Bo Jiang

One-step sol–gel preparation of PDMS–silica ORMOSILs as environment-resistant and crack-free thick antireflective coatings

Polydimethylsiloxane (PDMS)–silica ORMOSIL (organically modified silicate) sols were prepared by a one-pot sol–gel process using tetraethyl orthosilicate as an inorganic precursor and hydroxyl-terminated PDMS as an organic modifier, and antireflective (AR) coatings were prepared with these sols by dip coating. It was found that the addition of PDMS to silica sols significantly increased the viscosity and the controllable viscosity range of the silica sols, affording us a simple route to prepare very thick AR coatings with controlled thickness by a single deposition step. The coated fused silica substrates retained very high transmission of up to 99.9% at a determined wavelength. The addition of PDMS to the silica sols improved the hydrophobicity and abrasion-resistance of the coating, and prevented to some extent the coating from cracking which occurred in a pure inorganic thick AR coating. The PDMS–silica ORMOSIL AR coatings are stable after standing for 2 months at room temperature in an environment of 95% relative humidity. The relationship between structure and properties of the coatings is discussed considering the particle growth mechanism.

In Vivo Cartilage Engineering with Collagen Hydrogel and Allogenous Chondrocytes After Diffusion Chamber Implantation in Immunocompetent Host

In vivo cartilage reconstruction at an ectopic site was not successful in immunocompetent animals, possibly because of immunoreaction and the failure of material design. A diffusion chamber, which has been predominantly adopted to study cell differentiation, was effective in preventing host immune rejection, host cell invasion, and vascular invasion. In this study, we proposed to regenerate ectopic cartilage tissue in rabbits by implanting a diffusion-chamber system subcutaneously for 8 weeks. Inside the chamber, biomimetic scaffolds loaded with allogenous chondrocytes from newborn rabbits were enclosed. Tissue with characteristics of cartilage was formed inside the chamber with collagen gel as a scaffold, which was demonstrated using histological, immunohistochemical, and reverse transcriptase polymerase chain reaction assays. In contrast, for implant without diffusion chamber, vascular invasion was observed and results showed much less expression of cartilage extracellular matrix (ECM). Collagen type I hydrogel and sponge were compared as scaffolds. No cartilage tissue was found in the collagen sponge inside the chamber, presumably because of the different cell-seeding characteristics of gel. In addition, allogenous chondrocytes were adopted as a cell resource and were proved viable for the regeneration of cartilage tissue in this model. The results revealed that the diffusion chamber and scaffold design are both important in providing a more favorable biomimetic microenvironment for the formation of cartilage in vivo at an ectopic site, even with allogenous cells. Moreover, preliminary repair of a cartilage defect using the engineered tissue for 4 weeks showed the growth of new cartilage, obtaining a satisfactory interface with the original cartilage inside the defect. The model of engineering cartilage in vivo was proven to be useful. This study is the preliminary exploration for the reconstruction of ectopic cartilage in an immunocompetent host to be applied for cartilage repair. It may provide a valuable reference for the clinical application of cartilage repair.

Electrospun PCL/Gelatin composite fibrous scaffolds: mechanical properties and cellular responses

Abstract Electrospinning of hybrid polymer has gained widespread interest by taking advantages of the biological property of the natural polymer and the mechanical property of the synthetic polymer. However, the effect of the blend ratio on the above two properties has been less reported despite the importance to balance these two properties in various tissue engineering applications. To this aim, we investigated the electrospun PCL/Gelatin composite fibrous scaffolds with different blend ratios of 4:1, 2:1, 1:1, 1:2, 1:4, respectively. The morphology of the electrospun samples was observed by SEM and the result showed that the fiber diameter distribution became more uniform with the increase of the gelatin content. The mechanical testing results indicated that the 2:1 PCL/Gelatin sample had both the highest tensile strength of 3.7 MPa and the highest elongation rate of about 90%. Surprisingly, the 2:1 PCL/Gelatin sample also showed the best mesenchymal stem cell responses in terms of attachment, spreading, and cytoskeleton organization. Such correlation might be partly due to the fact that the enhanced mechanical property, an integral part of the physical microenvironment, likely played an important role in regulating the cellular functions. Overall, our results indicated that the PCL/Gelatin sample with the blend ratio of 2:1 was a superior candidate for scaffolds for tissue engineering applications.

