Mirosław Gibas

Oligomerisation of hydroxymethacrylates via Michael-type addition

Abstract Attempts to conduct step-growth addition polymerisation of monomethacrylates of oligoethylene glycols via Michael-type addition of hydroxyl groups to carbon–carbon double bonds are presented. In the presence of several basic, nucleophilic and acidic reagents, disproportionation to corresponding glycols and dimethacrylates has been observed while some of them were found to initiate oligomerisation according to afore-said mechanism. Optimal reaction conditions have been established. The most effective initiators, i.e. potassium tert-butoxide and sodium hydride were selected to obtain the series of oligomers. The products were characterised by 1H NMR, GPC and ESI-MS to confirm oligo(ether–ester) structure and to estimate molecular weight. The latter appeared to be in order of one thousand.

Impact of heating method on the flocculation process using thermosensitive polymer.

The impact of suspension heating method on the flocculation process using thermosensitive polymer is reported in this paper. In experiments a model suspension of chalk in RO water (purified by Reverse Osmosis) was destabilized using a copolymer of N-isopropylacrylamide (NIPAM) and cationic diallyldimethyl ammonium chloride (DADMAC). The measurements were made using a laboratory setup consisting of a mixing tank with four baffles, Rushton turbine, laser particle sizer Analysette 22 by Fritsch and a system of pump and thermostating devices. Two different modes of heating were used. In the first case the temperature of the system was gently raised above the Lower Critical Solution Temperature (LCST) using an electrical heater placed inside the tank, while in the second case the system temperature was rapidly raised by an injection of hot water directly into the tank. It was proven that heating method as well as the polymer concentration was crucial to the shape and size of created flocs.

Quantitative Analysis of Fractured Surfaces in PMnEDM-Based Dental Adhesive Bonds by Use of Optical Microscopy

The aim of this work was to characterize quantitatively the contribution of different failure modes during shear bond strength (SBS) measurements and to correlate both those sets of results. Four experimental dental adhesive systems were used to join dental composite with cobalt–based alloy plate. The samples were subjected to SBS measurements according to International Organization for Standardization (ISO) procedure and resulting fractures were examined by optical microscopy, including computer-aided processing of the images, to yield quantitative contributions of adhesive and cohesive failures. Identification of particular failure modes as well as quantitative determination of respective contributions appeared to be possible. The data were processed by statistical methods including Shapiro-Wilk and Mann-Whitney U tests. The results of fractographic analysis were found to correlate with SBS values. Contribution of adhesive failures appeared to determine the strength of adhesive bonds. A new dental adhesive system based on PM2EDM monomer exhibited a very good performance in respect to the metal alloy.

Evaluation of the Length of Primary Chains in Cross-Linked Poly(methacrylate)s

Two series of cross-linked polymers were examined by equilibrium swelling: poly(methyl methacrylate) cross-linked with different amounts of triethylene glycol dimethacrylate and poly(urethane dimethacrylate)s derived from dicarbamates of oligoethylene glycols monomethacrylates and aromatic diisocyanates. The method of estimation of the length of primary chains has been proposed based on the full form of the Flory-Rehner equation. This required comparing the network parameter values obtained by swelling and those derived from some other sources. In some cases the results had no physical meaning, whereas in others they appeared to be consistent. The latter for poly(urethane dimethacrylate)s yielded the length of poly(methacrylate) primary chains in the range of two to eight, which seemed to be a reasonable result.

The analysis of cytotoxicity of an experimental preparation used for the reduction of dentin hypersensitivity

BACKGROUND The problem of effective treatment of dentin hypersensitivity is still valid and not fully resolved. OBJECTIVES The aim of the study was to evaluate the potential toxicity against body tissues of an experimental preparation which is supposed to reduce dentin hypersensitivity and to compare it to a commercial formulation Seal & Protect (Dentsply) by means of measuring the activity of mitochondrial dehydrogenases (the MTT assay). MATERIAL AND METHODS The study used an original protective formulation which is supposed to eliminate hypersensitivity of dentin. A commercial preparation Seal & Protect (Dentsply) was used as the comparative material. Cytotoxic activity of the tested preparations (experimental and commercial) on murine lymphocyte cells CCL-1™ (NCTC clone 929) was determined in indirect contact with the use of the MTT test that measured the activity of the mitochondrial dehydrogenase enzyme. RESULTS A comparison of the results obtained in the MTT assay for the commercial preparation Seal & Protect (Dentsply) and the experimental formulation indicates that an experimental formulation has considerably lower cytotoxicity before polymerization, when compared to the commercial formulation, regardless of its dilution. However, after the polymerization of the commercial formulation was completed, its parameters improved significantly, especially for higher dilution values (1 : 10 and 1 : 15). Results for the experimental formulation are higher, particularly for the dilution value of 1 : 5. The overall summary of the results obtained from the MTT assay for the commercial preparation Seal & Protect (Dentsply) and the experimental formulation indicates that the experimental formulation had a significantly lower cytotoxicity before polymerization in comparison with the commercial formulation, regardless of dilution. CONCLUSIONS Estimating the biocompatibility of a given material is not simple, and measurement methods are rapidly evolving, as more and more is known about the interaction between dental materials and oral tissues, and also as a result of improvements in testing techniques.

Concept of experimental preparation for treating dentin hypersensitivity

Abstract Background Dentinal hypersensitivity (DH) is a diagnostic and therapeutic problem that is now appearing more frequently in modern dentistry. The aim of this work was to elaborate formulation of a new, original desensitizing preparation with prolonged action based on the knowledge of similar commercializations and to compare their performance in vitro. Methodology The analyses were performed with the aid of NMR spectroscopy. The experimental and commercial preparations were examined in vitro after thermocycling on human teeth by optical microscopy. The presence of the material on tooth tissue, its ability to penetrate into the tooth structure and its layer thickness were subjected to statistical analysis. Results A detailed knowledge on composition of commercial material was achieved from spectroscopic measurements. A new adhesive monomer was synthesized and incorporated into an experimental desensitizing formulation. The new monomer appeared to have comparable performance to the commercial one when regarding the affinity to tooth tissue and resistance to thermocycling. Conclusions The experimental formulation comprising a new adhesive monomer seems to be promising and could be applied in dental practice providing that biocompatibility is satisfactory.

Temperature-responsive hydrogels containing new LCST methacrylate macromonomers

Abstract A series of hydrogels were synthesized: homopolymers of new temperature-sensitive methacrylate macromonomers of ether-ester structure, derived from monomethacrylate of tetraethylene glycol via Michael-type addition - oligo(TTEGMMA), and copolymers of oligo(TTEGMMA) with N-isopropylacrylamide (NIPAAm) or 2-hydroxyethyl methacrylate (HEMA). Hydrogels based on oligo(TTEGMMA) demonstrate broad volume phase transition. Combination of oligo(TTEGMMA) with NIPAAm or HEMA yielded hydrogels having narrower phase transition and lower gel transition temperature (LGTT) up to 43 °C at the most, which is in the range of interest for most biomedical applications.