Synthesis of biocompatible nanocomposite hydrogels as a local drug delivery system

Nanocomposite biocompatible hydrogels (NCHG) were synthesised as model systems for in situ cured potentially local drug delivery devices for curing periodontal infections. The composite consists of the following components: nanoparticles (NPs), matrix gel, and chlorhexidine (CHX) as antibacterial drug. The NPs were obtained by free radical initiated copolymerization of the monomers, 2-hydroxyethyl methacrylate (HEMA) and polyethyleneglycol dimethacrylate (PEGDMA), in aqueous solution. The same monomers were used to prepare crosslinked matrices by photopolymerization. NCHGs were obtained by mixing NPs, monomers, and drug in an aqueous solution then crosslinked by photopolymerization. Mechanical properties, swelling behavior, and the kinetics of drug release have been investigated. It was found that compression strength values increased with increasing ratio of the crosslinker PEGDMA. Incorporation of NPs into the matrix resulted similar compression strength as the matrix hydrogel. The hydrated NCHGs swelled more slowly but admitted more water. The drug was incorporated in NPs by swelling in CHX aqueous solution or added to the solution of monomer mixture followed by photopolymerization. Studies of release kinetics revealed that on average 60% of the loaded drug was released. The most rapid release was observed over a 24 h period for matrix gels with low crosslinking density. For NCHGs, the release period exceeded 48 h. An unexpected result was observed for NCHGs without drug in the NPs. In this case, increasing release was observed for the first 24 h. Thereafter, however, the apparent quantity of detectable drug decreased dramatically.     

The physical process of melting and freezing

It is suggested that at the melting temperature the wavelength of the average thermal phonon vibration is equal to or is a harmonic of the distance separating the atomic layers in the crystal. This resonance between the phonon and lattice vibrations equals out the energy of the vibrating atoms in the surface layer. If this “uniform” energy is higher than the energy corresponding to the metastable transition state then all the surface atoms lose its position stability. In order to make the jump to the next potential well energy is required to overcome on the viscous resistance of the liquid. If this energy, latent heat of fusion, is supplied then the atomic/molecular sheet or platelets from the surface are detached and melting occurs. The proposed model is consistent with all of the characteristic features of melting and freezing. Equations calculating the average phonon wavelength and the corresponding lattice distance at the melting temperature are derived from fundamental thermodynamic relationships. The required thermodynamic parameters are determined from experiments of the nine selected highly symmetrical solids. The calculated wavelengths of the phonon vibration are equal to or is a harmonic of the $d$-spacing of the atomic/molecular layers in agreement with theory.     

On a Question of Erdős and Ulam

Ulam asked in 1945 if there is an everywhere dense rational set, i.e., 1 a point set in the plane with all its pairwise distances rational. Erdős conjectured that if a set S has a dense rational subset, then S should be very special. The only known types of examples of sets with dense (or even just infinite) rational subsets are lines and circles. In this paper we prove Erdős’ conjecture for algebraic curves by showing that no irreducible algebraic curve other than a line or a circle contains an infinite rational set.     

Quantitative and Qualitative Analysis of RAMEB in Soil

An HPLC method has been developed for determination of RAMEB in soil samplescontaminated with hydrocarbons. The extraction efficiency of RAMEB from soils wasfound to depend on the soil properties. The extraction method elaborated results in agood recovery from sandy and loamy soils, but only a poor recovery was obtained from soils of high clay content.A SPE method was worked out to remove the components disturbing the HPLCanalysis, and a one-peak method has been developed for the quantitative analyses.The isomer distribution of RAMEB was characterized by fingerprint chromatograms.The new methods have been applied for determination of RAMEB content in soilsamples from field treatment.     

Integral approximation sequences

Letn linear formsL _i onm variables be given, normalized so that all coefficients have absolute value at most unity. Letw ₁, ...,w _m be real numbers andx ₁, ...,x _m be integers. We sayE _i =L _i (w ₁, ...,w _m )-L _i (x ₁, ...,x _m ) is the error in approximating thew's by thex's with respect to formL _i It is shown that given anyw's there is an integral approximation ofx's so that the errorsE _i are small-roughly that simultaneously for alli.     

Integrated process for purification of plasmid DNA using aqueous two-phase systems combined with membrane filtration and lid bead chromatography

An integrated process for purifying a 6.1 kilo base pair (kbp) plasmid from a clarified Escherichia coli cell lysate based on an ultra/diafiltration step combined with polymer/polymer aqueous two-phase system and a new type of chromatography is described. The process starts with a volume reduction (ultrafiltration) and buffer exchange (diafiltration) of the clarified lysate using a hollow fibre membrane system. The concentrated and desalted plasmid solution is then extracted in a thermoseparating aqueous two-phase system, where the contaminants (RNA and proteins) to a large extent are removed. While the buffer exchange (diafiltration) is necessary in order to extract the plasmid DNA exclusively to the top phase, experiments showed that the ultrafiltration step increased the productivity of the aqueous two-phase system by a factor of more than 10. The thermoseparated water phase was then subjected to a polishing step using lid bead chromatography. Lid beads are a new type of restricted access chromatography beads, here with a positively charged inner core that adsorbed the remaining RNA while its inert surface layer prevented adsorption of the plasmid DNA thus passing in the flow-through of the column. Differently-sized plasmid DNA in the range of 2.7-20.5 kbp were also partitioned in the aqueous two-phase system. Within this size range, all plasmid DNA was exclusively extracted to the top phase. The complete process is free of additives and easy scalable for use in large scale production of plasmid DNA. The overall process yield for plasmid DNA was 69%.     

Comparison of helium and argon as collision gases in the high energy collision-induced decomposition of MH+ ions of peptides

Collision-induced decompositions (CID) of protonated peptides were studied using a four-sector mass spectrometer. The collision gases employed were helium and argon. The CID spectra of several peptides covering the molecular mass region of 905–2465 u were recorded. These investigations established several previously unrecognized differences between the CID spectra obtained with helium and argon as collision gases. These can be summarized as follows: (1) Structurally significant and specific side chain fragmentations (d_n ^f, w_n ^f and v_n, ion types) are greatly reduced or completely missing in the CID spectra obtained with helium as a collision gas compared to those obtained with argon. (2) As the peptide molecular mass increases, argon, which is heavier than helium, is increasingly more efficient than helium for generating fragment ions.     

Imperfect conjugate gradient algorithms for extended quadratic functions

Summary Generalized conjugate gradient algorithms which are invariant to a nonlinear scaling of a strictly convex quadratic function are described. The algorithms when applied to scaled quadratic functionsfR _n R ₁ of the formf(x)=h(F(x)) withF(x) strictly convex quadratic andhC ¹(R ₁) an arbitrary strictly monotone functionh generate the same direction vectors as for the functionF without perfect steps.     

Interaction of nonylphenyl and tributylphenyl ethylene oxide ionic surfactants with highly soluble cyclodextrin derivatives

The modification of the hydrophobicity of some ethoxylated nonylphenol and tributylphenol surfactants with various soluble -cyclodextrin polymers has been studied by reversed-phase chromatography. Stepwise regression analysis proved that the complex forming capacity of surfactants decreases with increasing diameter of the hydrophobic moiety of surfactants, the properties of the crosslinking agent used for preparation of the polymers has no significant effect on the host-guest interaction, the presence of carboxyl groups in the polymer considerably improved the complex stability.     

Note on asynchronous exponential growth for structured population models

In the present note we show asynchronous exponential growth for important age- and size-structured population models.