Zheng-Ming Huang

A review on polymer nanofibers by electrospinning and their applications in nanocomposites

Electrospinning has been recognized as an efficient technique for the fabrication of polymer nanofibers. Various polymers have been successfully electrospun into ultrafine fibers in recent years mostly in solvent solution and some in melt form. Potential applications based on such fibers specifically their use as reinforcement in nanocomposite development have been realized. In this paper, a comprehensive review is presented on the researches and developments related to electrospun polymer nanofibers including processing, structure and property characterization, applications, and modeling and simulations. Information of those polymers together with their processing conditions for electrospinning of ultrafine fibers has been summarized in the paper. Other issues regarding the technology limitations, research challenges, and future trends are also discussed.

Fabrication of drug-loaded electrospun aligned fibrous threads for suture applications.

In this work, drug-loaded fibers and threads were successfully fabricated by combining electrospinning with aligned fibers collection. Two different electrospinning processes, that is, blend and coaxial electrospinning, to incorporate a model drug tetracycline hydrochloride (TCH) into poly(L-lactic acid) (PLLA) fibers have been used and compared with each other. The resulting composite ultrafine fibers and threads were characterized through scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and tensile testing. It has been shown that average diameters of the fibers made from the same polymer concentration depended on the processing method. The blend TCH/PLLA fibers showed the smallest fiber diameter, whereas neat PLLA fibers and core-shell TCH-PLLA fibers showed a larger proximal average diameter. Higher rotating speed of a wheel collector is helpful for obtaining better-aligned fibers. Both the polymer and the drug in the electrospun fibers have poor crystalline property. In vitro release study indicated that threads made from the core-shell fibers could suppress the initial burst release and provide a sustained drug release useful for the release of growth factor or other therapeutic drugs. On the other hand, the threads from the blend fibers produced a large initial burst release that may be used to prevent bacteria infection. A combination of these results suggests that electrospinning technique provides a novel way to fabricate medical agents-loaded fibrous threads for tissue suturing and tissue regeneration applications.

Coaxial Electrospun Poly(L‐Lactic Acid) Ultrafine Fibers for Sustained Drug Delivery

A coaxial electrospinning technique to fabricate core‐shell ultrafine fiber mats for drug delivery application is described in this paper. Poly (L‐lactic acid) (PLLA) and tetracycline hydrochloride (TCH) were employed as the shell and core materials, respectively. To investigate the feasibility of the resulting fiber mats for use as drug release carriers, these electrospun fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile testing. In vitro drug release behavior was also examined by ultraviolet‐visible (UV‐VIS) spectroscopy. Results indicated that a reservoir‐type drug release device can be conveniently obtained through encapsulating TCH in the PLLA ultrafine fiber. The size of the ultrafine fibers had a significant effect on their physical‐chemical properties. Furthermore, a sustained TCH release from these fiber mats was also observed. Consequently, the electrospun ultrafine fiber mats containing drugs may be used as drug release carriers or made into biomedical devices such as sutures and wound dressings.

Performance study of braided carbon/PEEK composite compression bone plates

In addition to unidirectional laminates and short fiber reinforcements for compression bone plate developments in the literature, we have proposed using a textile structure, i.e. braid preform, for this purpose. In the present paper, the influence of braiding angles and plate thicknesses on the bending performance of the braided composite bone plates is investigated. As a result, the influence of the braiding angle, varied in a certain range, on the plate bending properties is not significant when the plate thickness is thin. This influence becomes higher with an increase in the plate thickness. A 10 degrees braiding angle has been seen to be appropriate for all the cases under consideration. The present study indicates that the braided composite plate with 2.6mm thickness can be suitable for forearm treatment whereas the braided composite plate of 3.2mm thickness is applicable to femur or tibia fixation.

A controlled release system of titanocene dichloride by electrospun fiber and its antitumor activity in vitro.

In order to improve both safety and efficacy of cancer chemotherapy of titanocene dichloride and overcome the shortcomings such as instability and short half-life in the human body, we report a controlled release system of titanocene dichloride by electrospun fiber and its in vitro antitumor activity against human lung tumor spca-1 cells. The system was developed by electrospinning. The release profiles of titanocene dichloride in PBS were researched by UV-Vis spectrophotometer. In vitro antitumor activities of the fibers were examined by MTT method. Titanocene dichloride was well incorporated in biodegradable poly(L-lactic acid) fibers. XRD results suggest that titanocene dichloride exists in the amorphous form in the fibers. The controlled release of titanocene dichloride can be gained for long time. MTT showed actual titanocene dichloride content 40, 80, 160 and 240 mg/L from the fibers mat, cell growth inhibition rates of 11.2%, 22.1%, 44.2% and 68.2% were achieved, respectively. The titanocene dichloride released has obvious inhibition effect against lung tumor cells. The system has an effect of controlled release of titanocene dichloride and may be used as an implantable anticancer drug in clinical applications in the future.

An introduction to biocomposites

Biocompatibility Constituent, Fabrication, and Characterization Mechanics of Composite Materials Designing with Composite Materials Biomedical Applications of Polymer Composites Case Studies

Fabrication of a new composite orthodontic archwire and validation by a bridging micromechanics model.

