A comprehensive database on physical properties of ionic liquids ͑ILs͒, which was collected from 109 kinds of literature sources in the period from 1984 through 2004, has been presented. There are 1680 pieces of data on the physical properties for 588 available ILs, from which 276 kinds of cations and 55 kinds of anions were extracted. In terms of the collected database, the structure-property relationship was evaluated. The correlation of melting points of two most common systems, disubstituted imidazolium tetrafluoroborate and disubstituted imidazolium hexafluorophosphate, was carried out using a quantitative structure-property relationship method.

Osteogenic differentiation and mineralization of bone marrow stromal (BMS) cells depends on the cells' interactions with bioactive peptides associated with the matrix proteins. The RGD peptides of ECM proteins interact with BMS cells through integrin surface receptors to facilitate cell spreading and adhesion. The BMP peptide corresponding to residues 73-92 of bone morphogenetic protein-2 promotes differentiation and mineralization of BMS cells. The objective of this work was to investigate the effects of RGD and BMP peptides, grafted to a hydrogel substrate, on osteogenic differentiation and mineralization of BMS cells. RGD peptide was acrylamide-terminated by reacting acrylic acid with the N-terminal amine group of the peptide to produce the functionalized Ac-GRGD peptide. The PEGylated BMP peptide was reacted with 4-carboxybenzenesulfonazide to produce an azide functionalized Az-mPEG-BMP peptide. Poly (lactide-co-ethylene oxide- co-fumarate) (PLEOF) macromer was cross-linked with Ac-GRGD peptide and propargyl acrylate to produce an RGD conjugated hydrogel. Az-mPEG-BMP peptide was grafted to the hydrogel by "click chemistry". The RGD and BMP peptide density on the hydrogel surface was 1.62+/-0.37 and 5.2+/-0.6 pmol/cm2, respectively. BMS cells were seeded on the hydrogels and the effect of RGD and BMP peptides on osteogenesis was evaluated by measuring ALPase activity and calcium content with incubation time. BMS cells cultured on RGD conjugated, BMP peptide grafted, and RGD+BMP peptide modified hydrogels showed 3, 2.5, and 5-fold increase in ALPase activity after 14 days incubation. BMS cells seeded on RGD+BMP peptides modified hydrogel showed 4.9- and 11.8-fold increase in calcium content after 14 and 21 days, respectively, which was significantly higher than RGD conjugated or BMP grafted hydrogels. These results demonstrate that RGD and BMP peptides, grafted to a hydrogel substrate, act synergistically to enhance osteogenic differentiation and mineralization of BMS cells. These findings are potentially useful in developing engineered scaffolds for bone regeneration.

Injectable in situ crosslinkable biomaterials seeded with multipotent progenitor cells and coupled with minimally invasive arthroscopic techniques are an attractive alternative for treating irregularly shaped osteochondral defects. An in situ crosslinkable poly(lactide-co-ethylene oxide-co-fumarate) (PLEOF) macromer has been developed with ultralow molecular weight poly(L-lactide) and poly(ethylene glycol) (PEG) units linked by fumaryl unit. The PLEOF macromer was crosslinked with the MMP-13 degradable peptide sequence QPQGLAK with acrylate end-groups or the methylene bisacrylamide (BISAM) crosslinker to form enzymatically or hydrolytically degradable hydrogels, respectively. Cell viability of the peptide crosslinker was significantly higher than that of BISAM. The relatively higher molecular weight peptide crosslinker significantly affected the water content and the rate of crosslinking (e.g., sol vs gel fraction). The addition of a small fraction of a highly reactive BISAM crosslinker to the PLEOF/peptide mixture reduced the gelation time and increased the elastic modulus while retaining enzymatic degradability of the hydrogel. Bone marrow stromal (BMS) cells were encapsulated in the peptide crosslinked PLEOF hydrogel; 84% of the encapsulated cells was viable after 1 week of incubation in osteogenic media. The encapsulated BMS cells differentiated to osteoblasts and produced a mineralized matrix, as measured by ALPase activity and calcium content. The degradation rate of the hydrogel depended on the ratio of the peptide to the BISAM crosslinker, MMP-13 concentration, and incubation time. The results demonstrate that the peptide crosslinked PLEOF hydrogel with tunable degradation characteristics is potentially useful as an injectable in situ crosslinkable carrier for bone marrow stromal cells.

