Level Of Cross-linking Research Articles

Impact Assessment of Cetyltrimethylammonium Bromide Treated Organically Modified Nanoclay-Polymer Composite on Soil Enzyme Activity and Root Volume

The effect of organically modified nanoclay-polymer composite was evaluated on soil enzyme activity and root volume at different growth stages viz. crown root initiation, tillering and panicle initiation of wheat (variety: HD 3059). Nanoclay-polymer composite was synthesized by in -situ polymerization of acrylic acid-acrylamide in presence of cetyltrimethylammonium bromide @ 60% neutralization degree and 0.5% cross-linker level and subsequently loaded with di-ammonium phosphate fertilizer (14 g di-ammonium phosphate per unit weight of nanoclay-polymer composite). Phosphorus loaded nanoclay-polymer composite and conventional diammonium phosphate fertilizer were applied (P dose-40 mg P2O5 kg−1 soil) to two types of soil (Alfisol and Inceptisol). Soil enzyme activity and root volume were studied independently with a factorial completely randomized design experiment. Results revealed that dehydrogenase enzyme activity in modified nanoclay-polymer composite increased by + 26.3 and + 19% over conventional fertilizer in Alfisol and Inceptisol respectively. Acid phosphatase activity (9.25 µg p-nitrophenol g−1 soil h−1) was highest at panicle initiation stage in Inceptisol whereas alkaline phosphatase activity was more at tillering in both soils. Root volume also increased by + 16.8% on applying nanoclay-polymer composite as compared to conventional fertilizer in Alfisol. The corresponding data in Inceptisol was + 13.1%. Therefore, it was concluded that nanoclay-polymer composite prepared from organoclay has a positive effect on soil enzyme activity as well as root volume.

Autoclavable physically-crosslinked chitosan cryogel as a wound dressing

Moist wounds were known to heal more rapidly than dry wounds. Hydrogel wound dressings were suitable for the moist wound healing because of their hyperhydrous structure. Chitosan was a strong candidate as a base material for hydrogel wound dressings because the polymer had excellent biological properties that promoted wound healing. We previously developed physically-crosslinked chitosan cryogels, which were prepared solely by freeze-thawing of a chitosan-gluconic acid conjugate (CG) aqueous solution, for wound treatment. The CG cryogels were disinfected by immersing in 70% ethanol before applying to wounds in our previous study. In the present study, we examined the influence of autoclave sterilization (121°C, 20min) on the characteristics of CG cryogel because complete sterilization was one of the fundamental requirements for medical devices. We found that optimum value of gluconic acid content of CG, defined as the number of the incorporated gluconic acid units per 100 glucosamine units of chitosan, was 11 for autoclaving. An increased crosslinking level of CG cryogel on autoclaving enhanced resistance of the gels to enzymatic degradation. Furthermore, the autoclaved CG cryogels retained favorable biological properties of the pre-autoclaved CG cryogels in that they showed the same hemostatic activity and efficacy in repairing full-thickness skin wounds as the pre-autoclaved CG cryogels. These results showed the great potential of autoclavable CG cryogels as a practical wound dressing.

Precise stimulation of near-infrared light responsive shape-memory polymer composites using upconversion particles with photothermal capability

The incorporation of thermally-induced shape-memory polymer (SMP) with photothermal fillers has been widely used in creating photoresponsive SMP composites (SMPCs). Near-infrared (NIR) light, which is safer for human tissues and naked eyes, has been widely used to trigger such intelligent SMPCs containing carbon nanomaterials, metal nanoparticles, or rare earth organic complexes. There is still a need to aim invisible NIR light beam remotely onto SMPCs to realize the precise shape recovery of their featured areas. Here, NaYF4:99.5%Yb3+, 0.5%Tm3+ particles presenting both upconversion and photothermal capabilities were utilized as multifunctional fillers in a crosslinked copolymer of methyl methacrylate and butyl acrylate, enabling the prepared SMPCs to transfer the NIR light at 980 nm simultaneously into both visible light and heat. The particles with a low content up to 1 phr did not vary the crosslinking level and glass transition temperature of the SMPC. With the aid of upconversion at a relatively low power density, the position of laser beam on SMPC surface was detected easily, facilitating the aim towards the area anticipated to be triggered without inducing a shape deformation. The subsequent increase in power density successfully resulted in the precise shape recovery with the recovery ratio higher than 90%. The concept of precise location before stimulation was demonstrated in the cases of multiple shape deformations, remote activation in the darkness, and microscale structured surfaces. The reported multifunctional nanoparticles truly executed the remote and precise trigger of SMPCs using invisible NIR light, which can be further exploited in other thermally-induced smart polymer composites.

