Gamma Radiation Sterilization Research Articles

Gamma, electron beam and X-ray irradiation effects on polymers in an advanced bone cement mixer device

The medical device industry has been investigating ways to increase the use of alternatives to cobalt-60 gamma radiation and ethylene-oxide gas sterilization, such as electron beam (E-beam) and X-ray radiation, due to regulatory and market pressures. One impediment to switching to E-beam or X-ray technology for sterilization is the lack of data on the effects of these radiation sources on medical device polymers. To provide such data this work considers irradiation and testing of a common single-use medical bone cement mixing system, the Stryker Advanced Cement Mixer (ACM®), that is composed of seven polymer materials. The ACM® devices considered here were processed to sterilization-relevant doses (15, 25, 50, and 70 kGy) using three radiation technologies: gamma, E-beam, and X-ray. The system and its polymer components were tested for product functionality, as well as mechanical and visual properties to determine how exposure effects may be influenced by radiation technology and dose level. We found that although there were instances of statistically significant differences in effects between the gamma-irradiated products and those irradiated with E-beam and X-ray, those effects were negligible in terms of retained functionality of the product and retained mechanical properties of the polymer components. Overall, results of this study demonstrate that, for of the effects studied, E-beam and X-ray are viable alternatives to cobalt-60 gamma radiation for sterilization of the polymer-based device investigated.

Comparative Review on E-Beam and Gamma Radiation Sterilization Methods: Effectiveness, Safety, and Cost Considerations

Comparative Review on E-Beam and Gamma Radiation Sterilization Methods: Effectiveness, Safety, and Cost Considerations

Effect of Sterilization Methods on Collagen Hydrolysate Obtained from Tuna Tendon

Collagen hydrolysates derived from tuna tendons have potential applications in various industries, but sterilization is crucial to ensure their safety. This study investigated the effects of ethylene oxide (EtO), beta radiation, and gamma radiation sterilization methods on the structural and functional properties of collagen hydrolysates using nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and differential scanning calorimetry (DSC). EtO sterilization caused significant physical and chemical changes in the hydrolysates, as evidenced by the altered appearance and 1H-NMR and 13C-NMR spectra. In contrast, beta and gamma radiation did not induce notable changes in the physical characteristics and NMR spectra. MALDI-TOF MS analysis revealed slight alterations in the molecular weight distribution after sterilization, with beta irradiation causing a minor decrease and gamma irradiation and EtO leading to small increases. DSC analysis showed shifts in the heat absorption peaks after sterilization, indicating changes in the thermal properties. The findings suggest that while all three methods effectively sterilize collagen hydrolysates, EtO causes more significant structural modifications compared to beta and gamma radiation. This study provides valuable insights into the impact of sterilization on collagen hydrolysates, facilitating the selection of appropriate methods for specific applications.

Dose-dependent effects of gamma radiation sterilization on the collagen matrix of human cortical bone allograft and its influence on fatigue crack propagation resistance

Fatigue crack propagation resistance and high-cycle S–N fatigue life of cortical bone allograft tissue are both negatively impacted in a radiation dose-dependent manner from 0 to 25 kGy. The standard radiation sterilization dose of 25–35 kGy has been shown to induce cleavage of collagen molecules into smaller peptides and accumulation of stable crosslinks within the collagen matrix, suggesting that these mechanisms may influence radiation-induced losses in cyclic fracture resistance. The objective of this study was to determine the radiation dose-dependency of collagen chain fragmentation and crosslink accumulation within the dose range of 0–25 kGy. Previously, cortical bone compact tension specimens from two donor femoral pairs were divided into four treatment groups (0 kGy, 10 kGy, 17.5 kGy, and 25 kGy) and underwent cyclic loading fatigue crack propagation testing. Following fatigue testing, collagen was isolated from one compact tension specimen in each treatment group from both donors. Radiation-induced collagen chain fragmentation was assessed using SDS-PAGE (n = 5), and accumulation of pentosidine, pyridinoline, and non-specific advanced glycation end products were assessed using a fluorometric assay (n = 4). Collagen chain fragmentation increased progressively in a dose-dependent manner (p < 0.001). Crosslink accumulation at all radiation dose levels increased relative to the 0 kGy control but did not demonstrate dose-dependency (p < 0.001). Taken together with our previous findings on fatigue crack propagation behavior, these data suggest that while collagen crosslink accumulation may contribute to reduced notched fatigue behavior with irradiation, dose-dependent losses in fatigue crack propagation resistance are mainly influenced by radiation-induced chain fragmentation.

