phosphate-buffered saline at 37°C. Moreover, those cross-linked electrospun zein fibers showed a potential in controlled drug delivery with a 58% drug-loading efficiency and a sustained profile drug release in artificial gastric juice.

Bio-thermoplastics from grafted chicken feathers for potential biomedical applications.

This research demonstrated the feasibility of using bio-thermoplastics developed from chicken feathers grafted with acrylates and methacrylates as scaffolds for tissue engineering. Keratin, the major protein in feathers, is a highly crosslinked biopolymer that has been reported to be biocompatible. However, it is difficult to break the disulfide bonds and make keratin soluble to develop materials for tissue engineering and other medical applications. Previously, keratin extracted from feathers using alkaline hydrolysis has been made into scaffolds but with poor water stability and mechanical properties. In this study, thermoplastic films were compression molded from chicken feathers grafted with 6 different acrylate monomers. The influence of the concentration and structures of grafted monomers on grafting parameters and the tensile strength, water stability and cytocompatibility of grafted feathers compression molded into films were investigated. It was found that the grafted feather films were water stable and had good strength and better supported cell growth than poly(lactic acid) films. Grafted feathers demonstrated the potential to be used for fabrication of biomaterials for various biomedical applications.

Cytocompatible and water-stable camelina protein films for tissue engineering

In this research, films with compressive strength and aqueous stability were developed from camelina protein (CP) for tissue engineering. Protein based scaffolds have poor mechanical properties and aqueous stability and generally require chemical or physical modifications to make them applicable for medical applications. However, these modifications such as crosslinking could reduce biocompatibility and/or degradability of the scaffolds. Using proteins that are inherently water-stable could avoid modifications and provide scaffolds with the desired properties. CP with a high degree of disulfide cross-linkage has the potential to provide water-stable biomaterials, but it is difficult to dissolve CP and develop scaffolds. In this study, a new method of dissolving highly cross-linked proteins that results in limited hydrolysis and preserves the protein backbone was developed to produce water-stable films from CP without any modification. Only 12 % weight loss of camelina films was observed after 7 days in phosphate buffer saline (PBS) at 37°C. NIH 3T3 fibroblasts could attach and proliferate better on camelina films than on citric acid cross-linked collagen films. Therefore, CP films have the potential to be used for tissue engineering, and this extraction-dissolution method can be used for developing biomedical materials from various water-stable plant proteins.

Ultrafine fibrous gelatin scaffolds with deep cell infiltration mimicking 3D ECMs for soft tissue repair

In this research, ultrafine fibrous scaffolds with deep cell infiltration and sufficient water stability have been developed from gelatin, aiming to mimic the extracellular matrices (ECMs) as three dimensional (3D) stromas for soft tissue repair. The ultrafine fibrous scaffolds produced from the current technologies of electrospinning and phase separation are either lack of 3D oriented fibrous structure or too compact to be penetrated by cells. Whilst electrospun scaffolds are able to emulate two dimensional (2D) ECMs, they cannot mimic the 3D ECM stroma. In this work, ultralow concentration phase separation (ULCPS) has been developed to fabricate gelatin scaffolds with 3D randomly oriented ultrafine fibers and loose structures. Besides, a non-toxic citric acid crosslinking system has been established for the ULCPS method. This system could endow the scaffolds with sufficient water stability, while maintain the fibrous structures of scaffolds. Comparing with electrospun scaffolds, the ULCPS scaffolds showed improved cytocompatibility and more importantly, cell infiltration. This research has proved the possibility of using gelatin ULCPS scaffolds as the substitutes of 3D ECMs.