Coating nanothickness degradable films on nanocrystalline hydroxyapatite particles to improve the bonding strength between nanohydroxyapatite and degradable polymer matrix.

Hydroxyapatite (HA) nanoparticles are similar to bone apatite in size, phase composition, and crystal structure. When compared with micron-size HA particles, nano-HA possesses improved mechanical properties and superior bioactivity for promoting bone growth and regeneration. However, scaffolds fabricated from nano-HA alone cannot meet the mechanical requirements for direct-loading applications. A number of studies suggest that nanostructured composites may offer surface and/or chemical properties of native bone, and therefore represent ideal substrates to support bone regeneration. However, a common problem with nanohydroxyapatite (nano-HA)-polymer composites is the weak binding strength between the nano-HA filler and the polymer matrix since they are two different categories of materials and cannot form covalent bonds between them during the mixing process. Often, the mechanical strength of the composite is compromised due to the phase separation of the HA filler from the polymer matrix during the tissue repair process. To overcome this problem, an ultrathin degradable polymer film was grafted onto the surface of nano-HA using a radio-frequency plasma polymerization technology from acrylic acid monomers. The treated nano-HA powders are expected to bind to the polymer matrix via covalent bonds, thus enhancing the mechanical properties of the resultant composites. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin polymer film (2 nm) was uniformly deposited on the surfaces of the nanoparticles. The HRTEM results were confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOFSIMS). Tensile tests performed on the specimens revealed that the degradable coating had improved elastic and strength properties when compared with the nondegradable and uncoated controls. XPS and TOSIMS data revealed that more functional carboxyl groups were formed on degradable coatings than cross-linked nondegradable coatings. Cytocompatibility assay demonstrated that both the degradable and nondegradable coatings are cytocompatible.

Proteomics and genomics of microgravity.

Many serious adverse physiological changes occur during spaceflight. In the search for underlying mechanisms and possible new countermeasures, many experimental tools and methods have been developed to study microgravity caused physiological changes, ranging from in vitro bioreactor studies to spaceflight investigations. Recently, genomic and proteomic approaches have gained a lot of attention; after major scientific breakthroughs in the fields of genomics and proteomics, they are now widely accepted and used to understand biological processes. Understanding gene and/or protein expression is the key to unfolding the mechanisms behind microgravity-induced problems and, ultimately, finding effective countermeasures to spaceflight-induced alterations. Significant progress has been made in identifying the genes/proteins responsible for these changes. Although many of these genes and/or proteins were observed to be either upregulated or downregulated, however, no large-scale genomics and proteomics studies have been published so far. This review aims at summarizing the current status of microgravity-related genomics and proteomics studies and stimulating large-scale proteomics and genomics research activities.