The role of protonation and conformational transition of polyamine grafts in platelet retention to polyamine-graft-PHEMA copolymer surfaces

Blood platelet retention on polyamine-graft-poly(2-hydroxyethyl methacrylate) (PHEMA) copolymer (HA) surface was investigated, focusing on pH and ionic strength of the surrounding medium to elucidate the nature of ionic interaction between platelets and HA copolymer surfaces. The conformational transition of polyamine graft chain in response to the protonation degree of amino groups was demonstrated to be an important factor influencing platelet retention on HA surfaces. When the polyamine graft chain exists in an extended conformation, protonated amino groups distribute from the matrix interface into the aqueous interior, resulting in the effective ionic interaction with platelets to increase their retention on HA copolymer surfaces. The number of protonated amino groups in polyamine portions crucially affected platelet retention. Worth noticing is that an introduction of a small but definite amount of cationic sites on the polymer surface led to significantly minimized platelet retention. It is considered that the surface property of PHEMA was drastically changed to a non-adhesive surface by introducing a small amount of protonated amino groups.     

Cell-attachment activities of surface immobilized oligopeptides RGD,RGDS, RGDV,RGDT, and YIGSR toward five cell lines

Tetrapeptides, Arg-Gly-Asp-Ser (RGDS), Arg-Gly-Asp-Val (RGDV), and Arg-Gly-Asp-Thr (RGDT), respectively, appearing in the cell-attachment domains of fibronectin, vitronectin, and collagen, and pentapeptide Tyr-Ile-Gly-Ser-Arg (YIGSR) appearing in B1 chain of laminin, were synthesized by liquid-phase procedure. Bioactivities of RGD, RGDX (X=S, V and T), YIGSR, and YIGSR-NH₂ as cell recognition determinants were investigated by cell-attachment test using these oligopeptides immobilized to ethylene-acrylic acid copolymer (PEA) film. The cell lines used were A431, NRK, CHO-K1, HeLa.S3, and RLC-16 cells. It was found that the residue X in RGDX plays an important role for cell-attachment activity of RGDX, and, regarding YIGSR, introduction of NH₂ residue at the C-terminal of the pentapeptide enhances the cell-attachment activity.     

An Innovative and Simple Approach to Functional Salivary Reservoir Fabrication

Saliva is a valuable oral fluid that is often taken for granted. Impaired salivary function is a major and a debilitating sequela of radiation treatment for patients with head and neck cancer. It can persist for years and thereby increases the risk of oral infection significantly. Moreover, it has a notably negative impact on the quality of life of such patients. To help overcome this problem, a number of techniques have been proposed for incorporating a reservoir containing salivary substitute into a removable prosthesis. A new design for a functional salivary reservoir is presented here. This design is simple to construct and easily maintained by the wearer. Details of its design, construction, and other potential advantages are presented.     

Comparative study of the shear bond strength of various veneering materials on grade II commercially pure titanium

PURPOSE

To compare the shear bond strength of various veneering materials to grade II commercially pure titanium (CP-Ti).

MATERIALS AND METHODS

Thirty specimens of CP-Ti disc with 9 mm diameter and 10 mm height were divided into three experimental groups. Each group was bonded to heat-polymerized acrylic resin (Lucitone 199), porcelain (Triceram), and indirect composite (Sinfony) with 7 mm diameter and 2 mm height. For the control group (n=10), Lucitone 199 were applied on type IV gold alloy castings. All samples were thermocycled for 5000 cycles in 5-55℃ water. The maximum shear bond strength (MPa) was measured with a Universal Testing Machine. After the shear bond strength test, the failure mode was assessed with an optic microscope and a scanning electron microscope. Statistical analysis was carried out with a Kruskal-Wallis Test and Mann-Whitney Test.

RESULTS

The mean shear bond strength and standard deviations for experimental groups were as follows: Ti-Lucitone 199 (12.11 ± 4.44 MPa); Ti-Triceram (11.09 ± 1.66 MPa); Ti-Sinfony (4.32 ± 0.64 MPa). All of these experimental groups showed lower shear bond strength than the control group (16.14 ± 1.89 MPa). However, there was no statistically significant difference between the Ti-Lucitone 199 group and the control group, and the Ti-Lucitone 199 group and the Ti-Triceram group. Most of the failure patterns in all experimental groups were adhesive failures.

CONCLUSION

The shear bond strength of veneering materials such as heat-polymerized acrylic resin, porcelain, and indirect composite to CP-Ti was compatible to that of heatpolymerized acrylic resin to cast gold alloy.     

Polystyrene‐block‐Polyisoprene Diblock‐Copolymer Micelles: Coupled Pressure and Temperature Effects

The structural changes of diblock‐copolymer micelles under pressures from 200 to 16 000 psi are investigated using small‐angle neutron scattering (SANS). Asymmetric polystyrene‐block‐polyisoprene (PS–PI) diblock copolymers are dissolved in decane, a selective solvent for PI, to form spherical micelles with a core of PS and a corona of PI. The micellar solutions are put under pressure at temperatures of 25 to 60 °C. At room temperature, elevating the pressure from 200 to 16 000 psi has no effect on the size of the micelles. While the micellar solutions remain stable, instantaneous association of micelles is detected. In contrast to micelles at atmospheric pressure, increasing the temperature at elevated pressures does not lead to dissociation of micelles; instead, the micelles aggregate and evolve into sheet‐like structures, reminiscent of a macroscopic phase separation. Furthermore, higher pressures lead to a smaller temperature range in which shape transitions take place.

