[Experimental studies of the biomechanical properties of the cornea]. / Eksperimental'nye issledovaniya biomekhanicheskikh svoistv rogovitsy.

The review presents the results of experimental studies of the biomechanical properties of the cornea. Selective evaluation of the individual corneal structures (for example, limiting membranes) using classical mechanical tests is to a certain extent limited due to the rather small thickness of these structures and the related difficulties in sample fixation. In real practice, the use of a method better adapted for conducting such studies - atomic force microscopy (AFM) - remains promising, since on the one hand it eliminates the need for mechanical capture and retention of the sample, and on the other - provides the capability for studying its segments separately.

Viscoelasticity in simple indentation-cycle experiments: a computational study.

Instrumented indentation has become an indispensable tool for quantitative analysis of the mechanical properties of soft polymers and biological samples at different length scales. These types of samples are known for their prominent viscoelastic behavior, and attempts to calculate such properties from the indentation data are constantly made. The simplest indentation experiment presents a cycle of approach (deepening into the sample) and retraction of the indenter, with the output of the force and indentation depth as functions of time and a force versus indentation dependency (force curve). The linear viscoelastic theory based on the elastic-viscoelastic correspondence principle might predict the shape of force curves based on the experimental conditions and underlying relaxation function of the sample. Here, we conducted a computational analysis based on this theory and studied how the force curves were affected by the indenter geometry, type of indentation (triangular or sinusoidal ramp), and the relaxation functions. The relaxation functions of both traditional and fractional viscoelastic models were considered. The curves obtained from the analytical solutions, numerical algorithm and finite element simulations matched each other well. Common trends for the curve-related parameters (apparent Young's modulus, normalized hysteresis area, and curve exponent) were revealed. Importantly, the apparent Young's modulus, obtained by fitting the approach curve to the elastic model, demonstrated a direct relation to the relaxation function for all the tested cases. The study will help researchers to verify which model is more appropriate for the sample description without extensive calculations from the basic curve parameters and their dependency on the indentation rate.

Biomechanical properties of the lens capsule: A review.

The lens capsule, a thin specialized basement membrane that encloses the crystalline lens, is essential for both the structural and biomechanical integrity of the lens. Knowing the mechanical properties of the lens capsule is important for understanding its physiological functioning, role in accommodation, age-related changes, and for providing a better treatment of a cataract. In this review, we have described the techniques used for the lens capsule biomechanical testing on the macro- and microscale and summarized the current knowledge about its mechanical properties.

Digging deeper: structural background of PEGylated fibrin gels in cell migration and lumenogenesis.

Fibrin is a well-known tool in tissue engineering, but the structure of its modifications created to improve its properties remains undiscussed despite its importance, e.g. in designing biomaterials that ensure cell migration and lumenogenesis. We sought to uncover the structural aspects of PEGylated fibrin hydrogels shown to contribute to angiogenesis. The analysis of the small-angle X-ray scattering (SAXS) data and ab initio modeling revealed that the PEGylation of fibrinogen led to the formation of oligomeric species, which are larger at a higher PEG : fibrinogen molar ratio. The improvement of optical properties was provided by the decrease in aggregates' sizes and also by retaining the bound water. Compared to the native fibrin, the structure of the 5 : 1 PEGylated fibrin gel consisted of homogenously distributed flexible fibrils with a smaller space between them. Moreover, as arginylglycylaspartic acid (RGD) sites may be partly bound to PEG-NHS or masked because of the oligomerization, the number of adhesion sites may be slightly reduced that may provide the better cell migration and formation of continuous capillary-like structures.

Viscoelastic mapping of cells based on fast force volume and PeakForce Tapping.

