Clustering of Cyclodextrin-Functionalized Microbeads by an Amphiphilic Biopolymer: Real-Time Observation of Structures Resembling Blood Clots

Abstract

Colloidal particles can be induced to cluster by adding polymers in a process called bridging flocculation. For bridging to occur, the polymer must bind strongly to the surfaces of adjacent particles, such as via electrostatic interactions. Here, we introduce a new system where bridging occurs due to specific interactions between the side chains of an amphiphilic polymer and supramolecules on the particle surface. The polymer is a hydrophobically modified chitosan (hmC) while the particles are uniform polymeric microbeads (∼160 μm in diameter) made by a microfluidic technique and functionalized on their surface by α-cyclodextrins (CDs). The CDs have hydrophobic binding pockets that can capture the n-alkyl hydrophobes present along the hmC chains. Clustering of CD-coated microbeads in water by hmC is visualized in real time using optical microscopy. Interestingly, the clustering follows two distinct stages: first, the microbeads are bridged into clusters by hmC chains, which occurs by the interaction of individual chains with the CDs on adjacent particles. Thereafter, additional hmC from the solution adsorbs onto the surfaces of the microbeads and an hmC "mesh" grows around the clusters. This growing nanostructured mesh can trap surrounding microsized objects and sequester them within the overall cluster. Such clustering is reminiscent of blood clotting where blood platelets initially cluster at a wound site, whereupon they induce growth of a protein (fibrin) mesh around the clusters, which entraps other passive cells. Clustering does not occur with the native chitosan (lacking hydrophobes) or with the bare particles (lacking CDs); these results confirm that the clustering is indeed due to hydrophobic interactions between the hmC and the CDs. Microbead clustering via amphiphilic biopolymers could be applicable in embolization, which is a surgical technique used to block blood flow to a particular area of the body, or in agglutination assays.

Recent Advances on Polymeric Beads or Hydrogels as Embolization Agents for Improved Transcatheter Arterial Chemoembolization (TACE)

“…To achieve a better embolization effect, material scientists tried to further conjugate microbeads into a polymeric mesh, using amphiphilic polymers. As a typical example, Arya et al (2017) designed biopolymer chitosan-glutaraldehyde (chitosan-GA) microbeads with surface modification, i.e., having sulfated α-cyclodextrin (α-CD) as host molecules on the microbead surfaces, by taking the advantages of electronic attraction between cationic chitosan-GA microbeads and anionic sulfated α-CD (Figure 3, upper panel). Furthermore, the reaction between hydrophilic chitosan and hydrophobic n-dodecyl aldehyde rendered amphiphilic chitosan derivatives, whose hydrophobic segments could form an inclusion complex with α-CD due to its hydrophobic inner cavity nature.…”

“…Schematic illustration of using amphiphilic hydrophobically modified chitosan (hmC) as cross-linking reagents for chitosan-glutaraldehyde (chitosan-GA) microbeads with surfaced modification of sulfated α-cyclodextrin (α-CD), as well as the self-assembly between hydrophobic chain of hmC and α-CD cavity, which could lead to formation of polymeric mesh outside microbeads for clotting applications. [Reproduced with permission from Arya et al (2017), Copyright 2017 American Chemical Society].…”