Protein fiber particles for biomedical applications

Ultrafine protein particles have been fabricated from natural fibres, such as silk and wool. Our studies suggested that particles could be used for fabricating tough macro-porous composites scaffolds for tissue engineering. They are also efficient for reversible binding of metal ions. We are currently analyzing the sorption properties, biocompatibility and biodegradability of a range of particles to evaluate possibility for biomedical and healthcare applications.

Tailoring the surface chemistry of carbon fiber and E-glass composites for improved adhesion

The main challenges in the manufacture of composite materials are low surface energy and the presence of silicon-containing contaminants, both of which greatly reduce surface adhesive strength. In this study, carbon fiber (CF) and E-glass epoxy resin composites were surface treated with the Accelerated Thermo-molecular adhesion Process (ATmaP). ATmaP is a multiaction surface treatment process where tailored nitrogen and oxygen functionalities are generated on the surface of the sample through the vaporization and atomization of n-methylpyrrolidone solution, injected via specially designed flame-treatment equipment. The treated surfaces of the polymer composites were analyzed using XPS, time of flight secondary ion mass spectrometry (ToF-SIMS), contact angle (CA) analysis and direct adhesion measurements. ATmaP treatment increased the surface concentration of polar functional groups while reducing surface contamination, resulting in increased adhesion strength. XPS and ToF-SIMS showed a significant decrease in silicon-containing species on the surface after ATmaP treatment. E-glass composite showed higher adhesion strength than CF composite, correlating with higher surface energy, higher concentrations of nitrogen and CO functional groups (from XPS) and higher concentrations of oxygen and nitrogen-containing functional groups (particularly C₂H₃O⁺ and C₂H₅NO⁺ molecular ions, from ToF-SIMS).

Modelling the side impact of carbon fiber tubes

Metallic tubes have been extensively studied for their crashworthiness as they closely resemble automotive crash rails. Recently, the demand to improve fuel economy and reduce vehicle emissions has led automobile manufacturers to explore the crash properties of light weight materials such as fibre reinforced polymer composites, metallic foams and sandwich structures in order to use them as crash barriers. This paper discusses the response of carbon fibre reinforced polymer (CFRP) tubes and their failure mechanisms during side impact. The energy absorption of CFRP tubes is compared to similar Aluminium tubes. The response of the CFRP tubes during impact was modelled using Abaqus finite element software with a composite fabric material model. The material inputs were given based on standard tension and compression test results and the in-plane damage was defined based on cyclic shear tests. The failure modes and energy absorption observed during the tests were well represented by the finite element model.

Real-time observation of fiber network formation in molecular organogel : supersaturation-dependent microstructure and its related rheological property

Low-molecular mass organic gelators self-organizing into three-dimensional fiber networks within organic solvents have attracted much attention in recent years. However, to date, how the microstructure of fiber network is formed in a gelation process and the key factors that govern the topological structure of a gel network remain to be determined. In this work, we address these issues by investigating the in situ formation of the gel networks in the N-lauroyl-l-glutamic acid di-n-butylamide (GP-1)/propylene glycol (PG) system. By using optical microscopy, the time evolution of the gel network microstructure was investigated under various supersaturation conditions. It is found that supersaturation is one of the key factors that govern the topological structure of a gel network. In particular, the creation of the junctions turns out to be supersaturation-dependent. The rheological experiments further revealed the correlation between topological structure and mechanical properties. It suggests that the rheological properties can be effectively modified by tuning the microstructure topology of the gel network. Our results reported here provide new physical insight into the formation kinetics of a molecular gel. Furthermore, this work could be important in constructing and engineering a supramolecular structure for the purpose of applications.

Architecture of fiber network : from understanding to engineering of molecular gels

A new approach of engineering of molecular gels was established on the basis of a nucleation-initiated network formation mechanism. A variety of gel network structures can be obtained by regulating the starting temperature of the sol−gel transition. This enables us to tune the network from the spherulitic domains pattern to the extensively interconnected fibrillar network. As the consequence of fibrous network structure turning, desirable rheological and other in-use properties of the materials can be obtained accordingly. This approach of micro-/nanostructural fabrication may open up a new route for micro-/nanofunctional materials engineering in general.

