Cross-linking of Polymers by Radiation

Effects of radiation dose and nitrogen purge on collagen scaffold properties

Sterilization of medical devices is commonly performed using radiation methods. However, collagen materials can be damaged when using standard radiation doses (25 kGy). Small increases of radiation dose can allow for increases in the acceptable initial bioburden load of aseptically manufactured devices while maintaining required sterility assurance levels, which is often critical in early stage translational settings. In this study, we hypothesized that small increases in radiation dose from 15 to 20 kGy would result in significant changes to several key characteristics of collagen scaffolds. Scaffolds were manufactured by lyophilizing the pepsin digest of dense bovine connective tissue in cylindrical molds and were irradiated at either 0, 15, 17.5, or 20 kGy with an additional group packaged in nitrogen and irradiated at 17.5 kGy. Groups were evaluated for changes to the soluble collagen and glycosaminoglycan mass fractions, protein banding patterns in electrophoresis, a collagen fragmentation assay, and resistance to enzymatic degradation. All parameters were statistically analyzed using one-way analysis of variance with Tukey's correction for multiple comparisons. The soluble collagen mass fraction was significantly decreased in the 20 kGy group; however, there was no significant effect of radiation dose or a nitrogen-rich environment on the other measured parameters, including protein banding patterns, fragmented collagen content, and resistance to enzymatic degradation.Statement of Clinical Significance: Collagen scaffolds have proven useful in clinical applications but can be damaged by standard radiation doses. Low-dose sterilization may be a viable alternative that minimally impacts key properties of these scaffolds.

Quantitative analysis of the effect of environmental-scanning electron microscopy on collagenous tissues

Environmental-scanning electron microscopy (ESEM) is routinely applied to various biological samples due to its ability to maintain a wet environment while imaging; moreover, the technique obviates the need for sample coating. However, there is limited research carried out on electron-beam (e-beam) induced tissue damage resulting from using the ESEM. In this paper, we use quantitative second-harmonic generation (SHG) microscopy to examine the effects of e-beam exposure from the ESEM on collagenous tissue samples prepared as either fixed, frozen, wet or dehydrated. Quantitative SHG analysis of tissues, before and after ESEM e-beam exposure in low-vacuum mode, reveals evidence of cross-linking of collagen fibers, however there are no structural differences observed in fixed tissue. Meanwhile wet-mode ESEM appears to radically alter the structure from a regular fibrous arrangement to a more random fiber orientation. We also confirm that ESEM images of collagenous tissues show higher spatial resolution compared to SHG microscopy, but the relative tradeoff with collagen specificity reduces its effectiveness in quantifying collagen fiber organization. Our work provides insight on both the limitations of the ESEM for tissue imaging, and the potential opportunity to use as a complementary technique when imaging fine features in the non-collagenous regions of tissue samples.