Wetting Behavior and Tribological Properties of Polymer Brushes on Laser-Textured Surface.

Polymer brush layers can act as effective lubricants owing to their low friction and good controllability. However, their application to the field of tribology is limited by their poor wear resistance. This study proposes a strategy combining grafting and surface texturing to extend the service life of polymer brushes. Surface microstructure and chemical composition were measured through scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Water contact angles were measured to evaluate the surface wettability of the grafted silicon-based surface texture. Results showed the distinct synergistic effect between polymer brushes and laser surface texturing (LST). The prepared polymer brushes on textured surface can be a powerful mechanism for friction reduction properties, which benefit from their strong hydration effect on the lubrication liquid and promote the formation of a local lubricating film. Moreover, the wear life of polymer brushes can be immensely extended, as micro-dimples on the textured surface can effectively protect the polymer brushes. This study presents a method to enhance the load-bearing capacity and wear resistance of the grafted surface of polymer brushes.

Sacrificial template method for the synthesis of three-dimensional nanofibrous 58S bioglass scaffold and its in vitro bioactivity and cell responses.

Three-dimensional nanofibrous scaffolds that morphologically mimic natural extracellular matrices hold great promises in tissue engineering and regenerative medicine due to their increased cell attachment and differentiation compared with block structure. In this work, for the first time, three-dimensional porous nanofibrous 58S bioglass scaffolds have been fabricated using a sacrificial template method. During the process, a natural three-dimensional nanofibrous bacterial cellulose was used as the sacrificial template on which precursor 58S glass was deposited via a sol-gel route. SEM and TEM results verify that the as-prepared 58S scaffolds can inherit the three-dimensional nanofibrous feature of bacterial cellulose. Pore structure characterizations by nitrogen adsorption-desorption and mercury intrusion porosimetry demonstrate that the 58S scaffolds are highly porous with a porosity of 75.1% and contain both mesopores (39.4 nm) and macropores (60 µm) as well as large BET surface area (127.4 m2 g-1). In vitro cell studies suggest that the 58S scaffold is bioactive and biocompatible with primary mouse osteoblast cells, suggesting that the nanofibrous structure of 58S is able to provide an appropriate environment for cellular functioning. These results strongly suggest that the three-dimensional nanofibrous 58S scaffold has great potential for application in bone tissue engineering and regenerative medicine.

Preparation, structural characterization, and in vitro cell studies of three-dimensional SiO2-CaO binary glass scaffolds built ofultra-small nanofibers.

Three-dimensional (3D) nanofibrous scaffolds hold great promises in tissue engineering and regenerative medicine. In this work, for the first time, 3D SiO2-CaO binary glass nanofibrous scaffolds have been fabricated via a combined method of template-assisted sol-gel and calcination by using bacterial cellulose as the template. SEM with EDS, TEM, and AFM confirm that the molar ratio of Ca to Si and fiber diameter of the resultant SiO2-CaO nanofibers can be controlled by immersion time in the solution of tetraethyl orthosilicate and ethanol. The optimal immersion time was 6h which produced the SiO2-CaO binary glass containing 60at.% Si and 40at.% Ca (named 60S40C). The fiber diameter of 60S40C scaffold is as small as 29nm. In addition, the scaffold has highly porous 3D nanostructure with dominant mesopores at 10.6nm and macropores at 20µm as well as a large BET surface area (240.9m2g-1), which endow the 60S40C scaffold excellent biocompatibility and high ALP activity as revealed by cell studies using osteoblast cells. These results suggest that the 60S40C scaffold has great potential in bone tissue regeneration.

Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics.

In this study, the isothermal crystallization process of poly(l-lactide) (PLLA) has been investigated using in situ XRD, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Linear and nonlinear extrapolation methods have been deployed to estimate the equilibrium melting temperature ( T m 0 ), which is used for analyzing the supercooling dependence of the PLLA spherulitic growth rate (G). A double-melting behavior observed for PLLA under crystallization Tc < 120 °C has been attributed to the formation of both α' and α crystals. The T m 0 values of both α' and α crystals have been evaluated using the linear method (172.8 °C) and nonlinear method (196.4 °C), with the nonlinear estimate being 23.6 °C higher. A discontinuity in the temperature dependence of spherulite growth rate is observed around 128.3 °C. Regime II⁻III transition is found to occur at 128.3 °C when T m 0 = 196.4 °C as estimated by the nonlinear extrapolation method.

Layered nanohydroxyapatite as a novel nanocarrier for controlled delivery of 5-fluorouracil.