Solvent-responsive floating liquid crystalline-molecularly imprinted polymers for gastroretentive controlled drug release system

Liquid crystalline-molecularly imprinted polymer (LC-MIP) particles were first found to possess the floating behavior on the aqueous medium. Combined with molecular recognition, the LC-MIP was fabricated as a novel class of the controlled-release gastric retentive DDS. The LC-MIP was made using co-polymerization of methacrylic acid, 4-methyl phenyl dicyclohexyl ethylene (LC monomer with vinyl group), and ethylene glycol dimethacrylate with S-amlodipine (S-AML) as model template drug. The optimum condition of the preparation of LC-MIP has been obtained relying on release behaviors of S-AML from the LC-MIP. The surface morphology of LC-MIP and three corresponding control samples, i.e., template-free LC-NIP, LC-free MIP, and LC-free NIP, were studied. Applying the LF model for the binding isotherm, imprinting factors was 2.80 for the LC-MIP with the crosslinking degree of 20.0%, whereas 6.70 for the LC-free MIP with high levels of crosslinker (80.0%). Furthermore, the phase transition behaviors of LC-based particles as well as drug-loaded LC elastomers were measured by a differential scanning calorimeter and the formed hydrogen bonding between S-AML and LC-MIP was demonstrated by FT-IR spectra. In vivo imaging experiment proved that the floating LC-MIP had significantly longer gastric residence time (>60min) than the non-floating MIP reference (<30min). In vivo pharmacokinetic study showed a plateau region between 1.5 and 22h on the plasma concentration from the LC-MIP. In spite of lower imprinting factor, the relative bioavailability of the gastro-floating LC-MIP was 180.5%, whereas only 111.7% of the LC-free MIP. As a conclusion, the LC-MIPs indicated potentials for oral administration due to the innovative combination of floating and controlled release properties.

Molecular characteristics of oxidized and cross-linked lotus (Nelumbo nucifera) rhizome starch

ABSTRACTLotus rhizome starch was isolated and subjected to chemical modification using different levels of oxidation, cross-linking, and dual modifications. Fourier transform infrared (FTIR) and X-ray diffraction analyses confirmed the successful modification of native starch. The carbonyl, carboxyl contents, and degree of cross-linking of modified starch were in the range of 0.03–0.07%, 0.07–0.15%, and 4.31–58.28%, respectively, for oxidized, cross-linked, and dual-modified starches. Amylose content varied from 13.57% to 20.60% for native and modified starches. Swelling power (SP) and solubility were temperature dependent and increased with increase in temperature. Oxidation and dual modification increased solubility, while cross-linking decreased solubility. Paste clarity, degree of crystallinity, and whiteness of starches increased significantly with increase in level of modifications. Peak, breakdown, and setback viscosities of the modified starches decreased with increase in modification. Phase transitions using DSC presented lower enthalpy values for modified starches. Gelatinization temperature increased due to modification whereas scanning electron micrographs revealed that modification altered the starch morphology.

