Designing new functional cosmetic ingredients from polyglycerol, a versatile bio-based platform for improved sustainability.

Polyglycerol (PG) is a well-known cosmetic ingredient and important precursor for the synthesis of a variety of cosmetic ingredients, such as surfactants, emulsifiers, and conditioning agents for hair and skin. When derived from renewable resources, PG can provide a more sustainable platform for the development of new ingredients with improved performance in cosmetic applications. This paper will discuss recent advances in the utilization of bio-based PG ingredients as alternatives to traditional ethoxylate chemistries for mild nonionic surfactants, substantive humectants, and micellar thickeners.

Impact of an anticaries mouthrinse on in vitro remineralization and microbial control.

Objective. The objective of this research was to evaluate the caries control potential of a new fluoride mouthrinse that also contained antimicrobial agents and a biofilm disrupting agent using different in vitro models. Methods. Four in vitro studies were conducted to assess the performance of this three pronged approach to caries control: (1) traditional enamel fluoride uptake, (2) surface microhardness study using pH cycling model and subsequent fluoride uptake, (3) a salivary biofilm flow-through study to determine the anti-microbial activity, and (4) a single species biofilm model measuring effect on biofilm matrix disruption. Results. The data showed that a LISTERINE rinse with fluoride, essential oils and xylitol was superior in promoting enamel fluoride uptake and in enhancing antimicrobial activity over traditional commercially available fluoridated products. An increase of the surface microhardness was observed when the LISTERINE rinse was used in combination with fluoridated toothpaste versus the fluoridated toothpaste alone. Finally, it was demonstrated that xylitol solutions disrupted and reduced the biovolume of biofilm matrix of mature Streptococcus mutans. Conclusion. These in vitro studies demonstrated that a fluoride mouthrinse with antimicrobial agent and biofilm matrix disrupting agent provided multifaceted and enhanced anti-caries efficacy by promoting remineralization, reducing acidogenic bacteria and disrupting biofilm matrix.

Anti-Arrhenius cleavage of covalent bonds in bottlebrush macromolecules on substrate.

Spontaneous degradation of bottlebrush macromolecules on aqueous substrates was monitored by atomic force microscopy. Scission of C ─ C covalent bonds in the brush backbone occurred due to steric repulsion between the adsorbed side chains, which generated bond tension on the order of several nano-Newtons. Unlike conventional chemical reactions, the rate of bond scission was shown to decrease with temperature. This apparent anti-Arrhenius behavior was caused by a decrease in the surface energy of the underlying substrate upon heating, which results in a corresponding decrease of bond tension in the adsorbed macromolecules. Even though the tension dropped minimally from 2.16 to 1.89 nN, this was sufficient to overpower the increase in the thermal energy (k(B)T) in the Arrhenius equation. The rate constant of the bond-scission reaction was measured as a function of temperature and surface energy. Fitting the experimental data by a perturbed Morse potential V = V(0)(1 - e(-ßx))(2) - fx, we determined the depth and width of the potential to be V(0) = 141 ± 19 kJ/mol and ß(-1) = 0.18 ± 0.03 Å, respectively. Whereas the V(0) value is in reasonable agreement with the activation energy E(a) = 80-220 kJ/mol of mechanical and thermal degradation of organic polymers, it is significantly lower than the dissociation energy of a C ─ C bond D(e) = 350 kJ/mol. Moreover, the force constant K(x) = 2ß(2)V(0) = 1.45 ± 0.36 kN/m of a strained bottlebrush along its backbone is markedly larger than the force constant of a C ─ C bond K(l) = 0.44 kN/m, which is attributed to additional stiffness due to deformation of the side chains.

Size separation of macromolecules during spreading.

Spreading of homogeneous mixtures of bottle-brush and linear macromolecules of poly(n-butylacrylate) on a solid substrate has been monitored on the molecular scale by atomic force microscopy. Despite the nearly identical chemical composition and similar molecular weight, brush-like macromolecules move markedly slower than linear chains. Moreover, smaller bottle-brushes have been shown to flow faster than the larger bottle-brushes, resulting in fractionation of the macromolecules along the spreading direction. This behavior was explained by the difference in sliding friction coefficient between the bottle-brush macromolecules and linear chains with the substrate. A theoretical model of molecular size separation is in a good agreement with experimental data.

"Fatal adsorption" of brushlike macromolecules: high sensitivity of C-C bond cleavage rates to substrate surface energy.

Adsorption-induced degradation of brushlike macromolecules was monitored through molecular imaging by atomic force microscopy. The rate constant for C-C bond cleavage was shown to be extremely sensitive to the substrate surface energy. A few percent increase in the surface energy from 69.2 to 71.2 mN/m led to an order of magnitude increase of the scission rate. The absolute values of the rupture forces ranging from 2.57 to 2.47 nN are in agreement with previously calculated and measured values for stretching surface-tethered molecules.

Flory theorem for structurally asymmetric mixtures.

The generalization of the Flory theorem for structurally asymmetric mixtures was derived and tested by direct visualization of conformational transformations of brushlike macromolecules embedded in a melt of linear chains. Swelling of a brush molecule was shown to be controlled not only by the degree of polymerization (DP) of the surrounding linear chains, N(B), but also by the DP of the brush's side chains, N, which determines the structural asymmetry of the mixed species. The boundaries of the swelling region were established by scaling analysis as N(2) < N (B) < N (A)/N, where N (A) is the degree of polymerization of the brush backbone. Experiment and theory demonstrated good agreement.

Adsorption-induced scission of carbon-carbon bonds.

Covalent carbon-carbon bonds are hard to break. Their strength is evident in the hardness of diamonds and tensile strength of polymeric fibres; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow, ultrasonic irradiation, receding meniscus and by directly stretching a single molecule with nanoprobes. Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations, but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon-carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this type-either to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites.

Oral health of psychiatric in-patients in Hong Kong.

BACKGROUND: Poor oral health has been reported among various psychiatric populations. Little is known regarding the oral health among psychiatric patients in Asia. AIMS: To examine the oral health status of a group of Chinese psychiatric in-patients in a long-term rehabilitation facility. METHODS: A dental survey using the WHO standardised dental evaluation form was conducted in adult psychiatric patients in a rehabilitation programme. A qualified dentist examined all consenting patients. RESULTS: Ninety-one patients (64.8% male; mean age: 44.7 +/- 9.9 years; mean length of illness: 20.3 +/- 11.5 years) were included in the study, the majority (80.2%) diagnosed with schizophrenia. Malocclusion was found in 79.1% of patients. The mean number of missing teeth was 9.5 +/- 8.9. Bleeding on probing, calculus, shallow and deep pockets were found in 7.1%, 71.8%, 72.9% and 28.2% of patients, respectively. Dental caries were found in 75.3% of dentate patients. The mean number of caries per patient was 5.5 +/- 6.1. Fifty-four per cent of patients needed dental extraction and 78.8% required conservative dental treatment. Older age and length of illness were significantly associated with poor dental health. CONCLUSIONS: Oral health status of chronic psychiatric patients seems to be considerably worse than that of the general population. Mental health professionals should pay more attention to preventive oral health habits of psychiatric patients.