Development of fast force volume (FFV), PeakForce Tapping (PFT), and related AFM techniques allow fast acquisition and mapping of a sample's mechanical properties. The methods are well-suited for studying soft biological samples like living cells in a liquid environment. However, the question remains how the measured mechanical properties are related to those acquired with the classical force volume (FV) technique conducted at low indentation rates. The difference is coming mostly from the pronounced viscoelastic behavior of cells, making apparent elastic parameters depending on the probing rate. Here, the viscoelastic analysis was applied directly to the force curves acquired with force volume or PeakForce Tapping by their post-processing based on the Ting's model. Maps from classical force volume, FFV and PFT obtained using special PFT cantilevers and cantilevers modified with microspheres were compared here. With the correct viscoelastic model, which was found to be the power-law rheology model, all the techniques have provided self-consistent results. The techniques were further modified for the mapping of the viscoelastic model-independent complex Young's modulus.

Tissue Engineered Neural Constructs Composed of Neural Precursor Cells, Recombinant Spidroin and PRP for Neural Tissue Regeneration.

We have designed a novel two-component matrix (SPRPix) for the encapsulation of directly reprogrammed human neural precursor cells (drNPC). The matrix is comprised of 1) a solid anisotropic complex scaffold prepared by electrospinning a mixture of recombinant analogues of the spider dragline silk proteins - spidroin 1 (rS1/9) and spidroin 2 (rS2/12) - and polycaprolactone (PCL) (rSS-PCL), and 2) a "liquid matrix" based on platelet-rich plasma (PRP). The combination of PRP and spidroin promoted drNPC proliferation with the formation of neural tissue organoids and dramatically activated neurogenesis. Differentiation of drNPCs generated large numbers of ßIII-tubulin and MAP2 positive neurons as well as some GFAP-positive astrocytes, which likely had a neuronal supporting function. Interestingly the SPRPix microfibrils appeared to provide strong guidance cues as the differentiating neurons oriented their processes parallel to them. Implantation of the SPRPix matrix containing human drNPC into the brain and spinal cord of two healthy Rhesus macaque monkeys showed good biocompatibility: no astroglial and microglial reaction was present around the implanted construct. Importantly, the human drNPCs survived for the 3 month study period and differentiated into MAP2 positive neurons. Tissue engineered constructs based on SPRPix exhibits important attributes that warrant further examination in spinal cord injury treatment.

[Developing forensic reference database by 18 autosomal STR for DNA identification in Republic of Belarus].

For the Republic of Belarus, development of a forensic reference database on the basis of 18 autosomal microsatellites (STR) using a population dataset (N = 1040), "familial" genotypic dataset (N = 2550) obtained from expertise performance of paternity testing, and a dataset of genotypes from a criminal registration database (N = 8756) is described. Population samples studied consist of 80% ethnic Belarusians and 20% individuals of other nationality or of mixed origin (by questionnaire data). Genotypes of 12346 inhabitants of the Republic of Belarus from 118 regional samples studied by 18 autosomal microsatellites are included in the sample: 16 tetranucleotide STR (D2S1338, TPOX, D3S1358, CSF1PO, D5S818, D8S1179, D7S820, THO1, vWA, D13S317, D16S539, D18S51, D19S433, D21S11, F13B, and FGA) and two pentanucleotide STR (Penta D and Penta E). The samples studied are in Hardy­Weinberg equilibrium according to distribution of genotypes by 18 STR. Significant differences were not detected between discrete populations or between samples from various historical ethnographic regions of the Republic of Belarus (Western and Eastern Polesie, Podneprovye, Ponemanye, Poozerye, and Center), which indicates the absence of prominent genetic differentiation. Statistically significant differences between the studied genotypic datasets also were not detected, which made it possible to combine the datasets and consider the total sample as a unified forensic reference database for 18 "criminalistic" STR loci. Differences between reference database of the Republic of Belarus and Russians and Ukrainians by the distribution of the range of autosomal STR also were not detected, corresponding to a close genetic relationship of the three Eastern Slavic nations mediated by common origin and intense mutual migrations. Significant differences by separate STR loci between the reference database of Republic of Belarus and populations of Southern and Western Slavs were observed. The necessity of using original reference database for support of forensic expertise practice in the Republic of Belarus was demonstrated.

