@article{ewins_han_bharti_robinson_velev_dimova_2022, title={Controlled adhesion, membrane pinning and vesicle transport by Janus particles}, volume={1}, ISSN={["1364-548X"]}, DOI={10.1039/d1cc07026f}, abstractNote={Iron-coated Janus particles are used to establish controlled adhesion and contact-line pinning to (artificial) cells enabling magnetic-field driven directed transport.}, journal={CHEMICAL COMMUNICATIONS}, author={Ewins, Eleanor J. and Han, Koohee and Bharti, Bhuvnesh and Robinson, Tom and Velev, Orlin D. and Dimova, Rumiana}, year={2022}, month={Jan} }
 @article{castellanos_bharti_velev_2021, title={Field-Driven Reversible Alignment and Gelation of Magneto-Responsive Soft Anisotropic Microbeads}, volume={125}, ISSN={["1520-5207"]}, DOI={10.1021/acs.jpcb.1c03158}, abstractNote={Magnetic fields offer untethered control over the assembly, dynamics, and reconfiguration of colloidal particles. However, synthesizing “soft” colloidal particles with switchable magnetic dipole moment remains a challenge, primarily due to strong coupling of the dipoles of the adjacent nanoparticles. In this article, we present a way to overcome this fundamental challenge based on a strategy to synthesize soft microbeads with tunable residual dipole moment. The microbeads are composed of a polydimethylsiloxane (PDMS) matrix with internally embedded magnetic nanoparticles (MNPs). The distribution and orientation of the MNPs within the PDMS bead matrix is controlled by an external magnetic field during the synthesis process, thus allowing for the preparation of anisotropic PDMS microbeads with internal magnetically aligned nanoparticle chains. We study and present the differences in magnetic interactions between microbeads containing magnetically aligned MNPs and microbeads with randomly distributed MNPs. The interparticle interactions in a suspension of microbeads with embedded aligned MNP chains result in the spontaneous formation of percolated networks due to residual magnetization. We proved the tunability of the structure by applying magnetization, demagnetization, and remagnetization cycles that evoke formation, breakup, and reformation of 2D percolated networks. The mechanical response of the microbead suspension was quantified by oscillatory rheology and correlated to the propensity for network formation by the magnetic microbeads. We also experimentally correlated the 2D alignment of the microbeads to the direction of earth’s magnetic field. Overall, the results prove that the soft magnetic microbeads enable a rich variety of structures and can serve as an experimental toolbox for modeling interactions in dipolar systems leading to various percolated networks, novel magneto-rheological materials, and smart gels.}, number={28}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Castellanos, Natasha I and Bharti, Bhuvnesh and Velev, Orlin D.}, year={2021}, month={Jul}, pages={7900–7910} }
 @article{han_shields_bharti_arratia_velev_2020, title={Active Reversible Swimming of Magnetically Assembled "Microscallops" in Non-Newtonian Fluids}, volume={36}, ISSN={["0743-7463"]}, DOI={10.1021/acs.langmuir.9b03698}, abstractNote={Miniaturized devices capable of active swimming at low Reynolds numbers are of fundamental importance and possess potential biomedical utility. The design of colloidal microswimmers requires not only miniaturizing reconfigurable structures but also understanding their interactions with media at low Reynolds numbers. We investigate the dynamics of "microscallops" made of asymmetric magnetic cubes, which are assembled and actuated using magnetic fields. One approach to achieving directional propulsion is to break the symmetry of the viscous forces by coupling the reciprocal motions of such microswimmers with the nonlinear rheology inherent in non-Newtonian fluids. When placed in shear-thinning fluids, the local viscosity gradient resulting from nonuniform shear stresses exerted by time-asymmetric strokes of the microscallops generates propulsive thrust through an effect we term "self-viscophoresis". Surprisingly, we found that the direction of propulsion changes with the size and structure of these assemblies. We analyze the origins of their directional propulsion and explain the variable propulsion direction in terms of multiple counterbalancing domains of shear dissipation around the microscale structures. The principles governing the locomotion of these microswimmers may be extended to other reconfigurable microbots assembled from colloidal-scale units.}, number={25}, journal={LANGMUIR}, author={Han, Koohee and Shields, C. Wyatt and Bharti, Bhuvnesh and Arratia, Paulo E. and Velev, Orlin D.}, year={2020}, month={Jun}, pages={7148–7154} }