Thermogravimetric–Fourier Transform Infrared Spectroscopy–Gas Chromatography/Mass Spectrometry Study of Volatile Organic Compounds from Coal Pyrolysis

The simultaneous use of thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy, and gas chromatography/mass spectrometry (GC/MS) with the same sample provides a unique method for studying coal pyrolysis. About 124 volatile organic compounds (VOCs) were identified by TG-FTIR-GC/MS during coal pyrolysis based on the characteristic fragments or Kovats index. These compounds included alkanes, α-olefins, benzene, toluene, ethylbenzene, xylenes, and phenols. n-Alkanes from C5 to C24 with regular one-carbon retention intervals in the GC/MS system were used to calculate the Kovats indexes of all compounds. From this study, temperature was the key factor affecting VOC release. The VOCs released below 400 °C represented only 23.1% of the total VOCs released during the pyrolysis of bituminous (coal BA). Thus, the use of thermal desorption (TD) with GC/MS to analyze coal pyrolysis provides VOC release information only below 400 °C. It would underestimate the VOC release because of the temperature limitation on the TD technique. The yields of phenolic hydrocarbons from lignite were higher than those from bituminous coal. This could be the result of a higher level of oxygen cross-linking in lignite than in bituminous coal, which was proven by the results of curve fitting and GC/MS. Thus, the release of VOCs is a function of coal rank.

Effects of high amylose corn starch and microbial transglutaminase on the textural and microstructural properties of wheat flour composite gels at high temperatures.

Although, transglutaminase was practically used in the production of noodles and pasta in Japan, but there is little academic and industrial knowledge concerning its utilization in the pasta or noodles. Moreover, long shelf-life noodle/pasta products have become popular in the Japanese market and in the emergency conditions like as floods or earthquake, but they can be stored for at least 5 months by applying heat treatment at 95C. Here, high amylose corn starch as a resistant starch, wheat flour, and microbial transglutaminase (MTGase) were selected as the main components in the composite gel (CG) systems to elucidate the effects of MTGase and Hylon on the texture, microstructure, and pasting behavior of CGs at high temperatures to produce long-life noodle/pasta products (about 2 years) through retort processing.

Synthesis and Study of Shape-Memory Polymers Selectively Induced by Near-Infrared Lights via In Situ Copolymerization.

Shape-memory polymers (SMPs) selectively induced by near-infrared lights of 980 or 808 nm were synthesized via free radical copolymerization. Methyl methacrylate (MMA) monomer, ethylene glycol dimethylacrylate (EGDMA) as a cross-linker, and organic complexes of Yb(TTA)2AAPhen or Nd(TTA)2AAPhen containing a reactive ligand of acrylic acid (AA) were copolymerized in situ. The dispersion of the organic complexes in the copolymer matrix was highly improved, while the transparency of the copolymers was negligibly influenced in comparison with the pristine cross-linked PMMA. In addition, the thermal resistance of the copolymers was enhanced with the complex loading, while their glass transition temperature, cross-linking level, and mechanical properties were to some extent reduced. Yb(TTA)2AAPhen and Nd(TTA)2AAPhen provided the prepared copolymers with selective photothermal effects and shape-memory functions for 980 and 808 nm NIR lights, respectively. Finally, smart optical devices which exhibited localized transparency or diffraction evolution procedures were demonstrated based on the prepared copolymers, owing to the combination of good transparency and selective light wavelength responsivity.

DSC investigation of bovine hide collagen at varying degrees of crosslinking and humidities

Bovine hide collagen (nonCLC; non-CrossLinked Collagen) was analysed by differential scanning calorimetry (DSC) at different hydration degrees and compared with hide collagen samples crosslinked with glutaraldehyde (CLC-GA) and chromium(III) ions (CLC-Cr), respectively. Crosslinking and drying were confirmed to increase the denaturation temperature. Different regions were assigned, that reflect the variation of the influence of water on the denaturation temperature. Furthermore, at moderate hydration degrees, the enthalpies of non-crosslinked collagen increase compared to the fully hydrated state. This reflects a glue-like action of water in the range of 25% hydration. Crosslinking of bovine hide collagen decreases the enthalpy by 25% in the fully hydrated state, even at very low levels of crosslinking This can be explained by intensive effects of the crosslinking agent on the hydration network of the collagen molecules, assuming that the enthalpies are principally a result of hydrogen bonding. At very low water contents DSC peaks of CLC-Cr completely disappear. This could be explained by competition between hydroxosulfochromate(III) complexes and collagen for water.

