Biomedical subjects

Kristian Helmerson

Publications and source records attributed to Kristian Helmerson.

3 recordsLinked to original sources

PubMed2006

Stable and robust polymer nanotubes stretched from polymersomes.

We create long polymer nanotubes by directly pulling on the membrane of polymersomes using either optical tweezers or a micropipette. The polymersomes are composed of amphiphilic diblock copolymers, and the nanotubes formed have an aqueous core connected to the aqueous interior of the polymersome. We stabilize the pulled nanotubes by subsequent chemical cross-linking. The cross-linked nanotubes are extremely robust and can be moved to another medium for use elsewhere. We demonstrate the ability to form networks of polymer nanotubes and polymersomes by optical manipulation. The aqueous core of the polymer nanotubes together with their robust character makes them interesting candidates for nanofluidics and other applications in biotechnology.

Chemical Phenomena↗

PubMed2005

Directed growth of pure phosphatidylcholine nanotubes in microfluidic channels.

The morphology of self-assembled phospholipid membranes (e.g., micelles, vesicles, rods, tubes, etc.) depends on the method of formation, secondary manipulation, temperature, and storage conditions. In this contribution, microfluidic systems are used to create pure phosphatidylcholine (PC) micro- and nanotubes with unprecedented lengths. Tubes up to several centimeters in length and aligned with the long axis of the microchannel were created from spots of dry films of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). These high aspect ratio structures, which, to our knowledge, represent the first examples of extended tubes formed from pure PC lipids, were examined by fluorescence microscopy, electron and optical microscopy, and optical manipulation tools (i.e., a laser trap and laser scalpel) to characterize structure and stability. In particular, the tubular structure was confirmed by observation of fluorescent dyes that were sequestered within the aqueous cavity or within the phospholipid tube. Compared to other phospholipid tubes, the tubes formed from PC lipids in microfluidic channels show high mechanical stability and rigidity that depend on tube size, age, and storage conditions.

Microfluidics↗

PubMed2002

Real-time measurement of spontaneous antigen-antibody dissociation.

We report observations in real time of thermally driven adhesion and dissociation between a monoclonal IgE antibody and its specific antigen N-epsilon-2,4-dinitrophenyl-L-lysine. Both molecules were attached to the surfaces of different polystyrene microspheres trapped by optical tweezers. Monitoring spontaneous successive attachment and detachment events allowed a direct determination of the reaction-limited detachment rate k(off) for a single bond and also for multiple bonds. We observed both positive and negative cooperativity between multiple bonds depending on whether the antigen was linked to the microsphere with or without a tether, respectively.

Antigen-Antibody Reactions↗