Polylactide-based microspheres prepared using solid-state copolymerized chitosan and d,l-lactide.

Amphiphilic chitosan-g-poly(d,l-lactide) copolymers have been manufactured via solid-state mechanochemical copolymerization and tailored to design polyester-based microspheres for tissue engineering. A single-step solid-state reactive blending (SSRB) using low-temperature co-extrusion has been used to prepare these copolymers. These materials have been valorized to stabilize microspheres processed by an oil/water emulsion evaporation technique. Introduction of the copolymers either in water or in the oil phase of the emulsion allowed to replace a non-degradable emulsifier typically used for microparticle preparation. To enhance cell adhesion, these copolymers were also tailored to bring amino-saccharide positively charged segments to the microbead surface. Size distribution, surface morphology, and total microparticle yield have been studied and optimized as a function of the copolymer composition.

[Mechanism of the reaction of glutaraldehyde with chitosan].

The regularities of the reaction of aminopolysaccharide chitosan with glutaraldehyde (GA) have been considered. The equilibrium forms of GA in water have been thoroughly studied by NMR spectroscopy. It has been established that at pH 5.6, the exchange of the protons of O=CHCH2 groups for deuterium occurs, indicating the presence of an anion, a product of the first stage of the aldol reaction; at pH > 7.2, the formation of the products of an aldol reaction and aldol condensation takes place. The kinetics of the reaction between the amino groups of chitosan and GA, the kinetics of gel formation in chitosan solutions in the presence of GA, and the kinetics of changes in the rigidity of gels formed have been studied by UV spectroscopy. IR spectra of cross-linked chitosan have been obtained. It has been shown that chitosan catalyzes the polymerization of GA to form inhomogeneous products; in this process, the length of oligomeric chains in modified or cross-linked chitosan and the concentration of coupled bonds increase with the GA concentration and pH of the reaction medium.

[Radiation methods for monitoring parameters of X-ray diagnostic apparatuses].

Capabilities of noninvasive dosimeters for radiation monitoring of parameters of X-ray diagnostic apparatuses are considered. It is shown that monitoring of the half-value layer using the Unfors-Xi detector makes it possible to correct the results of radiation contrast measurement taking into account the actual (measured) values of half-value layers. It also simplifies the procedure for half-value layer monitoring in radiation safety measurements.

[A heterogeneous air-filled ionization chamber without external power supply].

Possibility of the use of heterogeneous ionization chambers with air-filled interelectrode space for X-ray detection is discussed. Qualitative analysis of the process of generation of ionization current in the heterogeneous chamber without external power supply is performed. Experimental data presented in this work show that ionization chambers with triple heterogeneous structure provide high operating characteristics when connected in active integrator and current-to-voltage converter circuits (especially in the case of differential connection circuit).

[A study of digital x-ray detection systems with optical image transfer].

The work describes the performance characteristics of roentgenographic screen-optics-CCD-matrix systems based on the KRTs-1 digital roentgenographic system developed at SpektrAp, Ltd. The efficiency of X-ray detection is estimated from the minimum detectable contrast and maximum resolution. The effect of the X-ray imaging system components on the efficiency of detection is studied. The X-ray screen structure is shown to have a crucial effect on the efficiency of detection as estimated from the image resolution.

[Ionization chambers with preamplifiers for X-ray exposure metering systems].

Ionization chambers with preamplifiers available from SpektrAp, Ltd., are described. The ionization chambers are intended for use in X-ray automatic exposure systems of diagnostic X-ray apparatuses. The ionization chambers provide automated matching of their sensitivity to the sensitivity of modern intensifying screens. The preamplifier provides direct integration of the ionization chamber current. It can operate within the entire dose rate range of the roentgenographic mode and meets the requirements of modern diagnostic X-ray detectors to the dose range. Special techniques for increasing the noise immunity of preamplifiers are described. Performance specifications of the ionization chambers and preamplifiers are given.

