In vitro cytotoxicity of a low-shrinkage polymerizable liquid crystal resin monomer.

The objective of this study was to determine the in vitro cytotoxicity of novel, polymerizable liquid crystal resin monomers when placed in direct contact with dental and nondental cell lines. One common dimethacrylate and three liquid crystal compounds, Bis-glycidyl methacrylate (Bis-GMA), 2-(t-butyl)-1,4-bis-{4-(6-acryloxy-hexane-1-oxy)-benzoyloxy}-benzene (C6), 2-(t-butyl), 1-[6-(3-acryloxy-propionoxy)-hexane-1-oxy-benzoyloxy], 4-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy]-benxene (by-product), and a 3:2 mixture of C6 and by-product, respectively, were tested for relative cytotoxicity in vitro. Cultured dental and nondental cells were treated for 24 h with test compound dissolved in media over a fourfold range of concentration (10(-4) -10(-7) mol/L). Cytotoxicity was measured using the WST-1 reagent as an indicator of remaining cell numbers based on the reduction of WST-1 substrate by mitochondrial dehydrogenases in viable cells. Bis-GMA ID(50) was found to be consistent with ID(50) values reported in the literature. A small but significant difference in the sensitivity of the dental and nondental cells in regard to their response to this dimethacrylate was noted. The liquid crystal resin monomers were significantly less cytotoxic to all cell lines tested. ID(50) values of >1 x 10(-4) mol/L were registered for the C6 and by-product monomers alone. The 3:2 mixture of C6 and by-product had a slightly higher cytotoxicity (ID(50) = 1 x 10(-4) mol/L); however, this remained significantly less than that of Bis-GMA. The results demonstrate that the newly synthesized low-shrinkage, polymerizable liquid crystal resin monomers demonstrate a minimal cytotoxic effect on both dental and nondental cells. These data suggest that the low-shrinkage liquid crystal resin monomers will not elicit a response by oral tissues (pulp tissue) when used to repair carious lesions in posterior teeth.

A novel osteotropic biomaterial OG-PLG: Synthesis and in vitro release.

Statins (e.g., simvastatin) have shown to induce expression of the bone morphogenic protein-2 gene in bone cells, but they are not used clinically because of a lack of a suitable delivery device. The overall objective is to develop optimized statin delivery devices for bone regeneration. The specific objective was to determine the effect of grafting statins to biodegradable poly[lactide-co-glycolide] (PLG) on release kinetics. Simvastatin was grafted to PLG (OG-PLG) and characterized using contact-angle measurements, attenuated total reflectance-Fourier transform infrared, and ultraviolet-visible spectroscopy to determine success of the synthesis. An ultraviolet-visible assay for measuring release of statins and degraded OG-PLG in media was also developed. In vitro release studies using films and scaffolds made with PLG, PLG blended with simvastatin (PLG + Sim), and OG-PLG (simvastatin grafted to PLG) blended into PLG at different concentrations showed that release rate of OG-PLG from films was significantly greater than that of PLG + Sim. However, release rate from scaffolds showed PLG + Sim to be significantly higher than that of OG-PLG. The diffusion-controlled release kinetics of simvastatin from PLG + Sim seems to be more heavily affected by device morphology, whereas the degradation-controlled release kinetics seem to be less affected. In short, release kinetics can be modulated by grafting statins to PLG.

A novel osteotropic biomaterial OG-PLG: in vitro efficacy.

Previously, a novel osteotropic biomaterial, OG-PLG [simvastatin grafted to poly(lactide-co-glycolide), PLG], was synthesized and shown to have degradation-controlled release kinetics. The objective here was to determine the effect of grafting statins to PLG on bone regeneration in vitro. Rat bone marrow cells were stimulated in vitro with simvastatin dissolved in media, saponified simvastatin dissolved in media, simvastatin released through diffusion from emulsion freeze-dried scaffolds, and OG-PLG. Unstimulated cultures and cultures stimulated with dexamethasone were used as negative and positive controls, respectively. In vitro bone formation was assessed using the alkaline phosphatase (ALP) and von Kossa assays at different times up to 16 days. ALP analysis revealed that saponified simvastatin at 10(-7)M and OG-PLG significantly increased ALP expression at various time points. von Kossa assay showed that simvastatin, saponified simvastatin, and OG-PLG significantly enhanced mineralization, with the effect from OG-PLG being the most significant. In short, OG-PLG significantly enhanced in vitro bone cell mineralization beyond the effect of simvastatin or saponified simvastatin dissolved in media and simvastatin released via diffusion from scaffolds.