Fibulin-4 is essential for maintaining arterial wall integrity in conduit but not muscular arteries.

Homozygous or compound heterozygous mutations in fibulin-4 (FBLN4) lead to autosomal recessive cutis laxa type 1B (ARCL1B), a multisystem disorder characterized by significant cardiovascular abnormalities, including abnormal elastin assembly, arterial tortuosity, and aortic aneurysms. We sought to determine the consequences of a human disease-causing mutation in FBLN4 (E57K) on the cardiovascular system and vascular elastic fibers in a mouse model of ARCL1B. Fbln4E57K/E57K mice were hypertensive and developed arterial elongation, tortuosity, and ascending aortic aneurysms. Smooth muscle cell organization within the arterial wall of large conducting vessels was abnormal, and elastic fibers were fragmented and had a moth-eaten appearance. In contrast, vessel wall structure and elastic fiber integrity were normal in resistance/muscular arteries (renal, mesenteric, and saphenous). Elastin cross-linking and total elastin content were unchanged in large or small arteries, whereas elastic fiber architecture was abnormal in large vessels. While the E57K mutation did not affect Fbln4 mRNA levels, FBLN4 protein was lower in the ascending aorta of mutant animals compared to wild-type arteries but equivalent in mesenteric arteries. We found a differential role of FBLN4 in elastic fiber assembly, where it functions mainly in large conduit arteries. These results suggest that elastin assembly has different requirements depending on vessel type. Normal levels of elastin cross-links in mutant tissue call into question FBLN4's suggested role in mediating lysyl oxidase-elastin interactions. Future studies investigating tissue-specific elastic fiber assembly may lead to novel therapeutic interventions for ARCL1B and other disorders of elastic fiber assembly.

Synthesis and characterization of poly(N-tert-butylacrylamide-co-acrylamide) hydrogel with enhanced responsive properties

To synthesize a series of novel temperature sensitive hydrogels, N-tert-butylacrylamide (NtBA) and acrylamide (AAm) were used as the comonomers and polymerized by free-radical crosslinking copolymerizarion. The poly(ethylene glycol) (PEG) with molecular weight of 400, 4000 and 6000 g·mol-1 was used as the porogen. The equilibrium swelling capacity, swelling/deswelling kinetics and diffusion parameters of obtained hydrogels were systematically evaluated. As revealed by SEM micrographs, the macroporous structure of hydrogels can be modulated by the crosslinking level, PEG molecular weight and dosage. FTIR analysis demonstrated that the porogen PEG was completely leached out of the gel matrix. Compared with the conventional hydrogels, the PEG-modified (PGel) hydrogels exhibited enhanced temperature sensitivity and superior kinetics during the swelling, deswelling and pulsatile swelling processes. Controlled release of salicylic acid also demonstrated the good usability of PGel hydrogel, which rendered it great potential for controlled drug delivery systems.