 @article{han_shields_diwakar_bharti_lopez_velev_2017, title={Sequence-encoded colloidal origami and microbot assemblies from patchy magnetic cubes}, volume={3}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.1701108}, abstractNote={Sequence-encoded assembly of patchy magnetic microcubes enables making self-reconfiguring colloidal origami and “microbots.”}, number={8}, journal={SCIENCE ADVANCES}, author={Han, Koohee and Shields, C. Wyatt and Diwakar, Nidhi M. and Bharti, Bhuvnesh and Lopez, Gabriel P. and Velev, Orlin D.}, year={2017}, month={Aug} }
 @article{morales_bharti_dickey_velev_2016, title={Bending of Responsive Hydrogel Sheets Guided by Field-Assembled Microparticle Endoskeleton Structures}, volume={12}, ISSN={["1613-6829"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84960373963&partnerID=MN8TOARS}, DOI={10.1002/smll.201600037}, abstractNote={Hydrogel composites that respond to stimuli can form the basis of new classes of biomimetic actuators and soft robotic components. Common latex microspheres can be assembled and patterned by AC electric fields within a soft thermoresponsive hydrogel. The field-oriented particle chains act as endoskeletal structures, which guide the macroscopic bending pattern of the actuators.}, number={17}, journal={SMALL}, publisher={Wiley}, author={Morales, Daniel and Bharti, Bhuvnesh and Dickey, Michael D. and Velev, Orlin D.}, year={2016}, month={May}, pages={2283–2290} }
 @article{bharti_rutkowski_han_kumar_hall_velev_2016, title={Capillary Bridging as a Tool for Assembling Discrete Clusters of Patchy Particles}, volume={138}, ISSN={["0002-7863"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84996490588&partnerID=MN8TOARS}, DOI={10.1021/jacs.6b08017}, abstractNote={Janus and patchy particles are emerging as models for studying complex directed assembly patterns and as precursors of new structured materials and composites. Here we show how lipid-induced capillary bridging could serve as a new and nonconventional method of assembling patchy particles into ordered structures. Iron oxide surface patches on latex microspheres were selectively wetted with liquid lipid, driving the particle assembly into two- and three-dimensional clusters via interparticle capillary bridge formation. The liquid phase of the bridges allows local reorganization of the particles within the clusters and assists in forming true equilibrium configurations. The temperature-driven fluid-to-gel and gel-to-fluid phase transitions of the fatty acids within the bridge act as a thermal switch for cluster assembly and disassembly. By complementing the experiments with Monte Carlo simulations, we show that the equilibrium cluster morphology is determined by the patch characteristics, namely, their size, number, and shape. This study demonstrates the ability of capillary bridging as a versatile tool to assemble thermoresponsive clusters and aggregates. This method of binding particles is simple, robust, and generic and can be extended further to assemble particles with nonspherical shapes and complex surface chemistries enabling the formation of sophisticated colloidal molecules.}, number={45}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Bharti, Bhuvnesh and Rutkowski, David and Han, Koohee and Kumar, Aakash Umesh and Hall, Carol K. and Velev, Orlin D.}, year={2016}, month={Nov}, pages={14948–14953} }
 @article{bharti_kogler_hall_klapp_velev_2016, title={Multidirectional colloidal assembly in concurrent electric and magnetic fields}, volume={12}, ISSN={["1744-6848"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84988592817&partnerID=MN8TOARS}, DOI={10.1039/c6sm01475e}, abstractNote={Dipolar interactions between nano- and micron sized colloids lead to their assembly into domains with well-defined local order. The particles with a single dipole induced by an external field assemble into linear chains and clusters. However, to achieve the formation of multidirectionally organized nano- or microassemblies with tunable physical characteristics, more sophisticated interaction tools are needed. Here we demonstrate that such complex interactions can be introduced in the form of two independent, non-interacting dipoles (double-dipoles) within a microparticle. We show how this can be achieved by the simultaneous application of alternating current (AC)-electric field and uniform magnetic field to dispersions of superparamagnetic microspheres. Depending on their timing and intensity, concurrent electric and magnetic fields lead to the formation of bidirectional particle chains, colloidal networks, and discrete crystals. We investigate the mechanistic details of the assembly process, and identify and classify the non-equilibrium states formed. The morphologies of different experimental states are in excellent correlation with our theoretical predictions based on Brownian dynamics simulations combined with a structural analysis based on local energy parameters. This novel methodology of introducing and interpreting double-dipolar particle interactions may assist in the assembly of colloidal coatings, dynamically reconfigurable particle networks, and bidirectional active structures.}, number={37}, journal={SOFT MATTER}, author={Bharti, Bhuvnesh and Kogler, Florian and Hall, Carol K. and Klapp, Sabine H. L. and Velev, Orlin D.}, year={2016}, pages={7747–7758} }