A new technique based on tube shrinkage is proposed for the fabrication of composite archwires. Compared with a traditional pultrusion method, this new technique can avoid any fiber damage during the fabrication and can provide the archwire with a required curvature in its final clinical usage. The present paper focuses on the technique development and mechanical design and validation in terms of constituent materials by using a micromechanics bridging model. Prototype archwire has been fabricated using fiberglass and an epoxy matrix, with a wire diameter of 0.5mm and a 45% fiber volume fraction. Tensile and three-point bending tests have shown that the mechanical performance of the prototype composite archwire is comparable to that of a clinical Ni-Ti archwire. Another purpose of the present paper is to provide an efficient procedure for a critical design of composite archwires. For this to be possible, the ultimate load especially flexural load carrying ability of the composite archwire must be assessed from the knowledge of its constituent properties. However, difficulty exists in doing this, which comes from the fact that the failure of the utmost filament of the composite archwire subjected to initially the maximum bending stress does not imply its ultimate failure. Additional higher loads can still be applied and a progressive failure process is generated. In this paper, the circular archwire was discretized into a number of parallel laminae along its axis direction, and the bridging micromechanics model combined with the classical lamination theory has been applied to understand the progressive failure process with reasonable accuracy. Only the constituent fiber and matrix properties are required for this understanding. Nevertheless, the ultimate bending strength cannot be obtained only based on a stress failure criterion. This is because neither the first-ply nor the last-ply failure corresponds to the ultimate failure. An additional critical deflection (curvature) condition must be employed also. By using both the stress failure and the critical deflection conditions, the predicted load-deflection up to the ultimate failure agrees well with the measured data. Thereafter, different mechanical performances of composite archwires can be tailored before fabrication by choosing suitable constituent materials, their contents, and the archwire diameters. Several design examples have been shown in the paper.

Modeling inelastic and strength properties of textile laminates: a unified approach

A unified approach based on bridging micromechanics model to the simulation of inelastic and strength properties of textile (woven, braided, and knitted) fabric reinforced composite laminates is reviewed and summarized in this paper. The approach is performed ply by ply. While classical lamination theory is employed to determine the load shared by a lamina ply, the individual ply analysis essentially consists of three steps. In the first step, a representative volume element (RVE) of the lamina is isolated and the geometry of the textile preform in the RVE is identified. According to this geometrical description, the RVE is divided into a series of unidirectional (UD) composites whose orientations have all been known. Thus, the second step is concerned with the analysis of all the UD composites, which is accomplished by using the bridging model. The three fundamental quantities, i.e. the stress increments in the fiber, the stress increments in the matrix, and the overall compliance matrix of the composite, are explicitly obtained at each load level. The last step deals with an assemblage of all the UD composites to obtain the mechanical response characteristics of the considered ply. The ply failure is assumed if the internal stress state in any constituent attains its ultimate value, and a progressive failure process of the laminate results. Otherwise, the ply instantaneous compliance matrix is adapted to define the overall instantaneous stiffness matrix of the laminate for additional analysis. Ultimate failure strengths of different textile composite laminates subjected to in-plane, fatigue, as well as out-of plane bending loads have been obtained, which compare favorably with our experimental data.

Fabrication and characterization of chitosan coated braided PLLA wire using aligned electrospun fibers

The development of functionalized braided wires coated with chitosan that can be used for tissue suturing and tissue regeneration is the subject of this work. Poly(l-lactic acid) (PLLA) braided wires were successfully fabricated by combining an electrospinning technique and alignment collection with a mini-type braiding method. The resulting PLLA wires with and without chitosan coating were characterized through a variety of methods including scanning electron microscopy (SEM), X-ray photoelectronic spectra (XPS) and tensile mechanical testing. Hemolytic property, kinetic hemostasis behavior, platelet adhesion, erythrocyte adhesion, and water uptake ability of the wires were explored. The results showed that a nearly comparable mechanical behavior of the braided wires with some commercial suture could be obtained with well-aligned fibers, and no significant difference in tensile performances were recognized with and without the introduction of chitosan. The PLLA wires coated with chitosan were found to have better prohemostatic activity than those without a chitosan coating.

Correlation of the bridging model predictions of the biaxial failure strengths of fibrous laminates with experiments

Abstract In my other paper (in this issue), the bridging micromechanics model has been combined with the classical lamination theory to predict the progressive failure strengths or the entire stress–strain curves of a set of typical polymer resin based composite laminates subjected to different biaxial loads. The predictions were performed only using the constituent fiber and resin properties and the geometric parameters of the laminates specified independently. Comparison of the predictions with the experimental measurements provided by the failure exercise organizers is carried out in this paper. As a whole, the overall correlation between the theory and the experiments is reasonable. Some additional comments regarding the applications of the bridging model to the simulation of ultimate behavior of fibrous laminates are provided. Comparison of the predictions of each other with and without thermal residual stresses is also made. It is demonstrated that for most of the present epoxy resin based composites, the effect of the thermal residual stresses is grossly insignificant. Thus, a general conclusion may be that in most cases the thermal residual stresses can be neglected for a thermoset polymer resin based composite.