Jacek Michalik

Effect of radiation sterilization on the osteoinductive properties and the rate of remodeling of bone implants preserved by lyophilization and deep-freezing

The effect of various doses of ionizing radiation on the osteoinductive properties of decalcified bone matrices implanted heterotopically and on the rate of remodeling of nondecalcified bone grafts implanted orthotopically in allogeneic systems was studied. Decalcified bone matrices and nondecalcified bone grafts were preserved by lyophilization or by deep-freezing and were subsequently irradiated with appropriate doses at room temperature or at -72 degrees. Lyophilized matrices irradiated at room temperature with 35 and 50 kGy, respectively, were completely resorbed five weeks after heterotopic implantation into the muscles and did not induce osteogenesis, whereas the resorption of deep-frozen ones irradiated with the same doses at -72 degrees was slower and new bone formation was induced. The preservation of the osteoinductive capacity of irradiated, deep-frozen matrices may depend on two factors: reduction of radiation damage on the inducing agents and collagen irradiated in the presence of water, which may diminish the rate of matrix resorption. The rate of remodeling of undecalcified deep-frozen bone implants irradiated at -72 degrees and grafted orthotopically was higher than that of lyophilized ones irradiated at room temperature. It is possible that the temperature during irradiation plays a critical role in protection against radiation damage.

Sensitivity of the electron spin resonance technique as applied in histochemical research on normal and pathological calcified tissues

SummaryThe electron spin resonance (ESR) technique is proposed as a microchemical and/or histochemical method in research on mineralized tissues.It has been described in previous papers that ionizing radiation evokes stable paramagnetic centres in the crystalline fraction of mineral constituents of calcified tissues. These centres were used as a label in studies on resorption and creeping substitution of bone grafts.In this paper the sensitivity of the method and its application for determination of the crystallinity of various mammalian tissues were described.It was shown that: a) three single Haversian systems (osteons) isolated from a ca. 100 μm thick undecalcified section of human compact bone weighing around 10−4 g could be measured by the ESR technique; b) the crystallinity of mineral constituents of normal and pathological calcified tissues could be estimated as the ratio of the concentration of stable paramagnetic centres to the total ash content.Comparative ESR measurements were performed on compact bone of various mammalian species, human enamel and dentin, as well as on ageing bovine cartilage and atherosclerotic human aortas.

Multifrequency EPR study of carbonate- and sulfate-derived radicals produced by radiation in shells and corallite

Abstract Strzelczak, G., Vanhaelewyn, G., Stachowicz, W., Goovaerts, E., Callens, F. and Michalik, J. Multifrequency EPR Study of Carbonate- and Sulfate-Derived Radicals Produced by Radiation in Shells and Corallite. Shells of two sea mollusks (Venus sp.), pearl oyster (Meleagrina vulgaris) and corallite (white coral) were exposed to ionizing radiation (γ and X rays) and then examined by EPR spectroscopy in X, Q and W band. The resulting spectra were analyzed and the g values of the EPR lines in the multicomponent spectra were determined. The increased resolution in Q- and W-band spectra allowed us to assign the observed lines to CO2– ion radicals (isotropic and orthorhombic), SO2– isotropic, SO3– (isotropic and axial), and Mn2+ species. The assignments were confirmed by simulations of the spectra. Practical implications for the use of Q and/or W band in low-dose quantitative EPR measurements for dating and for accidental dose estimation are discussed.

Electron-Nuclear Double Resonance of Human Tooth Enamel Heated at 400°C

Abstract. Powdered tooth enamel heated at 400°C has been examined with electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIEPR) methods and compared with hydroxyapatite synthesized at high temperature. The EPR spectrum of the tooth enamel sample consists mainly of signals assigned to O− and CO2− radicals, in contradistinction to the synthetic apatite sample, where signals of O− and CO33− were detected. The ENDOR results of heated enamel show that the O− radical is located at an A site and interacts with three unequivalent sets of 31P nuclei and two unequivalent protons. This supports the model proposed for synthetic apatite. The EIEPR results show that the 31P and 1H ENDOR resonances originate from both O− and CO2− radicals and that the 23Na and 19F resonances originate only from a CO2− radical located probably at the surface.

Interaction of silver atoms with ethylene in Ag-SAPO-11 molecular sieve : an EPR and DFT study

The formation of silver–ethylene complexes in dehydrated Ag-SAPO-11 molecular sieve have been observed by electron paramagnetic resonance spectroscopy (EPR) after γ-irradiation at 77 K. Such reactive intermediate can play an important role in catalytic conversion of ethylene on silver loaded molecular sieves. The Ag(C2H4)2 stabilized inside relatively small channels of SAPO-11 molecular sieve it is observed even at 290 K. The ‘gas-phase’ geometries of Ag(C2H4) and Ag(C2H4)2 complexes, and respective hyperfine coupling constants were calculated applying DFT quantum chemical methods. The hyperfine coupling constants calculated for Ag(C2H4)2 complex of D2h symmetry are in very good agreement with those obtained experimentally.