Microengineering of supramolecular soft materials by design of the crystalline fiber networks

Crystalline spherulitic fiber networks are commonly observed in polymeric and supramolecular functional materials. The elasticity of materials with this type of network is low if interactions between the individual spherulites are weak (mutually exclusive). Improving the elasticity of these materials is necessary because of their important applications in many fields. In this work, the engineering of the microstructures and rheological properties of this type of material is carried out. A small molecule organogel formed by the gelation of N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol (PG) is used as an example. The elasticity of this material is improved by controlling the thermodynamic driving force, the supersaturation of the gelator, and by using a selected copolymer additive to manipulate the primary nucleation of GP-1. Because of the weak interactions between the GP-1 spherulites, with the same fiber mass, the elasticity of GP-1/PG gel is less than half of those of the other two gels formed by GP-1 and 2-hydroxystearlic acid in solvent benzyl benzoate (BB), which are supported by interconnecting spherulitic fiber networks. This work develops a robust approach to the engineering of supramolecular functional materials especially those with mutually exclusive spherulite fiber networks.

Kinetically controlled homogenization and transformation of crystalline fiber networks in supramolecular materials

Supramolecular materials with three-dimensional fiber networks have applications in many fields. For these applications, a homogeneous fiber network is essential in order to get the desired performance of a material. However, such a fiber network is hard to obtain, particularly when the crystallization of fiber takes place nonisothermally. In this work, a copolymer is used to kinetically control the nucleation and fiber network formation of a small molecular gelling agent, N-lauroyl-L-glutamic acid di-nbutylamide (GP-1) in benzyl benzoate. The retarded nucleation and enhanced mismatch nucleation of the gelator by the additive leads to the conversion of a mixed fiber network into a homogeneous network consisting of spherulites only. The enhanced structural mismatch of the GP-1 during crystallization is quantitatively characterized using the rheological data. This effect also leads to the transformation of an interconnecting (single) fiber network of GP-1 into a multidomain fiber network in another solvent, isostearyl alcohol. The approach developed is significant to the production of supramolecular materials with homogeneous fiber networks and is convenient to switch a single fiber network to a multidomain network without adjusting the thermodynamic driving force.

Architecture of a biocompatible supramolecular material by supersaturation-driven fabrication of fiber network

The architecture of a biocompatible organogel formed by gelation of a small molecule organic gelator, N-lauroyl-l-glutamic acid di-n-butylamide, in isostearyl alcohol was investigated based on a supersaturation-driven crystallographic mismatch branching mechanism. By controlling the supersaturation of the system, the correlation length that determines the mesh size of the fiber network was finely tuned and the rheological properties of the gel were engineered. This approach is of considerable significance for many gel-based applications, such as controlled release of drugs that requires precise control of the mesh size. A direct cryo-transmission electron microscopy (TEM) imaging technique capable of preserving the network structure was used to visualize its nanostructure.

Microengineering of soft functional materials by controlling the fiber network formation

The engineering of soft functional materials based on the construction of three-dimensional interconnecting self-organized nanofiber networks is reported. The system under investigation is an organogel formed by N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol. The engineering of soft functional materials is implemented by controlling primary nucleation kinetics of GP-1, which can be achieved by both reducing thermodynamic driving force and/or introducing a tiny amount of specific copolymers (i.e., poly(methyl methacrylate comethacrylic acid)). The primary nucleation rate of GP-1 is correlated to the number density of GP-1 spherulites, which determines the overall rheological properties of soft functional materials. The results show that the presence of a tiny amount of the polymer (0.01-0.06%) can effectively inhibit the nucleation of GP-1 spherulites, which leads to the formation of integrated fiber networks. It follows that with the additive approach, the viscoelasticity of the soft functional material is significantly enhanced (i.e., more than 1.5 times at 40 °C). A combination of the thermal and additive approach led to an improvement of 3.5 times in the viscosity of the gel.

Architecture and engineering of a supramolecular functional material by manipulating the nano-structure of fiber network

Three-dimensional fiber networks were created from an organogel system consisting mainly of elongated fibrils by using a nonionic surfactant as an additive. The presence of the surfactant molecules manipulates the network structure by enhancing the mismatch nucleation on the growing fiber tips. Both the fiber network structure and the rheological properties of the material can be finely tuned by changing the surfactant concentration, which provides a robust approach to the engineering of supramolecular soft functional materials.