 @article{richter_bharti_arrnstrong_brown_plemmons_paunov_stoyanov_velev_2016, title={Synthesis and characterization of biodegradable lignin nanoparticles with tunable surface properties}, volume={32}, number={25}, journal={Langmuir}, author={Richter, A. P. and Bharti, B. and Arrnstrong, H. B. and Brown, J. S. and Plemmons, D. and Paunov, V. N. and Stoyanov, S. D. and Velev, O. D.}, year={2016}, pages={6468–6477} }
 @article{richter_brown_bharti_wang_gangwal_houck_hubal_paunov_stoyanov_velev_et al._2015, title={An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core}, volume={10}, ISSN={["1748-3395"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84941042177&partnerID=MN8TOARS}, DOI={10.1038/nnano.2015.141}, abstractNote={Silver nanoparticles have antibacterial properties, but their use has been a cause for concern because they persist in the environment. Here, we show that lignin nanoparticles infused with silver ions and coated with a cationic polyelectrolyte layer form a biodegradable and green alternative to silver nanoparticles. The polyelectrolyte layer promotes the adhesion of the particles to bacterial cell membranes and, together with silver ions, can kill a broad spectrum of bacteria, including Escherichia coli, Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp. Ion depletion studies have shown that the bioactivity of these nanoparticles is time-limited because of the desorption of silver ions. High-throughput bioactivity screening did not reveal increased toxicity of the particles when compared to an equivalent mass of metallic silver nanoparticles or silver nitrate solution. Our results demonstrate that the application of green chemistry principles may allow the synthesis of nanoparticles with biodegradable cores that have higher antimicrobial activity and smaller environmental impact than metallic silver nanoparticles.}, number={9}, journal={NATURE NANOTECHNOLOGY}, author={Richter, A.P. and Brown, J.S. and Bharti, B. and Wang, A. and Gangwal, S. and Houck, K. and Hubal, E.A. Cohen and Paunov, V.N. and Stoyanov, S.D. and Velev, Orlin and et al.}, year={2015}, month={Sep}, pages={817-+} }
 @article{bharti_velev_2015, title={Assembly of reconfigurable colloidal structures by multidirectional field-induced interactions}, volume={31}, number={29}, journal={Langmuir}, author={Bharti, B. and Velev, O. D.}, year={2015}, pages={7897–7908} }
 @article{ghoorchian_simon_bharti_han_zhao_chilkoti_lopez_2015, title={Bioinspired reversibly cross-linked hydrogels comprising polypeptide micelles exhibit enhanced mechanical properties}, volume={25}, number={21}, journal={Advanced Functional Materials}, author={Ghoorchian, A. and Simon, J. R. and Bharti, B. and Han, W. and Zhao, X. H. and Chilkoti, A. and Lopez, G. P.}, year={2015}, pages={3122–3130} }
 @article{meissner_prause_bharti_findenegg_2015, title={Characterization of protein adsorption onto silica nanoparticles: influence of pH and ionic strength}, volume={293}, number={11}, journal={Colloid and Polymer Science}, author={Meissner, J. and Prause, A. and Bharti, B. and Findenegg, G. H.}, year={2015}, pages={3381–3391} }
 @article{bharti_fameau_velev_2015, title={Magnetophoretic assembly of flexible nanoparticles/lipid microfilaments}, volume={181}, ISSN={["1364-5498"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84937695218&partnerID=MN8TOARS}, DOI={10.1039/c4fd00272e}, abstractNote={The directed assembly of colloidal particles into linear chains and clusters is of fundamental and practical importance. In this study we characterize and analyse the mechanism of the magnetic field driven assembly of lipid-coated iron oxide nanoparticles into flexible microfilaments. Recently we showed that nanocapillary lipid binding can form a new class of magnetic nanoparticle-lipid microfilaments with unprecedented flexibility and self-healing properties. In the presence of a uniform magnetic field, the magnetophoretic attraction of the particles combined with interparticle dipole-dipole attraction drives the microfilament assembly. The fluid like lipid layer on the particles leads to stickiness on the surface of the filaments and the magnetic field concentration overcomes the potential electrostatic repulsion in the water phase. The lipid capillary bridges formed between the particles facilitate their permanent binding and sustain the flexible microfilament structure. We demonstrate that this surface stickiness combined with the magnetic response of the filaments can be used further to twist, bend and bundle the microfilaments into unusual structures.}, journal={FARADAY DISCUSSIONS}, author={Bharti, Bhuvnesh and Fameau, Anne-Laure and Velev, Orlin D.}, year={2015}, pages={437–448} }