Synthesis of low-shrinkage polymerizable methacrylate liquid-crystal monomers.

As a part of the continuous pursuit to develop an ideal resinous dental restorative material for use in large posterior cavity restorations, this article reports the easy, high-yield synthesis and the incredibly low polymerization shrinkage property of a new bifunctional liquid crystal (LC) monomer. This new polymerizable nematic liquid crystal is the next higher homolog of the acrylate monomer reported in a previous work.1 It remains liquid crystalline between room and mouth temperatures and can be polymerized to isotropic polymer with the use of the same visible light inhibitor system as used with conventional monomers. The structure of this new monomer has been confirmed to be 2-(t-butyl), 1,4-bis-[4-(6-methacryloxy-hexan-1-oxy)-benzoyloxy]-benzene. Unlike the synthesis of its acrylate homolog, when the same procedure is adopted for the synthesis of this compound, the recovery of the product is not split by a sizable amount of the by-product. Therefore, the reaction is cleaner, with high yield and a less labor-intensive purification procedure. Thus, the synthetic methodology has the potential for easy commercial scale-up. The monomer (V) polymerizes at room temperature with a shrinkage of about 2 vol %, as compared to > 8 vol % for conventional control (GTE), at similar degrees of conversion.

Osteoblast response to phospholipid modified titanium surface.

The objective of this study was to evaluate the effect of different phospholipid coatings on osteoblast responses in vitro. Commercially available phospholipids [phosphatidylcholine (PC), phosphatidyl-serine (PS) and phosphatidylinositol (PI)] were converted to their Ca-PL-PO(4) and were coated on commercially pure titanium (Ti) grade 2 disks. Using uncoated Ti surfaces as controls, cell responses to phospholipid-coated surfaces were evaluated using the American Type Culture Collection (Manassas, VA, USA) CRL-1486 human embryonic palatal mesenchyme cells (HEPM), an osteoblast precursor cell line, over a 14-day period. Total protein synthesis and alkaline phosphatase specific activity at 0, 7, and 14 days were measured. It was observed that Ti surfaces coated with PS exhibited enhanced protein synthesis and alkaline phosphatase specific activity compared to other phospholipids and uncoated surfaces. These results indicate the possible usefulness of PS-coated Ti surfaces for inducing enhanced bone formation and are very encouraging for bone and dental implantology.

Synthesis of low-shrinkage polymerizable liquid-crystal monomers.

Polymerization shrinkage remains a major barrier to the universal use of resin restorative in large posterior cavity preparations. A new bifunctional liquid crystal (LC) monomer, 2-(t-butyl), 1,4-bis-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy] benzene, with exceptionally low polymerization shrinkage, has recently been discovered. The purpose of this communication is to report a new, easy, high-yield synthetic route to synthesize this compound in comfortable larger batches. Synthetic and isolation details, chemical characteristics, and the polymerizable properties of a new structurally related by-product monomer, namely, 2-(t-butyl),1-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy], 4-[4-[6-(3-acryl oxy-propionoxy)-hexane-1-oxy]-benzoyloxy]-benzene, is also reported. The structural confirmation of this by-product indicates that it resulted from the Michael-type addition of acrylate ion on one of the terminal acryloxy groups of 2-(t-butyl), 1,4-bis-[4-(6-acryloxy-hexane-1-oxy)-benzoyloxy] benzene. The by-product itself, as well as the natural blend of the aforesaid both products as formed in the reaction mixture, also polymerized at room temperature with lesser volume shrinkage as compared to the conventional control (GTE) at similar degrees of conversion.

Acetaminophen differentially enhances social behavior and cortical cannabinoid levels in inbred mice.

