Sterilization Dose Research Articles

Fecundity, fertility and reproductive recovery of irradiated Queensland fruit fly Bactrocera tryoni

Pupae of the Queensland fruit fly or Q-fly Bactrocera tryoni (Froggatt) are irradiated routinely to induce reproductive sterility in adults for use in sterile insect technique programmes. Previous studies suggest that adult sexual performance and survival under nutritional and crowding stress are compromised by the current target dose of radiation for sterilization (70–75 Gy), and that improved mating propensity and survival under stress by irradiated males may be achieved by reducing the target sterilization dose without reducing the level of induced sterility. This raises the question of the amount by which the irradiation dose can be reduced before residual fertility becomes unacceptable. The present study measures the levels of residual fertility in male and female irradiated Q-flies at different irradiation doses (20, 30, 40, 50, 60 and 70 Gy), and investigates the possibility that fecundity and fertility increase between 10–15 and 30–35 days post emergence. Male flies require a higher dose than females to induce sterility, with no residual fertility found in females irradiated at doses of 50 Gy or above, and no residual fertility found in males irradiated at doses of 60 Gy or above. Irradiated females are more fecund at 30–35 days post emergence than at 10–15 days. However, fertility does not increase between 10 and 15 days post emergence and 30–35 days, even at doses below 50 Gy. The present study shows that there is scope to reduce the target sterilization dose for Q-flies below that of the current dose range (70–75 Gy) at the same time as retaining an adequate safety margin above radiation doses at which residual fertility can be expected.

Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films ( M w : 167–553 kg mol −1) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose ( D g ) as well as gel–sol analysis and swelling tests for doses above D g indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials.

The influence of radiation sterilisation on some β-blockers in the solid state

Six derivatives of aryloxyalkylaminopropanol of known β-adrenolytic activity (acebutolol, alprenolol, atenolol, metoprolol, pindolol, propranolol) in solid phase were exposed to the ionising radiation generated by e-beam of high-energy electrons from an accelerator (∼10 MeV) in doses from 25 to 400 kGy. To establish the effects of irradiation on their physico-chemical properties, the compounds were then analysed by differential scanning calorimetry (DSC), scanning electron microscope (SEM), X-ray diffraction (XRD) and FT-IR spectrometry. The standard sterilisation dose (25 kGy) was found to cause no changes in only one derivative – acebutolol, whereas in the other derivatives the irradiation caused colour changes, differences in X-ray diffraction patterns and in the character of DSC curves, including a decrease in the melting point. For each derivative one clear peak corresponding to the process of melting was observed and its position shifted towards lower temperatures with increasing dose of irradiation. For all compounds studied the value of the shift was between 0.1 and 1.0 °C. For alprenolol, propranolol and metoprolol linear relations were found between the irradiation dose and the decrease in the melting point, described by the correlation coefficient (between 0.9446 and 0.9864). No changes were observed in the FT-IR spectra and in the SEM images of the compounds studied.

Characterization of blends of PP with vitamins “C” and “E” exposed to gamma radiation at sterilization dose

In this study, the influence of two vitamins (C and E) on the properties of isotactic polypropylene (PP) exposed to gamma radiation at the minimal sterilization dose of 25 kGy was evaluated. To do so, PP was blended in solution with the vitamins at varying concentrations. These formulations were irradiated with gamma rays at a dose of 25 kGy from a 60Co source and then characterized using different techniques such as FTIR, GPC, DSC, TGA, and tensile testing. The incorporation of the different vitamins, either individually or combined, did not avoid the formation of carbonyl groups in the PP after irradiation. Moreover, the average molecular weight of the polypropylene decreased significantly, even in those samples where the additives were present. Tensile tests unfolded an increased stiffness in those samples with individual additives, whereas a decrease was detected in those systems with a combination of them. A decrease in both tensile strength and elongation at break was displayed by the compounds when compared to irradiated PP. An increase in the crystallization temperature was detected when Vitamins C and E were incorporated into the PP, which demonstrated a nucleating effect of these compounds. The highest nucleating effect was found for concentrations of 0.3% of Vitamin E and 0.5% of Vitamin C. For these formulations, more homogeneous melting endotherms and narrower crystallization exotherms were obtained. An increase in the nucleating density in PP was observed as well, when a combination of Vitamins E/C (0.5/0.5%) was employed.