 @article{bharti_velev_2015, title={Multidirectional, Multicomponent Electric Field Driven Assembly of Complex Colloidal Chains}, volume={229}, ISSN={["0942-9352"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84938102593&partnerID=MN8TOARS}, DOI={10.1515/zpch-2014-0543}, abstractNote={Abstract External fields (magnetic and electric) present a simple, robust and efficient route to manipulate and assemble colloidal particles. We report how biparticle dispersions can be assembled into well-defined arrays of tunable morphology using external AC electric field. Binary dispersions of strongly and weakly charged colloidal particles were arranged into linear composite chains via dipole-dipole attraction. The frequency of the applied electric field was the first control parameter for reversibly tuning the biparticle attraction from longitudinal assembly (in the direction of field) to the traverse one (perpendicular to the field). We show that in addition to frequency, spatial limitations play a key role in the assembly process and may assist in the formation of short bidirectional chain-like clusters or characteristic highly structured strings of colloidal triplets. Thus, we control the long-range organization through a combination of particle size ratio, concentration ratio and field frequency. The new strategy to reconfigure the microstructures can find application in better control of the field driven colloidal assembly processes and may be extended to the formation of more complex and precisely arranged particle networks.}, number={7-8}, journal={ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS}, author={Bharti, Bhuvnesh and Velev, Orlin D.}, year={2015}, month={Aug}, pages={1075–1088} }
 @article{bharti_fameau_rubinstein_velev_2015, title={Nanocapillarity-mediated magnetic assembly of nanoparticles into ultraflexible filaments and reconfigurable networks}, volume={14}, ISSN={["1476-4660"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84945490464&partnerID=MN8TOARS}, DOI={10.1038/nmat4364}, abstractNote={Capillary forces at the nanoscale can be harnessed for the magnetically directed assembly of lipid-shell-coated nanoparticles into ultraflexible microfilaments and network structures. The fabrication of multifunctional materials with tunable structure and properties requires programmed binding of their building blocks1,2. For example, particles organized in long-ranged structures by external fields3,4 can be bound permanently into stiff chains through electrostatic or van der Waals attraction4,5, or into flexible chains through soft molecular linkers such as surface-grafted DNA or polymers6,7,8,9,10,11. Here, we show that capillarity-mediated binding between magnetic nanoparticles coated with a liquid lipid shell can be used for the assembly of ultraflexible microfilaments and network structures. These filaments can be magnetically regenerated on mechanical damage, owing to the fluidity of the capillary bridges between nanoparticles and their reversible binding on contact. Nanocapillary forces offer opportunities for assembling dynamically reconfigurable multifunctional materials that could find applications as micromanipulators, microbots with ultrasoft joints, or magnetically self-repairing gels.}, number={11}, journal={NATURE MATERIALS}, author={Bharti, Bhuvnesh and Fameau, Anne-Laure and Rubinstein, Michael and Velev, Orlin D.}, year={2015}, month={Nov}, pages={1104-+} }
 @article{meissner_prause_di tommaso_bharti_findenegg_2015, title={Protein immobilization in surface-functionalized SBA-15: Predicting the uptake capacity from the pore structure}, volume={119}, number={5}, journal={Journal of Physical Chemistry. C}, author={Meissner, J. and Prause, A. and Di Tommaso, C. and Bharti, B. and Findenegg, G. H.}, year={2015}, pages={2438–2446} }
 @article{kukobat_minami_hayashi_hattori_matsuda_sunaga_bharti_asakura_kaneko_2015, title={Sol-gel chemistry mediated Zn/Al-based complex dispersant for SWCNT in water without foam formation}, volume={94}, journal={Carbon}, author={Kukobat, R. and Minami, D. and Hayashi, T. and Hattori, Y. and Matsuda, T. and Sunaga, M. and Bharti, B. and Asakura, K. and Kaneko, K.}, year={2015}, pages={518–523} }
