@article{Huang2024,

title = {A universal strategy for decoupling stiffness and extensibility polymer networks},

author = {Baiqiang Huang and Shifeng Nian and Li-Heng Cai},

doi = {10.1126/sciadv.adq3080},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Science Advances},

volume = {10},

pages = {eadq3080},

abstract = {Since the invention of polymer networks in the 19th century (e.g., crosslinked natural rubber by Goodyear), it has been a dogma that stiffer networks are less stretchable, a trade-off inherent to the molecular nature of polymer network strands. Here, we report a universal strategy for decoupling the stiffness and extensibility of single-network elastomers. Instead of using linear polymers as network strands, we use foldable bottlebrush polymers, which feature a collapsed backbone grafted with many linear side chains. Upon elongation, the collapsed backbone unfolds to release stored length, enabling remarkable extensibility. By contrast, the network elastic modulus is inversely proportional to the network strand mass and is determined by the side chains. We validate this concept by creating a series of unentangled single-network elastomers with nearly constant Young's modulus (30 kPa) while increasing tensile breaking strain by 40-fold, from 20% to 800%. We show that this strategy applies to networks of different polymer species and topologies. Our discovery opens an avenue for developing polymer networks with extraordinary mechanical properties.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{He2024a,

title = {Bottlebrush polyethylene glycol nanocarriers translocate across human airway epithelium via molecular architecture-enhanced endocytosis},

author = {Zhi Jian He, Baiqiang Huang, and Li Heng Cai},

doi = {10.1021/acsnano.4c01983},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {ACS Nano},

volume = {18},

issue = {27},

pages = {17586–17599},

abstract = {Pulmonary drug delivery is critical for the treatment of respiratory diseases. However, the human airway surface presents multiple barriers to efficient drug delivery. Here, we report a bottlebrush poly(ethylene glycol) (PEG-BB) nanocarrier that can translocate across all barriers within the human airway surface. Guided by a molecular theory, we design a PEG-BB molecule consisting of a linear backbone densely grafted by many (∼1000) low molecular weight (∼1000 g/mol) polyethylene glycol (PEG) chains; this results in a highly anisotropic, wormlike nanocarrier featuring a contour length of ∼250 nm, a cross-section of ∼20 nm, and a hydrodynamic diameter of ∼40 nm. Using the classic air-liquid-interface culture system to recapitulate essential biological features of the human airway surface, we show that PEG-BB rapidly penetrates through endogenous airway mucus and periciliary brush layer (mesh size of 20-40 nm) to be internalized by cells across the whole epithelium. By quantifying the cellular uptake of polymeric carriers of various molecular architectures and manipulating cell proliferation and endocytosis pathways, we show that the translocation of PEG-BB across the epithelium is driven by bottlebrush architecture-enhanced endocytosis. Our results demonstrate that large, wormlike bottlebrush PEG polymers, if properly designed, can be used as a carrier for pulmonary and mucosal drug delivery.},

keywords = {Bioengineering, Biomaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Kim2024,

title = {3D printable modular soft elastomers from physically cross-linked homogeneous associative polymers},

author = {Myoeum Kim and Shifeng Nian and Daniel A. Rau and Baiqiang Huang and Jinchang Zhu and Guillaume Freychet and Mikhail Zhernenkov and Li-Heng Cai},

doi = {10.1021/acspolymersau.3c00021},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {ACS Polymers Au},

volume = {4},

number = {2},

pages = {98–108},

abstract = {Three-dimensional (3D) printing of elastomers enables the fabrication of many technologically important structures and devices. However, there remains a critical need for the development of reprocessable, solvent-free, soft elastomers that can be printed without the need for post-treatment. Herein, we report modular soft elastomers suitable for direct ink writing (DIW) printing by physically cross-linking associative polymers with a high fraction of reversible bonds. We designed and synthesized linear-associative-linear (LAL) triblock copolymers; the middle block is an associative polymer carrying amide groups that form double hydrogen bonding, and the end blocks aggregate to hard glassy domains that effectively act as physical cross-links. The amide groups do not aggregate to nanoscale clusters and only slow down polymer dynamics without changing the shape of the linear viscoelastic spectra; this enables molecular control over energy dissipation by varying the fraction of the associative groups. Increasing the volume fraction of the end linear blocks increases the network stiffness by more than 100 times without significantly compromising the extensibility. We created elastomers with Young's moduli ranging from 8 kPa to 8 MPa while maintaining the tensile breaking strain around 150%. Using a high-temperature DIW printing platform, we transformed our elastomers to complex, highly deformable 3D structures without involving any solvent or post-print processing. Our elastomers represent the softest melt reprocessable materials for DIW printing. The developed LAL polymers synergize emerging homogeneous associative polymers with a high fraction of reversible bonds and classical block copolymer self-assembly to form a dual-cross-linked network, providing a versatile platform for the modular design and development of soft melt reprocessable elastomeric materials for practical applications.},

keywords = {Advanced (Bio)Manufacturing, Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Zhu2024,

title = {Voxelated bioprinting of modular double-network bio-ink droplets},

author = {Jinchang Zhu and Yi He and Yong Wang and Li-Heng Cai},

url = {https://doi.org/10.1038/s41467-024-49705-z},

doi = {10.1038/s41467-024-49705-z},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Nature Communications},

volume = {15},

pages = {5902},

abstract = {Analogous of pixels to two-dimensional pictures, voxels—in the form of either small cubes or spheres—are the basic building blocks of three-dimensional objects. However, precise manipulation of viscoelastic bio-ink voxels in three-dimensional space represents a grand challenge in both soft matter science and biomanufacturing. Here, we present a voxelated bioprinting technology that enables the digital assembly of interpenetrating double-network hydrogel droplets made of polyacrylamide/alginate-based or hyaluronic acid/alginate-based polymers. The hydrogels are crosslinked via additive-free and biofriendly click reaction between a pair of stoichiometrically matched polymers carrying norbornene and tetrazine groups, respectively. We develop theoretical frameworks to describe the crosslinking kinetics and stiffness of the hydrogels, and construct a diagram-of-state to delineate their mechanical properties. Multi-channel print nozzles are developed to allow on-demand mixing of highly viscoelastic bio-inks without significantly impairing cell viability. Further, we showcase the distinctive capability of voxelated bioprinting by creating highly complex three-dimensional structures such as a hollow sphere composed of interconnected yet distinguishable hydrogel particles. Finally, we validate the cytocompatibility and in vivo stability of the printed double-network scaffolds through cell encapsulation and animal transplantation.},

