Wirasak Smitthipong

Mussel-inspired hydrogels for biomedical and environmental applications

This mini-review highlights the very recent development of mussel-inspired hydrogels in biomedical and environmental fields. 3,4-Dihydroxyphenyl-L-alanine (DOPA) and its analogues can not only function as cross-linking mediators in constructing the hydrogel network, but also participate in various intermolecular and surface interactions. The developed mussel-inspired hydrogels have important applications in biomedical field as tissue adhesives, drug delivery carriers and coating materials, or in environmental field as pollutant adsorbents, according to the different physicochemical properties that are attributed to different DOPA chemistries.

Polyethylene green composites reinforced with cellulose fibers (coir and palm fibers): effect of fiber surface treatment and fiber content

Coir and palm fibers from agricultural waste were investigated as reinforcement for low density polyethylene (LDPE). The effect of fiber preparation with alkaline treatment and with/without bleaching on fiber physical properties was also an objective of this study. The chemical composition and FTIR (Fourier transform infrared spectroscopy) results confirmed that palm fibers had less impurity than coir fibers. This could be the reason for a greater fiber-matrix interfacial interaction of the palm fibers as compared to that of coir fibers, which was in good agreement with the estimation of surface free energy of the dispersion component. Moreover, fiber bleaching improved the single fiber pullout stress. Composites with both alkaline treated and bleached fibers, at different fiber contents (5, 10, 15, and 20 wt.%), were manufactured using a compression molding machine. Addition of both fibers in the LDPE matrix resulted in composites with a higher Young’s modulus compared to that of homopolymer. The Young’s modulus of the composites increased with the effect of either fiber content or fiber bleaching. Differential scanning calorimetry (DSC) showed that composites reinforced with both types of fibers had a single melting temperature peak, indicating the existence of only one type of crystalline species. Moreover, there were no significant differences in the melting temperatures for the fiber reinforced composites and the homo-LDPE. The heat of fusion decreased in the case of fiber reinforced composites.

Effect of pineapple leaf fiber-reinforced thermoplastic starch/poly(lactic acid) green composite: Mechanical, viscosity, and water resistance properties

In this article, we investigated the properties of thermoplastic starch (TPS) with pineapple leaf fiber (PALF)/poly(lactic acid) (PLA) composite compared to both TPS with a PALF composite and TPS/PLA blend. The composite is prepared by a single-screw extruder. It appears that the TPS with PALF/PLA composite gives better mechanical properties and water resistance than the TPS/PLA blend, but it presents the same flow behavior (based on the power law index) as the PLA alone.

Specific interaction of DNA-functionalized polymer colloids

As a chemically based assembly system, DNA is a key player for use in the reversible and specific interactions of an advanced material. In this approach, we work with a one-component system where a number of DNA single strands are grafted on the surface of micro-sized particles. The interactions between the DNA-functionalized particles are controlled by the addition of DNA linker in solution, which has complementary sequences with the DNA strands grafted on the particles. The hydrogen bonding based on Watson-Crick pairing is the driving force to form double stranded DNA. Several techniques have been used to characterize this system; for example, optical microscopy, AFM, DLS and flow cytometry. The two DNA strands reversibly separate (denature) above a characteristic melting temperature of DNAs base pair sequences. The melting temperature of DNA in the study is in good agreement with that of calculation based on the thermodynamic point of view.

Chemical structure, thermal and mechanical properties of poly(nucleotide)–cationic amphiphile films

Here we report on the characterization of transparent supramolecular films blended with negatively charged polymers with cationic amphiphiles. The films are prepared by conjugating, through electrostatics, the cationic amphiphiles to the poly(nucleotide) backbone then through hydrophobic interactions, in consequence, to form amphiphatic films. Fourier-transformed infrared spectroscopy (FT-IR) spectra present the chemical structure of the poly(nucleotide) and cationic amphiphile in the films. Homopoly(nucleotides) are used as the reference materials. The chain length and secondary structure of the poly(nucleotide) can affect the mechanical and thermal behaviors of the films.

DNA-functionalized polystyrene particles and their controlled self-assembly

DNA-functionalized polystyrene colloids and their thermodynamic characteristics are investigated here. This system is built on micro-sized polymer bids with different lengths of DNA spacer grafted onto the surface of the particles. Two types of DNA linkers were designed to create a bridge between complementary DNA-functionalized particles, to better understand the effect of the DNA sequence on an annealing temperature (Tm) of the aggregation. The disassembly of the polymeric scaffold based on DNA melting is in a good agreement with that calculated from the thermodynamic information. However, the length and the topology of the DNA spacer are important for the experimental melting point because of the effect of the directionality of the double-stranded DNA between the DNA-grafted particles and DNA linker.

Supramolecular cooperative-assembly of polyelectrolyte films

In this report we investigate and compare the characteristics of the cooperative-assembly of double-stranded DNA and random coil poly(styrene sulfonate) mixed with didodecyldimethylammonium bromide (DDAB). Film formation is attributed primarily to electrostatic interactions between anionic phosphate or sulfonate groups (DNA or PSS) and cationic ammonium groups of DDAB. It appears that the elasticity and morphology of such films are dependent on the length and the structure of polymers. Ethidium bromide (a nucleic acid stain and intercalating agent) was employed to probe the structure of polymers based on the photoluminescence response of this dye.

Effect of Non-Rubber Components on Properties of Sulphur Crosslinked Natural Rubbers

Non-rubber components (mainly proteins and lipids) in natural rubber (NR) play important roles for controlling the properties of NR. Crosslinking process creates intermolecular chemical bonds in order to obtain a three-dimensional network, resulting in more elastic rubber. Sulphur crosslinking is the most popular method and is applied in the present study. Two types of NR were prepared, namely, whole natural rubber (WNR) and purified natural rubber (PNR). PNR was deproteinized by centrifugation method and then acetone extraction. These rubbers were crosslinked by an efficient vulcanization (EV) system. They were cured for three curing times (1xt90, 2xt90, 3xt90) at 150°C. WNR presents shorter curing time than PNR because there are some phospholipids and proteins which are natural accelerators for curing reaction. The presence of non-rubber components seems to play a major role on crosslinking density and adhesion phenomenon for rubber/glass system. AFM images of WNR show more heterogeneity and roughness compared to PNR.

Influence of Non-Rubber Components on NR Surface Modification by Chlorination

Natural rubber (NR) is a very useful elastomer and renewable polymer with outstanding properties compared to synthetic elastomers. However, as a natural polymer, the non-rubber species (proteins, phospholipids, carbohydrate, etc.) have to be considered carefully for the understanding of the surface and interfacial properties. Especially these components can markedly affect the frictional and adhesive properties of the rubber surface. Although many methods can be used to modify the surface properties, chlorination remains one of the easiest way.The present study deals with surface modification of peroxide crosslinked NRs and synthetic cis-1,4 polysioprene as reference samples by chlorination. Surface and frictional properties of these different rubbers were analyzed by various complementary techniques The influence of critical parameters on wetting, frictional and mechanical properties were investigated and will be discussed

Self-assembly nucleic acid-based biopolymers: learn from the nature

This review highlights the recent developments in nucleic acid-based based materials for biomedical applications and functional devices. DNA and RNA are anionic macromolecules composing sugar-phosphate backbone, which usually structure as rod-like double helix with base pair stacking. Electrostatic interactions are the main components in the complex formed between anionic nucleic acid and cationic molecule. These nucleic acid-based biopolymers have significant potential as functional materials for drug delivery, biosensors, and a scaffold for many biodegradable materials.