Encapsulation of degraded DNA in alginate hydrogels: Rheological characterization and applicability to forensic...

Forensic biomaterials are on the rise, with efforts focused on developing realistic tissue and blood mimetics. The incorporation of small and degraded DNA into these materials enhances their realism and functionality, which has implications for research and training across forensic science. It is therefore important to understand the physicochemical and conformational changes that DNA undergoes during ex vivo degradation. Large fragments of highly concentrated genomic and phage DNA in solution have been characterized using rheology; however, this amount and size of DNA are atypical in DNA extracted from forensic evidence. In this work, we investigated how the addition of synthetic DNA oligos and genomic DNA extracted from bloodstains deposited for up to 19 months influenced the rheological properties of polymer systems intended for forensic biomaterial synthesis. We used FTIR spectroscopy to probe interactions between DNA and the encapsulating matrix and automated gel electrophoresis to record DNA quality/quantity metrics, both of which supported our rheological findings. Encapsulating DNA within an alginate-based, ionically crosslinked hydrogel produced the greatest differentiation in rheological profiles among DNA with varying physical properties. The distinct conformations and sizes of encapsulated DNA oligos exhibited significantly different responses during strain amplitude sweeps (p < 0.05). We also observed moderate correlations between the rheological responses of DNA extracts and the time since deposition of corresponding bloodstains (r = -0.57 to r = 0.62). This indicates that dilute, polydisperse and degraded genomic DNA extracts can modulate the rheological properties of the encapsulating hydrogel, highlighting the need to consider the type of DNA included in forensic biomaterials. Our results demonstrate the potential for rheology to serve as a complementary technique when analyzing encapsulated dilute DNA oligos and degraded DNA.