Influence of electron beam irradiation doses on bone regeneration by octacalcium phosphate collagen composites

Structure and properties of the acellular porcine cornea irradiated with electron beam and its in-situ implantation

Different sterilization doses of the electron beam (E-beam) will change the properties of biomaterials and affect their clinical application. Acellular porcine cornea (APC) is a promising corneal substitute to alleviate the shortage of corneal resources. The residual DNA was significantly reduced to 18.50 ± 3.19 ng/mg, and the clearance rate of α-Gal was close to 100% after the treatment with freezing-thawing combined enzyme, indicating that the decellularization was effective. The effects of different E-beam doses at 0, 2, 8, 15, and 25 kGy on the APC were studied. With the increase in irradiation dose, the transmittance, tensile strength, and swelling ratio of APC gradually decreased, but the resistance to enzymatic degradation was stronger than that of non-irradiated APC, especially at 8 kGy. The structure of APC was denser after irradiation, but the dose of 25 kGy could cause partial collagen fiber fracture and increase the pore size. The cell viability of the APC irradiated by 15 and 25 kGy were greater than 80%. After the implantation in rabbit corneas, there was no obvious neovascularization and inflammation, but the dose of 25 kGy had a more destructive effect on the chemical bonds of collagen, which made the APC easier to be degraded. The thickness of APC in the 25 kGy group was thinner than that in the 15 kGy group 1 year after surgery, and the epithelium grew more slowly, so the E-beam dose of 15 kGy might be more suitable for the sterilization of APC.

Electron-Beam Irradiated Recombinant Human Collagen-Phosphorylcholine Corneal Implants Retain Pro-Regeneration Capacity

Sterilization of biodegradable, collagen-based implants is challenging as irradiation sterilization methods can alter their mechanical properties. Electron beam (EB) irradiation is a terminal sterilization method that has been used for biologically-derived implants. Here, recombinant human collagen type III-phosphorylcholine (RHCIII-MPC) hydrogels were irradiated with EB doses of 17, 19, or 21 kGy and their subsequent biocompatibility and ability to promote regeneration in rabbit corneas was evaluated. Unirradiated hydrogels stored in 1% chloroform in phosphate-buffered saline (C-PBS) were the controls. There were no significant differences between irradiated and non-irradiated samples in optical or physical properties (tensile strength, modulus, elasticity), or the ability to support cell growth. However, irradiated implants were more sensitive to high levels of collagenase than unirradiated controls and the C-PBS implants had increased cell growth compared to EB and controls at 72 h. Corneal implants e-beamed at 17 kGy or e-beamed and subsequently frozen (EB-F) to increase shelf-life showed no adverse biological effects of the irradiation. EB, EB-F, and C-PBS implanted corneas all rapidly re-epithelialized but showed mild neovascularization that resolved over 6 months. The regenerated neo-corneas were transparent at 6 months post-operation. In vivo confocal microscopy confirmed normal morphology for the epithelium, stroma, sub-basal nerves and unoperated endothelium. Histology showed that all the regenerated corneas were morphologically similar to the normal. Immunohistochemistry indicated the presence of a differentiated corneal epithelium and functional tear film. In conclusion, the e-beamed corneal implants performed as well as non-irradiated control implants, resulting in fully regenerated neo-corneas with new nerves and without blood vessels or inflammation that may impede vision or corneal function. Therefore, a complete validation study to establish EB irradiation as an effective means for corneal implant sterilization prior to clinical application is necessary as a next step.

Clinical study of octacalcium phosphate and collagen composite in oral and maxillofacial surgery

Octacalcium phosphate and its collagen composite have been recognized as bone substitute materials possessing osteoconductivity and biodegradation properties. We evaluated the effectiveness of octacalcium phosphate and its collagen composite used for bone augmentation in major oral and maxillofacial surgeries in a clinical trial. Octacalcium phosphate and its collagen composite were used in cases of sinus floor elevation in 1- and 2-stage, socket preservation, cyst, and alveolar cleft procedures. A total of 60 patients were evaluated for effectiveness after the implantation of octacalcium phosphate and its collagen composite. Although sinus floor elevation in 1-stage, cyst, and alveolar cleft cases met the criteria for the judgment of success, sinus floor elevation in 2-stage and socket preservation groups did not meet the criteria in the initial evaluation. However, an additional evaluation for reconfirmation revealed the effectiveness of octacalcium phosphate and its collagen composite in those groups, and all evaluation results ultimately indicated the success of this clinical trial. Therefore, this clinical trial suggested that application of octacalcium phosphate and its collagen composite for oral and maxillofacial surgery was safe and effective and that octacalcium phosphate and its collagen composite could be a bone substitute candidate instead of autologous bone.

Bone regeneration by freeze-dried composite of octacalcium phosphate collagen and teriparatide

OBJECTIVE

Octacalcium phosphate (OCP) and collagen (col) composite (OCPcol) demonstrated superior bone regeneration properties, and its commercialization appears to be forthcoming. As a practical medical material for new combination products, we developed a freeze-dried composite with OCPcol and teriparatide (TPTD) (OCPcolTPTDf), and investigated its bone regenerative properties.

MATERIALS AND METHODS

A disk of OCPcol was made by mixing OCP granules and atelocollagen for medical use. Then, OCPcolTPTDf was prepared by impregnation of the OCPcol disk with 1.0 or 0.1 µg of TPTD solution (OCPcolTPTDf 1.0 and OCPcolTPTDf 0.1, respectively) followed by lyophilization. In vitro release profiles of TPTD from OCPcolTPTDf were determined using an enzyme-linked immunosorbent assay. Implantation of OCPcolTPTDf or OCPcol was carried out for a rat critical-sized calvarial defect. And five defects in each group were collected after 12 weeks of implantation.

RESULTS

The retention-release profiles of TPTD from OCPcolTPTDf supported a higher degree of retention of TPTD. Radiographic, histological, and histomorphometric examinations indicated that regenerated bone was filled in most of the defects of the OCPcolTPTDf. Additionally, the OCPcolTPTDf groups showed significantly enhanced bone regeneration compared with the OCPcol group.

CONCLUSIONS

These results suggested that this newly developed bone regenerative composite could be a practical medical material.