Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide nanoparticles (SPIONs). Achieving sufficient cellular uptake of SPIONs is a challenge that has traditionally been met by exposing cells to elevated concentrations of SPIONs or by prolonging exposure times (up to 72 hr). However, these strategies are likely to mediate toxicity. Here, we present the synthesis of the protein-based SPION magnetoferritin as well as a facile surface functionalization protocol that enables rapid cell magnetization using low exposure concentrations. The SPION core of magnetoferritin consists of cobalt-doped iron oxide with an average particle diameter of 8.2 nm mineralized inside the cavity of horse spleen apo-ferritin. Chemical cationization of magnetoferritin produced a novel, highly membrane-active SPION that magnetized human mesenchymal stem cells (hMSCs) using incubation times as short as one minute and iron concentrations as lows as 0.2 mM

High-Resolution Patterned Cellular Constructs by Droplet-Based 3D Printing.

Bioprinting is an emerging technique for the fabrication of living tissues that allows cells to be arranged in predetermined three-dimensional (3D) architectures. However, to date, there are limited examples of bioprinted constructs containing multiple cell types patterned at high-resolution. Here we present a low-cost process that employs 3D printing of aqueous droplets containing mammalian cells to produce robust, patterned constructs in oil, which were reproducibly transferred to culture medium. Human embryonic kidney (HEK) cells and ovine mesenchymal stem cells (oMSCs) were printed at tissue-relevant densities (10(7) cells mL(-1)) and a high droplet resolution of 1 nL. High-resolution 3D geometries were printed with features of ≤200 μm; these included an arborised cell junction, a diagonal-plane junction and an osteochondral interface. The printed cells showed high viability (90% on average) and HEK cells within the printed structures were shown to proliferate under culture conditions. Significantly, a five-week tissue engineering study demonstrated that printed oMSCs could be differentiated down the chondrogenic lineage to generate cartilage-like structures containing type II collagen

Artificial membrane-binding proteins stimulate oxygenation of stem cells during engineering of large cartilage tissue

Restricted oxygen diffusion can result in central cell necrosis in engineered tissue, a problem that is exacerbated when engineering large tissue constructs for clinical application. Here we show that pre-treating human mesenchymal stem cells (hMSCs) with synthetic membrane-active myoglobin-polymer–surfactant complexes can provide a reservoir of oxygen capable of alleviating necrosis at the centre of hyaline cartilage. This is achieved through the development of a new cell functionalization methodology based on polymer–surfactant conjugation, which allows the delivery of functional proteins to the hMSC membrane. This new approach circumvents the need for cell surface engineering using protein chimerization or genetic transfection, and we demonstrate that the surface-modified hMSCs retain their ability to proliferate and to undergo multilineage differentiation. The functionalization technology is facile, versatile and non-disruptive, and in addition to tissue oxygenation, it should have far-reaching application in a host of tissue engineering and cell-based therapies

Kinetics of adsorption of lysozyme at the air-water interface and the role of protein charge

The adsorption kinetics of hen egg white lysozyme at the air-water interface has been studied using specular neutron reflectometry. Experiments were performed at a number of pH values to examine the effect of charge on the rate of protein adsorption. Solutions of hen egg white lysozyme in air Contrast matched water at 1 mg/mL were made. These allow direct determination of the surface excess of protein. High repetition experiments, with short collection times, were used to accurately determine only the surface excess-derived from the product of the film thickness and the scattering length density of the layer. The kinetic traces at pH values where the protein is charged are well fitted by a first-order rate equation with two linear regions, where the change in the gradient occurs as the surface concentration reaches a steady state. This behaviour is characteristic of the transport and distortion of protein molecules, followed by rearrangement in the surface layer. The equilibrium concentration is a function of protein charge with steady state surface concentrations reaching 1.4 mg m-2 at pH 4 and 3 mg m-2 at pH 11. Protein charge is inversely related to the rate of adsorption. This dependency has been explored through thermodynamic analysis

Protein-Poly(silicic) Acid Interactions at The Air/Solution Interface

The structure of the interface generated by a spread layer of β-casein on an aqueous colloidal poly(silicic) acid subphase is described. The results are compared with data for the protein alone spread at the air/water interface and the silicate solution