     

Tandem Action of SNS–Cr and CGC–Ti in Preparation of Ethylene–1‐Hexene Copolymers from Ethylene Feedstock

Ethylene–1‐hexene copolymer materials, ranging from semicrystalline linear low‐density poly­ethylene (LLDPE) to completely amorphous polyethylenes (PEs), are prepared from ethylene alone in a single reactor by the tandem polymerization of bis(2‐dodecylsulfanyl‐ethyl)amine–CrCl₃ (SNS–Cr) and (N‐tert‐butylamido) (tetramethylcyclopentadienyl)–titanium dichloride (CGC–Ti) at 75 °C and under atmospheric pressure. The polymerization activities are on the order of 10⁵–10⁶ g (mol Ti)^?1 h^?1. 1‐Hexene incorporation in the resulting copolymers can be adjusted by varying the Cr–Ti molar ratio and/or applying a short period of pre‐trimerization. Copolymers with high 1‐hexene incorporation up to 15 mol% are obtained. Few vinyl and vinylene chain ends are detected by ¹³C NMR, suggesting that 1‐hexene does not act as a chain‐transfer agent. Narrow molecular‐weight distributions with polydispersities from 1.9 to 2.6 are obtained, characteristic of a single‐active‐site nature of the catalyst system.

     

Long-term effects of various cleaning methods on polypropylene/ethylene copolymer retainer material

Objectives:To evaluate long-term light transmittance, surface roughness, and flexural modulus of polypropylene/ethylene copolymer retainer material after exposure to different cleaning methods.Materials and Methods:Standardized polypropylene/ethylene copolymer retainer specimens (n = 70, 50.8 mm × 12.7 mm × 1.0 mm) were subjected to seven chemical cleaning solutions: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H₂O₂ for 6 months. The specimens were exposed to the different solutions twice a week for 15 minutes or according to manufacturer''s instructions, then stored in artificial saliva at 37°C. Another group of specimens (n = 10) were brushed with a standardized toothbrushing machine for 2 minutes twice a week. At baseline and 6 months, light transmittance, surface roughness, and flexural modulus of the specimens were quantified using spectrophotometry, profilometry and three-point bend testing, respectively. Qualitative analysis was performed using a scanning electron microscope (SEM). Statistical analyses were performed at a significance level of .05.Results:The results showed that light transmittance decreased significantly from baseline for all cleaning methods at 6 months. For an individual method, no significant differences were observed between specimens at baseline and 6 months in surface roughness and flexural modulus. No discernible differences in surface features were observed on SEM images.Conclusions:The results indicate that different cleaning methods affect the long-term light transmittance of the studied polypropylene/ethylene copolymer retainer material. However, for an individual cleaning method, no significant differences were shown for surface roughness or flexural modulus values at 6-months compared to baseline.     

Unidirectionally aligned line patterns driven by entropic effects on faceted surfaces

A simple, versatile approach to the directed self-assembly of block copolymers into a macroscopic array of unidirectionally aligned cylindrical microdomains on reconstructed faceted single crystal surfaces or on flexible, inexpensive polymeric replicas was discovered. High fidelity transfer of the line pattern generated from the microdomains to a master mold is also shown. A single-grained line patterns over arbitrarily large surface areas without the use of top-down techniques is demonstrated, which has an order parameter typically in excess of 0.97 and a slope error of 1.1 deg. This degree of perfection, produced in a short time period, has yet to be achieved by any other methods. The exceptional alignment arises from entropic penalties of chain packing in the facets coupled with the bending modulus of the cylindrical microdomains. This is shown, theoretically, to be the lowest energy state. The atomic crystalline ordering of the substrate is transferred, over multiple length scales, to the block copolymer microdomains, opening avenues to large-scale roll-to-roll type and nanoimprint processing of perfectly patterned surfaces and as templates and scaffolds for magnetic storage media, polarizing devices, and nanowire arrays.     

Simplified Technique for Orbital Prosthesis Fabrication: A Clinical Report

Loss of orbital content can cause functional impairment, disfigurement of the face, and psychological distress. Rehabilitation of an orbital defect is a complex task, and if reconstruction by plastic surgery is not possible or not desired by the patient, the defect can be rehabilitated by an orbital prosthesis. The prosthetic rehabilitation in such cases depends on the precisely retained, user‐friendly removable maxillofacial prosthesis. Many times, making an impression of the orbital area with an accurate record of surface details can be a difficult procedure. The critical areas are making a facial moulage, mold preparation, and attaching the retention device, particularly when eyeglass frames are used. This case focuses on these hindrance factors. A simple basket was used for the impression tray to obtain the facial moulage. A putty mold was used, and attachment of the prosthesis to a retention device was accomplished with positional distance. This method proves to be an economical and simple way of making an orbital prosthesis.