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

Abstract

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.

Keywords: Allogenic bone; Bony regeneration; Electron beam irradiation; Synthetic bone; Xenogenic bone.

Figure 1

Schematic drawing of the basic compositions of human bone.

Figure 2

Basic study designs showing the electron beam irradiated bone materials, according to their origin, energy, and radiation dose.

Figure 3

Basic units of the electron beam irradiation devices in EB Tech Co., Daejeon, South Korea. Specimens holding tables (A), monitoring device, and the actual radiation dosages according to the set energy (B), and schematic time-tables of the clinical, radiologic, and histologic study of a calvarial defect model grafted with electron beam-irradiated bone materials (C).

Figure 4

Implantation of each bone material and the evaluation process showing the exposed bilateral frontal bone of the Sprague-Dawley rat (A), 5.0-mm-diameter perforations of the frontal bone were created with a round bur, avoiding damage to the internal brain tissues (B), implantation of each perforated calvarial wound (C), acquired frontal bone tissue including the perforated area and covering periosteal membrane after 8 weeks (D) and 16 weeks (E).

Figure 5

Elementary analysis of BBP® and Bio-cera® according to the different conditions of EBI.

Figure 6

The X-ray diffraction (XRD) patterns of BMP® with several strong X-ray deflection peaks noted not to change with different EBI conditions.

Figure 7

Horizontal radiographic views of the BMP® implanted frontal bone after 8 weeks, no beam treatment (A), 1 MeV-60 kGy (B), 1 MeV-120 kGy (C), 2 MeV-60 kGy (D), and 2 MeV-120 kGy (E).

Figure 8

Comparison of the coronal Micro-CT views of the regenerated frontal bone under the different conditions after 8 and 16 weeks (right) of the electron beam-irradiated BMP® implantation. No beam treatment (A,F), 1 MeV-60 kGy (B,G), 1 MeV-120 kGy (C,H), 2 MeV-60 kGy (D,I), and 2 MeV-120 kGy (E,J).

Figure 9

Comparison of bone marrow density in the Bio-cera® and BMP® bone materials, showing a slight increase in the 1 MeV-60 Gy and 2 MeV-60 Gy irradiated BMP®.

Figure 10

Photomicrographs of the regenerated frontal bone after 8 (left) and 16 weeks (right) after electron beam-irradiated BMP® implantation, with the coronal views of each condition are compared.

Figure 11

Schematic drawings of the basic electron beam accelerator including the electron gun, cathodic emitter, grid, anode, magnetic focusing lens and magnetic deflection coil. This accelerator includes the beam-defining system in electron mode.