Porphyrin effect on the surface morphology of amphiphilic polymers as observed by atomic force microscopy.

Complexes of porphyrin photosensitizers (PPS) with triblock copolymers of ethylene- and propylene oxide - Pluronics(®) - exhibit markedly increased activity in the generation of singlet oxygen in aqueous media, as compared to pure porphyrins. Pluronics are amphiphilic polymers with surfactant properties suitable for a number of medical applications. PPS-Pluronic systems are considered as promising agents for photodynamic therapy which implies generation of singlet oxygen in the water-based human tissue. Importantly, Pluronics are capable of solubilization of not only water-soluble, but also hydrophobic PPS providing their transfer into the aqueous phase. It has been shown earlier that specific interactions of PPS with Pluronics must play a primary role for the photocatalytic properties of PPS-Pluronic systems. In the process of solubilization of a hydrophobic porphyrin by a Pluronic, both components are dissolved in an organic solvent, which is then removed, and the dry film is re-dissolved in water. Apparently, the initial binding between the porphyrin and the lipophilic part of the polymer takes place already at the stage of the film formation. We applied atomic force microscopy (AFM) to visualize structures formed by Pluronics upon their interactions with meso-tetraphenylporphyrin (TPP). We studied the surface structure of Pluronics(®) F87, F108 and F127 crystallized alone or together with TPP on silicon substrates from chloroform solutions. We found Pluronics to form similar dendritic structures independently of their molecular weight and degree of hydrophobicity. In the presence of TPP, though, we observed formation of distinct convex structures on top of the Pluronic dendrites. These structures appeared to consist of multiple flat layers placed on top of each other. Their sizes varied among the three Pluronics. We believe that TPP aggregates interact with the hydrophobic units of Pluronics causing the polymer chains to pack themselves in a distinct manner around those TPP-containing "cores". These interactions apparently direct formation of complexes between the porphyrin and the polymer upon their dissolution in water, thus resulting in the encapsulation of TPP aggregates inside a Pluronic micelle. A single mechanism for the TPP solubilization by Pluronics is consistent with the same catalytic activity of the three TPP-Pluronic systems observed in the photooxidation of tryptophan.

[Late diagnosis of celiac disease].

A 45 year-old woman presented with late-diagnosed celiac disease, marked disorders of calcium and bone metabolism, and severe osteoporosis. Weak enteral symptoms delayed diagnosis. High efficiency of agluten and vitamin D therapy was documented.

A bioluminescent signal system: detection of chemical toxicants in water.

Prototype technologies of a bioluminescent signal system (BSS) based on the luminous bacterium Photobacterium phosphoreum and three enzymatic bioluminescence systems have been proposed for detecting and signalling the presence of toxicants in water systems. A number of pesticides, mostly known as poisonous substances, similar in their structures and physicochemical properties, have been taken as model compounds of chemical agents. The effect of toxicants (organophosphates, derivatives of dithiocarbamide acid, and pyrethroid preparations) on the bioluminescence of the four systems has been analysed. EC(50) and EC(80) have been determined and compared to the maximum permissible concentration for each of the analysed substances. The triple-enzyme systems with ADH and trypsin have been shown to be more sensitive to organophosphorous compounds (0.13-11 mg/L), while the triple-enzyme system with trypsin is highly sensitive to lipotropic poison, a derivative of dithiocarbamine acid (0.03 mg/L). Sensitivities of the triple-enzyme systems to pyrethroid preparations are similar to those of luminous bacteria (0.9-5 mg/L). The results can be used to construct an alarm-test bioluminescence system for detecting chemical toxicants, based on intact bacteria or enzyme systems.

The effect of porphyrin supramolecular structure on singlet oxygen photogeneration.