THE EFFECT OF HYDROGEL DRESSING COPOLYMER POLI(VINYLPIRROLIDONE) (PVP) - k- CARRAGEENAN PREPARED BY RADIATION AND HEALING TIMES ON THE RADIUS REDUCTIONS BURN INJURIED OF WISTAR WHITE RAT

The pre-clinical study of poly (vinyl pirrolidone) (PVP)-k- carrageenan hydrogel has been carried out. The aim of this study is to investigate the effect of hydrogel for healing burn injuried in the rats. The hydrogels were prepared by g-irradiation of aqueous solutions of 15 wt.-% PVP and 2 wt.-% k- carrageenan at a sterilization dose of 25 kGy. The physico-chemical properties of hydrogels were investigated. The results showed that the hydrogels suitable as candidate for wound dressing with gel fraction of 90 ± 5 (%), the water absorption was 4500 ± 55 (w/w), the water content was 83 ± 2 (%), tensile strength was 1,5 ± 0,1 kg/cm2 and adhesiveness was 0. The effect of the hydrogel as wound dressing was evaluated by attaching to a burn of the back skin of rats as a function of time observation. Advantages of the hydrogel were slightly faster rate of reducing radius diameter of injured burn skin, easy removal without damage to renewed skin. Keywords: hydrogel, irradiation, copolymer, PVP, k carrageenan, diameter

Validation of 11 kGy as a Radiation Sterilization Dose for Frozen Bone Allografts

A radiation sterilization dose (RSD) of 25 kGy is deleterious to bone allografts. This study aimed to establish a lower RSD for bone allografts using method 1 of International Standard Organisation 11137.2:2006. This provides a database to select an RSD corresponding to an allograft's bioburden, given that the bioburden's gamma resistance is equal to or less than the standard. This can be verified by irradiating 100 allografts at a dose selected to provide a sterility assurance level of 10 −2. The bioburden of our allografts was 0, which prescribed a verification dose of 1.3 kGy. After irradiating 100 allografts, sterility tests returned no positive cultures. We therefore validated an RSD of 11 kGy for allografts with that bioburden. According to the standard, this RSD provides a sterility assurance level of 10 −6 for bone allografts.

Computer and field evaluations in support of the VD max approach for selected sterilization doses greater than 25 kGy

Originally, the VD max approach was developed to substantiate a selected sterilization dose of 25 kGy. Thereafter, computer and field evaluations demonstrated the value of the approach for substantiation of selected sterilization doses less than 25 kGy. Verification of the use of the approach for substantiation of sterilization doses in excess of 25 kGy is now needed. The results of the computer evaluations conducted on the VD max approach with 35 challenge microbial populations at sterilization doses of 30 and 35 kGy generally gave outcomes consistent with those observed previously, namely, safe and unambiguous. Outcomes perceived as unsafe have been shown to be a peculiarity of the manner of assembling challenge microbial populations. Field evaluations involving substantiation of four selected sterilization doses greater than 25 kGy and associated sterilization dose auditing gave acceptable outcomes. The present findings further affirm the value and reliability of the VD max approach.

Identification of radiolysis products of solid thiamphenicol

Spectroscopic and chromatographic methods (HPLC, HPLC–MS, NMR) were used to observe, separate and identify products of radiolysis of thiamphenicol (TF), irradiated in the solid state at room temperature and atmospheric pressure with an electron beam from a linear accelerator to doses between 25 and 800 kGy. Nine products of radiolysis of thiamphenicol were identified, among them were TF amine, dichloroacetic acid, 4-methylsulfonylbenzoic acid, demono- and dedichloroderivative of TF, 2,2-dichloro- N-{3-hydroxy-1-[4-(methylsulfonyl)phenyl]-1-oxopropan-2-yl}acetamide and 3-({1,3-dihydroxy-1-[4-(methylsulfonyl)phenyl]propan-2-yl}amino)-3-oxopropanoic acid. The process of radiodegradation of TF was proposed as consisting of several parallel primary reactions (dehalogenation, oxidation of the OH group at C 1, hydrolysis of the amide bond, a rapture of the C 2–C 3 bond of propan-1-ol) and secondary reactions (carboxylation and oxidation). The use of high doses, well above the sterilization dose of 25 kGy, allowed observation of changes of TF content as a function of radiation dose, calculation of radiolytic yield (G −TF) and kinetic parameters of the degradation reaction. It was found that the standard sterilizing dose lowers the content of TF by only 0.1% and the radiolytic efficacy of the process of radiodegradation is 0.76 molecules/100 eV. Further increase in the dose lowers the content of TF to 92.1% for 800 kGy dose and leads to an increase in the value of G −TF. It was also found that the summative process of radiodegradation of TF exposed to a beam of electrons of 10 kGy/s follows the first order reaction kinetics with a degradation constant of k = 0.001 s −1. On the basis of the experiments conducted it can be stated that the radiolysis of TF in the presence of an E-beam, in substantia, follows multidirectional course in the same way as radiolysis of chloramphenicol. TF exposed to the standard sterilizing dose of 25 kGy degrades only by 0.1%, the amount acceptable by the ICH, and forms only one product of radiolysis (TF amine) and therefore we conclude that it can be sterilized by ionizing radiation under the conditions described above.