keywords = {Advanced (Bio)Manufacturing, Biomaterials, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{He2024,

title = {A gel-coated air-liquid-interface culture system with tunable substrate stiffness matching healthy and diseased lung tissues},

author = {Zhi Jian He and Catherine Chu and Riley Dickson and Kenichi Okuda and Li-Heng Cai},

url = {https://doi.org/10.1152/ajplung.00153.2023},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {American journal of physiology. Lung cellular and molecular physiology},

volume = {326},

number = {3},

pages = {L292–L302},

abstract = {Since its invention in the late 1980s, the air-liquid-interface (ALI) culture system has been the standard in vitro model for studying human airway biology and pulmonary diseases. However, in a conventional ALI system, cells are cultured on a porous plastic membrane that is much stiffer than human airway tissues. Here, we develop a gel-ALI culture system by simply coating the plastic membrane with a thin layer of hydrogel with tunable stiffness matching that of healthy and fibrotic airway tissues. We determine the optimum gel thickness that does not impair the transport of nutrients and biomolecules essential to cell growth. We show that the gel-ALI system allows human bronchial epithelial cells (HBECs) to proliferate and differentiate into pseudostratified epithelium. Furthermore, we discover that HBECs migrate significantly faster on hydrogel substrates with stiffness matching that of fibrotic lung tissues, highlighting the importance of mechanical cues in human airway remodeling. The developed gel-ALI system provides a facile approach to studying the effects of mechanical cues in human airway biology and in modeling pulmonary diseases.},

keywords = {Bioengineering, Biomaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Nian2023,

title = {Dynamics of associative polymers with high density of reversible bonds},

author = {Shifeng Nian and Shalin Patil and Siteng Zhang and Myoeum Kim and Quan Chen and Mikhail Zhernenkov and Ting Ge and Shiwang Cheng and Li-Heng Cai},

doi = {10.1103/PhysRevLett.130.228101},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Physical Review Letters},

volume = {130},

number = {22},

pages = {228101},

publisher = {American Physical Society},

abstract = {An associative polymer carries many stickers that can form reversible associations. For more than 30 years, the understanding has been that reversible associations change the shape of linear viscoelastic spectra by adding a rubbery plateau in the intermediate frequency range, at which associations have not yet relaxed and thus effectively act as crosslinks. Here, we design and synthesize new classes of unentangled associative polymers carrying unprecedentedly high fractions of stickers, up to eight per Kuhn segment, that can form strong pairwise hydrogen bonding of ∼20kBT without microphase separation. We experimentally show that reversible bonds significantly slow down the polymer dynamics but nearly do not change the shape of linear viscoelastic spectra. This behavior can be explained by a renormalized Rouse model that highlights an unexpected influence of reversible bonds on the structural relaxation of associative polymers.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Zhu2023,

title = {All-aqueous printing of viscoelastic droplets in yield-stress fluids},

author = {Jinchang Zhu and Li-Heng Cai},

url = {https://doi.org/10.1016/j.actbio.2022.09.031},

doi = {10.1016/j.actbio.2022.09.031},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Acta Biomaterialia},

volume = {165},

number = {2023},

pages = {60–71},

publisher = {Elsevier Ltd},

abstract = {All-aqueous printing of viscoelastic droplets (aaPVD) in yield-stress fluids is the core of an emerging voxelated bioprinting technology that enables the digital assembly of spherical bio-ink particles (DASP) to create functional tissue mimics. However, the mechanism of aaPVD is largely unknown. Here, by quantifying the dynamics of the whole printing process in real-time, we identify two parameters critical to aaPVD: (1) acceleration of print nozzle, and (2) droplet/nozzle diameter ratio. Moreover, we distinguish three stages associated with aaPVD: droplet generation, detachment, and relaxation. To generate a droplet of good roundness, the ink should be a highly viscous shear-thinning fluid. Using particle image velocimetry and scaling theory, we establish a universal description for the droplet displacements at various printing conditions. Along the direction of nozzle movement, the droplet displacement is determined by the detachment number, a dimensionless parameter defined as the ratio between the dragging force from the nozzle and the confinement force from the supporting matrix. Perpendicular to the direction of nozzle movement, the droplet displacement is determined by the Oldroyd number, a dimensionless parameter that describes the yielded area of the supporting matrix near the print nozzle. For a relaxed droplet, the droplet tail length is independent of droplet/nozzle diameter ratio but determined by the nozzle acceleration. We conclude that printing droplets of good fidelity requires a relatively large droplet/nozzle diameter ratio and intermediate nozzle accelerations. These ensure that the droplet is more solid-like to not flow with the nozzle to form a tadpole-like morphology and that the confinement force from the yield-stress fluid is large enough to prevent large droplet displacement. Our results provide the knowledge and tools for in situ generating and depositing highly viscoelastic droplets of good roundness at prescribed locations in 3D space, which help establish the foundational science for voxelated bioprinting. Statement of significance: Analogues of pixels to two-dimensional (2D) pictures, voxels – in the form of small cubes or spheres – are the basic units of three-dimensional (3D) objects. All-aqueous printing of viscoelastic droplets (aaPVD) is the core of voxelated bioprinting, an emerging technology that uses spherical bio-ink voxels as building blocks to create 3D tissue mimics. Unlike existing technologies relying on the classic Rayleigh-Plateau instability to generate droplets, aaPVD exploits previously unexplored nonlinear fluid dynamics of complex fluids to precisely manipulate viscoelastic droplets in 3D space. The developed knowledge and tools not only help advance biomanufacturing but also stimulate new research directions in soft matter and complex fluids.},

keywords = {Advanced (Bio)Manufacturing, Bioengineering, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Nian2023a,

title = {Unexpected folding of bottlebrush polymers in melts},

author = {Shifeng Nian and Baiqiang Huang and Guillaume Freychet and Mikhail Zhernenkov and Li-Heng Cai},

doi = {10.1021/acs.macromol.2c02053},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Macromolecules},

