Rheological and mechanical properties of hydroxypropyl methylcellulose-based hydrogels and cryogels controlled by AOT and SDS micelles

HYPOTHESIS

The type and concentration of surfactants affect the rheological behavior of hydroxypropyl methylcellulose (HPMC) chains in hydrogels, influencing the microstructure and mechanical properties of HPMC cryogels.

EXPERIMENTS

Hydrogels and cryogels containing HPMC, AOT (bis (2-ethylhexyl) sodium sulfosuccinate or dioctyl sulfosuccinate salt sodium, two C8 chains and sulfosuccinate head group), SDS (sodium dodecyl sulfate, one C12 chain and sulfate head group), and sodium sulfate (salt, no hydrophobic chain) at different concentrations were investigated using small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), rheological measurements, and compressive tests.

FINDINGS

SDS micelles bound to the HPMC chains building "bead necklaces", increasing considerably the storage modulus G' values of the hydrogels and the compressive modulus E values of the corresponding cryogels. The dangling SDS micelles promoted multiple junction points among the HPMC chains. AOT micelles and HPMC chains did not form "bead necklaces". Although AOT increased the G' values of the hydrogels, the resulting cryogels were softer than pure HPMC cryogels. The AOT micelles are probably embedded between HPMC chains. The AOT short double chains rendered softness and low friction to the cryogel cell walls. Therefore, this work demonstrated that the structure of the surfactant tail can tune the rheological behavior of HPMC hydrogels and hence the microstructure of the resulting cryogels.

Tuning the Mechanical and Thermal Properties of Hydroxypropyl Methylcellulose Cryogels with the Aid of Surfactants

The mechanical and thermal properties of cryogels depend on their microstructure. In this study, the microstructure of hydroxypropyl methylcellulose (HPMC) cryogels was modified by the addition of ionic (bis (2-ethylhexyl) sodium sulfosuccinate, AOT) and non-ionic (Kolliphor^® EL) surfactants to the precursor hydrogels (30 g/L). The surfactant concentrations varied from 0.2 mmol/L to 3.0 mmol/L. All of the hydrogels presented viscous behavior (G″ > G′). Hydrogels containing AOT (c > 2.0 mmol/L) led to cryogels with the lowest compressive modulus (13 ± 1 kPa), the highest specific surface area (2.31 m²/g), the lowest thermal conductivity (0.030 W/(m·°C)), and less hygroscopic walls. The addition of Kolliphor^® EL to the hydrogels yielded the stiffest cryogels (320 ± 32 kPa) with the lowest specific surface area (1.11 m²/g) and the highest thermal conductivity (0.055 W/(m·°C)). Density functional theory (DFT) calculations indicated an interaction energy of −31.8 kcal/mol due to the interaction between the AOT sulfonate group and the HPMC hydroxyl group and the hydrogen bond between the AOT carbonyl group and the HPMC hydroxyl group. The interaction energy between the HPMC hydroxyl group and the Kolliphor^® EL hydroxyl group was calculated as −7.91 kcal/mol. A model was proposed to describe the effects of AOT or Kolliphor^® EL on the microstructures and the mechanical/thermal properties of HPMC cryogels.

Cetuximab has an inhibitory effect on cell motility in SCC-4 oral squamous cell carcinoma cell line