The Impacts of the Sterilization Method and the Electrospinning Conditions of Nanofibrous Biodegradable Layers on Their Degradation and Hemocompatibility Behavior.

The use of electrospun polymeric biodegradable materials for medical applications is becoming increasingly widespread. One of the most important parameters regarding the functionality of nanofiber scaffolds during implantation and the subsequent regeneration of damaged tissues concerns their stability and degradation behavior, both of which are influenced by a wide range of factors (the properties of the polymer and the polymer solution, the technological processing approach, the sterilization method, etc.). This study monitored the degradation of nanofibrous materials fabricated from degradable polyesters as a result of the sterilization method applied (ethylene oxide and gamma irradiation) and the solvent system used to prepare the spun polymer solution. Aliphatic polyesters PCL and PLCL were chosen for this study and selected with respect to the applicability and handling in the surgical setting of these nanofibrous materials for vascular bandaging. The results revealed that the choice of solvent system exerts a significant impact on degradation during sterilization, especially at higher gamma irradiation values. The subsequent enzyme-catalyzed degradation of the materials following sterilization indicated that the choice of the sterilization method influenced the degradation behavior of the materials. Whereas wave-like degradation was evident concerning ethylene oxide sterilization, no such behavior was observed following gamma-irradiation sterilization. With concern for some of the tested materials, the results also indicated the potential for influencing the development of degradation within the bulk versus degradation from the surface of the material. Both the sterilization method and the choice of the spinning solvent system were found to impact degradation, which was observed to be most accelerated in the case of PLCL (L-lactide-co-caprolactone copolymer) electrospun from organic acids and subsequently sterilized using gamma irradiation. Since we planned to use these materials in cardiovascular applications, it was decided that their hemocompatibility would also be tested. The results of these tests revealed that changes in the structures of the materials initiated by sterilization may exert thrombogenic and anticoagulant impacts. Moreover, the microscopic analysis suggested that the solvent system used in the preparation of the materials potentially affects the behavior of erythrocytes; however, no indication of the occurrence of hemolysis was detected.

Influence of ethylene oxide and gamma irradiation sterilization processes on the degradation behaviour of poly(lactic acid) (PLA) in the course of artificially accelerated aging

To promote the application of bio-based materials in the field of medical technology, it is essential to conduct additional research, focusing on their long-term performance after sterilization. For this purpose, the study examines the aging behaviour of three poly(lactic-acid) (PLA) materials, sterilized with either ethylene oxide or gamma irradiation, over a two years aging period, in accordance with ASTM F1980-21. During these investigations, a direct correlation between moisture absorption and degradation progression was observed. Crystallinity increased, due to chain scission mainly in amorphous regions, resulting in a reduction in melting peak temperature. Tensile strength and elongation at break, decreased with aging, accompanied by embrittlement. Color analysis revealed that Luminy® L130 brightened during aging, while NP HT 202 and NP HT 203 shifted towards green and yellow tones, attributed to the release of softeners from the materials. Regardless of the initial condition, the degradation process followed a two-stage linear process with an acceleration in the second phase, possibly due to the formation of catalytic end groups. The impact of sterilization is predominantly observed concerning the initial condition of the materials before aging and therefore affects the shelf life rather than the course of aging.