Electrical behavior of stored erythrocytes after exposure to gamma radiation and the role of α-lipoic acid as radioprotector

The effects of gamma rays (25, 50 and 100 Gy) on stored erythrocytes were studied by measuring their dielectric properties and observing their morphology under scanning electron microscopy. Alpha lipoic acid (a potent natural antioxidant) was introduced prior to irradiation for radioprotection. It can be concluded that the dose level of 25 Gy can be considered a safe sterile dose; however, irradiation doses of 50 and 100 Gy should be applied with the addition of alpha-acid to preserve the cell viability.

Sterilization of Products Contaminated with Pyronema domesticum

Product recalls due to non-sterility occurred between 1993 and 1994 among manufacturers that were sterilizing cotton products sourced from China using ethylene oxide (EO). The primary contaminant was identified as a pyrophilous mold from the class Discomycetes, Pyronema domesticum. Multiple references suggest this organism has special needs for reproducing and maintaining the two assumed resistant stages of this organism (ascospores and sclerotia). Sterilization resistance studies were performed using a China-sourced cotton product that was naturally contaminated with P. domesticum. These studies showed the organisms to have: 1) a low resistance to moist heat sterilization at 250 degrees F (121 degrees C); a resistance to radiation no greater than that predicted by the bioburden-based resistance model (i.e., Population C) used for dose determination Method 1 described in ANSI/AAMI/ISO 11137-2:2006--Sterilization of health care products--Radiation--Part 2: Establishing the sterilization dose; and 3) a high resistance to EO processing.

Radiation sterilization of skin allograft

In the treatment of burns or accidental loss of skin, cadaveric skin allografts provide an alternative to temporarily cover a wounded area. The skin bank facility is indispensable for burn care. The first human skin bank was established in Argentina in 1989; later, 3 more banks were established. A careful donor selection is carried out according to the national regulation in order to prevent transmissible diseases. As cadaveric human skin is naturally highly contaminated, a final sterilization is necessary to reach a sterility assurance level (SAL) of 10 −6. The sterilization dose for 106 batches of processed human skin was determined on the basis of the Code of Practice for the Radiation Sterilization of Tissue Allografts: Requirements for Validation and Routine Control (2004) and ISO 11137-2 (2006). They ranged from 17.6 to 33.4 kGy for bioburdens of >10–162.700 CFU/100 cm 2. The presence of Gram negative bacteria was checked for each produced batch. From the analysis of the experimental results, it was observed that the bioburden range was very wide and consequently the estimated sterilization doses too. If this is the case, the determination of a tissue-specific dose per production batch is necessary to achieve a specified requirement of SAL. Otherwise if the dose of 25 kGy is preselected, a standardized method for substantiation of this dose should be done to confirm the radiation sterilization process.

Characteristics study of clear polymethylmethacrylate dosimeter, Radix W, in several kGy range

Basic characteristics of Radix W, a commercially available undyed polymethylmethacrylate (PMMA) dosimeter conventionally used by readout at 320 nm, were studied in the dose range of 0.5–8 kGy, for its wide application especially for the evaluation of the sterilization dose and the quality assurance of food irradiation. The characteristics of dose response, the effect of irradiation temperature, and its stability after irradiation were examined over candidate readout wavelengths of 270–320 nm. The dose response readout at shorter wavelength is higher than that at longer wavelength, and 280 nm is the suitable readout wavelength for measurement of dose range of 0.5–8 kGy. The post-irradiation stability of dose response for 6 kGy is less than 1% within 24 h after irradiation at an irradiation temperature of 20 °C. Dose response is higher with temperature at irradiation temperatures in the range of −40 to 20 °C.

Comparative study of effect of low and medium dose rate of γ irradiation on microporous polysulfone membrane using spectroscopic and imaging techniques

The effect of low (LDR) and medium dose rate (MDR) of γ irradiation at low doses (0–100 kGy) on the structural and chemical changes of microporous polysulfone (PSf) membrane has been studied using UV–vis, FTIR, SEM and dead-end filtration techniques. PSf membrane was cast by phase inversion method. Irradiation was done at room temperature in air media. The doses chosen were 0–100 kGy for LDR and 0–50 kGy for MDR; they were below and above sterilization dose. Analysis of UV–vis and IR spectra and SEM images obtained suggested that chain scissions and crosslink had occurred simultaneously in the irradiated membranes in both cases. This radio-oxidation effects observed start at a very low dose i.e. 1.66 kGy and increase with increase in dose. It is supported by the flux values obtained; it is increased with increase in dose. The results indicate that a very low dose γ irradiation was able to change the physicochemical characteristics of microporous PSf membrane which depend on dose rate of exposure.