The use of poly(ethylene glycol) (PEG) hydrogels in tissue engineering is limited by their persistence in the site of regeneration. In an attempt to produce inert hydrolytically degradable PEG-based hydrogels, star (SPELA) poly(ethylene glycol-co-lactide) acrylate macromonomers with short lactide segments (<15 lactides per macromonomer) were synthesized. The SPELA hydrogel was characterized with respect to gelation time, modulus, water content, sol fraction, degradation, and osteogenic differentiation of encapsulated marrow stromal cells (MSCs). The properties of SPELA hydrogel were compared with those of the linear poly(ethylene glycol-co-lactide) acrylate (LPELA). The SPELA hydrogel had higher modulus, lower water content, and lower sol fraction than the LPELA. The shear modulus of SPELA hydrogel was 2.2 times higher than LPELA, whereas the sol fraction of SPELA hydrogel was 5 times lower than LPELA. The degradation of SPELA hydrogel depended strongly on the number of lactide monomers per macromonomer (nL) and showed a biphasic behavior. For example, as nL increased from 0 to 3.4, 6.4, 11.6, and 14.8, mass loss increased from 7 to 37, 80, 100% and then deceased to 87%, respectively, after 6 weeks of incubation. The addition of 3.4 lactides per macromonomer (<10 wt % dry macromonomer or <2 wt % swollen hydrogel) increased mass loss to 50% after 6 weeks. Molecular dynamic simulations demonstrated that the biphasic degradation behavior was related to aggregation and micelle formation of lactide monomers in the macromonomer in aqueous solution. MSCs encapsulated in SPELA hydrogel expressed osteogenic markers Dlx5, Runx2, osteopontin, and osteocalcin and formed a mineralized matrix. The expression of osteogenic markers and extent of mineralization was significantly higher when MSCs were encapsulated in SPELA hydrogel with the addition of bone morphogenetic protein-2 (BMP2). Results demonstrate that hydrolytically degradable PEG-based hydrogels are potentially useful as a delivery matrix for stem cells in regenerative medicine.

Biomineralization is mediated by extracellular matrix (ECM) proteins with amino acid sequences rich in glutamic acid. The objective of this study was to investigate the effect of calcium phosphate deposition on aligned nanofibres surface-modified with a glutamic acid peptide on osteogenic differentiation of rat marrow stromal cells. Blend of EEGGC peptide (GLU) conjugated low molecular weight polylactide (PLA) and high molecular weight poly(lactide-co-glycolide) (PLGA) was electrospun to form aligned nanofibres (GLU-NF). The GLU-NF microsheets were incubated in a modified simulated body fluid for nucleation of calcium phosphate crystals on the fibre surface. To achieve a high calcium phosphate to fibre ratio, a layer-by-layer approach was used to improve diffusion of calcium and phosphate ions inside the microsheets. Based on dissipative particle dynamics simulation of PLGA/PLA-GLU fibres, > 80% of GLU peptide was localized to the fibre surface. Calcium phosphate to fibre ratios as high as 200%, between those of cancellous (160%) and cortical (310%) bone, was obtained with the layer-by-layer approach. The extent of osteogenic differentiation and mineralization of marrow stromal cells seeded on GLU-NF microsheets was directly related to the amount of calcium phosphate deposition on the fibres prior to cell seeding. Expression of osteogenic markers osteopontin, alkaline phosphatase (ALP), osteocalcin and type 1 collagen increased gradually with calcium phosphate deposition on GLU-NF microsheets. Results demonstrate that surface modification of aligned synthetic nanofibres with EEGGC peptide dramatically affects nucleation and growth of calcium phosphate crystals on the fibres leading to increased osteogenic differentiation of marrow stromal cells and mineralization.