Effect of gamma irradiation and supercritical carbon dioxide sterilization with Novakill™ or ethanol on the fracture toughness of cortical bone.

Sterilization of structural bone allografts is a critical process prior to their clinical use in large cortical bone defects. Gamma irradiation protocols are known to affect tissue integrity in a dose dependent manner. Alternative sterilization treatments, such as supercritical carbon dioxide (SCCO2 ), are gaining popularity due to advantages such as minimal exposure to denaturants, the lack of toxic residues, superior tissue penetration, and minor impacts on mechanical properties including strength and stiffness. The impact of SCCO2 on the fracture toughness of bone tissue, however, remains unknown. Here, we evaluate crack initiation and growth toughness after 2, 6, and 24 h SCCO2 -treatment using Novakill™ and ethanol as additives on ~11 samples per group obtained from a pair of femur diaphyses of a canine. All mechanical testing was performed at ambient air after 24 h soaking in Hanks' balanced salt solution (HBSS). Results show no statistically significant difference in the failure characteristics of the Novakill™-treated groups whereas crack growth toughness after 6 and 24 h of treatment with ethanol significantly increases by 37% (p = .010) and 34% (p = .038), respectively, compared to an untreated control group. In contrast, standard 25 kGy gamma irradiation causes significantly reduced crack growth resistance by 40% (p = .007) compared to untreated bone. FTIR vibrational spectroscopy, conducted after testing, reveals a consistent trend of statistically significant differences (p < .001) with fracture toughness. These trends align with variations in the ratios of enzymatic mature to immature crosslinks in the collagen structure, suggesting a potential association with fracture toughness. Additional Raman spectroscopy after testing shows a similar trend with statistically significant differences (p < .005), which further supports that collagen structural changes occur in the SCF-treated groups with ethanol after 6 and 24 h. Our work reveals the benefits of SCCO2 sterilization compared to gamma irradiation.

The Process of Sterilizing Tattoo Inks Releases Formaldehyde

Introduction: Around 12% of Europeans and 20% of Americans have at least one tattoo. Tattoo inks, the substances used to create tattoos on the body, consist of chemicals that contain formaldehyde, which can be harmful to human health. The amount of formaldehyde present in commercially available tattoo inks and its causes are not well understood. Methods: We investigated the levels of formaldehyde in tattoo ink products sold in different countries and identified the factors contributing to its production. We also explored methods to reduce formaldehyde generation in tattoo inks. Seven tattoo inks from various brands were tested. Results: Formaldehyde release was predominantly associated with gamma radiation sterilization. Formaldehyde levels were observed to be higher in compositions containing organic components compared to those with inorganic components, irrespective of sterilization method and container type. Glycerin released over seven times more formaldehyde than other components during gamma-ray sterilization. Conclusion: The results suggest that the presence of hydroxyl groups in carbon organic compounds in tattoo ink leads to photodegradation during gamma-ray radiation sterilization, resulting in increased concentrations of formaldehyde. Further research is needed to examine the chemical reactions occurring during sterilization processes and identify alternative sterilization methods that minimize formaldehyde formation. Additionally, the development of tattoo inks with reduced formaldehyde content and the establishment of strict quality control measures can help ensure the safety of tattooing practices.

Biomechanical aspects of radiation sterilization of composite material “Carbon FC” for medicine

The process of volumetric sterilization by gamma-irradiation of composite cellular material actively used for bone defect replacement in medicine is studied. The purpose of this study is to substantiate the necessary doses of gamma-irradiation for sterilization of highly porous carbon material "Carbon-FC" without reducing its mechanical characteris-tics. The technique of volumetric sterilization of the material under study and its testing for microbiological sterility is described. The results of mechanical tests of samples be-fore and after gamma-irradiation are given. Recommendations on selection of ionizing radiation doses providing microbicidal effect without reduction of strength properties during compression of the material under study are given.