Regulation of the osteoblastic and chondrocytic differentiation of stem cells by the extracellular matrix and subsequent bone formation modes

While various factors have been reported to direct stem cell differentiation lineage, little is known about how nature orchestrates the mesenchymal stem cell (MSC) differentiation and bone morphogenesis during skeleton development and bone regeneration. The present study reports that the matrix has a critical regulating effect on MSC differentiation and the subsequent bone formation modes. A simply combined hydroxyapatite (HA)-collagen matrix stimulates the MSC differentiation into the osteoblastic lineage and leads to a straightforward intramembranous bone formation mode, in contrast to the chondrocytic differentiation and endochondral mode observed on HA-synthetic hydrogel matrix. The accelerated MSC condensation and robust MSC-matrix and MSC-MSC interactions on collagen-based matrix might be the critical factors contributing to such events, likely through the orchestrated signal cascades and cellular events modulated by the extracellular matrix. The results demonstrate that matrix plays critical role in modulating the stem cell differentiation lineage and bone formation mode, which has been largely overlooked.

Experimental and theoretical study of dilute polyacrylamide solutions: effect of salt concentration

AbstractThe structure and intrinsic viscosity of the partially hydrolyzed polyacrylamide (HAPM) and polyacrylamide (PAM) in aqueous solution were investigated by comparative studies of molecular dynamics simulation over a wide range of the NaCl concentration. The radius of gyration (Rg), the hydrodynamic radius (Rh) and the ratio of the radius gyration and the hydrodynamic radius (ρ) were calculated for the PAM or HPAM in solutions with different NaCl concentrations at 298xa0K. The conformational changes of the polymer chain in different aqueous solution were discussed according to the molecular shapes. It was found that the change of the Rh or the Rg can reflect the change in the [η]. And the changes in the structure of the polymer chain with different NaCl concentrations were discussed via the ρ which can predict [η] changes. The results showed that behavior of the polymer solution calculated from the simulation agreed with the experimental measurements. Furthermore, the radial distribution functions for the HPAM solutions were investigated, which verified the micro-mechanism for the change of the structure. The results of this research showed that the computational method used in this work has practical applicability.n FigureThe characteristics of the dilute polyacrylamide solution have been studied to find the relations between the microstructure of the polymer chain and the intrinsic viscosity by MD simulation. It successfully provides us the useful information and to guide experimental synthesis more efficiently.

Effects of material and surface functional group on collagen self-assembly and subsequent cell adhesion behaviors

Collagen fibrous network not only provides structural support for cells but also serves as critical environment modulating various cell functions. Various factors would influence the collagen self-assembly but the effect of substrate surface on such process has been rarely studied. Here we examined the effects of materials (Ti and hydroxyapatite) and their surface characteristics (with and without the enrichment of hydroxyl group) on collagen self-reconstitution and fibrous network formation, and on subsequent cell adhesion and cytoskeleton organization of mesenchymal stem cells (MSCs). For both Ti and hydroxyapatite (HA) substrates, the enrichment of hydroxyl group (OH) on substrate surfaces promoted the collagen self-reconstitution and facilitated the formation of the fibrous network after 4h immersion in phosphate buffer solution (PBS), while all samples showed clear fibrous network formation after 2 day soaking in PBS. Compared with the Ti surfaces, the HA surfaces facilitated the self-reconstitution of collagen, leading to a more mature fibrous network with a twisted structure and enhanced lateral aggregation of fibrils. The fibrous network difference resulted in different behaviors of the subsequent MSC adhesion and spreading. The MSCs had the best adhesion and cytoskeleton organization on the OH enriched HA surface with collagen modification. Our results suggested that both the material selection and the hydroxyl group significantly influenced the collagen self-assembly and fibrous network formation and, as a result, the subsequent cell adhesion behaviors.