[Development of systems for digital fluorography and roentgenography on the basis of x-ray image intensifiers (XRII)].

A comparative review of characteristics of digital detectors for fluorography and roentgenography. Modern digital detection systems on the basis of X-ray image intensifiers (XRII) were demonstrated to be superior in terms of both X-ray image parameters and radiation safety of patient. Specifications of a new detection system for fluorography and roentgenography available from SpektrAP Ltd. (Russia) were described.

[Determination of the detective efficiency of X-ray diagnostic systems by visual assessment of the maximal resolution].

Methods of calculation of the detective efficiency of X-ray diagnostic systems and corresponding radiation dose are discussed. These methods are based on evaluation of limiting visually detectable resolution of a test pattern. Resulting dose values are compared with those inherent in an ideal system.

[Determination of total filtration and half attenuation layer in X-ray diagnostic units by relative radiation output]. / Opredelenie summarnoi filtratsii i sloia polovinnogo oslableniia v rentgenodiagnosticheskikh apparatakh po otnositel'nomu radiatsionnomu vykhodu.

Described is a relatively simple technique applicable to estimating the independent and additional filtration of X-ray images by the relative radiation output with a voltage generation range of 50 to 120 kB. It is shown as possible to determine the half-attenuation first layer in its aluminum equivalent and without using any aluminum filters. The suggested technique can be used in turn-over and regular tests of medical X-ray units as well as in their exploitation.

[Determination of the efficiency of registration of X-ray diagnostic systems by visually detected minimal radiation contrast]. / Opredelenie registratsii éffektivnosti registratsii rentgenovskikh diagnosticheskikh sistem po vizual'no vyiavliaemomu minimal'nomu radiatsionnomu kontrastu.

Described in the paper is a relatively simple method for the determination of the efficiency of registration of X-ray diagnostic systems by the whole tract of transformation of radiation contrast from the spot of contrast-sensitivity test to the visual registration of image. It is just enough to have the contrast sensitivity test and to measure the dose at test location. On the basis of the visually registered minimal contrast the efficiency of registration of a diagnostic system is evaluated by the radiation-contrast parameter. The suggested method can be used at handover tests and in testing the X-ray systems during their exploitation.

[Portable small size X-ray dosimeter DER-01M designed for dose control and its intensity in X-ray diagnostics]. / Perenosnoi malogabaritnyi rentgenovskii dozimetr DER-01M dlia kontrolia dozy i moshchnosti pri rentgenodiagnostike.

Described in the paper is a portable small-size X-ray dosimeter DER-0.1 M designed by the Research Institute for Introscopy, Research Production Amalgamation "Spectr", for monitoring the dose and its intensity in the manufacturing and exploitation of general-purpose and specialized X-ray units. A flat-parallel ionizing chamber is used in the device as a radiation detector. The related technical characteristics are contained in the paper.

[Analysis of dosage loads on patients and personnel in the use of "FSTs-U-01" x-ray image-enhanced fluorography]. / Analiz dozovykh nagruzok na patsientov i personal pri rabote na fliuorografe s URI "FSTs-U-01."

The paper considers the specific features of formation of dosage loads during studies on a digital fluorograph with movable X-ray image amplifier. It is concluded that smaller weekly dosage loads should be used for this type of fluorographs than those described in relevant normative documents.

[The ID-03 X-ray dosimeter for monitoring the radiation parameters of X-ray equipment in roentgenography]. / Rentgenovskii dozimetr ID-03 dlia kontrolia radiatsionnykh parametrov rentgenovskikh ustanovok v rezhime rentgenografii.

The paper presents an [symbol: see text]-03 X-ray dosimeter designed by the Research Institute of Introscopy, Spektr Moscow Research-and-Production Association, for monitoring the radiation parameters of X-ray plants at roentgenography. A Si(Li)-based semiconductor detector with the p-i-n structure is used as a detector of X-ray radiation. The technical data of the dosimeter are given.