A simulation study on enhancing sterilization efficiency in medical plastics through gamma radiation optimization

Gamma radiation is progressively emerging as an effective method to enhance the sterilization efficiency of medical plastics including Polyvinyl chloride (PVC). The parameters of the radiation facility will affect the efficiency of radiation sterilization. To investigate these effects, we simulate the gamma radiation sterilization performance of PVC material sample using Monte Carlo Method. The simulation results indicated that compared with the sterilization time of 20–90 min from high-temperature steam sterilization of medical waste, by optimizing the parameters of the model radiation facility, the radiation sterilization time can be reduced to 6.61 min. The optimized model facility parameters are as follows: the gamma photon energy is 1.25 MeV, the model space is 300 × 300 × 300 cm3, the reflective layer material is concrete and its thickness is 8 cm, the PVC sample layer area is 100 × 100 cm2, the distance between the radiation source and the PVC sample layer is 150 cm, the energy deposition in the bottom layer of the PVC sample layer is 1.31315 × 10–6 MeV/g. This study offers a potentially feasible way for PVC sterilization, while also providing a crucial reference for the further promotion and application of radiation sterilization technology.

Determination of gamma radiation sterilization dose on bioceramic BCP-Sr-Ag as bone graft according to ISO 11137 standards

Background: BCP-Sr-Ag as a bone graft needs to be sterilized. One way of sterilization is to use gamma radiation. Sterilization by gamma radiation requires the correct sterilization dose. Based on ISO 11137 the determination of the sterilization dose through 3 steps: determination bioburden, determination of verification dose, and determination of sterilization dose. Purpose:Determination of gamma radiation sterilization dose on BCP-Sr-Ag bioceramic as bone graft based on ISO 11137 through determination bioburden, determination verification dose, and determination of sterilization dose. Method: A total 30 samples of 3 different batch BCP-Sr-Ag were determined for bioburden using TSA media. A total 100 samples of BCP-Sr-Ag were irradiated with a verification dose using cobalt-60 gamma source. The 100 samples then tested for sterilization using TSA media to determine the sterilization dose. Results: The average bioburden values of batches 1,2, and 3 were 56,8;61,8; and 60,5 CFU. The average value of the whole batch is 59,7 CFU. Based on ISO 11137, the verification dose is 7,4 kGy and the sterilization dose is 20,5 kGy. Conclusion: The average bioburden value of the entire batch was 59,7 CFU. The bioburden value used for verification dose determination is 64,22 CFU so the the gamma radiation sterilization dose is 20,5 kGy.

Processing and Use of Radiation Sterilized Human Amniotic Membrane Allografts as Biological Dressings of Wounds in Children: A Review

Radiation sterilized human amniotic membrane allografts are used as biological dressing of wounds in rehabilitative surgery. The amniotic membrane is used in many different clinical situations such as: heat burn, chemical burns, diabetic wound/ diabetic foot ulcer, leprotic ulcer, abdominal wall reconstruction, pterigium removal site, peripheral corneal ulcer, in the management of pressure sore, etc.Non-viable lyophilized/oven-dried radiation sterilized amniotic membrane allografts could be processed for utilization as temporary biological dressing of wounds. The allografts used clinically should not be the carriers of germs or a source of infection. Human chorio-amniotic membranes collected for processing as tissue allografts to be used as biological dressings were reported to be contaminated with microorganisms such as species of Staphylococcus, Micrococcus, Bacillus and Pseudomonas.However, oven dried (40ºC) or freeze dried (-50ºC) human amniotic membranes were found to be sterilized by irradiation with the dose of 25 kiloGray (kGy) of gamma radiation.Careful screening and selection of tissue donors, proper processing and gamma radiation sterilization of human amniotic membranes minimize the risk of disease transmission to recipients through allografts.&#x0D; DS (Child) H J 2021; 38(1): 49-55

