Multifunctional organic–inorganic composite luminescent nanospheres

A simple general strategy was successfully developed for the preparation of magnetic–luminescent multifunctional nanocomposites by incorporating fluorescent (pyrene) and magnetic (Fe₃O₄) components simultaneously into a poly(styrene‐co‐methacrylic acid) [poly(St‐co‐MAA)] copolymer matrix. The nanospheres so prepared were characterized using scanning electron microscopy (SEM), powder X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The prepared magnetic–fluorescent inorganic–organic nanocomposites have excellent magnetic and photoluminescent properties. They can be used in magnetic separation of trace amounts of sample, fluorescence detection and imaging applications, including magnetic resonance imaging (MRI) and fluorescence imaging. The fluorescence quenching of the nanospheres in the presence of different amounts of Cu²⁺ ions was also investigated. Under optimal experimental conditions, the relative fluorescence intensity of the composite nanosphere colloidal solution is proportional to the concentration of Cu²⁺ ions, which indicates that these multifunctional nanocomposites can be used for the magnetic separation and fluorescence detection of Cu²⁺ ions. Copyright © 2011 John Wiley & Sons, Ltd.     

On prediction of optical properties of two- and multiphase nanocomposites for nanomedicine

The theory of optical properties of nanoparticles is considered with the aid of dispersion relations, which are based on the Kramers-Kronig analysis. It is shown that one can utilize rather general dispersion relations, which hold for liquid matrices that contain nanoparticles. Wiener bounds incorporating the Kramers-Kronig analysis are utilized in assessment of the complex permittivity of a nanoparticle.     

小鼠前成骨细胞MC3T3-E1在自组装多肽水凝胶支架中的成骨分化

目的研究MC3T3-E1细胞在自组装多肽水凝胶支架上的生长和成骨分化.方法在多肽水凝胶支架RADA16上接种MC3T3-E1细胞,荧光染色观察细胞形态和存活情况;组织化学染色检测MC3T3-E1细胞碱性磷酸酶活性以及细胞外钙质沉积;RT-PCR分析成骨特异性基因的表达.结果 MC3T3-E1细胞在水凝胶支架RADA16上粘附铺展良好,呈纺锤样形态.诱导培养后支架上的细胞有较高水平的碱性磷酸酶表达和矿化基质沉积.此外,骨分化特异性基因骨桥蛋白和骨涎蛋白也有表达,且表达量随培养时间的延长而增多.结论 在自组装水凝胶内MC3T3-E1细胞可向成骨方向分化,并能在凝胶内产生矿化的细胞外基质.     

The endothelization of polyhedral oligomeric silsesquioxane nanocomposites

It has been recognized that seeding vascular bypass grafts with endothelial cells is the ideal method of improving their long-term patency rates. The aim of this study was to assess the in vitro cytocompatibility of a novel silica nanocomposite, polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU) and hence elicit its feasibility at the vascular interface for potential use in cardiovascular devices such as vascular grafts. Using primary human umbilical vein endothelial cells (HUVEC), cell viability and adhesion were studied using AlamarBlue assays, whereas cell proliferation on the polymer was assessed using the PicoGreen dye assay. Cellular confluence and morphology on the nanocomposite were analyzed using light and electron microscopy, respectively. Our results showed that there was no significant difference between cell viability in standard culture media and POSS-PCU. Endothelial cells were capable of adhering to the polymer within 30 min of contact (Student's t-test, p<0.05) with no difference between POSS-PCU and control cell culture plates. POSS-PCU was also capable of sustaining good cell proliferation for up to 14d even from low seeding densities (1.0×10³ cells/cm²) and reaching saturation by 21 d. Microscopic analysis showed evidence of optimal endothelial cell adsorption morphology with the absence of impaired motility and morphogenesis. In conclusion, these results support the application of POSS-PCU as a suitable biomaterial scaffold in bio-hybrid vascular prostheses and biomedical devices.     

Synthesis and characterization of thermo-sensitive semi-IPN hydrogels based on poly(ethylene glycol)-co-poly(ε-caprolactone) macromer, N-isopropylacrylamide, and sodium alginate

Thermo-sensitive semi-IPN hydrogels were prepared via in situ copolymerization of N-isopropylacrylamide (NIPAAm) with poly(ethylene glycol)-co-poly(ε-caprolactone) (PEG-co-PCL) macromer in the presence of sodium alginate by UV irradiation technology. The effects of the sodium alginate content, temperature, and salt on the swelling behavior of the as-obtained hydrogels were studied. The results showed that the swelling ratio of the hydrogels increased with the increasing sodium alginate content at the same temperature, and decreased with the increase in temperature. The salt sensitivity of the semi-IPN hydrogels was dependent on the content of sodium alginate introduced in the hydrogels. The mechanical rheology of the hydrogels and in vitro release behavior of bovine serum albumin (BSA) in situ encapsulated within the hydrogels were also investigated. It was found that the introduction of sodium alginate with semi-IPN structure improved mechanical strength of the hydrogels and the cumulative release percentage of BSA from the hydrogels. Such double-sensitive semi-IPN hydrogel materials could be exploited as potential candidates for drug delivery carriers.     