Reactive antioxidants for peroxide crosslinked polyethylene

Three synthesised reactive (graftable) antioxidants, r-AO, with hindered phenol and hindered amine antioxidant functions, were examined for their grafting efficiency in polyethylene and their retention and stabilising performance in peroxide-crosslinked polyethylene pipe material. Their level of grafting in un-crosslinked high density polyethylene, HDPE, and the extent of their retention in highly peroxide-crosslinked HDPE (PEXa) material (both laboratory prepared samples and PEXa pipes produced by commercial processes) were determined after stringent solvent extraction methodologies. The uniformity of distribution of the r-AOs in the PEXa pipes (across the length and thickness of the pipes) were examined using infrared-microscopy and compared with similarly produced PEXa pipes containing commercial antioxidants having the same antioxidant functions. The extent of interference of the graftable hindered phenol and hindered amine antioxidants with the peroxide crosslinking process in the PEXa materials was assessed by comparing the level of crosslinking achieved against analogously prepared samples containing a conventional hindered phenol antioxidant (Irganox 1076).The results obtained showed that the presence of the graftable (r-AOs) antioxidants did not affect the level of crosslinking of the PEXa pipes which remained high (>85%) and that they were retained to a very high extent in the PEXa material after solvent extraction, and are very uniformly distributed across the length and thickness of PEXa pipes. The long-term stabilising performance of the graftable r-AOs in the PEXa material (in both laboratory prepared samples and in peroxide crosslinked pipes produced by commercial processes) was also examined using complimentary methods: oxidative induction time (OIT) before and after solvent extraction, physical embrittlement following oven ageing at 125 °C, as well as by a hydrostatic pressure tests conducted (with water inside and air outside) at 115 °C and 2.5 MPa pressure. The stabilising efficacy of the r-AOs was compared with that of conventionally stabilised PEXa material containing analogous antioxidant functions produced in the same way. The level of retention (in the pipes) of the graftable antioxidants and their long-term stabilising performance was shown to be significantly higher than that of the conventional AOs under all the test conditions used here.

Poly (vinylidene fluoride)/fluororubber/silicone rubber thermoplastic vulcanizates prepared through core-shell dynamic vulcanization: Formation of different rubber/plastic interfaces via controlling the core from “soft” to “hard”

In the previous report, we proposed a novel core-shell dynamic vulcanization technique to prepare a fluorosilicone thermoplastic vulcanizate (TPV) based on poly (vinylidene fluoride) (PVDF), fluororubber (FKM) and silicone rubber (SR). However, we did not discuss the relationship between the structure and properties of the TPV from the viewpoint of core-shell structure. For example, why the mechanical properties of a shell-crosslinked TPV were inferior to that of a core-crosslinked TPV? In this paper, we have valuable insights on this issue and provide guide for regulating core-shell structure in polymer blends. We found that SR molecule chains were possibly forced to migrate to the interface between PVDF and FKM under strong shearing during dynamic vulcanization. When DCP content <0.4 wt%, some of the soft SR formed films, and most of it formed “soft” particles. When DCP content ≥0.4 wt%, all of SR formed “hard” particles, and thus a perfect core-shell structure was formed after the crosslinking of FKM. The mechanical properties of the TPVs were also largely improved with increasing levels of crosslinking in SR.

Determination of In Situ Esterification Parameters of Citric Acid-Glycerol Based Polymers for Wood Impregnation

The development of wood treatments is of increasing industrial importance. A novel technique for improving the properties of lodgepole pine and white pine through modification of the microstructure is described. The present investigation is devoted to the synthesis and determination of in situ parameters of citric acid and glycerol based polymers for wood impregnation. This solvent free approach is environmentally friendly and achieved through an esterification condensation reaction under acidic conditions. Crude glycerol and citric acid reactants were cross-linked via a curing process at 160 °C creating a polymer with only water as the byproduct. The ester bonds and crosslinking levels were controlled using different catalysts and citric acid contents and related to the reaction time and temperature. The nature of bonding within the polymers and at the wood cell walls was determined by FT-IR analysis. The thermal properties such as glass transition temperature (Tg) were studied using TGA/DSC and the effect of citric acid content and catalyst type determined. Dimensional stability of impregnated wood samples improved above 50% for each sample with HCl and p-TSA catalysts compared to control samples. FTIR spectra were studied to show the presence of the ester linkages of the polymer in situ at the wood cell walls. Bonding between the polymer and wood macromolecules were observed by scanning electron microscopy and interpreted as evidence of chemical bonds at the wood cells. When prepared using a catalyst, the polymer was intimately incorporated into wood structure significantly improving the substrate dimensional stability. Enhanced stability makes this approach of particular interest for exterior wood products especially as a green renewable option for the wood industry.

