Abstract
The defensive slime of hagfish consists of a polyanionic mucin hydrogel that synergistically interacts with a fiber network forming a coherent and elastic hydrogel in high ionic strength seawater. In seawater, the slime deploys in less than a second entrapping large quantities of water by a well-timed thread skein unravelling and mucous gel swelling. This rapid and vast hydrogel formation is intriguing, as high ionic strength conditions generally counteract the swelling speed and ratio of polyelectrolyte hydrogels. In this work we investigate the effect of ionic strength and seawater cations on slime formation dynamics and functionality. In the absence of ionic strength skeins swell radially and unravel uncontrolled, probably causing tangling and creating a confined thread network that entraps limited water. At high ionic strength skeins unravel, but create a collapsed and dense fiber network. High ionic strength conditions therefore seem crucial for controlled skein unraveling, however not sufficient for water retention. Only the presence of naturally occurring Ca2+ or Mg2+-ions allowed for an expanded network and full water retention probably due to Ca2+-mediated vesicle rupture and cross-linking of the mucin. Our study demonstrates that hagfish slime deployment is a well-timed, ionic-strength, and divalent-cation dependent dynamic hydrogel formation process.
Highlights
In this work we investigate the effect of ionic strength and seawater cations on slime formation dynamics and functionality
Slime in Milli-Q initially retained 7.5 g of water, which is roughly 50% less compared to the 14.7 g retained in seawater (Fig. 2c). We suggest that this effect is caused by altered network formation dynamics
In this study we demonstrate the crucial role of ionic strength and seawater cations - especially Ca2+ - for the formation dynamics and functionality of hagfish slime
Summary
The captured hagfish were transferred to a seawater fed basin and subsequent slime exudate sampling was performed according to the approved ethical application by the Forsøksdyrutvalget (FOTS ID 6912) and followed a modified protocol of Herr et al.[9] described by Böni et al.[25]. Viscosity measurements with hagfish mucins were done by mixing mucin vesicles suspension with seawater, diluted seawater, or Milli-Q. Water retention measurements to assess slime functionality were performed according to a protocol of Böni et al.[25]. The concentration of cations (Na+, K+, Ca2+, Mg2+) in seawater and in seawater that interacted with hagfish slime was determined using flame atomic absorption spectroscopy (AAS). Slime samples were prepared as for the water retention measurements and slime was removed using the in-house built mixing device described above. All data generated or analysed in this study are included in this published article and its Supplementary Information files
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