 @article{bharti_findenegg_velev_2014, title={Analysis of the Field-Assisted Permanent Assembly of Oppositely Charged Particles}, volume={30}, ISSN={["0743-7463"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84902155442&partnerID=MN8TOARS}, DOI={10.1021/la5009335}, abstractNote={We characterize experimentally and analyze analytically a novel electric-field-assisted process for the assembly of permanent chains of oppositely charged microparticles in an aqueous environment. Long chains of oppositely charged particles are rapidly formed when an external electric field is applied and break up into permanent linear fragments upon switching off the field. The resulting secondary chains are stabilized by attractive electrostatic and van der Waals interactions between the particles. We find that the length of the permanent chains is strongly dependent on the relative size (microsphere diameter D) of small and large particles and can be tuned by varying the particle size ratio s = Dsm/Dlg and particle number ratio r = Nsm/Nlg. Three latex microsphere systems of different particle size ratio, s = 0.9, 0.45, and 0.225, were characterized at different particle number ratios r by determining experimentally the length distribution of the permanent chains. The results are compared with statistical models based on a one-step or two-step process of forming the primary chains. We find that the one-step model is applicable to the system of similarly sized particles (s = 0.9) and the two-step chaining model is applicable to the system of dissimilarly sized particles (s = 0.225), where the large particles form chains first and the small ones serve as binders, which are later drawn in the junctions. Long permanent chains are formed only from particles of dissimilar size for which our model predicts a linear increase in the mean chain length with increasing r. On the basis of these results, we formulate a set of assembly rules for permanent colloidal chain formation by oppositely charged particles. The results make possible the precise large-scale formation of particle chains of any length, which can serve as components in new gels, biomaterials, and fluids with controlled rheology.}, number={22}, journal={LANGMUIR}, author={Bharti, Bhuvnesh and Findenegg, Gerhard H. and Velev, Orlin D.}, year={2014}, month={Jun}, pages={6577–6587} }
 @article{shields_zhu_yang_bharti_liu_yellen_velev_lopez_2013, title={Field-directed assembly of patchy anisotropic microparticles with defined shape}, volume={9}, ISSN={["1744-6848"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84884128329&partnerID=MN8TOARS}, DOI={10.1039/c3sm51119g}, abstractNote={Electromagnetic fields can generate orientation-dependent, long range interactions between colloidal components that direct their assembly into highly ordered structures, such as small ordered clusters, chains, and large crystalline lattices. While much effort has been devoted to exploring the assembly of spherical colloids, few reports have investigated the directed assembly of non-spherical particles with Janus or patchy morphologies. Here, we use photolithographic techniques to fabricate a wide range of anisotropically shaped patchy particles and follow their assembly in liquid suspensions under the influence of electric and magnetic fields. We analyze the assembly of several types of patchy particles across a range of field parameters and fluid compositions, and report a number of distinct, well-ordered, assembly architectures including cylindrical, prismatic, and staggered chains. The structures assembled from anisotropic patchy components provide a glimpse into the range of architectures that can be created by combining field directed assembly with rationally designed particles. By using numerical simulations to model the electric and magnetic field interactions between these particles, we interpret the results of the assembly process and explain how they can be controlled by the position of the metal facet, the frequency (for AC fields), or magnetic susceptibility of the medium. The resulting structures, and similar ones produced through the field-directed assembly of patchy anisotropic particles, can possess unique electrical and optical properties and may have potential applications in a number of future technology applications such as microactuators, metamaterials and multiferroic materials.}, number={38}, journal={SOFT MATTER}, author={Shields, C. Wyatt and Zhu, Shan and Yang, Ye and Bharti, Bhuvnesh and Liu, Jonathan and Yellen, Benjamin B. and Velev, Orlin D. and Lopez, Gabriel P.}, year={2013}, pages={9219–9229} }
 @article{bharti_findenegg_velev_2012, title={Co-assembly of oppositely charged particles into linear clusters and chains of controllable length}, volume={2}, journal={Scientific Reports}, author={Bharti, B. and Findenegg, G. H. and Velev, O. D.}, year={2012} }