Novel micromanipulation studies of biological and non-biological materials

Many biological and non-biological materials in the form of microscopic particles (or microparticles) are used to produce functional products for a wide range of industrial sectors including pharmaceutical and medical, chemical, agrochemical, food and feed, personal and household care. Understanding their mechanical properties is essential for predicting their behaviour in manufacturing and processing, and for maximising their performance in end-use applications. However, it had not been possible to determine the mechanical properties of single microparticles until the author, as the main contributor, developed a novel micromanipulation technique at the University of Birmingham. The technique is capable of determining the mechanical properties of both biological and non-biological particles as small as 400 nm in diameter, and can be used for obtaining force-displacement data of single microparticles at large deformations, including those corresponding to rupture. The technique was enhanced by mathematical modelling and finite element analysis in order to allow intrinsic material properties to be determined, for example, the particle (or particle wall) elastic modulus, viscoelastic and plastic properties, and stress/strain at rupture. For biological materials, applications of this technique include understanding mechanical damage to animal cells in suspension cultures, yeast and bacterial disruption in downstream processing equipment, biomechanics of chondrocytes and chondrons for tissue engineering, and adhesion and cohesion of biofilms and food fouling deposits. For non-biological materials, applications include understanding and controlling particle breakage in processing equipment, and the formulation of microcapsules with optimum mechanical strength to achieve controlled release and targeted delivery of functional active ingredients. The research on micromanipulation has been sponsored by BBSRC, EPSRC, DEFRA, DTI, EU, the Royal Society K C Wong Fellowships and 19 national and international companies, and has resulted in more than one hundred academic publications. The knowledge generated has also assisted these companies to commercialise particulate functional products

Development of perfume microcapsules with triggered release by mechanical forces

Microcapsules have found applications or have potential applications in a wide range of industrial sectors. They can have many functions, including stabilization of active ingredients and/or realization of their controlled release. Microcapsules for such applications should have desirable structure and properties, including size, shell thickness, permeability, mechanical strength and surface composition, which may be achieved using appropriate formulation and processing conditions. Different types of microcapsules ranging from one micron to hundreds of microns in size have been prepared for various applications, such as for making pressure-sensitive materials, carriers of drugs, cells, enzyme and active ingredients used in detergents and human care products. A unique technique called micromanipulation has been applied to determine the mechanical properties of these microcapsules. This technique is based on compression of single micro-particles between two flat surfaces and simultaneous measurement of the force applied to them. From direct micromanipulation measurements, the force required to cause a given deformation of single microcapsules, diameter, visco-elastic-plastic behaviour, rupture force and deformation at rupture can be obtained. Numerical modelling of the force versus deformation data with appropriate constitutive equations of the shell materials based on finite element analysis can be used to determine their intrinsic property parameters, such as Young’s modulus, yield stress, plastic modulus, and stress/strain at rupture. The mechanical properties of microcapsules with a shell of melamine formaldehyde containing a core of perfume have been extensively investigated, which combined with the data of their chemical composition, structure, leakage, and adhesion on fabric surfaces have been used to optimise their formulation and processing conditions, leading to commercialization of perfume microcapsules in detergents. The details of these studies will be presented

An improved Liouville type theorem for Beltrami flows

In this note, we improved the Liouville type theorem for the Beltrami flows. Two different methods are used to prove it. One is the monotonicity method, and the other is proof by contradiction. The conditions that we proposed on Beltrami flows are significantly weaker than previously known conditions.Comment: to appear in Nonlinearit