volume = {56},

number = {6},

pages = {2551–2559},

abstract = {Bottlebrush molecules are branched polymers with a long linear backbone densely grafted by many relatively short linear side chains. Such a unique molecular architecture enables bottlebrush polymers with properties and functions inaccessible by their linear counterparts. The existing understanding is that, in melts of bottlebrush polymers, the interbackbone distance decreases as the grafting density of side chains becomes smaller. Here, we experimentally discover a behavior opposite to all existing works: the interbackbone distance increases monotonically as the grafting density decreases. To explain these remarkable experimental findings, we develop a theory by accounting for the incompatibility between the backbone and side chains within a bottlebrush molecule. The backbone polymer folds into a cylindrical core with all grafting sites on its surface to reduce interfacial free energy. As the grafting density decreases, the backbone collapses; this process not only increases the diameter of the cylindrical core but also reduces the distance between grafting sites in space, such that the extension of side chains is not alleviated. Our discovery presents a paradigm-shifting understanding of the molecular structure of bottlebrush polymers.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Zhu2022,

title = {Digital assembly of spherical viscoelastic bio-ink particles},

author = {Jinchang Zhu and Yi He and Linlin Kong and Zhijian He and Kaylen Y. Kang and Shannon P. Grady and Leander Q. Nguyen and Dong Chen and Yong Wang and Jose Oberholzer and Li-Heng Cai},

doi = {10.1002/adfm.202109004},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {Advanced Functional Materials},

volume = {32},

number = {6},

pages = {1–11},

abstract = {3D bioprinting additively assembles bio-inks to manufacture tissue-mimicking biological constructs, but with the typical building blocks limited to 1D filaments. Here, it is developed a voxelated bioprinting technique for the digital assembly of spherical particles (DASP), which are effectively 0D voxels—the basic unit of 3D structures. It is shown that DASP enables on-demand generation, deposition, and assembly of viscoelastic bio-ink droplets. A two-parameter diagram is developed to outline the viscoelasticity of bio-inks required for printing spherical particles of good fidelity. Moreover, a strategy is developed for engineering bio-inks with independently controllable viscoelasticity and mesh size, two of the most important yet intrinsically coupled physical properties of biomaterials. Using DASP, mechanically robust, multiscale porous scaffolds composed of interconnected yet distinguishable hydrogel particles are created. Finally, it is demonstrated the application of the scaffolds in encapsulating human pancreatic islets for sustained responsive insulin release. Together with the knowledge of bio-ink design, DASP might be used to engineer highly heterogeneous, yet tightly organized tissue constructs for therapeutic applications.},

keywords = {Advanced (Bio)Manufacturing},

pubstate = {published},

tppubtype = {article}

}

@article{Nian,

title = {Dynamic mechanical properties of self-assembled bottlebrush polymer networks},

author = {Shifeng Nian and Li-Heng Cai},

url = {https://pubs.acs.org/doi/10.1021/acs.macromol.2c01204},

year  = {2022},

date = {2022-01-01},

urldate = {2022-01-01},

journal = {Macromolecules},

volume = {55},

number = {18},

pages = {8058–8066},

abstract = {We systematically investigate the effects of composition on the dynamic mechanical properties of bottlebrush polymer networks self-assembled by linear–bottlebrush–linear triblock copolymers. We fix the molecular architecture of the bottlebrush, which consists of 51 poly(dimethyl siloxane) (PDMS) side chains of 5 kg/mol and has a molecular weight of 255 kg/mol, and increase only the volume fraction f of the linear poly(benzyl methacrylate) (PBnMA) blocks. As f increases from 0.05 to 0.41, the network shear modulus G at room temperature increases from ∼4 to ∼100 kPa. Yet, depending on the network morphology, the relation between G and f exhibits two regimes. (i) For sphere morphology, G is nearly a constant; yet, because of a large fraction of loops, the absolute value of G is about 40% of the stiffness Gm of the PDMS bottlebrush matrix. (ii) For cylinder morphology, G increases slowly with f but remains nearly 4 orders of magnitude lower than 109 Pa for the glassy cylinders formed by the end PBnMA blocks. We explain this remarkable behavior by modeling the polymer as a polycrystalline material consisting of randomly oriented grains, and each grain is a fiber-reinforced composite. We propose a modified Halpin–Tsai model to describe the shear modulus of such a polycrystalline material: G = Gm(1+ζf)/(1–f), in which ζ is an adjustable parameter that describes the grain size relative to the fiber diameter. Above the glass-transition temperature of end blocks, the reinforcement to network modulus from the glassy fibers diminishes, such that G becomes a constant of the matrix stiffness. Our results not only reveal previously unexplored molecule–structure–property relations of self-assembled bottlebrush polymer networks but also provide a new class of soft, solvent-free, and reprocessable polymeric materials with a wide range of controllable stiffness.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Nian2021,

title = {Three-dimensional printable, extremely soft, stretchable, and reversible elastomers from molecular architecture-directed assembly},

author = {Shifeng Nian and Jinchang Zhu and Haozhe Zhang and Zihao Gong and Guillaume Freychet and Mikhail Zhernenkov and Baoxing Xu and Li-Heng Cai},

doi = {10.1021/acs.chemmater.0c04659},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Chemistry of Materials},

volume = {33},

number = {7},

pages = {2436–2445},

abstract = {3D printing elastomers enables the fabrication of many technologically important structures and devices such as tissue scaffolds, sensors, actuators, and soft robots. However, conventional 3D printable elastomers are intrinsically stiff; moreover, the process of printing often requires external mechanical support and/or post-treatment. Here, we exploit the self-assembly of a responsive linear-bottlebrush-linear triblock copolymer to create stimuli-reversible, extremely soft, and stretchable elastomers and demonstrate their applicability as inks for in situ direct-write printing 3D structures without the aid of external mechanical support or post-treatment. By developing a procedure for controlled synthesis of such architecturally designed block copolymers, we create elastomers with extensibility up to 600% and Young's moduli down to ∼102 Pa, 106 times softer than plastics and more than 102 times softer than all existing 3D printable elastomers. Moreover, the elastomers are thermostable and remain to be solid up to 180 °C, yet they are 100% solvent-reprocessable. Their extreme softness, stretchability, thermostability, and solvent-reprocessability bode well for future applications.},

keywords = {Advanced (Bio)Manufacturing, Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Shen2021,

