Research ArticleBIOMOLECULES

Enzymatically active biomimetic micropropellers for the penetration of mucin gels

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Science Advances  11 Dec 2015:
Vol. 1, no. 11, e1500501
DOI: 10.1126/sciadv.1500501
  • Fig. 1 Mechanism for mucin penetration.

    Schematic illustration of the propulsion strategy of H. pylori through mucin gels and the catalytically active magnetic micropropellers presented here. The enzyme on the helices’ surface hydrolyzes urea and liquefies the environment via the resulting local rise in pH.

  • Fig. 2 Acid-stable, enzyme-functionalized micropropellers.

    (A) Fabrication process of acid-stable, enzyme-functionalized magnetic micropropellers consisting of GLAD on top of a monolayer of silica beads, ALD to protect the resulting magnetic helices, enzyme immobilization, and ultrasonication in solution to remove the particles from the wafer. (B) ESB-SEM (energy-selective backscatter–scanning electron microscopy) image of a magnetic micropropeller, with the Ni section clearly visible. Scale bar, 500 nm.

  • Fig. 3 Urease activity.

    SiO2 beads (~50 μm in diameter) functionalized with urease using GA coupling, in a solution of 100 mM urea colored with the pH indicator bromothymol blue. The beads were dried on a coverslip and micrographs were recorded 1, 2, 3, 4, and 5 min after the addition of urea solution. The blue coloring clearly demonstrates the increase in pH due to catalytic urea hydrolysis.

  • Fig. 4 Mucin rheology.

    (A) Viscoelastic properties of reconstituted PGMs at different pH conditions. A 2% solution of PGMs exhibits a clear sol-gel transition between pH 4.5 and pH 7. Closed symbols denote the storage modulus G′(f), and open symbols denote the loss modulus G″(f). (B) Gelation of the PGM solution is neither suppressed by the addition of 1 mM bile salts (BS; sodium glycodeoxycholate and sodium taurocholate) nor suppressed by the addition of 20 mM urea, the use of 5.5 mM HCl instead of a pH 4.5 reconstitution buffer, or ultrasonication.

  • Fig. 5 Propulsion in mucin gels.

    (A to D) Tracks of micropropellers with (B and D) and without (A and C) urease immobilized on the surface, in an acidified 2% mucin gel with (A and B) and without (C and D) 20 mM urea over a time frame of 25 s. The particles were propelled in the x direction at a frequency of 30 Hz and a magnetic field strength of 10 mT. Each graph shows the tracks from one video recording. (E) The average velocity under these conditions is shown and represents an average of a minimum of 50 particles tracked over at least 10 s. Only the x component of the velocity was taken into account; the small drift in the y direction that can sometimes be observed when the particles are close to the glass surface [as in (D)], or “kinks” in the y direction due to hydrodynamic interactions with another propeller in proximity [as in the topmost trajectory in (B)], was neglected. The corresponding videos can be found in the Supplementary Materials.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/11/e1500501/DC1

    Movie S1. Magnetic microhelices in neutral PGM solutions (0.5% mucin in the left panel and 0.25% in the right panel) being propelled in the x direction at a frequency of 30 Hz and a magnetic field strength of 10 mT.

    Movie S2. Magnetic microhelices with and without urease immobilized on the surface in an acidified 2% mucin gel containing 1 mM bile salts, with and without 20 mM urea over a time frame of 40 s.

  • Supplementary Materials

    This PDF file includes:

    • Legends for movies S1 and S2

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Magnetic microhelices in neutral PGM solutions (0.5% mucin in the left panel and 0.25% in the right panel) being propelled in the x direction at a frequency of 30 Hz and a magnetic field strength of 10 mT.
    • Movies S2 (.avi format). Magnetic microhelices with and without urease immobilized on the surface in an acidified 2% mucin gel containing 1 mM bile salts, with and without 20 mM urea over a time frame of 40 s.

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