Biomedical subjects

Chao Zhu

Publications and source records attributed to Chao Zhu.

5 recordsLinked to original sources

PubMed2007

Reversible vesicle restraint in response to spatiotemporally controlled electrical signals: a bridge between electrical and chemical signaling modes.

Microelectronic devices employ electrons for signaling whereas the nervous system signals using ions and chemicals. Bridging these signaling differences would benefit applications that range from biosensing to neuroprosthetics. Here, we report the use of localized electrical signals to perform an operation common to chemical signaling in the nervous system. Specifically, we employ electrical signals to restrain vesicles reversibly. We perform this operation using the stimuli-responsive aminopolysaccharide chitosan that is able to electrodeposit onto cathode surfaces in response to localized electrical stimuli. We show that surfactant-vesicles and liposomes can be co-deposited with chitosan and are entrapped (i.e., restrained) within the deposited film's matrix. Vesicle co-deposition could be controlled spatially and temporally using microfabricated wafers with independent electrode addresses. Finally, we show that vesicles restrained within the deposited chitosan matrix can be mobilized under mildly acidic conditions (pH <6.5) that resolubilize chitosan. Potentially, the ability to restrain and mobilize chemical signals that are segregated within vesicles may allow microfluidic systems to access the rich diversity offered by chemical signaling.

Animals↗

PubMed2007

Testing the proportional odds model for interval-censored data.

This paper discusses the goodness-of-fit test for the proportional odds model for K-sample interval-censored failure time data, which frequently occur in, for example, periodic follow-up survival studies. The proportional odds model has a feature that allows the ratio of two hazard functions to be monotonic and converge to one and provides an important tool for the modeling of survival data. To test the model, a procedure is proposed, which is a generalization of the method given in Dauxois and Kirmani [Dauxois JY, Kirmani SNUA (2003) Biometrika 90:913-922]. The asymptotic distribution of the procedure is established and its properties are evaluated by simulation studies

Biometry↗

PubMed2006

Bioinspired vesicle restraint and mobilization using a biopolymer scaffold.

Biology employs vesicles to package molecules (e.g., neurotransmitters) for their targeted delivery in response to specific spatiotemporal stimuli. Biology is also capable of employing localized stimuli to exert an additional control on vesicle trafficking; intact vesicles can be restrained (or mobilized) by association with (or release from) a cytoskeletal scaffold. We mimic these capabilities by tethering vesicles to a biopolymer scaffold that can undergo (i) stimuli-responsive network formation (for vesicle restraint) and (ii) enzyme-catalyzed network cleavage (for vesicle mobilization). Specifically, we use the aminopolysaccharide chitosan as our scaffold and graft a small number of hydrophobic moieties onto its backbone. These grafted hydrophobes can insert into the bilayer to tether vesicles to the scaffold. Under acidic conditions, the vesicles are not restrained by the hydrophobically modified chitosan (hm-chitosan) because this scaffold is soluble. Increasing the pH to neutral or basic conditions allows chitosan to form interpolymer associations that yield a strong, insoluble restraining network. Enzymatic hydrolysis of this scaffold by chitosanase cleaves the network and mobilizes intact vesicles. Potentially, this approach will provide a controllable means to store and liberate vesicle-based reagents/therapeutics for microfluidic/medical applications.

Chitosan↗

PubMed2005

Hydrodynamic fragmentation of nanoparticle aggregates at orthokinetic coagulation.

Hydrodynamic forces on a doublet of large particles or aggregates during sedimentation cause the non-inertial fragmentation of the doublet, if the doublet Reynolds number and Stokes number are small. In lio-dispersed systems, this non-inertial fragmentation is known to promote the wet classification of large particles whereas the small particles are aggregated (in the secondary minimum) and hence cannot be separated despite the electrostatic repulsion. In aero-dispersed systems with negligible electrostatic repulsion, it is possible to have a narrower separation between two interacting particles so that the attractive surface forces such as van der Waals force could increase in orders of magnitude. As a result, the doublet fragmentation by the aerodynamic detaching force becomes very difficult or even impossible in sedimentation at a small Re. However, this study shows that, when extending above analysis for the interacting fractal aggregates of nanoparticles in a suspension, it is still possible to have aggregate (doublet of two nano-aggregates) fragmentation by the aerodynamic detaching force because the surface forces for nanoparticle contact between two aggregates may be in orders of magnitude smaller than that for micron-sized particles. Even with multiple contacts between two interacting nanoparticle aggregates, this prediction of aggregate fragmentation may still be valid because the contacts may break step by step due to the aggregate rolling along each other caused by a short-range aerodynamic interaction during their differential settling. The aerodynamics of aero-dispersed nanoparticle aggregates is analogous to the hydrodynamics of lio-dispersed solid particles. Therefore the hydrodynamic fragmentation model may be used to partially interpret the stability of nanoparticle fluidization process. Our model indicates that, without continued doublet fragmentation of nano-aggregates, the fluidized nanoparticle suspension would be de-fluidized within minutes via the cascading aggregation. However, the experimental evidence of a sustained operation of fluidization of nanoparticle aggregates over a very long time period without changing the size of nanoparticle aggregates indicates that there is a dynamic balance between the aggregation and fragmentation of nano-aggregates in nanoparticle fluidization. The prediction of critical size of nanoparticle aggregates caused by fragmentation in stabilized fluidization agrees with our in situ measurements.

Kinetics↗

PubMed2003

Novel functionally grafted pseudo-semi-interpenetrating networks constructed by reactive linear-dendritic copolymers.

This paper describes the synthesis of amphiphilic pseudo-semi-interpenetrating polymer networks (pseudo-semi-IPNs) containing linear poly(styrene) and poly(ethylene glycol) (PEG) cross-linked through monodendritic fragments. A unique feature of the synthetic strategy is the permanent attachment of the linear segment to the PEG network by a transesterification reaction between the hydroxyl groups at both ends of the PEG and peripheral ethyl ester moieties in the monodendron portion of a linear poly(styrene)-dendritic poly(benzyl ether) AB block copolymer. The proceeding of the reaction is monitored by (1)H NMR and size exclusion chromatography (SEC). The formation of an interlock structure between the linear block and the network matrix in the pseudo-semi-IPN is evidenced by the results from spectroscopic analyses and differential scanning calorimetry measurements. The accessibility of functional centers in the grafted semi-IPN is confirmed by model reactions with fluorescent markers, fluorescence spectroscopy, and NMR techniques and shows the potential of these novel materials as sequestering reagents for resin capture-release applications in parallel synthesis, combinatorial chemistry, and advanced drug design.

Journal Article↗