Encapsulation of degraded DNA in alginate hydrogels: rheological characterization and applicability to forensic science

Forensic biomaterials are on the rise, with efforts in developing ex vivo tissue and blood mimetics. Incorporation of small and degraded DNA into these materials has implications for research and training across many areas of forensic science. 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 adding 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 found that encapsulating DNA within an alginate-based, ionically crosslinked hydrogel produced the greatest differentiation in rheological profiles among DNA with varying physical properties. The different 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 and the time since deposition of bloodstains used for DNA extraction (r = -0.57 to r = 0.62). This indicates that dilute, polydisperse and degraded genomic DNA extracts can effectively modulate the rheological properties of the encapsulating hydrogel. Our results demonstrate the viability of using rheology as a technique to analyze encapsulated dilute DNA oligos and degraded DNA while highlighting the need to consider the type of oligos included in forensic biomaterials.