The impact of sterilization, body environment condition and raster orientation on tensile-shear cracking of sub-sized 3D printed specimens

Use of 3D printed parts in biomedical applications has received attention recently. The applied loads, manufacturing pre-processing factors or in vivo conditions may affect the reliability and integrity of such implants. To obtain deeper understand regarding the cracking resistance and microstructure of extrusion-based 3D printed acrylonitrile butadiene styrene (ABS) material a number of sub-sized and short bend beam samples are manufactured. The influence of raster orientation, Gamma radiation sterilization, body environment (saline 0.9% at temperature of 37 °C) and combined Sterilized process & body environment was studied on the mixed-mode I + II fracture toughness and strain energy release rate values. It was observed that exposing the 3D printed ABS material to Gamma-radiation process can increase noticeably the mixed mode fracture resistance compared to the control sample. Printing pattern with raster orientation of ±45° provided a higher mixed-mode fracture envelope compared to pattern of 0/90° for all investigated environments. The microstructure study of SEM pictures obtained from the investigated samples showed dominantly ductile type fracture with some evidences such as formation of dimples and ridge markings. The depth and number of ridge markings and dimples were increased by moving towards mode II (shear mode loading) and for the samples exposed to body environment.

Low-Dose Gamma Radiation Sterilization for Decellularized Tracheal Grafts

One of the main key aspects in ensuring that a transplant evolves correctly is the sterility of the medium. Decellularized tracheal transplantation involves implanting an organ that was originally in contact with the environment, thus not being sterile from the outset. While the decellularization protocol (through detergent exposition [2% sodium dodecyl sulfate], continuous stirring, and osmotic shocks) is conducted in line with aseptic measures, it does not provide sterilization. Therefore, one of the main challenges is ensuring sterility prior to in vivo implantation. Although there are established gamma radiation sterilization protocols for inorganic materials, there are no such measures for organic materials. Additionally, the protocols in place for inorganic materials cannot be applied to organic materials, as the established radiation dose (25 kGy) would completely destroy the implant. This paper studies the effect of an escalated radiation dose in a decellularized rabbit trachea. We maintained the dose range (kGy) and tested escalated doses until finding the minimal dose at which sterilization is achieved. After determining the dose, we studied effects of it on the organ, both histologically and biomechanically. We determined that while 0.5 kGy did not achieve sterility, doses of both 1 kGy and 2 kGy did, with 1 kGy, therefore, being the minimal dose necessary to achieve sterilization. Microscopic studies showed no relevant changes compared to non-sterilized organs. Axial biomechanical characteristics were not altered at all, and only a slight reduction in the force per unit of length that the organ can radially tolerate was observed. We can therefore conclude that 1 kGy achieves complete sterilization of decellularized rabbit trachea with a minimal, if any, effects on the organ.

Repair of tendons treated with peracetic acid-ethanol and gamma irradiation by EDC combined with NHS: a morphological, biochemical and biomechanical study in vitro.