Structure and dynamics of triethylamine and tripropylamine radical cations generated in AlPO4-5 by ionizing radiation : an EPR and MO study

An EPR study was carried out to investigate both the structure and molecular dynamics of triethylamine (Et3N) and tripropylamine (Pr3N) radical cations generated in γ-irradiated AlPO4-5 from neutral mother molecules incorporated as an organic template. Both Et3N+• and Pr3N+• radical cations were stable at 300 K and showed strongly temperature-dependent EPR spectral line-shapes in the temperature range from 77 to 300 K. The spectral change was successfully explained by assuming a two-site exchange model in which two inequivalent β-hydrogens interchange their positions with each other. The experimental spectra were quantitatively analyzed by a simulation method using the exchange rate as a variable parameter. From an Arrhenius plot of the rate constants, activation energies of 9.1 and 11.4 kJ mol−1 were evaluated for Et3N+• and Pr3N+• in AlPO4-5, respectively.

Decrease of the crystallinity of bone mineral in osteopetrotic rats

Abstract The membraneous and long bones of three groups of Fatty Orl-op rats i.e. phenotypically normal animals, osteopetrotic (op/op) mutants, and op/op mutants cured by transplantation of normal bone marrow were compared with regard to the amount and crystallinity of inorganic constituents. The electron spin resonance spectrometry based on measurements of stable paramagnetic centers induced by ionizing radiation in the crystalline lattice of bone hydroxyapatite was used for evaluation of crystallinity of bone mineral. The crystallinity coefficient defined as the ratio of spin concentration of these centers to the total ash content of the sample was calculated. In compact bone of op/op mutants a small increase (about 4%) of mineral content was observed, while the crystallinity of mineral was significantly lower, reaching about 80% of the value found in the phenotypically normal littermates. In op/op mutants cured by transplantation of normal bone marrow the trend for normalization was found. These observations demonstrate the possibility that the crystallinity of bone mineral can be used as a parameter in the diagnosis and monitoring of the therapy in osteopetrosis.

Initial studies on the crystallinity of the mineral fraction and ash content of isolated human and bovine osteons differing in their degree of calcification

SummarySeveral groups containing 10–15 isolated osteons differing in their degree of maturity were analysed. Samples were isolated from undecalcified human and bovine bone sections. The crystallinity coefficient, defined as the ratio of the number of radiation-induced paramagnetic defects in the crystalline lattice of hydroxyapatite to the total ash content, was calculated. The results were compared with measurements performed on fragments of total cortical bone, primary periosteal bone, and inner circumferential lamellar bone. The results show a higher crystallinity of fully calcified osteons as compared with that found at the initial stage of calcification. No differences in the ash content were observed between human osteons, from different stages of calcification evaluated morphologically and by X-ray absorption. These differences were evident when bovine osteons differing in their stage of calcification were compared. Human fully calcified osteons contain 60% ash and their crystallinity coefficient is 52.1. Human osteons at the initial stage of calcification contain 57% ash and their crystallinity coefficient is 40.6. The same parameters for fully calcified bovine osteons and for bovine osteons at the initial stage of calcification are 59% ash, 62.6 crystallinity coefficient and 46% ash, 43.0 crystallinity coefficient, respectively.

Organosilver radicals in gamma-irradiated Ag–NaA zeolite with methanol adsorbate

Hydroxyalkyl silver radicals, Ag·CH2OH+ in γ-irradiated Ag–NaA zeolites with adsorbed methanol have been studied by EPR spectroscopy. These adducts, for silver loadings greater than one Ag+ per unit cell, are formed directly after irradiation at 77 K. For lower Ag+ content they appear on annealing above 140 K. It is postulated that the Ag+ location in the zeolite lattice plays a crucial role in this process, and two different mechanisms of Ag·CH2OH+ formation are discussed depending on Ag+ location inside or outside a β-cage.

Radiation-induced paramagnetic centers in research on bone physiopathology.

It has been found that ionizing radiation induces stable paramagnetic centers in the crystalline lattice of bone hydroxyapatite (HA). These defects, which can be detected and measured by electron spin resonance (ESR) spectrometry, can be treated as a new kind of biologic marker and used for the following: (1) evaluation of crystallinity of bone mineral, because the yield of these centers depends on the size of HA crystals; (2) quantification of the rebuilding process of radiation-sterilized bone grafts, because of the stability of the centers; and (3) estimation of the dose of ionizing radiation absorbed by living organisms, because of the linear relation between the dose of ionizing radiation and the yield of radiation-induced paramagnetic centers in bone mineral.