PubMed · 5337955
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D N Rampley. 1967. Embedding media for electron microscopy.. https://pubmed.ncbi.nlm.nih.gov/5337955/
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Halloysite is a naturally occurring microtubular aluminosilicate mineral. The highly water soluble cationic drug, diltiazem HCl, was shown to bind to the polyanionic surfaces of the material to achieve a slight sustained release effect on dissolution testing due to reversible chemisorption and/or hindered release from the drug loaded lumen. A greater sustained release effect was more apparent when the less water soluble cationic drug, propranolol HCl, was examined. Attempts to further delay drug release by loading diltiazem HCl from a polyvinylpyrrolidone solution into the halloysite had little effect. However, a range of cationic polymers, including chitosan cross-linked with glutaraldehyde, was shown to bind to halloysite and was used to achieve significant delayed drug release. Coating with adequate polyethyleneimine was particularly effective at delaying drug release, being dependent on the architecture of the interaction between the polycation and the mineral. When a range of alkyl-2-cyanoacrylate monomers applied from a non-aqueous solvent by an in situ polymerisation procedure was examined, diltiazem HCl loaded halloysite dispersed in poly-iso-butyl cyanoacrylate was found to be the most effective at reducing the burst effect noted with aqueous coating systems.
A novel process for the preparation of water-borne biomaterials for hard tissue repair from injectable precursors is described, where the precursors form crosslinked materials in situ under physiological conditions. The precursors react by means of a Michael-type addition reaction that makes use of addition donors such as pentaerythritol tetrakis 3'-mercaptopropionate (QT) and addition acceptors such as poly(ethylene glycol) diacrylate 570 MW (PEGDA), pentaerythritol triacrylate (TA), and poly(propylene glycol) diacrylate 900 MW (PPODA). These crosslinked materials (at 75 wt% solid), prepared from water dispersions or reverse emulsions, showed ultimate strengths in compression of 1.8 +/- 0.2 and 6.7 +/- 0.5 MPa and ultimate deformations of 35 +/- 2+/- and 37 +/- 2%, respectively. Scanning electron microscopy (SEM) shows that the morphology of the precursors templated the morphology of the final materials. The current study indicates that it is possible to obtain injectable high-modulus materials that have appropriate mechanical properties and gelation kinetics for tissue augmentation and stabilization applications such as mechanical stabilization of the intervertebral disc annulus.
Chemical feature based pharmacophore models were elaborated for angiotensin II receptor subtype 1 (AT(1)) antagonists using both a quantitative and a qualitative approach (Catalyst HypoGen and HipHop algorithms, respectively). The training sets for quantitative model generation consisted of 25 selective AT(1) antagonists exhibiting IC(50) values ranging from 1.3 nM to 150 microM. Additionally, a qualitative pharmacophore hypothesis was derived from multiconformational structure models of the two highly active AT(1) antagonists 4u (IC(50) = 0.2 nM) and 3k (IC(50) = 0.7 nM). In the case of the quantitative model, the best pharmacophore hypothesis consisted of a five-features model (Hypo1: seven points, one hydrophobic aromatic, one hydrophobic aliphatic, a hydrogen bond acceptor, a negative ionizable function, and an aromatic plane function). The best qualitative model consisted of seven features (Hypo2: 11 points, two aromatic rings, two hydrogen bond acceptors, a negative ionizable function, and two hydrophobic functions). The obtained pharmacophore models were validated on a wide set of test molecules. They were shown to be able to identify a range of highly potent AT(1) antagonists, among those a number of recently launched drugs and some candidates presently undergoing clinical tests and/or development phases. The results of our study provide confidence for the utility of the selected chemical feature based pharmacophore models to retrieve structurally diverse compounds with desired biological activity by virtual screening.