Effect of gamma radiation and accelerated electron beam on stable paramagnetic centers induction in bone mineral: influence of dose, irradiation temperature and bone defatting

Immobilizing Bactericides on Dental Resins via Electron Beam Irradiation

Polymerizable bactericides, such as quaternary ammonium compound-based monomers, have been intensively studied as candidates for immobilizing antibacterial components on dental resin. However, they predominantly exhibit a bacteriostatic behavior, rather than bactericidal, as the immobilized components are left with insufficient molecular movement to disrupt the bacterial surface structure through contact-mediated action. In this study, we developed a novel strategy to increase the density of the immobilized bactericide and enhance its antibacterial/antibiofilm properties by combining a surface-grafting technique with electron beam irradiation. A solution of the quaternary ammonium compound-based monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), was coated on polymethyl methacrylate (PMMA) resin specimens at the concentrations of 30, 50, and 80 wt%. The coated resins were subsequently exposed to 10 MeV of electron beam irradiation at 50 and 100 kGy, followed by thermal stabilization at 60 °C. The antibacterial effect was evaluated by inoculating a Streptococcus mutans suspension on the coated PMMA resin samples, which exhibited bactericidal effects even after 28 d of aging (P < 0.05, Tukey's honestly significant difference test). Transmission electron microscopy and bacteriolytic activity evaluation revealed that the S. mutans cells had sustained membrane depolarization. Furthermore, the antibiofilm effects against S. mutans and bacteria collected from human saliva were assessed. The thickness and the percentage of membrane-intact cells of the S. mutans and multispecies biofilms formed on the MDPB-immobilized surfaces were significantly lower than the uncoated PMMA specimens, even after 28-d aging (P < 0.05, Tukey's honestly significant difference test). Thus, the immobilization of antibacterial MDPB via electron beam irradiation induced rapid membrane depolarization, increasing membrane permeability and eventually causing cell death. Our strategy substantially enhances the antibacterial properties of the resinous materials and inhibits biofilm formation, therefore demonstrating significant potential for preventing infectious diseases in the oral environment.

Decellularized xenografts in regenerative medicine: From processing to clinical application

Decellularized xenografts are an inherent component of regenerative medicine. Their preserved structure, mechanical integrity and biofunctional composition have well established them in reparative medicine for a diverse range of clinical indications. Nonetheless, their performance is highly influenced by their source (ie species, age, tissue) and processing (ie decellularization, crosslinking, sterilization and preservation), which govern their final characteristics and determine their success or failure for a specific clinical target. In this review, we provide an overview of the different sources and processing methods used in decellularized xenografts fabrication and discuss their effect on the clinical performance of commercially available decellularized xenografts.

Electron beam effect on biomaterials I: focusing on bone graft materials

BACKGROUND

To develop biocompatible bony regeneration materials, allogenic, xenogenic and synthetic bones have been irradiated by an electron beam to change the basic structures of their inorganic materials. The optimal electron beam energy and individual dose have not been established for maximizing the bony regeneration capacity in electron beam irradiated bone.

RESULTS

Commercial products consisting of four allogenic bones, six xenogenic bones, and six synthetic bones were used in this study. We used 1.0-MeV and 2.0 MeV linear accelerators (power: 100 KW, pressure; 115 kPa, temperature; -30 to 120°C, sensor sensitivity: 0.1-1.2 mV/kPa, generating power sensitivity: 44.75 mV/kPa, supply voltage: 50.25 V), and a microtrone with different individual irradiation doses such as 60 kGy and 120 kGy. Additional in vitro analyses were performed by elementary analysis using field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and confocal laser scanning microscopy (CLSM). In vivo clinical, radiographic, and micro-computed tomography (Micro-CT) with bone marrow density (BMD) analysis was performed in 8- and 16-week-old Spraque-Dawley rats with calvarial defect grafts.

CONCLUSIONS

Electron beam irradiation of bony substitutes has four main effects: the cross-linking of biphasic calcium phosphate bony apatite, chain-scissioning, the induction of rheological changes, and microbiological sterilization. These novel results and conclusions are the effects of electron beam irradiation.

High-dose electron beam sterilization of soft-tissue grafts maintains significantly improved biomechanical properties compared to standard gamma treatment

Allografts have gained increasing popularity in anterior cruciate ligament (ACL) reconstruction. However, one of the major concerns regarding allografts is the possibility of disease transmission. Electron beam (Ebeam) and Gamma radiation have been proven to be successful in sterilization of medical products. In soft tissue sterilization high dosages of gamma irradiation have been shown to be detrimental to biomechanical properties of grafts. Therefore, it was the objective of this study to compare the biomechanical properties of human bone-patellar tendon-bone (BPTB) grafts after ebeam with standard gamma irradiation at medium (25 kGy) and high doses (34 kGy). We hypothesized that the biomechanical properties of Ebeam irradiated grafts would be superior to gamma irradiated grafts. Paired 10 mm-wide human BPTB grafts were harvested from 20 donors split into four groups following irradiation with either gamma or Ebeam (each n = 10): (A) Ebeam 25 kGy, (B) Gamma 25 kGy, (C) Ebeam 34 kGy (D) Gamma 34 kGy and ten non-irradiated BPTB grafts were used as controls. All grafts underwent biomechanical testing which included preconditioning (ten cycles, 0-20 N); cyclic loading (200 cycles, 20-200 N) and a load-to-failure (LTF) test. Stiffness of non-irradiated controls (199.6 ± 59.1 N/mm) and Ebeam sterilized grafts did not significantly differ (152.0 ± 37.0 N/mm; 192.8 ± 58.0 N/mm), while Gamma-irradiated grafts had significantly lower stiffness than controls at both irradiation dosages (25 kGy: 126.1 ± 45.4 N/mm; 34 kGy: 170.6 ± 58.2 N/mm) (p < 0.05). Failure loads at 25 kGy were significantly lower in the gamma group (1,009 ± 400 N), while the failure load was significantly lower in both study groups at high dose irradiation with 34 kGy (Ebeam: 1,139 ± 445 N, Gamma: 1,073 ± 617 N) compared to controls (1,741 ± 304 N) (p < 0.05). Creep was significantly larger in the gamma irradiated groups (25 kGy: 0.96 ± 1.34 mm; 34 kGy: 1.06 ± 0.58 mm) than in the Ebeam (25 kGy: 0.50 ± 0.34 mm; 34 kGy: 0.26 ± 0.24 mm) and control (0.20 ± 0.18 mm) group that did not differ significantly. Strain difference was not different between either control or study groups (controls: 1.0 ± 0.03; Ebeam 34 kGy 1.04 ± 0.018; Gamma 34 kGy 1.0 ± 0.028; 25 kGy: 1.4 ± 2,0; 34 kGy: 1.1 ± 1.1). The most important result of this study was that ebeam irradiation showed significantly less impairment of the biomechanical properties than gamma irradiation. Considering the results of this study and the improved control of irradiation application with electronic beam, this technique might be a promising alternative in soft-tissue sterilization.