Validation of 15 kGy as a radiation sterilisation dose for bone allografts manufactured at the Queensland Bone Bank: application of the VDmax 15 method

ISO 11137-2006 (ISO 11137-2a 2006) provides a VDmax 15 method for substantiation of 15 kGy as radiation sterilisation dose (RSD) for health care products with a relatively low sample requirement. Moreover, the method is also valid for products in which the bioburden level is less than or equal to 1.5. In the literature, the bioburden level of processed bone allografts is extremely low. Similarly, the Queensland Bone Bank (QBB) usually recovers no viable organisms from processed bone allografts. Because bone allografts are treated as a type of health care product, the aim of this research was to substantiate 15 kGy as a RSD for frozen bone allografts at the QBB using method VDmax 15-ISO 11137-2: 2006 (ISO 11137-2e, Procedure for method VDmax 15 for multiple production batches. Sterilisation of health care products - radiation - part 2: establishing the sterilisation dose, 2006; ISO 11137-2f, Procedure for method VDmax 15 for a single production batch. Sterilisation of health care products - radiation - part 2: establishing the sterilisation dose, 2006). 30 femoral heads, 40 milled bone allografts and 40 structural bone allografts manufactured according to QBB standard operating procedures were used. Estimated bioburdens for each bone allograft group were used to calculate the verification doses. Next, 10 samples per group were irradiated at the verification dose, sterility was tested and the number of positive tests of sterility recorded. If the number of positive samples was no more than 1, from the 10 tests carried out in each group, the verification was accepted and 15 kGy was substantiated as RSD for those bone allografts. The bioburdens in all three groups were 0, and therefore the verification doses were 0 kGy. Sterility tests of femoral heads and milled bones were all negative (no contamination), and there was one positive test of sterility in the structural bone allograft. Accordingly, the verification was accepted. Using the ISO validated protocol, VDmax 15, 15 kGy was substantiated as RSD for frozen bone allografts manufactured at the QBB.

The influence of composition of porous copolyester scaffolds on reactions induced by irradiation sterilization

In our previous work regarding radiation sterilization of porous scaffolds we have concluded that the composition and microstructure of the polymer chain are a key factor influencing the degradation reactions occurring upon irradiation. In this work we in contrast reported on the effects of high-energy irradiation on the thermal and mechanical properties. Electron beam (EB)- and γ-irradiation sterilization were used in order to finalize the properties of a series of porous scaffolds comprised of different aliphatic polyester copolymers. The results presented here show that, for both sterilization methods, the crystallinity increased for all copolymers of 1,5-dioxepan-2-one (DXO) and l, l-lactide (LLA) at the minimum sterilization dose. The same was true of the ε-caprolactone (CL)- and LLA-containing copolymers upon EB sterilization, while a reduction in crystallinity were found upon γ-irradiation. As was anticipated, it was shown that crystallinity also is a characteristic of the copolymer influencing the effects of the irradiation-induced reactions. Both the onset temperature and the temperature corresponding to the maximum rate of weight loss increased after irradiation and hence the thermal stability was increased. This is a result of a simultaneous lengthening of the chains by cross-linking reactions and a shortening by random chain-scissions occurring throughout the molecule, which lead to the formation of new endgroups with higher thermal stability. Scaffolds of crystalline polymers retained more of their initial tensile properties after irradiation compared to amorphous materials. The result previously published, showing that the composition was a key factor influencing the degradation reactions occurring upon irradiation, was augmented here.

The role of ascorbate and histidine in fibrinogen protection against changes following exposure to a sterilizing dose of γ-irradiation