Three-dimensional biomimetic hyaluronic acid hydrogels to investigate glioblastoma stem cell behaviors

Glioblastoma multiforme (GBM) is the deadliest form of primary brain tumor. GBM tumors are highly heterogeneous, being composed of tumor cells as well as glioblastoma stem cells (GSCs) that contribute to drug resistance and tumor recurrence following treatment. To develop therapeutic strategies, an improved understanding of GSC behavior in their microenvironment is critical. Herein, we have employed three-dimensional (3D) hyaluronic acid (HA) hydrogels that allow the incorporation of brain microenvironmental cues to investigate GSC behavior. U87 cell line and patient-derived D456 cells were cultured as suspension cultures (serum-free) and adherently (in the presence of serum) and were then encapsulated in HA hydrogels. We observed that all the seeded single cells expanded and formed spheres, and the size of the spheres increased with time. Increasing the initial cell seeding density of cells influenced the sphere size distribution. Interestingly, clonal expansion of serum-free grown tumor cells in HA hydrogels was observed. Also, stemness marker expression of serum and/or serum-free grown cells was altered when cultured in HA hydrogels. Finally, we demonstrated that HA hydrogels can support long-term GSC culture (up to 60 days) with retention of stemness markers. Overall, such biomimetic culture systems could further our understanding of the microenvironmental regulation of GSC phenotypes.     

Encapsulation in LentiKats of Dextransucrase from Leuconostoc mesenteroides NRRL B-1299, and its Effect on Product Selectivity

Insoluble (cell-bound) dextransucrase from Leuconostoc mesenteroides B-1299 was encapsulated in highly elastic and stable hydrogels formed by polyvinyl alcohol. The gelation was carried out by controlled partial drying at room temperature, resulting in lens-shaped particles, called LentiKats. A similar recovery of activity (approximately 55%) was achieved when compared with entrapment in calcium alginate gels. Under reaction conditions, the protein leakage in LentiKats was reduced from 18% to 4% by pre-treatment of the dextransucrase with glutaraldehyde. The immobilized dextransucrases were tested in the acceptor reaction with methyl α-D-glucopyranoside. The conversion to oligosaccharides using Lentikat-dextransucrase was higher than that obtained for alginate-dextransucrase, probably due to the reduction of diffusional limitations derived from its lenticular shape. In addition, a shift of selectivity towards the synthesis of oligosaccharides containing α(1→2) bonds was observed for the Lentikat-biocatalysts. These non-digestible compounds are supposed to be specifically fermented by beneficial species of the human microflora (prebiotic effect). The Lentikat-entrapped dextransucrase can be efficiently reused in this process at least for five cycles of 24 h.     

Arginine functionalization of hydrogels for heparin binding—a supramolecular approach to developing a pro‐angiogenic biomaterial

Our aim was to synthesize a biomaterial that stimulates angiogenesis for tissue engineering applications by exploiting the ability of heparin to bind and release vascular endothelial growth factor (VEGF). The approach adopted involved modification of a hydrogel with positively charged peptides (oligolysine or oligoarginine) to achieve heparin binding. Precursor hydrogels were produced from copolymerization of N‐vinyl pyrolidone, diethylene glycol bis allyl carbonate and acrylic acid (PNDA) and functionalized after activation of the carboxylic acid groups with trilysine or triarginine peptides (PNDKKK and PNDRRR). Both hydrogels were shown to bind and release bioactive VEGF165 with arginine‐modified hydrogel outperforming the lysine‐modified hydrogel. Cytocompatibility of the hydrogels was confirmed in vitro with primary human dermal fibroblasts and human dermal microvascular endothelial cells (HUDMECs). Proliferation of HUDMECs was stimulated by triarginine‐functionalized hydrogels, and to a lesser extent by lysine functionalized hydrogels once loaded with heparin and VEGF. The data suggests that heparin‐binding hydrogels provide a promising approach to a pro‐angiogenic biomaterial. Biotechnol. Bioeng. 2013; 110: 296–317. © 2012 Wiley Periodicals, Inc.     

Helical spring template fabrication of cell‐laden microfluidic hydrogels for tissue engineering

Cell‐laden microfluidic hydrogels find great potential applications in microfluidics, tissue engineering, and drug delivery, due to their ability to control mass transport and cell microenvironment. A variety of methods have been developed to fabricate hydrogels with microfluidic channels, such as molding, bioprinting, and photopatterning. However, the relatively simple structure available and the specific equipment required limit their broad applications in tissue engineering. Here, we developed a simple method to fabricate microfluidic hydrogels with helical microchannels based on a helical spring template. Results from both experimental investigation and numerical modeling revealed a significant enhancement on the perfusion ability and cell viability of helical microfluidic hydrogels compared to those with straight microchannels. The feasibility of such a helical spring template method was also demonstrated for microfluidic hydrogels with complex three‐dimensional channel networks such as branched helical microchannels. The method presented here could potentially facilitate the development of vascular tissue engineering and cell microenvironment engineering. Biotechnol. Bioeng. 2013; 110: 980–989. © 2012 Wiley Periodicals, Inc.