Maintenance of cancer stem cells (CSCs) is regulated by the tumor microenvironment. Synthetic hydrogels provide the flexibility to design three-dimensional (3D) matrices to isolate and study individual factors in the tumor microenvironment. The objective of this work was to investigate the effect of matrix modulus on tumorsphere formation by breast cancer cells and maintenance of CSCs in an inert microenvironment without the interference of other factors. In that regard, 4T1 mouse breast cancer cells were encapsulated in inert polyethylene glycol diacrylate hydrogels and the effect of matrix modulus on tumorsphere formation and expression of CSC markers was investigated. The gel modulus had a strong effect on tumorsphere formation and the effect was bimodal. Tumorsphere formation and expression of CSC markers peaked after 8 days of culture. At day 8, as the matrix modulus was increased from 2.5 kPa to 5.3, 26.1, and 47.1 kPa, the average tumorsphere size changed from 37 -6 mm to 57 -6, 20 -4, and 12 -2 mm, respectively; cell number density in the gel changed from 0.8 -0.1 · 10 5 cells/mL to 1.7 -0.2 · 10 5 , 0.4 -0.1 · 10 5 , and 0.2 -0.1 · 10 5 cells/mL after initial encapsulation of 0.14 · 10 5 cells/mL; and the expression of CD44 breast CSC marker changed from 17 -4-fold to 38 -9-, 3 -1-, and 2 -1-fold increase compared with the initial level. Similar results were obtained with MCF7 human breast carcinoma cells. Mouse 4T1 and human MCF7 cells encapsulated in the gel with 5.3 kPa modulus formed the largest tumorspheres and highest density of tumorspheres, and had highest expression of breast CSC markers CD44 and ABCG2. The inert polyethylene glycol hydrogel can be used as a model-engineered 3D matrix to study the role of individual factors in the tumor microenvironment on tumorigenesis and maintenance of CSCs without the interference of other factors.

The fibrillar structure and sub-micron diameter of electrospun nanofibers can be used to reproduce the morphology and structure of the natural extracellular matrix (ECM). The objective of this work was to investigate the effect of fiber alignment on osteogenic differentiation of bone marrow stromal (BMS) cells. Random and aligned poly(L-lactide) (PLLA) nanofibers were produced by collecting the spun fibers on a stationary plate and a rotating wheel, respectively, as the ground electrode. Morphology and alignment of the BMS cells seeded on the fibers were characterized by SEM. The effect of fiber orientation on osteogenic differentiation of BMS cells was determined by measuring alkaline phosphatase (ALPase) activity, calcium content, and mRNA expression levels of osteogenic markers. There was a strong correlation between the fiber and cell distributions for the random (p=0.16) and aligned (p=0.81) fibers. Percent deviation from ideal randomness (PDIR) values indicated that cells seeded on the random fibers (PDIR=6.5%) were likely to be distributed randomly in all directions while cells seeded on the aligned fibers (PDIR=86%) were highly likely to be aligned with the direction of fibers. BMS cell seeded on random and aligned fibers had similar cell count and ALPase activity with incubation time, but the calcium content on aligned fibers was significantly higher after 21 days compared to that of random fibers (p=0.003). Osteopontin (OP) and osteocalcin (OC) expression levels of BMS cells on fibers increased with incubation time. However, there was no difference between the expression levels of OP and OC on aligned vs. random fibers. The results indicate that BMS cells aligned in the direction of PLLA fibers to form long cell extensions, and fiber orientation affected the extent of mineralization, but it had no effect on cell proliferation or mRNA expression of osteogenic markers.

Carbon molecular sieve (CMS) membranes with rigid and uniform pore structures are ideal candidates for high temperature- and pressure-demanded separations, such as hydrogen purification from the steam methane reforming process. Here, we report a facile and scalable method for the fabrication of cellulose-based asymmetric carbon hollow fiber membranes (CHFMs) with ultramicropores of 3–4 Å for superior H2 separation. The membrane fabrication process does not require complex pretreatments to avoid pore collapse before the carbonization of cellulose precursors. A H2/CO2 selectivity of 83.9 at 130 °C (H2/N2 selectivity of >800, H2/CH4 selectivity of >5700) demonstrates that the membrane provides a precise cutoff to discriminate between small gas molecules (H2) and larger gas molecules. In addition, the membrane exhibits superior mixed gas separation performances combined with water vapor- and high pressure-resistant stability. The present approach for the fabrication of high-performance CMS membranes derived from cellulose precursors opens a new avenue for H2-related separations.