No abstract

Gold nanorods emit strong photoluminescence under two photon excitation; the efficient two photon lumininescence (TPL) arises from the local field enhancement assisted by surface plasmons. The surface plasmon effects on the TPL efficiency and spectrum are investigated by measuring the TPL of gold nanorods with various aspect ratios. A large TPL efficiency is found when incident light wavelength coincides with the longitudinal surface plasmon mode of the gold nanorods. However, the emission spectra of nanorods with various aspect ratios look similar and exhibit modest surface plasmon features, which implies a major non-radiative decay of excited surface plasmons.

Electrospinning is a simple and efficient method of fabricating a non-woven polymeric nanofiber matrix. However, using fluorinated alcohols as a solvent for the electrospinning of proteins often results in protein denaturation. TEM and circular dichroism analysis indicated a massive loss of triple-helical collagen from an electrospun collagen (EC) matrix, and the random coils were similar to those found in gelatin. Nevertheless, from mechanical testing we found the Young's modulus and ultimate tensile stresses of EC matrices were significantly higher than electrospun gelatin (EG) matrices because matrix stiffness can affect many cell behaviors such as cell adhesion, proliferation and differentiation. We hypothesize that the difference of matrix stiffness between EC and EG will affect intracellular signaling through the mechano-transducers Rho kinase (ROCK) and focal adhesion kinase (FAK) and subsequently regulates the osteogenic phenotype of MG63 osteoblast-like cells. From the results, we found there was no significant difference between the EC and EG matrices with respect to either cell attachment or proliferation rate. However, the gene expression levels of OPN, type I collagen, ALP, and OCN were significantly higher in MG63 osteoblast-like cells grown on the EC than in those grown on the EG. In addition, the phosphorylation levels of Y397-FAK, ERK1/2, BSP, and OPN proteins, as well as ALP activity, were also higher on the EC than on the EG. We further inhibited ROCK activation with Y27632 during differentiation to investigate its effects on matrix-mediated osteogenic differentiation. Results showed the extent of mineralization was decreased with inhibition after induction. Moreover, there is no significant difference between EC and EG. From the results of the protein levels of phosphorylated Y397-FAK, ERK1/2, BSP and OPN, ALP activity and mineral deposition, we speculate that the mechanism that influences the osteogenic differentiation of MG63 osteoblast-like cells on EC and EG is matrix stiffness and via ROCK-FAK-ERK1/2.

A polycaprolactone (PCL) nanofibrous composite matrix having mesoporous bioactive glass nanoparticles (MBG) was fabricated using the electrospinning method, and the microstructural, physical and biological properties of the composite matrix were characterized. The fiber diameters of PCL, 5 % MBG/PCL (5 M-PCL) and 10 % MBG/PCL (10 M-PCL) were 575 ± 162 nm, 312 ± 134 nm and 321 ± 144 nm, respectively. The bioactivity of the composite matrix was evaluated by soaking the matrix in 1.5× simulated body fluid; the MBG/PCL matrix showed a better biomineralization capability than did the PCL matrix. The biological performance of the PCL and the MBG/PCL were evaluated using an in vitro culture of MG63 osteoblast-like cells. We found that the cell attachment and proliferation rates were significantly higher on the 10 M-PCL than on the PCL. Moreover, the expression of several genes, including ANX-V, type I collagen and OCN, ALP activity, the deposition of calcium, and the BSP protein, were also significantly higher on 10 M-PCL than PCL. These results indicated that MBG/PCL has the ability to support cell attachment, growth, and differentiation and can also yield high bioactivity. Therefore, MBG/PCL could be potentially applied in bone implants.

No abstract

Collagen, a critical part of the extra-cellular matrix of tissues, is a popular native material for building scaffolding for tissue-engineering applications. To mimic the structural and functional profiles of materials found in the native extra-cellular matrix, numerous efforts have been made toward developing a novel scaffold combining collagen with other biomacromolecules. All of these works have been focused on improving the mechanical or biochemical properties of the collagen-based matrix. Unfortunately, most of these studies have failed to consider the nanostructure of collagen in the complex matrix. The aim of our study was to investigate the aggregation pattern of collagen after addition of polysaccharides with positive or negative charge, the dose-response relationship, and the effect on reconstitution kinetics. Generally, collagen self-assembles into fibrils with a diameter of around 95 nm but, in the presence of various polysaccharides in varying amounts, collagen self-assembles into different shapes with larger diameters compared with collagen alone. Although the morphology and diameter of the collagen fibrils varies with reconstitution conditions, the D-periods of the fibrils all remained the same regardless of the species or concentration of polysaccharides. The kinetics of fibril formation was determined from turbidity-time curves. All turbidity curves demonstrated that polysaccharides only alter the lag time and time frame of reconstitution, but have no significant effect on the mechanism of reconstitution. Together our data indicate that the presence of biomacromolecules can alter the kinetics and the 3D fibril ultrastructure of assembled collagen and that the consequent structural changes may affect cellular responses in medical applications.

No abstract

The purpose of the current study is to evaluate the carrier capability of collagen-hydroxyapatite microspheres to the bone morphogenic proteins (BMP). After anesthesia, a bone defect (6.0 mm in diameter and 10.0 mm in depth) was created at the distal femoral condyles of New Zealand white rabbits. These 10.0 mm3 defects were then completely filled with the implant materials. After 2, 4, 6, and 8 weeks, the animals were sacrificed and histological evaluations were performed. The results showed that when the defects were left untreated, there was no evidence of bone formation during the eight-week experimental period. In the group treated with collagen-hydroxyapatite microspheres without BMP-4, the defect was filled with fibrous tissue and inflammatory cells, while active bone formation with mature marrow tissue formation was evident in the defect treated with collagen-hydroxyapatite microspheres containing BMP-4. Collagen-hydroxyapatite microspheres were expected to be replaced by the regenerated bone structure as the bone reconstruction and bone remodelling process occurred. It was apparent that bone regeneration was influenced by the addition of BMP-4. Collagen-hydroxyapatite microspheres were good carriers for bone morphogenic proteins.