title = {Effects of vimentin intermediate filaments on the structure and dynamics of in vitro multicomponent interpenetrating cytoskeletal networks},

author = {Yinan Shen, Huayin Wu, Peter J. Lu and Dianzhuo Wang and Marjan Shayegan and Hui Li and Weichao Shi and Zizhao Wang and Li-Heng Cai and Jing Xia and Meng Zhang and Ruihua Ding and Harald Herrmann and Robert Goldman and Fred C. Mackintosh and Arturo Moncho-Jordá and David A. Weitz},

url = {https://doi.org/10.1103/PhysRevLett.127.108101},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Physical Review Letters},

volume = {127},

number = {10},

pages = {108101},

publisher = {American Physical Society},

abstract = {We investigate the rheological properties of interpenetrating networks reconstituted from the main cytoskeletal components: filamentous actin, microtubules, and vimentin intermediate filaments. The elastic modulus is determined largely by actin, with little contribution from either microtubules or vimentin. However, vimentin dramatically impacts the relaxation, with even small amounts significantly increasing the relaxation time of the interpenetrating network. This highly unusual decoupling between dissipation and elasticity may reflect weak attractive interactions between vimentin and actin networks.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Xia2021,

title = {Anomalous mechanics of Zn2+-modified fibrin networks},

author = {Jing Xia and Li-Heng Cai and Huayin Wu and Frederick C. MacKintosh and David A. Weitz},

doi = {10.1073/pnas.2020541118},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Proceedings of the National Academy of Sciences of the United States of America},

volume = {118},

number = {10},

pages = {e2020541118},

abstract = {Fibrin is the main component of blood clots. The mechanical properties of fibrin are therefore of critical importance in successful hemostasis. One of the divalent cations released by platelets during hemostasis is Zn2+; however, its effect on the network structure of fibrin gels and on the resultant mechanical properties remains poorly understood. Here, by combining mechanical measurements with three-dimensional confocal microscopy imaging, we show that Zn2+ can tune the fibrin network structure and alter its mechanical properties. In the presence of Zn2+, fibrin protofibrils form large bundles that cause a coarsening of the fibrin network due to an increase in fiber diameter and reduction of the total fiber length. We further show that the protofibrils in these bundles are loosely coupled to one another, which results in a decrease of the elastic modulus with increasing Zn2+ concentrations. We explore the elastic properties of these networks at both low and high stress: At low stress, the elasticity originates from pulling the thermal slack out of the network, and this is consistent with the thermal bending of the fibers. By contrast, at high stress, the elasticity exhibits a common master curve consistent with the stretching of individual protofibrils. These results show that the mechanics of a fibrin network are closely correlated with its microscopic structure and inform our understanding of the structure and physical mechanisms leading to defective or excessive clot stiffness.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Nianb,

title = {Self-assembly of flexible linear-semiflexible bottlebrush-flexible linear triblock copolymers},

author = {Shifeng Nian and Zhouhao Fan and Guillaume Freychet and Mikhail Zhernenkov and Stefanie Redemann and Li-Heng Cai},

doi = {10.1021/acs.macromol.1c01911},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Macromolecules},

volume = {54},

number = {20},

pages = {9361–9371},

abstract = {Block copolymer (BCP) self-assembly is a fundamental process in which incompatible blocks spontaneously form organized microstructures with broad practical applications. Classical understanding is that the domain spacing is limited by the contour length of the polymer backbone. Here, using a combination of molecular design, chemical synthesis, small-/wide-angle X-ray scattering, transmission electron microscopy, and electron tomography, we discover that this molecular picture does not hold for architecturally semiflexible BCPs. For strongly segregated linear-semiflexible bottlebrush-linear triblock copolymers, the size of the bottlebrush domain can be twice the bottlebrush backbone contour length. The mechanism of such anomalous self-assembly is likely that the interfacial repulsion between the incompatible blocks is large enough to pull a part of the linear end blocks into the bottlebrush domain. This effectively increases the bottlebrush domain size. Moreover, the semiflexible bottlebrush widens the regime for the cylinder morphology that is associated with the volume fraction of the end blocks fCSFB (0.10, >0.41). This window is much wider than that for flexible linear BCPs, fCF (0.14, 0.35), and that predicted by the recent self-consistent field theory for linear-bottlebrush BCPs of the same chemistry and molecular architecture. Our experimental findings reveal previously unrecognized mechanisms for the self-assembly of architecturally complex BCPs.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2020,

title = {Capillary transfer of soft films},

author = {Yue Zhang and Mengtian Yin and Yongmin Baek and Kyusang Lee and Giovanni Zangari and Li-Heng Cai and Baoxing Xu},

doi = {10.1073/pnas.2000340117},

year  = {2020},

date = {2020-03-01},

urldate = {2020-03-01},

journal = {Proceedings of the National Academy of Sciences},

volume = {117},

number = {10},

pages = {5210–5216},

publisher = {National Academy of Sciences},

abstract = {Existing transfer technologies in the construction of film-based electronics and devices are deeply established in the framework of native solid substrates. Here, we report a capillary approach that enables a fast, robust, and reliable transfer of soft films from liquid in a defect-free manner. This capillary transfer is underpinned by the transfer front of dynamic contact among receiver substrate, liquid, and film, and can be well controlled by a selectable motion direction of receiver substrates at a high speed. We demonstrate in extensive experiments, together with theoretical models and computational analysis, the robust capabilities of the capillary transfer using a versatile set of soft films with a broad material diversity of both film and liquid, surface-wetting properties, and complex geometric patterns of soft films onto various solid substrates in a deterministic manner.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2020,

title = {Dissolvable Polyacrylamide Beads for High-Throughput Droplet DNA Barcoding},

author = {Yongcheng Wang and Ting Cao and Jina Ko and Yinan Shen and Will Zong and Kuanwei Sheng and Wenjian Cao and Sijie Sun and Li-Heng Cai and Ying Lin Zhou and Xin Xiang Zhang and Chenghang Zong and Ralph Weissleder and David Weitz},