This work is to show that activity of porphyrins in singlet oxygen generation (SOG) is determined not only by their molecular structure but also by supramolecular structure of porphyrin containing systems. This is demonstrated by results of studies of SOG in the gas phase by vacuum deposited tetraphenylporphyrin (TPP) layers under photoexcitation conditions. The structure of the layers was studied by atomic force microscopy (AFM), TEM in diffraction regime (TED) and by the flicker-noise spectroscopy (FNS) method. It was shown that substrates affect the deposited layers structure only at earlier stages of the layer formation. AFM and TED data, together with FNS quantitative parameters of TPP layers, show directly that the chemical activity of solid-phase systems can be determined not only by their chemical nature but also by their supramolecular structure.

[Analysis of association of Col1a1 gene alleles with the development of osteoporosis]. / Analiz assotsiatsii allelei gena Col1a1 s razvitiem osteoporoza.

Allele frequencies of the G-->T polymorphism at the regulatory region of the Collal gene in the population of the northwestern Russia (control group) and in osteoporotic patients were estimated by the RFLP method based on PCR-mediated site-directed mutagenesis. Three patient groups with radiologically confirmed osteoporosis were examined. Group 1 consisted of 64 patients with severe osteoporosis complicated by fractures (SO); group 2 included 15 children with idiopathic osteoporosis (IO); group 3 consisted of 98 women with postmenopausal osteoporosis developed at the background of estradiol-deficiency state (PMO). The frequency of functionally defective allele s in the control group was 16.7%. It was statistically different from that in the SO patients (48.4%) (P < 0.01) and in the IO children (40%) (P < 0.01). The frequency of allele s in the PMO patients constituted 23.0% and it was similar to that in the control group (P > 0.05). Analysis of the Collal alleles provides early detection of the individuals with hereditary predisposition to osteoporosis and prophylaxis of the disease at the presymptomatic stage.

Modal liquid crystal wavefront corrector.

Results are presented of the properties of a liquid crystal wavefront corrector for adaptive optics. The device is controlled using modal addressing in which case the device behaves more like a continuous facesheet deformable mirror than a segmented one. Furthermore, the width and shape of the influence functions are electrically controllable. We describe the construction of the device, the optical properties, and we show experimental results of low order aberration generation.

[Evaluation of aqueous compartments of the body by integral bioimpedance spectrometry in x-ray surgical interventions in children]. / Otsenka vod'nykh sektorov organizma metodom integral'noi bioimpedansnoi spektrometrii pri rentgenokhirurgicheskikh vmeshatel'stvakh u detei.

There were studied 14 children (mean age 5.71 +/- 0.60 years, body weight 18.95 +/- 3.50 kg, height 101.0 +/- 4.03 cm) with initially normal osmotic and volumic status. Plasma osmolarity, blood aldosterone level, aqueous compartments balance were (evaluated by segmented bioimpedance spectrometry), urine osmolarity and diuresis were investigated after bolus injection of x-ray contrast agent (RCA) urografin-60% (mean volume 2 ml/kg for 2-4 sec). A statistically significant gradual decrease in the total volume of water (TVW) in the organism was observed, with 8.53% deficiency of TVW by the second hour after RCA injection in comparison with the initial level. TVW deficiency developed as the result of diuresis which increased 7-fold in the presence of increased plasma osmolarity after injection of RCA bolus. Correction of the volume of circulating blood and plasma was carried out mainly at the expense of intracellular liquid, whose deficiency was actually 4.5 times higher than of extracellular liquid. Bioimpedance spectrometry indicated centralized redistribution of water in the organism, as TVW deficiency was mainly due to water in the limbs. The results indicate the need in infusion therapy after RCA injection in order to correct the resultant water deficit.

[Experimental basis and clinical evaluation of indomethacin efficacy in patients with ischemic stroke]. / Eksperimental'noe obosnovanie i otsenka éffektivnosti primeneniia indometatsina pri lechenii bol'nykh s ishemicheskim insul'tom.