Supratherapeutic doses of the analgesic acetaminophen (paracetomol) are reported to promote social behavior in Swiss mice. However, we hypothesized that it might not promote sociability in other strains due to cannabinoid CB(1) receptor-mediated inhibition of serotonin (5-HT) transmission in the frontal cortex. We examined the effects of acetaminophen on social and repetitive behaviors in comparison to a cannabinoid agonist, WIN 55,212-2, in two strains of socially-deficient mice, BTBR and 129S1/SvImJ (129S). Acetaminophen (100mg/kg) enhanced social interactions in BTBR, and social novelty preference and marble burying in 129S at serum levels of ≥70 ng/ml. Following acetaminophen injection or sociability testing, anandamide (AEA) increased in BTBR frontal cortex, while behavior testing increased 2-arachidonyl glycerol (2-AG) levels in 129S frontal cortex. In contrast, WIN 55,212-2 (0.1mg/kg) did not enhance sociability. Further, we expected CB(1)-deficient (+/-) mice to be less social than wild-type, but instead found similar sociability. Given strain differences in endocannabinoid response to acetaminophen, we compared cortical CB(1) and 5-HT(1A) receptor density and function relative to sociable C57BL/6 mice. CB(1) receptor saturation binding (Bmax=958±117 fmol/mg protein), and affinity for [(3)H] CP55,940 (K(D)=3±0.8 nM) was similar in frontal cortex among strains. CP55,940-stimulated [(35)S] GTPγS binding in cingulate cortex was 136±12, 156±22, and 75±9% above basal in BTBR, 129S and C57BL/6 mice. The acetaminophen metabolite para-aminophenol (1 µM) failed to stimulate [(35)S] GTPγS binding. Hence, it appears that other indirect actions of acetaminophen, including 5-HT receptor agonism, may underlie its sociability promoting properties outweighing any CB(1) mediated suppression by locally-elevated endocannabinoids in these mice.

In vitro gentamicin sustained and controlled release from chitosan cross-linked films.

A novel wound dressing film was investigated for controlled and sustained delivery of gentamicin, while covering and protecting the wound. Chitosan was cross-linked with Hexamethylene 1,6-bis (aminocarboxysulfonate) to prepare the wound dressing films. Cross-linking reaction was required to control the water retention and release of encapsulated gentamicin. Cross-linked films swell less and became more hydrophilic than chitosan film itself. However, this behavior was inversely proportional to the degree of cross-linking. In vitro gentamicin release from the cross-linked films, at physiological conditions of pH and temperature, was studied for 2 weeks. The effects of gentamicin initial concentration and cross-linking ratio on the kinetics of gentamicin release were evaluated. Results showed that the diffusion rate was governed by initial concentration of gentamicin and degree of cross-linking, since higher gentamicin initial concentration and degree of cross-linking promoted the slower release, while lower gentamicin initial concentration and degree of cross-linking promoted the faster one.

Osteoblast response and calcium deposition on phospholipid modified surfaces.

In this study, the effect of calcium phosphate complexed phospholipid (Ca-PL-PO4) coatings on solid surfaces on the in vitro calcium (Ca) deposition and on the osteoblast responses was evaluated. Commercially available phospholipids were converted to their Ca-PL-PO4, and were coated on glass Petri dishes. The coated dishes were immersed in the simulated body fluid for up to 14 days under sterilized conditions at 37 degrees C, and the amount of calcium (Ca) deposited was quantified. Similarly, by measuring the alkaline phosphatase specific activity, the differentiation of osteoblast precursor cells were evaluated after seeding the cells on Ca-PL-PO4 coated cell culture plastics. It was observed that all Ca-PL-PO4 enhanced Ca deposition on coated surfaces. The, polar head group of phospholipids in coated surfaces was observed to have an influence on the Ca deposition as well as the osteoblast differentiation. Among the phospholipids evaluated, phosphatidylserine (Ca-PS-PO4) exhibited the strongest calcium deposition and more enhanced alkaline phosphatase specific activity. It was therefore concluded from this study that Ca-PS-PO4 surface modification may be an alternative method for enhancing bone-implant interactions.