doi = {10.1002/advs.201903463},

year  = {2020},

date = {2020-02-01},

urldate = {2020-02-01},

journal = {Advanced Science},

volume = {7},

number = {8},

pages = {1–8},

publisher = {John Wiley & Sons, Ltd},

abstract = {Droplet-based single cell sequencing technologies, such as inDrop, Drop-seq, and 10X Genomics, are catalyzing a revolution in the understanding of biology. Barcoding beads are key components for these technologies. What is limiting today are barcoding beads that are easy to fabricate, can efficiently deliver primers into drops, and thus achieve high detection efficiency. Here, this work reports an approach to fabricate dissolvable polyacrylamide beads, by crosslinking acrylamide with disulfide bridges that can be cleaved with dithiothreitol. The beads can be rapidly dissolved in drops and release DNA barcode primers. The dissolvable beads are easy to synthesize, and the primer cost for the beads is significantly lower than that for the previous barcoding beads. Furthermore, the dissolvable beads can be loaded into drops with >95% loading efficiency of a single bead per drop and the dissolution of beads does not influence reverse transcription or the polymerase chain reaction (PCR) in drops. Based on this approach, the dissolvable beads are used for single cell RNA and protein analysis.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Ding2020,

title = {Rapid isolation of antigen-specific B-cells using droplet microfluidics},

author = {Ruihua Ding and K. -C. Kuo-Chan Hung and Anindita Mitra and L. W. Lloyd W Ung and Daniel Lightwood and Ran Tu and Dale Starkie and Li-Heng Cai and Linas Mazutis and Shaorong Chong and D. A. Weitz and J. A. Heyman},

doi = {10.1039/d0ra04328a},

year  = {2020},

date = {2020-01-01},

urldate = {2020-01-01},

journal = {RSC Advances},

volume = {10},

number = {45},

pages = {27006–27013},

publisher = {Royal Society of Chemistry},

abstract = {© The Royal Society of Chemistry. Monoclonal antibodies are powerful tools for scientific research and are the basis of numerous therapeutics. However, traditional approaches to generate monoclonal antibodies against a desired target, such as hybridoma-based techniques and display library methods, are laborious and suffer from fusion inefficiency and display bias, respectively. Here we present a platform, featuring droplet microfluidics and a bead-based binding assay, to rapidly identify and verify antigen-binding antibody sequences from primary cells. We used a defined mixture of hybridoma cells to characterize the system, sorting droplets at up to 100 Hz and isolating desired hybridoma cells, comprising 0.1% of the input, with a false positive rate of less than 1%. We then applied the system to once-frozen primary B-cells to isolate rare cells secreting target-binding antibody. We performed RT-PCR on individual sorted cells to recover the correctly paired heavy- and light-chain antibody sequences, and we used rapid cell-free protein synthesis to generate single-chain variable fragment-format (scFv) antibodies from fourteen of the sorted cells. Twelve of these showed antigen-specific binding by ELISA. Our platform facilitates screening animal B-cell repertoires within days at low cost, increasing both rate and range of discovering antigen-specific antibodies from living organisms. Further, these techniques can be adapted to isolate cells based on virtually any secreted product. This journal is},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2020a,

title = {The rheology property of organogels based on 3D helical nanofilament bnetworks self-assembled by bent-core liquid crystals},

author = {Xing Zheng Wang and Chen Jing Yang and Li-Heng Cai and Dong Chen},

doi = {10.7498/aps.69.20200332},

year  = {2020},

date = {2020-01-01},

urldate = {2020-01-01},

journal = {Acta Physica Sinica},

volume = {69},

number = {8},

pages = {86102},

publisher = {物理学报},

abstract = {In the B4 phase of bent-core liquid crystals, smectic layers of tilted achiral bent-core molecules are chiral and polar, which, driven by intra-layer structural mismatch, eventually twist into helical nanofilaments. We design a NOBOW/hexadecane organogel system, which is different from traditional organogel system, and the studied organogels show reversible gel-liquid transitions under temperature cycles. At high temperature, the NOBOW molecules dissolve in hexadecane and the storage modulus and viscous modulus show typical liquid characteristics. At low temperature, the mobility of NOBOW molecules decreases and the storage modulus of the organogels increases as the temperature decreases. We conduct a rheology experiment to systematically investigate the viscoelasticity of the organogel to understand the property of the organogel and develop the application in soft matter. The viscoelastic studies of the organogels reveal that the helical nanofilaments are internally strained and their 3D networks are relatively stiff, which provides an in-depth insight into the properties of the organogels and paves the way for their applications in soft matter.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2020,

title = {Molecular understanding for large deformations of soft bottlebrush polymer networks},

author = {Li Heng Cai},

doi = {10.1039/d0sm00759e},

year  = {2020},

date = {2020-01-01},

urldate = {2020-01-01},

journal = {Soft Matter},

volume = {16},

number = {27},

pages = {6259–6264},

publisher = {Royal Society of Chemistry},

abstract = {Networks formed by crosslinking bottlebrush polymers are a class of soft materials with stiffnesses matching that of 'watery' hydrogels and biological tissues but contain no solvents. Because of their extreme softness, bottlebrush polymer networks are often subject to large deformations. However, it is poorly understood how molecular architecture determines the extensibility of the networks. Using a combination of experimental and theoretical approaches, we discover that the yield strain γy of the network equals the ratio of the contour length Lmax to the end-to-end distance R of the bottlebrush between two neighboring crosslinks: γy = Lmax/R - 1. This relation suggests two regimes: (1) for stiff bottlebrush polymers, γy is inversely proportional to the network shear modulus G, γy ∼ G-1, which represents a previously unrecognized regime; (2) for flexible bottlebrush polymers, γy ∼ G-1/2, which recovers the behavior of conventional polymer networks. Our findings provide a new molecular understanding of the nonlinear mechanics for soft bottlebrush polymer networks. This journal is},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Nian2019,

title = {Molecular architecture directs linear-bottlebrush-linear triblock copolymers to self-assemble to soft reprocessable elastomers},

author = {Shifeng Nian and Huada Lian and Zihao Gong and Mikhail Zhernenkov and Jian Qin and Li-Heng Cai},