The purpose of this study was to investigate whether 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) combined with n-hydroxysuccinimide (NHS) can repair tendon damage caused by peracetic acid-ethanol and gamma irradiation sterilization. The semitendinosus tendons of 15 New Zealand white rabbits were selected as experimental materials, and the tendons were sterilized in a solution containing 1% (v/w) peracetic acid and 24% (v/w) ethanol. After 15kGy gamma irradiation sterilization, the tendons were randomly divided into three groups (n = 10). The tendons were repaired with EDCs of 0, 2.5 and 5mM combined with 5mM NHS for 6h, the tendons were temporarily stored at - 80 ± °C. The arrangement and spatial structure of collagen fibers were observed by light microscopy and scanning electron microscopy, the collagen type and collagen crimp period were observed under a polarizing microscope, and the collagen fibril diameter and its distribution were measured by transmission electron microscopy, from which the collagen fibril index and mass average diameter were calculated. The resistance of collagen to enzymolysis was detected by the free hydroxyproline test, and tensile fracture and cyclic loading tests of each group of tendons were carried out, from which the elastic modulus, maximum stress, maximum strain, strain energy density and cyclic creep strain were calculated. The obtained results showed that the gap between loose collagen fibers in the 0mM control group was wider, the parallel arrangement of tendons in the 2.5 and 5mM groups was more uniform and regular and the fiber space decreased, the crimp period in the 5mM group was lower than that in the 0mM group (P < 0.05), and the concentration of hydroxyproline in the 5mM group (711.64 ± 77.95μg/g) was better than that in the control group (1150.57 ± 158.75μg/g). The elastic modulus of the 5mM group (424.73 ± 150.96MPa) was better than that of the 0mM group (179.09 ± 37.14MPa). Our results show that EDC combined with NHS can repair damaged tendons after peracetic acid-ethanol and gamma radiation treatment, and 5mM EDC has better morphological performance, anti-enzymolysis ability and biomechanical properties than 2.5mM EDC.

Efficacy of gamma irradiation for the sterilization of Indian meal moth, Plodia interpunctella

Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), is a cosmopolitan pest of stored grain commodities & processed food. About 30% of crop losses occur due to pests & diseases each year in Bangladesh. Due to negative effects of pesticides or the increasing resistance of the pests we adopted an alternative way i.e. Sterile Insect Technique methods, friendly to the environment. This experiment was done by implementing gamma irradiation (Cobalt-60) for sterilization of Indian meal moth to suppress the reproductive potential of the moth. Present study reveals that gamma radiation surprisingly prevented egg production, the number of eggs was zero at all the doses that we selected, when treated male were mated with treated female adults (TM x TF) in F1 generation. Higher doses of radiation were more effective on late adults to control the population in F1 generation than parental generation. 500 Gy dose was completely effective on late adults to prevent the hatchability for all cross schedules that we did in F1 generation. This (TM x TF) would be sufficient to control the fecundity & hatchability of late adults, Plodia interpunctella. The main objective of using SIT was to prevent the losses of this stored grain pest while mitigating the risks of pesticides on the environment, non- target organisms including human health.

Evaluation of the Effects of Gamma Radiation Sterilization on Rhein-Loaded Biodegradable Microparticles for the Treatment of Osteoarthritis

In previous work, we reported on the design of biodegradable rhein-loaded PLGA microparticles for the treatment of osteoarthritis. Considering that a formulation designed for intra-articular administration must meet sterility requirements to guarantee its safety, in this study the effect of gamma radiation sterilization on these microparticles was evaluated. The size, morphology, and surface characteristics of the microparticles and the encapsulation efficiency of rhein were not affected by the sterilization process. Although DSC and PXRD analyses suggested otherwise, rhein release profiles were not altered by gamma radiation. The release of rhein from the microparticles was fitted to a Gompertz model. In conclusion, the results of this study suggest that gamma radiation is a suitable method for the sterilization of rhein-loaded PLGA microparticles to enable their intra-articular administration in order to provide a therapeutic solution to patients suffering from chronic joint diseases.

The effect of source animal age, decellularization protocol, and sterilization method on bovine acellular dermal matrix as a scaffold for wound healing and skin regeneration.