Cetuximab is a chimeric monoclonal antibody that acts as a competitive antagonist, by binding to EGFR. This cell signalling pathways regulates tumor progression. The oral squamous cell carcinoma undergoes to regional spreading and distant metastasis. This study aimed to evaluate the effect of treatment with Cetuximab on cell migration and invasion in OSCC cells, by using the SCC-4 cell line. Cell migration and cell invasion assay were performed and actin cytoskeleton of control and treated with Cetuximab cells were evaluated. Differences were considered significant when p<0.05.Cetuximab inhibited the migration of SCC-4 cells at three concentrations: 1 µg/mL, 50 µg/mL and 100 µg/mL (p<0.0001) in a dose-dependent manner. The number of SCC-4 treated cells with 1 μg/mL that migrated through the membrane was statistically different from 50 μg/mL (p<0.001) and 100 μg/mL (p<0.0001), and between 50 μg/mL and 100 μg/mL (p<0.01). Cetuximab 50 μg/mL inhibited cell invasion through the MatrigelTM compared with SCC-4 control cells (p<0.01). Cetuximab 50 μg/mL affected the organization of the actin cytoskeleton. Cetuximab has an inhibitory effect on actin cytoskeleton organization, cell migration and invasion, suggesting that Cetuximab treatment can be important to avoid oral squamous cell carcinoma metastasis.

High density oligonucleotide and DNA probe arrays for the analysis of target DNA

The acquisition of sequence, expression and other information concerning genetic material constitutes a crucial component of the modern revolution in molecular biology. One important advance in this area is the development of high density oligonucleotide/DNA microarrays which allows the rapid sequence analysis of genomic target samples in addition to diagnostic possibilities with respect to genetic and infectious disease. In the present article we review protocols for the design of such microarrays and their principles of operation. Together with a look at some recent applications we include brief remarks as to the possibilities for the future.

Interactions of HIV-1 TAR RNA with Tat-derived peptides discriminated by on-line acoustic wave detector

The human immunodeficiency virus type I is strongly regulated at the transcriptional level through the interaction of an 86-amino acid protein (Tat) with a viral messenger RNA transcript. Accordingly, the binding of this protein and other cellular factors to the RNA has constituted a significant target for the development of anti-HIV drugs. In the present work, we describe the detection of the binding of two Tat-derived peptides, of 12 and 40 amino acids in length, with chemically synthesized RNA by an acoustic wave sensor. Immobilization of the nucleic acid to the sensor surface, which was incorporated in an on-line system, was effected using the biotin-neutravidin interaction. As expected, the changes in series resonance frequency and motional resistance for the two peptides indicate reversible interactions in both cases that can be further characterized by the calculation of kinetic off-rates. Of particular interest is the nature of the two frequency-based signals, which are in opposite directions for the two peptides. These results together with those obtained for the surface interactions of neutravidin and biotinylated RNA confirm that the thickness shear mode sensor, mass-response model involving the well-known Sauerbrey expression is invalid when applied to operation in liquids.

Hybridization of complementary strand and single-base mutated oligonucleotides detected with an on-line acoustic wave sensor

The hybridization of a biotinylated 25-mer oligonucleotide probe with complementary, non-complementary and single-base mutated 25-mer targets at the liquid-solid (neutravidin-modified) interface of a thickness-shear mode acoustic wave device was studied. The sensor was incorporated into an on-line configuration capable of both variable flow and stop-flow experiments. Under ambient temperature conditions different signals were obtained for the complementary and non-complementary cases. At higher temperatures, the former system exhibits behaviour characteristic of the production of intermediate duplexes which are decomposed by the re-introduction of buffer solution. The use of these conditions allows the distinction of binding events involving a set of single-base mutated 25-mers. Different responses were obtained depending on both the nature of the instigated mismatch in base pairing and on the location of mutation.

Acoustic waves and the real-time study of biochemical macromolecules at the liquid/solid interface

The adsorption of the proteins, bovine serum albumin, fibrinogen, avidin and neutravidin (non-glycosylated form of avidin) to a variety of surfaces imposed on thickness shear mode sensors in examined in a flow-injection analysis format. In all cases, adsorption of these moieties was essentially irreversible, although the magnitude of adsorption was dependent on surface free energy and functional group chemistry. Also described is the direct, real-time detection of the binding of peptides to HIV-1 TAR RNA bound on a thickness-shear mode (TSM) sensor surface. The results clearly indicate that responses are discriminatory for two different peptides. In order to provide a theoretical backcloth for the experimental measurements, a new model for the operation of the TSM in liquids is presented.