doi = {10.1021/acsmacrolett.9b00721},

year  = {2019},

date = {2019-01-01},

urldate = {2019-01-01},

journal = {ACS Macro Letters},

volume = {8},

number = {11},

pages = {1528–1534},

publisher = {American Chemical Society},

abstract = {Linear-bottlebrush-linear (LBBL) triblock copolymers represent an emerging system for creating multifunctional nanostructures. Their self-assembly depends on molecular architecture but remains poorly explored. We synthesize polystyrene-block-bottlebrush polydimethylsiloxane-block-polystyrene triblock copolymers with controlled molecular architecture and use them as a model system to study the self-assembly of LBBL polymers. Unlike classical stiff rod-flexible linear block copolymers that are prone to form highly ordered nanostructures such as lamellae, at small weight fractions of the linear blocks, LBBL polymers self-assemble to a disordered sphere phase, regardless of the bottlebrush stiffness. Microscopically, characteristic lengths increase with the bottlebrush stiffness by a power of 2/3, which is captured by a scaling analysis. Macroscopically, the formed nanostructures are ultrasoft, reprocessable elastomers with shear moduli of about 1 kPa, two orders of magnitude lower than that of conventional polydimethylsiloxane elastomers. Our results provide insights on exploiting the self-assembly of LBBL polymers to create soft functional nanostructures.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Haney2019,

title = {Millimeter-size Pickering emulsions stabilized with Janus microparticles},

author = {Bobby Haney and Dong Chen and Li-Heng Cai and David Weitz and Subramanian Ramakrishnan},

doi = {10.1021/acs.langmuir.9b00058},

year  = {2019},

date = {2019-01-01},

urldate = {2019-01-01},

journal = {Langmuir},

volume = {35},

number = {13},

pages = {4693–4701},

publisher = {American Chemical Society},

abstract = {The ability to make stable water-in-oil and oil-in-water millimeter-size Pickering emulsions is demonstrated using Janus particles - particles with distinct surface chemistries. The use of a highly cross-linked hydrophobic polymer network and the excellent water-wetting nature of a hydrogel as the hydrophobic and hydrophilic sides, respectively, permit distinct wettability on the Janus particle. Glass capillary microfluidics allows the synthesis of Janus particles with controlled sizes between 128 and 440 μm and control over the hydrophilic-to-hydrophobic domain volume ratio of the particle from 0.36 to 12.77 for a given size. It is shown that the Janus particle size controls the size of the emulsion drops, thus providing the ability to tune the structure and stability of the resulting emulsions. Stability investigations using centrifugation reveal that particles with the smallest size and a balanced hydrophilic-to-hydrophobic volume ratio (Janus ratio) form emulsions with the greatest stability against coalescence. Particles eventually jam at the interface to form nonspherical droplets. This effect is more pronounced as the hydrogel volume is increased. The large Janus particles permit facile visualization of particle-stabilized emulsions, which result in a better understanding of particle stabilization mechanisms of formed emulsions.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Button2018,

title = {Roles of mucus adhesion and cohesion in cough clearance},

author = {Brian Button and Henry P. Goodell and Eyad Atieh and Yu-Cheng Cheng Chen and Robert Williams and Siddharth Shenoy and Elijah Lackey and Nathan T. Shenkute and Li-Heng Cai and Robert G. Dennis and Richard C. Boucher and Michael Rubinstein},

doi = {10.1073/pnas.1811787115},

year  = {2018},

date = {2018-12-01},

urldate = {2018-12-01},

journal = {Proceedings of the National Academy of Sciences of the United States of America},

volume = {115},

number = {49},

pages = {12501–12506},

publisher = {National Academy of Sciences},

abstract = {Clearance of intrapulmonary mucus by the high-velocity airflow generated by cough is the major rescue clearance mechanism in subjects with mucoobstructive diseases and failed cilial-dependent mucus clearance, e.g., subjects with cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD). Previous studies have investigated the mechanical forces generated at airway surfaces by cough but have not considered the effects of mucus biophysical properties on cough efficacy. Theoretically, mucus can be cleared by cough from the lung by an adhesive failure, i.e., breaking mucus-cell surface adhesive bonds and/or by cohesive failure, i.e., directly fracturing mucus. Utilizing peel-testing technologies, mucus-epithelial surface adhesive and mucus cohesive strengths were measured. Because both mucus concentration and pH have been reported to alter mucus biophysical properties in disease, the effects of mucus concentration and pH on adhesion and cohesion were compared. Both adhesive and cohesive strengths depended on mucus concentration, but neither on physiologically relevant changes in pH nor bicarbonate concentration. Mucus from bronchial epithelial cultures and patient sputum samples exhibited similar adhesive and cohesive properties. Notably, the magnitudes of both adhesive and cohesive strength exhibited similar velocity and concentration dependencies, suggesting that viscous dissipation of energy within mucus during cough determines the efficiency of cough clearance of diseased, hyperconcentrated, mucus. Calculations of airflow-induced shear forces on airway mucus related to mucus concentration predicted substantially reduced cough clearance in small versus large airways. Studies designed to improve cough clearance in subjects with mucoobstructive diseases identified reductions of mucus concentration and viscous dissipation as key therapeutic strategies.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Wu2017,

title = {Tough self-healing elastomers by molecular enforced integration of covalent and reversible networks},

author = {Jinrong Wu and Li-Heng Cai and David A. Weitz},

doi = {10.1002/adma.201702616},

year  = {2017},

date = {2017-10-01},

urldate = {2017-10-01},

journal = {Advanced Materials},

volume = {29},

number = {38},

pages = {1702616},

publisher = {John Wiley & Sons, Ltd},

abstract = {Self-healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to “dry” elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid “dry” elastomer that is very tough with fracture energy 13500 Jm−2 comparable to that of natural rubber. Moreover, the elastomer can self-heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self-healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self-healing polymers of practical usage.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Xing2017,

title = {Graphene oxide induced crosslinking and reinforcement of elastomers},

author = {Wang Xing and Hengyi Li and Guangsu Huang and Li-Heng Cai and Jinrong Wu},

doi = {10.1016/j.compscitech.2017.03.006},

year  = {2017},

date = {2017-01-01},

urldate = {2017-01-01},

journal = {Composites Science and Technology},

volume = {144},

pages = {223–229},

abstract = {Conventional elastomer processing requires crosslinking elastomer using specific chemical reagents and reinforcing it using filler particles. Here we report a method to simultaneously crosslink and reinforce styrene-butadiene rubber (SBR) using graphene oxide (GO). We find that GO not only acts as an effective reinforcing filler, but also is capable of generating free radicals upon heating, enabling covalent crosslinking of SBR. Moreover, the interaction between GO surface and SBR polymers results in an interfacial layer in which the density of crosslinks increases towards to the GO surface, thus interfacial layer shows much slower relaxation dynamics than the bulk rubber. The unique role of GO allows GO/SBR nanocomposites to have better mechanical properties than SBR crosslinked with conventional sulfur or dicumyl peroxide. The concept of using GO as both a filler and crosslinking agent may enable the discovery of polymeric nanocomposites with exceeding mechanical properties.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Qin2017,