Layered materials intercalated by drug molecules have attracted much attention since they exhibit improved safety and effectiveness in drug delivery. In this work, layered nanohydroxyapatite (L-nHAp) was synthesized by template method and a model anticancer drug 5-fluorouracil (5FU) was loaded by intercalation technique. The morphology and structure of L-nHAp/5FU hybrids were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). XRD and FTIR revealed the successful drug intercalation into the gallery of L-nHAp. TGA evidenced enhanced thermal stability of the drug molecules in the gallery of L-nHAp. The in vitro release experiments demonstrated that the release of 5FU from L-nHAp/5FU was slower than that from rodlike nanohydroxyapatite (R-nHAp)/5FU. Furthermore, the release of 5FU from L-nHAp/5FU hybrid could be fitted by first-order, Higuchi, and Rigter-Pappas models. It is believed that L-nHAp may be a promising carrier for anticancer drugs.

Mechanical properties and cytotoxicity of nanoplate-like hydroxyapatite/polylactide nanocomposites prepared by intercalation technique.

Hydroxyapatite (HAp) in the forms of fiber, needle, and whisker has been employed as fillers in polymer composites. Herein, nanoplate-like HAp synthesized by template-assisted self-assembly was used to reinforce polylactide (PLA) nanocomposites via the solution intercalation method. Dynamic and static mechanical properties and cytotoxicity of the as-prepared HAp/PLA nanocomposites were assessed in addition to characterizations by XRD, FTIR, and TGA. XRD analysis confirms the formation of exfoliated structure in the HAp/PLA nanocomposites. The HAp/PLA nanocomposites exhibit better static and dynamic mechanical properties than unreinforced PLA. Furthermore, the HAp/PLA nanocomposite with an optimum HAp content of 20wt% (20HAp/PLA) demonstrates not only the best mechanical performance but also the highest thermal stability among the nanocomposite samples. Cell studies using a mouse fibroblast cell line (L929) suggest that 20HAp/PLA shows excellent biocompatibility, which makes it a promising material for biomedical applications.

Surface controlled calcium phosphate formation on three-dimensional bacterial cellulose-based nanofibers.

Studies on the early calcium phosphate (Ca-P) formation on nanosized substrates may allow us to understand the biomineralization mechanisms at the molecular level. In this work, in situ formation of Ca-P minerals on bacterial cellulose (BC)-based nanofibers was investigated, for the first time, using the X-ray absorption near-edge structure (XANES) spectroscopy. In addition, the influence of the surface coating of nanofibers on the formation of Ca-P minerals was determined. Combined with XRD analysis, XANES results revealed that the nascent precursor was ACP (amorphous calcium phosphate) which was converted to TCP (ß-tricalcium phosphate), then OCP (octacalcium phosphate), and finally to HAP (hydroxyapatite) when phosphorylated BC nanofibers were the templates. However, the formation of nascent precursor and its transformation process varied depending on the nature of the coating material on nanofibrous templates. These results provide new insights into basic mechanisms of mineralization and can lead to the development of novel bioinspired nanostructured materials.

Constructing a novel three-dimensional scaffold with mesoporous TiO2 nanotubes for potential bone tissue engineering.

Three-dimensional (3D) nanofibrous scaffolds for tissue engineering have been widely studied while 3D scaffolds made of nanotubes are rarely reported. Herein, we report a novel 3D porous network-structured scaffold built of mesoporous TiO2 nanotubes. The TiO2 nanotubes were synthesized using the template-assisted sol-gel method followed by calcination. Bacterial cellulose (BC) with 3D network structure was used as the template. TEM observation confirms the formation of tubular TiO2 nanotubes. The as-synthesized TiO2 nanotubes exhibit an average outer diameter of less than 100 nm and mesoporous walls consisting of aggregated TiO2 nanoparticles with a size of around 7 nm. SEM and TEM observations reveal that the TiO2 nanotube scaffold possesses 3D porous network structure and the surfaces of TiO2 nanotubes are rugged with nanotopography. Additionally, the scaffold built of mesoporous nanotubes with a mesopore size of 3.3 nm exhibits an extremely large surface area of 1629 m2 g-1. The capacity of the scaffold to support cell proliferation and osteogenic differentiation was evaluated using CCK-8 assay, alkaline phosphatase (ALP), and calcium content assay. The scaffold shows enhanced cell growth and proliferation and improved ALP activity and mineralization compared to the TCPS (tissue culture plate) control. Furthermore, the ALP activity of the scaffold is as high as a hydroxyapatite-coated nanofibrous scaffold. The enhanced proliferation and osteogenic differentiation of the TiO2 nanotube scaffold is ascribed to the outer surface roughness of TiO2 nanotubes, 3D porous network structure, mesopores, and large surface area.

Creation of macropores in three-dimensional bacterial cellulose scaffold for potential cancer cell culture.