Sodium ascorbate and histidine were employed to protect fibrinogen against modifications followed by a gamma-irradiation process that could potentially inactivate the blood-borne viruses in plasma-derived products. Fibrinogen was irradiated (50 kGy total dose, on dry ice) using a 60Co source. Samples were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blot. Carbonyl groups were measured by the 2,4-dinitrophenylhydrazine-coupled method, and the fibrinogen clotting activity was assessed by different functional assays. In irradiated fibrinogen, the carbonyl group concentration was elevated three-fold versus control; and moderate fragmentation of largely Aalpha and Bbeta chains was revealed. The rate of thrombin-catalyzed fibrinogen polymerization was inhibited (average 50%) with normal fibrinopeptide release and with a minor decrease of total clottable fibrinogen and alpha-polymer formation. Ascorbate reduced the incorporation of carbonyls to the fibrinogen molecule (by > 50% at 50 mmol/l; P < 0.001). Contrary to ascorbate, which alone delayed the fibrinogen polymerization rate, histidine abolished irradiation-induced inhibition of fibrinogen polymerization (by 80% at 50 mmol/l; P < 0.001). In conclusion, even though ascorbate effectively protects fibrinogen from oxidation due to its adverse effects on fibrinogen function, it may not serve as a suitable radioprotective. On the contrary, the first definite evidence is provided that radiation-sterilized fibrinogen in the presence of histidine greatly retains its clotting capability.

Radiation synthesis of PVP/CMC hydrogels as wound dressing

Carboxymethyl cellulose (CMC) and poly( N-vinyl pyrrolidone) (PVP) were blended to synthesize hydrogels by 60Co γ-ray irradiation. A series of hydrogels were prepared with three compositions, i.e. PVP:CMC = 5:5, 6:4 and 7:3. The properties of the hydrogels such as gel fraction, gel strength, swelling behavior and moisture retention were investigated. Compared with pure PVP and CMC hydrogels, PVP/CMC blend hydrogels possessed improved gel strength, flexibility and transparency. As the content of PVP in PVP/CMC blend hydrogels increased, the gel fraction increased while the swelling rate decreased. The hydrogels with optimal properties were obtained in a composition of PVP/CMC = 6/4 with sterilization dose (25 kGy) and further characterized by FT-IR and SEM. Properties concerning the application of wound dressing were performed by comparison with a commercial hydrogel wound dressing to find a similar moisture retention capability and improved swelling rate. The improved properties as well as the cheapness of the materials suggest that PVP/CMC blend hydrogel can be good candidate as wound dressing.

Effectiveness of DOP mobilizer on the radiolysis of a semi-crystalline ethylene–propylene copolymer

The role of dioctyl phthalate, DOP, added as a radiation stabilizer (mobilizer) to a commercial, medical grade polypropylene has been examined by FTIR and XPS analyses. It was found that the DOP degraded during γ-irradiation to a sterilization dose under vacuum at 298 K and that the degradation products, which included a variety of oxygenated and aromatic compounds, diffused to the polymer surface.

Vitamin C hinders radiation cross-linking in aqueous poly(vinyl alcohol) solutions

Poly(vinyl alcohol) (PVA) is a promising semi-crystalline material for biomedical applications. It is soluble in water and can be formed into hydrogels by freezing and thawing or crystallizing from an aqueous theta solution such as that of polyethylene glycol (PEG). Radiation cross-linking caused by sterilization or high dose irradiation of concentrated PVA solutions could compromise some properties of these hydrogels. Therefore, we hypothesized that radiation cross-linking of PVA solutions and PVA–PEG theta gels could be prevented by using the antioxidant vitamin C as an anticross-linking agent. Our hypothesis tested positive. Vitamin C concentrations of 0.75 and 4.5 mol/mol of PVA repeating unit could prevent cross-linking in 17.5 wt/v% PVA solutions made with PVA molecular weight of 115,000 g/mol irradiated to 25 and 100 kGy, respectively. Vitamin C also prevented cross-linking in 25 kGy irradiated PVA–PEG theta gels containing up to 5 wt% PEG and decreased the viscosity of those up to 39 wt%.

Experiences using IAEA Code of practice for radiation sterilization of tissue allografts: Validation and routine control

Problems of tissue allografts in using International Standard (ISO) 11137 for validation of radiation sterilization dose (RSD) are limited and low numbers of uniform samples per production batch, those are products obtained from one donor. Allograft is a graft transplanted between two different individuals of the same species. The minimum number of uniform samples needed for verification dose (VD) experiment at the selected sterility assurance level (SAL) per production batch according to the IAEA Code is 20, i.e., 10 for bio-burden determination and the remaining 10 for sterilization test. Three methods of the IAEA Code have been used for validation of RSD, i.e., method A1 that is a modification of method 1 of ISO 11137:1995, method B (ISO 13409:1996), and method C (AAMI TIR 27:2001). This paper describes VD experiments using uniform products obtained from one cadaver donor, i.e., cancellous bones, demineralized bone powders and amnion grafts from one life donor. Results of the verification dose experiments show that RSD is 15.4 kGy for cancellous and demineralized bone grafts and 19.2 kGy for amnion grafts according to method A1 and 25 kGy according to methods B and C.