title = {Ultrafast nanofiltration through large-area single-layered graphene membranes},

author = {Yanzhe Qin and Yongyou Hu and Stephan Koehler and Li-Heng Cai and Junjie Wen and Xiaojun Tan and Weiwei L. Xu and Qian Sheng and Xu Hou and Jianming Xue and Miao Yu and David Weitz},

doi = {10.1021/acsami.7b00504},

year  = {2017},

date = {2017-01-01},

urldate = {2017-01-01},

journal = {ACS Applied Materials and Interfaces},

volume = {9},

number = {11},

pages = {9239–9244},

abstract = {Perforated single-layered graphene has demonstrated selectivity and flux that is orders of magnitude greater than state-of-the-art polymer membranes. However, only individual graphene sheets with sizes up to tens of micrometers have been successfully fabricated for pressurized permeation studies. Scaling-up and reinforcement of these atomic membranes with minimum cracks and pinholes remains a major hurdle for practical applications. We develop a large-area in situ, phase-inversion casting technique to create 63 cm2 high-quality single-layered perforated graphene membranes for ultrafast nanofiltration that can operate at pressures up to 50 bar. This result demonstrates the feasibility of our technique for creating robust large-area, high quality, single-layered graphene and its potential use as a pressurized nanofiltration membrane.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2017,

title = {Biocompatible amphiphilic hydrogel-solid dimer particles as colloidal surfactants},

author = {Dong Chen and Esther Amstad and Chun Xia Zhao and Li-Heng Cai and Jing Fan and Qiushui Chen and Mingtan Hai and Stephan Koehler and Huidan Zhang and Fuxin Liang and Zhenzhong Yang and David A. Weitz},

doi = {10.1021/acsnano.7b03110},

year  = {2017},

date = {2017-01-01},

urldate = {2017-01-01},

journal = {ACS Nano},

volume = {11},

number = {12},

pages = {11978–11985},

abstract = {Emulsions of two immiscible liquids can slowly coalesce over time when stabilized by surfactant molecules. Pickering emulsions stabilized by colloidal particles can be much more stable. Here, we fabricate biocompatible amphiphilic dimer particles using a hydrogel, a strongly hydrophilic material, and achieve large contrast in the wetting properties of the two bulbs, resulting in enhanced stabilization of emulsions. We generate monodisperse single emulsions of alginate and shellac solution in oil using a flow-focusing microfluidics device. Shellac precipitates from water and forms a solid bulb at the periphery of the droplet when the emulsion is exposed to acid. Molecular interactions result in amphiphilic dimer particles that consist of two joined bulbs: one hydrogel bulb of alginate in water and the other hydrophobic bulb of shellac. Alginate in the hydrogel compartment can be cross-linked using calcium cations to obtain stable particles. Analogous to surfactant molecules at the interface, the resultant amphiphilic particles stand at the water/oil interface with the hydrogel bulb submerged in water and the hydrophobic bulb in oil and are thus able to stabilize both water-in-oil and oil-in-water emulsions, making these amphiphilic hydrogel-solid particles ideal colloidal surfactants for various applications.},

keywords = {Polymers and Soft Matter},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2016,

title = {One-step microfluidic fabrication of polyelectrolyte microcapsules in aqueous conditions for protein release},

author = {Liyuan Zhang and Li-Heng Cai and Philipp S. Lienemann and Torsten Rossow and Ingmar Polenz and Queralt Vallmajo-Martin and Martin Ehrbar and Hui Na and David J. Mooney and David A. Weitz},

doi = {10.1002/anie.201606960},

year  = {2016},

date = {2016-01-01},

urldate = {2016-01-01},

journal = {Angewandte Chemie - International Edition},

volume = {55},

number = {43},

pages = {13470–13474},

abstract = {We report a microfluidic approach for one-step fabrication of polyelectrolyte microcapsules in aqueous conditions. Using two immiscible aqueous polymer solutions, we generate transient water-in-water-in-water double emulsion droplets and use them as templates to fabricate polyelectrolyte microcapsules. The capsule shell is formed by the complexation of oppositely charged polyelectrolytes at the immiscible interface. We find that attractive electrostatic interactions can significantly prolong the release of charged molecules. Moreover, we demonstrate the application of these microcapsules in encapsulation and release of proteins without impairing their biological activities. Our platform should benefit a wide range of applications that require encapsulation and sustained release of molecules in aqueous environments.},

keywords = {Bioengineering, Biomaterials},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2016,

title = {Hidden in the mist no more: physical force in cell biology},

author = {Karin Wang and Li-Heng Cai and Bo Lan and Jeffrey J. Fredberg},

doi = {10.1038/nmeth.3744},

year  = {2016},

date = {2016-01-01},

urldate = {2016-01-01},

journal = {Nature Methods},

volume = {13},

number = {2},

pages = {124–125},

abstract = {To drive its migration through a fibrillar matrix—and thus to spread, invade or metastasize—a cancer cell must exert physical forces. The first visualization of these forces in three dimensions reveals surprising migration dynamics.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2015a,

title = {Soft Poly(dimethylsiloxane) elastomers from architecture-driven entanglement free design},

author = {Li-Heng Cai and Thomas E. Kodger and Rodrigo E. Guerra and Adrian F. Pegoraro and Michael Rubinstein and David A. Weitz},

doi = {10.1002/adma.201502771},

year  = {2015},

date = {2015-09-01},

urldate = {2015-09-01},

journal = {Advanced Materials},

volume = {27},

number = {35},

pages = {5132–5140},

abstract = {Soft, solvent-free poly(dimethylsiloxane) elastomers are fabricated by a one-step process via crosslinking bottlebrush polymers. The bottlebrush architecture prevents the formation of entanglements, resulting in elastomers with precisely controllable low moduli from 1 to 100 kPa, below the lower limit of traditional elastomers; moreover, the solvent-free nature enables their negligible adhesiveness compared to commercially available silicone products of similar stiffness.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2015,