Experimental work provides evidence for a benefit from indometacinum use (3 mg/kg daily for 4 days) in model of focal brain ischemia in rabbits was. The efficacy of this drug (25 mg 3 times a day for 14-18 days) in patients with ischemic stroke has been studied. The focal brain ischemia in rabbits was induced by 3 hours' bilateral occlusion of common carotid arteries. After that several parameters of hydroionic homeostasis, lactatdehydrogenase and superoxide dismutase were measured in serum and CSF. Neurological status, hemostasis parameters and blood lipid spectrum were examined in patients with ischemic stroke. The results clearly show the antihypoxic effect of indometacinum by bringing ion balance as well as the activities of lactate dehydrogenase's and superoxide dismutase to normal values. Decrease of neurological deficit, improvement of lipid spectrum and haemocoagulating system were observed in the treated patients with ischemic stroke.

[An HIV prevalence study by means of sentinel epidemiological surveillance among injection narcotic abusers in Saint Petersburg]. / Izuchenie rasprostranennosti VICh metodom dozornogo épidnadzora sredi potrebitelei in''ektsionnykh narkotikov v Sankt-Peterburge.

The data on the study of the spread of HIV infection among injecting drug users in St. Petersburg, carried out by the method of the random testing of blood remaining in used syringes, are presented. Injecting drug users visiting buses working in accordance with the program "Buses for Assistance to Drug Addicts" were chosen as a study group. The exchange of syringes was one of the elements of this program. The work was carried out in two areas with a high concentration of drug users. The eluates from syringes used by 300 persons were studied. The average rate of the spread of HIV in the cohort under study was 12%. The results were indicative of a high degree of the spread of HIV among injecting drug users in St. Petersburg. Epidemiological patrol surveillance proved to be an effective method for the evaluation of the epidemiological situation in a highly inaccessible group of the population.

[The morphofunctional characteristics of the duodenum in an osteopenic syndrome in children and adolescents]. / Morfofunktsional'nye osobennosti dvenadtsatiperstnoi kishki pri osteopenicheskom sindrome u detei i podrostkov.

AIM: The study of duodenal morphology in children and adolescents with skeletal deformity. MATERIALS AND METHODS: Clinical, hormonal examinations, x-ray investigation of the skeleton with spinal NMR-tomography, gastroduodenoscopy with target biopsy were performed in 41 patients aged 7 to 18 on after treatment for broken spine. RESULTS: Atrophic duodenitis found in most of the patients presented without dyspepsia, with symptoms of duodenitis in 8 patients, osteoporosis in 36% of patients. NMR-tomography rejected compression-broken spine in 22 patients. CONCLUSION: Disturbed absorption of calcium and atrophic alterations in the duodenal mucosa are thought responsible for disturbance of calcium metabolism and formation of bone tissue.

[Radiation diagnosis of involutional osteopenia]. / Luchevaia diagnostika involitsionnoi osteopenii.

160 patients with involutive osteopaenia were investigated. The diagnostic possibilities of roentgenography, magnetic resonance imaging and computed tomography were evaluated. There was determined that roentgenography gives the possibility to determine the common localisation and the expressiveness of the pathologic process. MRI and CT give a valuable additional information on early stages of osteopaenia and it's complications.

[ATP-dependent proteinase La from Escherichia coli]. / ATP-zavisimaia proteinaza La iz Escherichia coli.

Homogeneous preparations of the ATP-dependent La proteinase from E. coli and two its mutant forms, containing an alanine residue instead of Ser679 or Ser368, were isolated. Ser679 was shown to be catalytically active rather than Ser368 as suggested in the literature. To choose between the alternative structures of the gene lon La proteinase fragments within the controversial regions were analysed and the gene structure established at the Laboratory of Proteolytic Enzymes (Institute of Bioorganic Chemistry) was confirmed. Inactivity of La proteinase in some in vitro systems suggests its functioning in vivo to be not autonomous, requiring additional factors.