Propulsion in cubomedusae : mechanisms and utility

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 8 (2013): e56393, doi:10.1371/journal.pone.0056393.Evolutionary constraints which limit the forces produced during bell contractions of medusae affect the overall medusan morphospace such that jet propulsion is limited to only small medusae. Cubomedusae, which often possess large prolate bells and are thought to swim via jet propulsion, appear to violate the theoretical constraints which determine the medusan morphospace. To examine propulsion by cubomedusae, we quantified size related changes in wake dynamics, bell shape, swimming and turning kinematics of two species of cubomedusae, Chironex fleckeri and Chiropsella bronzie. During growth, these cubomedusae transitioned from using jet propulsion at smaller sizes to a rowing-jetting hybrid mode of propulsion at larger sizes. Simple modifications in the flexibility and kinematics of their velarium appeared to be sufficient to alter their propulsive mode. Turning occurs during both bell contraction and expansion and is achieved by generating asymmetric vortex structures during both stages of the swimming cycle. Swimming characteristics were considered in conjunction with the unique foraging strategy used by cubomedusae.This work was supported by an ONR MURI award (N000140810654) and National Science Foundation grant OCE 0623508 to JHC, SPC, JOD. And the work was supported by the Roger Williams University Foundation to Promote Scholarship

Thermal Aggregation Properties of Nanoparticles Modified with Temperature Sensitive Copolymers

In this paper, we describe the use of a temperature responsive polymer to reversibly assemble gold nanoparticles of various sizes. Temperature responsive, low critical solution temperature (LCST) pNIPAAm-<i>co</i>-pAAm polymers, with transition temperatures (<i>T</i>_C) of 51 and 65 °C, were synthesized with a thiol modification, and grafted to the surface of 11 and 51 nm gold nanoparticles (AuNPs). The thermal-responsive behavior of the polymer allowed for the reversible aggregation of the nanoparticles, where at <i>T</i> < <i>T</i>_C the polymers were hydrophilic and extended between particles. In contrast, at <i>T</i> > <i>T</i>_C, the polymer shell undergoes a hydrophilic to hydrophobic phase transition and collapses, decreasing interparticle distances between particles, allowing aggregation to occur. The AuNP morphology and polymer conjugation were probed by TEM, FTIR, and ¹H NMR. The thermal response was probed by UV–vis and DLS. The structure of the assembled aggregates at <i>T</i> > <i>T</i>_C was studied via in situ small-angle X-ray scattering, which revealed interparticle distances defined by polymer conformation

Multifunctional DNA-Gold Nanoparticles for Targeted Doxorubicin Delivery

In this report we describe the synthesis, characterization, and cytotoxic properties of DNA-capped gold nanoparticles having attached folic acid (FA), a thermoresponsive polymer (<i>p</i>), and/or poly­(ethylene glycol) (PEG) oligomers that could be used to deliver the anticancer drug doxorubicin (DOX) in chemotherapy. The FA-DNA oligomer used in the construction of the delivery vehicle was synthesized through the reaction of the isolated folic acid <i>N</i>-hydroxysuccinimide ester with the amino-DNA and the conjugated DNA product was purified using high performance liquid chromatography (HPLC). This approach ultimately allowed control of the amount of FA attached to the surface of the delivery vehicle. Cytotoxicity studies using SK-N-SH neuroblastoma cells with drug loaded delivery vehicles were carried out using a variety of exposure times (1–48 h) and recovery times (1–72 h), and in order to access the effects of varying amounts of attached FA, in culture media deficient in FA. DOX loaded delivery vehicles having 50% of the DNA strands with attached FA were more cytotoxic than when all of the strands contained FA. Since FA stimulates cell growth, the reduced cytotoxicity of vehicles fully covered with FA suggests that the stimulatory effects of FA can more than compensate for the cytotoxic effects of the drug on the cell population. While attachment of hexa-ethylene glycol PEG(18) to the surface of the delivery vehicle had no effect on cytotoxicity, 100% FA plus the thermoresponsive polymer resulted in IC₅₀ = 0.48 ± 0.01 for an exposure time of 24 h and a recovery time of 1 h, which is an order of magnitude more cytotoxic than free DOX. Confocal microscopic studies using fluorescence detection showed that SK-N-SH neuroblastoma cells exposed to DOX-loaded vehicles have drug accumulation inside the cell and, in the case of vehicles with attached FA and thermoresponsive polymer, the drug appears more concentrated. Since the biological target of DOX is DNA, the latter observation is consistent with the high cytotoxicity of vehicles having both FA and the thermoresponsive polymer. The study highlights the potential of DNA-capped gold nanoparticles as delivery vehicles for doxorubicin in cancer chemotherapy

Using Temperature-Sensitive Smart Polymers to Regulate DNA-Mediated Nanoassembly and Encoded Nanocarrier Drug Release

In this paper we describe the use of a temperature-responsive polymer to regulate DNA interactions in both a DNA-mediated assembly system and a DNA-encoded drug delivery system. A thermoresponsive pNIPAAm-<i>co</i>-pAAm polymer, with a transition temperature (<i>T</i>_C) of 51 °C, was synthesized with thiol modification and grafted onto gold nanoparticles (Au NPs) also containing single-stranded oligonucleotides (ssDNA). The thermoresponsive behavior of the polymer regulated the accessibility of the sequence-specific hybridization between complementary DNA-functionalized Au NPs. At <i>T</i> < <i>T</i>_C, the polymer was hydrophilic and extended, blocking interaction between the complementary sequences at the periphery of the hydrodynamic diameter. In contrast, at <i>T</i> > <i>T</i>_C, the polymer shell undergoes a hydrophilic to -phobic phase transition and collapses, shrinking below the outer ssDNA, allowing for the sequence-specific hybridization to occur. The potential application of this dynamic interface for drug delivery is shown, in which the chemotherapy drug doxorubicin (DOX) is bound to double-stranded DNA (dsDNA)-functionalized Au NPs whose sequences are known to be high-affinity intercalation points for it. The presence of the polymer capping is shown to decrease drug release kinetics and equilibrium at <i>T</i> < <i>T</i>_C, but increase release at <i>T</i> > <i>T</i>_C, thus improving the cytotoxicity of the encoded nanocarrier design