Sol–gel silica antireflective coating with enhanced abrasion-resistance using polypropylene glycol as porogen

AbstractnSilica antireflective (AR) coatings with high transmittance and enhanced abrasion-resistance were synthesized by sol–gel process using polypropylene glycol (PPG) as porogen. The effects of molecular weight of PPG and weight ratio of PPG to SiO2 on the refractive index and abrasion-resistance of the coating were systematically studied and compared with those of polyethylene glycol (PEG). Experimental data showed that the refractive index decreased with increasing the weight ratio to SiO2 and molecular weight of both PEG and PPG, but PPG was much more effective than PEG. In the case of same molecular weight, PPG modified coating has the higher porosity than PEG modified one. When the weight ratio of PPG to SiO2 is in a low level, the PPG-containing silica AR coatings exhibit the good abrasion-resistance. PPG is liquid at room temperature and the better solubility than PEG. These effective and economic AR coatings with enhanced abrasion-resistance have potential value in the field of solar thermal collectors.

Molecular design of modified polyacrylamide for the salt tolerance

AbstractIn our work, three kinds of functional monomers were selected to modify polyacrylamide (PAM) or partially hydrolyzed polyacrylamide (HPAM) by molecular dynamics simulation so as to achieve the stronger salt-tolerance of modified HM-HPAM. The radius of gyration (Rg), the hydrodynamic radius (RH), the effective length (Lef) and the intrinsic viscosity ([η]) for modified PAM or HPAM were studied in aqueous solutions with different ionic strength at 298xa0K. The results showed that modified HM-HPAM has a stronger salt tolerance and the salt tolerance increases gradually from HM-HPAM1 to HM-HPAM3 because the monomers with different steric hindrance would reduce the curliness of molecular chains and, consequently, improve the salt tolerance. So, introducing the steric hindrance monomer into polymer will increase the salt tolerance of the polymer and it is indicated that the simulated results agree with the experimental results very well. Furthermore, the radial distribution function (RDF) has been used to investigate the effect of NaCl on the hydration of the –COOˉ groups of the HM-HPAM from microscopic view.n FigureThe effect of different structures of the HM-HPAM on the salt-tolerance

Collagen nanofilm immobilized on at surfaces by electrodeposition method.

A simple electrodeposition method is presented for the preparing of collagen nanofilms (EAT) on anodic oxidized titanium surfaces (AT). The nanofilms were observed by scanning electron microscopy and atomic force microscopy. Functional TiOx layers with anionic groups of --PO(4), --SO(4) and --OH were investigated on the AT surface by X-ray photoelectron spectroscopy; X-ray diffraction results indicated that the AT surface was composed mainly of anatase and rutile. The bioactive electrodeposited TiOx layers on the AT surface showed lower water contact angles and higher surface energy than pure titanium surfaces (CT) and displayed higher collagen molecule immobilization.

Effect of water in amorphous polyvinyl formal: insights from molecular dynamics simulation

In this study, molecular dynamics simulations were performed to study the influence of water on polyvinyl formal. The effects of adding different concentrations of water (0, 0.23, 0.47, 0.94, 1.40, 1.86, 2.76, 3.65 and 4.52xa0wt%) to a copolymer of polyvinyl acetal, polyvinyl alcohol, and polyvinyl acetate were investigated. Simulated results clearly indicated that the radius of gyration of the polymer chain decreased whereas the cohesive energy density increased with the addition of water molecules. The diffusion coefficient initially decreased and then monotonically increased with increasing water concentration, and the same trend was observed for the fractional free volume. The results provide insights into the molecular structural and physical properties of polyvinyl formal with different water contents.