Healing the full-thickness skin wounds has remained a challenge. One of the most frequently used grafts for skin regeneration is xenogeneic acellular dermal matrices (ADMs), including bovine ADMs. This study investigated the effect of the source animal age, enzymatic versus non-enzymatic decellularization protocols, and gamma irradiation versus ethylene oxide (EO) sterilization on the scaffold. ADMs were prepared using the dermises of fetal bovine or calf skins. All groups were decellularized through chemical and mechanical methods, unless T-FADM samples, in which an enzymatic step was added to the decellularization protocol. All groups were sterilized with ethylene oxide (EO), except G-FADM which was sterilized using gamma irradiation. The scaffolds were characterized through scanning electron microscopy, differential scanning calorimetry, tensile test, MTT assay, DNA quantification, and real-time PCR. The performance of the ADMs in wound treatment was also evaluated macroscopically and histologically. All ADMs were effectively decellularized. In comparison to FADM (EO-sterilized fetal ADM), morphological, and mechanical properties of G-FADM, T-FADM, and CADM (EOsterilized calf ADM) were changed to different extents. In addition, the CADM and G-FADM were thermally more stable than the FADM and T-FADM. Although all ADMs were noncytotoxic, the wounds of the FADM, T-FADM, and G-FADM groups were contracted to almost 30.0% of the original area on day 7, significantly faster than the CADM (17.5% ± 1.7) and control (12.2% ± 1.59) groups. However, by day 21, all ADMs were mostly closed except for the untreated group (60.1 ± 1.8). Altogether, fetal source and EO-sterilized samples performed better than calf source and gamma-sterilized samples unless in some mechanical properties. There was no added value in using enzymatic treatment during the decellularization process. Our results suggest that the age, decellularization, and sterilization methods of animal source should be selected based on the clinical requirements.

Evaluation of ethylene oxide, gamma radiation, dry heat and autoclave sterilization processes on extracellular matrix of biomaterial dental scaffolds

Scaffolds used to receive stem cells are a promising perspective of tissue regeneration research, and one of the most effective solutions to rebuild organs. In the near future will be possible to reconstruct a natural tooth using stems cells, but to avoid an immune-defensive response, sterilize the scaffold is not only desired, but also essential to be successful. A study confirmed stem cells extracted from rat’s natural teeth, and implanted into the alveolar bone, could differentiate themselves in dental cells, but the scaffold’s chemistry, geometry, density, morphology, adherence, biocompatibility and mechanical properties remained an issue. This study intended to produce a completely sterilized dental scaffold with preserved extracellular matrix. Fifty-one samples were collected, kept in formaldehyde, submitted to partial demineralization and decellularization processes and sterilized using four different methods: dry heating; autoclave; ethylene-oxide and gamma-radiation. They were characterized through optical images, micro-hardness, XRD, EDS, XRF, SEM, histology and sterility test. The results evidenced the four sterilization methods were fully effective with preservation of ECM molecular arrangements, variation on chemical composition (proportion of Ca/P) was compatible with Ca/P proportional variation between enamel and dentine regions. Gamma irradiation and ethylene oxide presents excellent results, but their viability are compromised by the costs and technology’s accessibility (requires very expensive equipment and/or consumables). Excepted gamma irradiation, all the sterilization methods more than sterilizing also reduced the remaining pulp. Autoclave presents easy equipment accessibility, lower cost consumables, higher reduction of remaining pulp and complete sterilization, reason why was considered the most promising technique.

A proposed new configuration of a shuffle-dwell gamma irradiator

A gamma irradiator is a well-developed installation for gamma radiation sterilization. A “shuffle-dwell” mode is preferable for high dose applications. A novel configuration of a shuffle-dwell gamma irradiator is proposed to increase energy utilization and throughput, which would result in higher profitability. While the minimum distance between any irradiation position and each source pencil, the minimum distance between the neighboring irradiation positions and the size of source pencils are kept the same as the current configuration, the irradiation positions and source pencils are rearranged based on the fact that radiation is emitted in an isotropic fashion. The computational results suggest that the proposed configuration requires an 8.7% smaller area and exposes the product to 11.8% more gamma radiation in a 10.7% shorter irradiation time. In other words, the proposed configuration needs a smaller area and shorter irradiation time to have a better performance compared to the current shuffle-dwell gamma irradiator. Note that the claim is based primarily on an analytical calculation. Experimental and manufacturing among other practical considerations will be taken into account in the future work to exhaustively evaluate the performance of the proposed configuration and to compare it with that of the traditional configuration.