There is an increasing need for an effective in vitro model that can resemble the 3-D nature of tumor microenvironments. In this work, a 3-D bacterial cellulose (BC) scaffold with macropores was fabricated by a facile freeze drying method for potential culture of cancer cells. This in vitro study reported, for the first time, the role of macropores in the adjustment of cancer cell behavior when compared with previous results cultured in BC scaffolds without macropores. The scaffold was characterized by SEM and mercury intrusion porosimeter. A human breast cancer cell line (MDA-MB-231) cultured in the macroporous BC scaffold was examined via cell proliferation, histological and SEM analyses. The results demonstrated that the macroporous scaffold provided a good environment for cell viability, adhesion, proliferation, and infiltration. These findings suggested that the macroporous BC scaffold might have great potential for use in the in vitro culture of cancer cells.

One-step in situ biosynthesis of graphene oxide-bacterial cellulose nanocomposite hydrogels.

Graphene oxide-bacterial cellulose (GO/BC) nanocomposite hydrogels with well-dispersed GO in the network of BC are successfully developed using a facile one-step in situ biosynthesis by adding GO suspension into the culture medium of BC. During the biosynthesis process, the crystallinity index of BC decreases and GO is partially reduced. The experimental results indicate that GO nanosheets are uniformly dispersed and well-bound to the BC matrix and that the 3D porous structure of BC is sustained. This is responsible for efficient load transfer between the GO reinforcement and BC matrix. Compared with the pure BC, the tensile strength and Young's modulus of the GO/BC nanocomposite hydrogel containing 0.48 wt% GO are significantly improved by about 38 and 120%, respectively. The GO/BC nanocomposite hydrogels are promising as a new material for tissue engineering scaffolds.

Evolution of morphology of bacterial cellulose scaffolds during early culture.

Morphological characteristics of a fibrous tissue engineering (TE) scaffold are key parameters affecting cell behavior. However, no study regarding the evolution of morphology of bacterial cellulose (BC) scaffolds during the culture process has been reported to date. In this work, BC scaffolds cultured for different times starting from 0.5h were characterized. The results demonstrated that the formation of an integrated scaffold and its 3D network structure, porosity, fiber diameter, light transmittance, and the morphology of hydroxyapatite (HAp)-deposited BC scaffolds changed with culture time. However, the surface and crystal structure of BC fibers did not change with culture time and no difference was found in the crystal structure of HAp deposited on BC templates regardless of BC culture time. The findings presented herein suggest that proper selection of culture time can potentially enhance the biological function of BC TE scaffold by optimizing its morphological characteristics.

Preparation of three-dimensional braided carbon fiber-reinforced PEEK composites for potential load-bearing bone fixations. Part I. Mechanical properties and cytocompatibility.

In this study, we focused on fabrication and characterization of three-dimensional carbon fiber-reinforced polyetheretherketone (C3-D/PEEK) composites for orthopedic applications. We found that pre-heating of 3-D fabrics before hot-pressing could eliminate pores in the composites prepared by 3-D co-braiding and hot-pressing techniques. The manufacturing process and the processing variables were studied and optimum parameters were obtained. Moreover, the carbon fibers were surface treated by the anodic oxidization and its effect on mechanical properties of the composites was determined. Preliminary cell studies with mouse osteoblast cells were also performed to examine the cytocompatibility of the composites. Feasibility of the C3-D/PEEK composites as load-bearing bone fixation materials was evaluated. Results suggest that the C3-D/PEEK composites show good promising as load-bearing bone fixations.

The inhibition of lamellar hydroxyapatite and lamellar magnetic hydroxyapatite on the migration and adhesion of breast cancer cells.

Hydroxyapatite nanoparticles have been reported to exhibit potent anti-tumor effects in some cancer cells. In our previous study, we have successfully synthesized two types of hydroxyapatite nanoparticles, laminated hydroxyapatite (L-HAp) and laminated magnetic hydroxyapatite (LM-HAp). In this study, we wanted to investigate the effects of L-HAp and LM-HAp with various concentrations on human breast cancer MDA-MB-231 cells. Cell proliferation was assessed with a MTT colorimetric assay. Scratch and adhesion assays were used to detect the effects of these two materials on migration and adhesion. The expressions of integrin ß1 and Akt were measured by Western blotting. Our results showed that L-HAp and LM-HAp had little cell cytotoxicity and significantly reduced cell mobility and adhesion. LM-HAp showed greater inhibitor ability on migration and adhesion of MDA-MB-231 cells. Moreover, results from western blotting showed that L-HAp and LM-HAp impacted the phosphorylation of integrin ß1, but showed no regular impact on Akt. This study suggests that L-HAp and LM-HAp may be potential anti-tumor and delivery system for breast cancer therapy.