Collagen-based fibrous scaffold for spatial organization of encapsulated and seeded human mesenchymal stem cells.

Living tissues consist of groups of cells organized in a controlled manner to perform a specific function. Spatial distribution of cells within a three-dimensional matrix is critical for the success of any tissue-engineering construct. Fibers endowed with cell-encapsulation capability would facilitate the achievement of this objective. Here we report the synthesis of a cell-encapsulated fibrous scaffold by interfacial polyelectrolyte complexation (IPC) of methylated collagen and a synthetic terpolymer. The collagen component was well distributed in the fiber, which had a mean ultimate tensile strength of 244.6+/-43.0 MPa. Cultured in proliferating medium, human mesenchymal stem cells (hMSCs) encapsulated in the fibers showed higher proliferation rate than those seeded on the scaffold. Gene expression analysis revealed the maintenance of multipotency for both encapsulated and seeded samples up to 7 days as evidenced by Sox 9, CBFA-1, AFP, PPARgamma2, nestin, GFAP, collagen I, osteopontin and osteonectin genes. Beyond that, seeded hMSCs started to express neuronal-specific genes such as aggrecan and MAP2. The study demonstrates the appeal of IPC for scaffold design in general and the promise of collagen-based hybrid fibers for tissue engineering in particular. It lays the foundation for building fibrous scaffold that permits 3D spatial cellular organization and multi-cellular tissue development.

Improving mechanical stability and density distribution of hepatocyte microcapsules by fibrin clot and gold nano-particles.

Bio-artificial livers (BAL) with microencapsulated hepatocytes have the typical limitations in maintaining hepatocyte functions, mechanical stability and uniform perfusion in packed or fluidized-bed bioreactors. We have previously developed microcapsules with enhanced hepatocyte functions. Here we have introduced a fibrin network inside microcapsules by (1) mixing collagen and fibrinogen with the encapsulated hepatocytes to support the cells; (2) submerging the microcapsules into a thrombin solution to induce the formation of an insoluble fibrin network inside the microcapsules. Fracture analysis on the microcapsules revealed significant improvement in mechanical stability. We have also introduced different amounts of gold nano-particles into microcapsules to achieve different densities for uniform bioreactor perfusion. These gold nano-particles also improved the mechanical stability of the microcapsules. Both the fibrin network and gold nano-particles exhibited the additional benefits of enhancing certain bio-functions of the encapsulated hepatocytes. The applications of these improved microcapsules in the development of bio-artificial livers are discussed.

TEM and STEM analysis on heat-treated and in vitro plasma-sprayed hydroxyapatite/Ti-6Al-4V composite coatings.

A cogent understanding of the microstructure, and indeed nano-structure, of hydroxyapatite (HA) and the interface between Ti-6Al-4V and HA is crucial to its appropriateness as a biomaterials. This paper reports the analysis of plasma-sprayed HA/Ti-6Al-4V composites by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to elucidate the intricate nature of the materials following plasma spray processing and in vitro evaluation. The novel Ti-6Al-4V/HA composite coating, with approximately 48 wt% HA, had demonstrated attractive tensile adhesion strength (approximately 28 MPa) and improved Young's modulus (approximately 55 GPa). Experimental results demonstrated that amorphous calcium phosphate and fine HA grains were formed during rapid splat solidification in the as-sprayed composite coatings. Small Ti-6Al-4V grains were observed adjacent to the amorphous calcium phosphate. The coatings were further heat treated at 600 degrees C for 6 h, and significant crystallisation of the amorphous calcium phosphate phase took place. However, complete crystallisation was not achieved at this temperature, as the coatings invariably contained a small amount of amorphous calcium phosphate phase in some local regions. After immersion in simulated body fluid for 2 weeks and 10 weeks, TEM and STEM confirmed that the interfaces inside the coating maintained good microstructural integrity.

Multi-layered microcapsules for cell encapsulation.

Mechanical stability, complete encapsulation, selective permeability, and suitable extra-cellular microenvironment, are the major considerations in designing microcapsules for cell encapsulation. We have developed four types of multi-layered microcapsules that allow selective optimization of these parameters. Primary hepatocytes were used as model cells to test these different microcapsule configurations. Type-1 microcapsules with an average diameter of 400 microm were formed by complexing modified collagen with a ter-polymer shell of 2-hydroxyethyl methylacrylate (HEMA), methacrylic acid (MAA) and methyl methacrylate (MMA), resulting in a capsule thickness of 2-5 microm. Cells in these microcapsules exhibited improved cellular functions over those cultured on collagen monolayers. Type-II microcapsules were formed by encapsulating the Type-I microcapsules in another 2-5 microm ter-polymer shell and a approximately 5 microm collagen layer between the two ter-polymer shells to ensure complete cell encapsulation. Type-II microcapsules comprised of a macro-porous exoskeleton with materials such as alumina sol-gel coated on the Type-I microcapsules. Nano-indendation assay indicated an improved mechanical stability over the Type-I microcapsules. Type-IV microcapsules were created by encapsulating Type-III microcapsules in another 2-5 microm ter-polymer shell, with the aim of imparting a negatively charged smooth surface to minimize plasma protein absorption and ensure complete cell encapsulation. The permeability for nutrient exchange, cellular functions in terms of urea production and mechanical stability of the microcapsules were characterized. The advantages and limitations of these microcapsules for tissue engineering are discussed.

Characterization and third-order optical nonlinearities of uniform surface-modified CdS nanoparticles.

Size-controlled uniform surface-capped CdS nanoparticles were readily prepared by an improved inverse microemulsion technique using hexanethiol as co-surfactant. The third-order optical nonlinearities were studied for the first time by newly-developed Z-scan technique, from which the enhanced nonlinear optical responses were observed after heat-treatment.