Influence of physico-chemical modification of waxy corn starch on changes in its structure

The paper presents a study on structure changes of waxy corn starches after physicochemical modification. The hydrothermal treatment (physical modifications) allowed to obtain pre-gelatinised starch (Merigel) or untreated starch of cook-up type (Resistamyl). Different degrees of cross-linking (low, medium and high) and medium level of substitution were the results of chemical modification of starch. The changes in the structure of modified starch were analysed with the use of the methods of low temperature nitrogen adsorption/desorption and of water vapour sorption. The BET equation was used to determine monolayer capacity (am) from isotherms of water vapour desorption, while the BJH equation was used to determine the surface area (SBJH), volume (VBJH) and mean diameter of pores (DBJH). Starches of the pre-gelatinisation type were characterised by SBETN2 values in the range of 0.18–0.45 m2/g, and starches of the cook-up type - 0.13–0.66 m2/g. Higher values of SBJH were noted for the cook-up starches (SBJH: 0.23–0.60 m2/g) in reference to the starches of the pre-gelatinisation type (SBJH: 0.12–0.32 m2/g). The medium degree of cross-linking of pre-gelatinisation type starches caused a lowering of the value of their monolayer capacity (am ads, am des), while for the cook-up type starches an increase of that value was observed, determined with adsorption and desorption water vapour isotherms. Porosity of the modified starch was determined with the use of mercury porosimetry. A decrease of porosity was noted for starch of the cook-up type (porosity 38.3–52.3%), compared to native waxy corn starch (59.3%). Starches of the pre-gelatinisation type (Merigel) were characterised by an increase of the value in question with increase in the degree of cross-linking: low ML (53.5%) < medium MM (59.2%) < high MH (65.7%). Starches of pre-gelatinisation type were characterised by pore volume (VMP) values in the range of 0.83–1.34 cm3/g, while starches of coo-up type had VMP values in the range of 0.57–0.79 cm3/g.

Microscale Compression and Shear Testing of Soft Materials Using an MEMS Microgripper With Two-Axis Actuators and Force Sensors

This paper reports a microelectromechanical systems (MEMS)-based microgripper, integrating two-axis actuators and force sensors, for microscale compression and shear testing of soft materials. The device employs V-beam electrothermal actuators to drive an active gripping arm and compress or shear a microscale sample grasped at the gripping tips, and two triplate differential capacitive sensors to measure the compression and shear forces applied to the sample with nanonewton resolution (compressive force resolution: 7.7 nN, and shear force resolution: 57.5 nN). Using the microgripper, we demonstrate, for the first time, on-chip compression and shear testing of polydimethylsiloxane (PDMS) microstructures prepared at different crosslinking levels. We believe that this device will be useful for accurately characterizing mechanical properties of a variety of microscale soft materials.

Alginate based hydrogel for tissue regeneration: optimization, antibacterial activity and mechanical properties

Purpose: In this work our aim was to reveal the relationship between sodium alginate concentration and crosslinking level, also the ratio of release of the antibacterial additives: silver nanoparticles and metronidazole. Moreover, we examine obtained hydrogel as a potential dressing material for regenerative medicine. Design/methodology/approach: In the research specimens of hydrogels were tested to define their mechanical and physicochemical properties like antibacterial activity against gramnegative Escherichia coli and gram-positive Staphylococcus aureus, viscosity and conductivity. Findings: The concentration of alginate and presence of antibacterial additives influence on the crosslinking level. Mechanical properties of hydrogels are similar to human skin. Only hydrogels with addition of metronidazole and AgNP inhibits bacteria growth after 18 h. In case of gram-negative Escherichia coli both of the aseptic additives inhibits bacteria growth, but sodium alginate hydrogel with silver nanoparticles gives better results in tests with grampositive Staphylococcus aureus. Research limitations/implications: The presence of metronidazole in hydrogel, especially its incorporation and binding with mannuronic and guluronic acid residues must be clarified in more advanced research. Practical implications: Obtained results shows that sodium alginate hydrogels with 0.1mg/ml of alginate, due to its properties are proper as a dressing material. Based on the results, and more advanced tests with metronidazole, we can consider dressing design. Originality/value: Unique value of this work is that we completed the gap in knowledge about the relation of crosslinking level and mechanical properties with are crucial to proper tissue healing and addition of popular aseptic agents.

