Hydrogel microspheres: influence of chemical composition on surface morphology, local elastic properties, and bulk mechanical characteristics

Hydrogel microspheres, beads, and capsules of uniform size, differing in their chemical composition, have been prepared by electrostatic complex formation of sodium alginate with divalent cations and polycations. These have served as model spheres to study the influence of the chemical composition on both surface characteristics and bulk mechanical properties. Resistance to compression experiments yielding the compression work clearly identified differences as a function of the composition, with forces at maximal compression in the range of 34-455 mN. The suitability and informative value of atomic force microscopy have been confirmed for the case where surface characterization is performed in a liquid environment equivalent to physiological conditions. Surface imaging and mechanical response to indentation revealed different average surface roughness and Young's moduli for all hydrogel types ranging from 0.9 to 14.4 nm and from 0.4 to 440 kPa, respectively. The hydrogels exhibited pure elastic behavior. Despite a relatively high standard deviation, resulting from both surface and batch heterogeneity, nonoverlapping ranges of Young's moduli were reproducibly identified for the selected model spheres. The findings indicate the reliability of contact mode atomic force microscopy to quantify local surface properties, which may have an impact on the biocompatibility of alginate-based hydrogel materials of different composition and conditions of preparation. Moreover, it seems that local elastic properties and bulk mechanical characteristics are subject to analogous composition influences.     

Cancer cell recognition--mechanical phenotype

The major characteristics of cancer metastasis is the ability of the primary tumor cells to migrate by way of the blood or lymph vessels and to form tumors at multiple, distant sites. There are evidences that cancer progression is characterized by disruption and/or reorganization of cytoskeleton (i.e. cellular scaffold). This is accompanied by various molecular alterations influencing the overall mechanical resistance of cells. Current approach in diagnosis focuses mainly on microbiological, immunological, and pathological aspects rather than on the biomechanics of diseases. The determination of mechanical properties of an individual living cell has became possible with the development of local measurement techniques, such as atomic force microscopy, magnetic or optical tweezers. The advantage of them lies in the capability to measure living cells at a single cell level and in liquid conditions, close to natural environment. Here, we present the studies on mechanical properties of single cells originating from various cancers. The results show that, independently of the cancer type (bladder, melanoma, prostate, breast and colon), single cells are characterized by the lower Young's modulus, denoting higher deformability of cancerous cells. However, the obtained Young's modulus values were dependent on various factors, like the properties of substrates used for cell growth, force loading rate, or indentation depth. Their influence on elastic properties of cells was considered. Based on these findings, the identification of cancerous cells based on their elastic properties was performed. These results proved the AFM capability in recognition of a single, mechanically altered cell, also in cases when morphological changes are not visible. The quantitative analysis of cell deformability carried out using normal (reference) and cancerous cells and, more precisely, their characterization (qualitative and quantitative) can have a significant impact on the development of methodological approaches toward precise identification of pathological cells and would allow for more effective detection of cancer-related changes.     

The reaction of 2-nitrosopyridine with nitrile oxides: First synthesis of 1,2,4-triazolo[1,5-a]pyridine 1,3-Di-N-oxides

Reactions of 2-nitrosopyridine with nitrile oxides afford either the novel title compounds or the corresponding 1,2,4-triazolo[1,5-a]pyridine 3-oxides.     

Sample preparation procedure for PIXE elemental analysis on soft tissues

Neutral aqueous solutions of Nickel II-diethylenetriaminepentaacetate (DTPA) were irradiated using -rays both in the presence and in the absence of oxygen. A radiolytic mechanism has been proposed and discussed. It has been suggested that the radiolytic degradation of the ligand is due to the formation of OH^* during radiolysis.     

Friction force microscopy as an alternative method to probe molecular interactions

Friction force microscopy was applied to study protein-carbohydrate interactions that are important in many cellular recognition processes. The expression and structure of carbohydrates can be investigated using lectins as molecular probes since they recognize different types of sugar molecules. Lectins (concanavalin A and lentil lectin, recognizing mannose-type carbohydrates) were attached to the probing tip and carboxypeptidase Y (possessing complementary carbohydrates) was immobilized on a modified glass surface using microcontact printing. The results obtained from friction force maps and dependencies on the loading rate (measured in a physiological buffer) were divided in two distinct groups. The first group of results obtained for lectin-protein complexes was assigned to molecular recognition events, whereas the other including all control measurements was attributed to nonspecific interaction. All results presented here indicate that friction force microscopy can be successfully employed to study recognition processes.     

Structural, thermodynamic and mechanical properties of Zr-based binary nanowires (ZrCu and Zr2Ni) by molecular dynamics

We present molecular dynamics simulation results of two representative cases of nanowires (NWs) of binary alloys, a glass former (ZrCu) and an alloy that becomes amorphous under chemical substitution of its elements (Zr₂Ni). The simulations were based on semiempirical potential models in analogy to the tight-binding scheme in the second moment approximation. We explored the structural characteristics of NWs of various sizes, and we determined several quantities like melting points, strain–stress curves and Young's modulus. We found that for all NWs, the Zr terminations are energetically favored, while Zr₂Ni NWs adopt rounded cross-sectional shapes and ZrCu, octagonal. From the obtained results, it is established that most of the NW properties differ substantially from those exhibited by their bulk counterparts; e.g., lower melting points and greater yield strengths, while under tensile strain they exhibit clear brittle character. In addition, it is found that their mechanical response to deformation is not very sensitive to the imposed strain rates.