Biosorption and selective separation of acetophenone and 1-phenylethanol with polysaccharide-based polymers

A polysaccharide-based polymer (abbrev., SMP) was prepared via the crosslinking of starch with 4,4-methylene diphenyl diisocyanate and employed as an adsorbent for selective separation of acetophenone (AP) and 1-phenylethanol (PE) which coexist extensively in petrochemical by-products and effluents. The successful crosslinking was proved by FTIR and XPS, and the rough morphology as well as porous structure was also demonstrated in XRD, SEM and N2 adsorption-desorption analysis. Using SMP as adsorbent, the adsorption kinetics and isotherms were both investigated in single-component system. Both kinetic and thermodynamic parameters of the adsorption process were obtained. Further thermodynamic investigation indicated that the adsorption was exothermic and spontaneous. Compared to the starch-based polymers whose frameworks contain no phenyl ring, SMP exhibits both higher selectivity and capacity for AP in the competitive adsorption. Additionally, increasing the level of crosslinking in SMP favors its adsorption performance. Furthermore, continuous adsorption-desorption indicated high separation ability and regeneration efficiency of SMP. Finally, the mechanism studies suggested that the adsorption mechanisms may be physisorption involving noncovalent interactions, permitting preference to AP over PE.

DSC characterization of rabbit corneas treated with Stryphnodendron adstringens (Mart.) Coville extracts

Keratoconus is an eye ectasia that affects the cornea causing distortion of vision. Corneal crosslinking promoted by riboflavin photo-stimulated at 365 nm is a treatment used successfully to block the keratoconus progression. In this study, we characterize rabbit corneas subjected to enhanced crosslinking using different vegetable extracts prepared from Stryphnodendron adstringens (Mart.) Coville bark by differential scanning calorimetry. The extracts tested in this study were: aqueous, ketonic, ethanolic, ethyl acetate and hydroalcoholic, which revealed high levels of polyphenols, such as proanthocyanidins. The corneas, obtained from the slaughter rabbits, were divided into groups: control (consisting of untreated corneal samples) and S. adstringens, where the samples were subjected to 4% vegetable extracts for 2 h. The DSC profiles of the corneas were obtained in nitrogen atmosphere. The results showed that temperature and enthalpy of denaturation of the corneal samples treated with S. adstringens were higher than the control group. The control group presents temperature and enthalpy values of 59.8 ± 1.1 °C and 24.6 ± 2.7 J g−1, respectively. After crosslinking with ketone extract, the values were 90.1 ± 1.1 °C and 39.9 ± 2.7 J g−1. These results show that S. adstringens is efficient to increment the crosslinking level of the corneas.

A facile strategy for fine-tuning the stability and drug release of stimuli-responsive cross-linked micellar nanoparticles towards precision drug delivery.

Precision drug delivery has a great impact on the application of precision oncology for better patient care. Here we report a facile strategy for fine-tuning the stability, drug release and responsiveness of stimuli-responsive cross-linked nanoparticles towards precision drug delivery. A series of micellar nanoparticles with different levels of intramicellar disulfide crosslinkages could be conveniently produced with a mixed micelle approach. These micellar nanoparticles were all within a size range of 25-40 nm so that they could take full advantage of the enhanced permeability and retention (EPR) effect for tumor-targeted drug delivery. The properties of these nanoparticles such as critical micelle concentration (CMC), stability, drug release and responsiveness to a reductive environment could be well correlated with the levels of crosslinking (LOC). Compared to the micellar nanoparticles with a LOC at 0% that caused the death of animals of two species (mouse and rat) due to the acute toxicity such as hemolysis, the nanoparticles at all other levels of crosslinking were much safer to be administered into animals. The in vitro antitumor efficacy of micellar nanoparticles crosslinked at lower levels (20% & 50%) were much more effective than that of 100% crosslinked micellar nanoparticles in SKOV-3 ovarian cancer cells.