title = {Hopping diffusion of nanoparticles in polymer matrices},

author = {Li-Heng Cai and Sergey Panyukov and Michael Rubinstein},

doi = {10.1021/ma501608x},

year  = {2015},

date = {2015-01-01},

urldate = {2015-01-01},

journal = {Macromolecules},

volume = {48},

number = {3},

pages = {847–862},

publisher = {American Chemical Society},

abstract = {We propose a hopping mechanism for diffusion of large nonsticky nanoparticles subjected to topological constraints in both unentangled and entangled polymer solids (networks and gels) and entangled polymer liquids (melts and solutions). Probe particles with size larger than the mesh size ax of unentangled polymer networks or tube diameter ae of entangled polymer liquids are trapped by the network or entanglement cells. At long time scales, however, these particles can diffuse by overcoming free energy barrier between neighboring confinement cells. The terminal particle diffusion coefficient dominated by this hopping diffusion is appreciable for particles with size moderately larger than the network mesh size ax or tube diameter ae. Much larger particles in polymer solids will be permanently trapped by local network cells, whereas they can still move in polymer liquids by waiting for entanglement cells to rearrange on the relaxation time scales of these liquids. Hopping diffusion in entangled polymer liquids and networks has a weaker dependence on particle size than that in unentangled networks as entanglements can slide along chains under polymer deformation. The proposed novel hopping model enables understanding the motion of large nanoparticles in polymeric nanocomposites and the transport of nano drug carriers in complex biological gels such as mucus.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Henderson2014,

title = {Cystic fibrosis airway secretions exhibit mucin hyperconcentration and increased osmotic pressure},

author = {Ashley G. Henderson and Camille Ehre and Brian Button and Lubna H. Abdullah and Li-Heng Cai and Margaret W. Leigh and Genevieve C. DeMaria and Hiro Matsui and Scott H. Donaldson and C. William Davis and John K. Sheehan and Richard C. Boucher and Mehmet Kesimer},

doi = {10.1172/JCI73469},

year  = {2014},

date = {2014-01-01},

urldate = {2014-01-01},

journal = {Journal of Clinical Investigation},

volume = {124},

number = {7},

pages = {3047–3060},

abstract = {The pathogenesis of mucoinfective lung disease in cystic fibrosis (CF) patients likely involves poor mucus clearance. A recent model of mucus clearance predicts that mucus flow depends on the relative mucin concentration of the mucus layer compared with that of the periciliary layer; however, mucin concentrations have been difficult to measure in CF secretions. Here, we have shown that the concentration of mucin in CF sputum is low when measured by immunologically based techniques, and mass spectrometric analyses of CF mucins revealed mucin cleavage at antibody recognition sites. Using physical size exclusion chromatography/differential refractometry (SEC/dRI) techniques, we determined that mucin concentrations in CF secretions were higher than those in normal secretions. Measurements of partial osmotic pressures revealed that the partial osmotic pressure of CF sputum and the retained mucus in excised CF lungs were substantially greater than the partial osmotic pressure of normal secretions. Our data reveal that mucin concentration cannot be accurately measured immunologically in proteolytically active CF secretions; mucins are hyperconcentrated in CF secretions; and CF secretion osmotic pressures predict mucus layer-dependent osmotic compression of the periciliary liquid layer in CF lungs. Consequently, mucin hypersecretion likely produces mucus stasis, which contributes to key infectious and inflammatory components of CF lung disease.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Stukalin2013,

title = {Self-healing of unentangled polymer networks with reversible bonds},

author = {Evgeny B. Stukalin and Li-Heng Cai and N. Arun Kumar and Ludwik Leibler and Michael Rubinstein},

doi = {10.1021/ma401111n},

year  = {2013},

date = {2013-09-01},

urldate = {2013-09-01},

journal = {Macromolecules},

volume = {46},

number = {18},

pages = {7525–7541},

publisher = {American Chemical Society},

abstract = {Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess nonequilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. © 2013 American Chemical Society.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Button2012,

title = {A periciliary brush promotes the lung health by separating the mucus layer from airway epithelia},

author = {B. Button and L. -H. Cai and C. Ehre and M. Kesimer and D. B. Hill and J. K. Sheehan and R. C. Boucher and M. Rubinstein},

doi = {10.1126/science.1223012},

year  = {2012},

date = {2012-08-01},

urldate = {2012-08-01},

journal = {Science},

volume = {337},

number = {6097},

pages = {937–941},

abstract = {Mucus clearance is the primary defense mechanism that protects airways from inhaled infectious and toxic agents. In the current gel-on-liquid mucus clearance model, a mucus gel is propelled on top of a “watery” periciliary layer surrounding the cilia. However, this model fails to explain the formation of a distinct mucus layer in health or why mucus clearance fails in disease. We propose a gel-on-brush model in which the periciliary layer is occupied by membrane-spanning mucins and mucopolysaccharides densely tethered to the airway surface. This brush prevents mucus penetration into the periciliary space and causes mucus to form a distinct layer. The relative osmotic moduli of the mucus and periciliary brush layers explain both the stability of mucus clearance in health and its failure in airway disease.},

keywords = {Bioengineering},

pubstate = {published},

tppubtype = {article}

}

@article{Cai2011,

title = {Mobility of nonsticky nanoparticles in polymer liquids},

author = {Li-Heng Cai and Sergey Panyukov and Michael Rubinstein},

doi = {10.1021/ma201583q},

year  = {2011},

date = {2011-01-01},

urldate = {2011-01-01},

journal = {Macromolecules},

volume = {44},

number = {19},

pages = {7853–7863},

publisher = {American Chemical Society},

abstract = {We use scaling theory to derive the time dependence of the mean-square displacement 〈Δr2〉 of a probe nanoparticle of size d experiencing thermal motion in polymer solutions and melts. Particles with size smaller than solution correlation length undergo ordinary diffusion (〈Δr2(t)〉 ∼ t) with diffusion coefficient similar to that in pure solvent. The motion of particles of intermediate size (< d < a), where a is the tube diameter for entangled polymer liquids, is subdiffusive (〈Δr2(t)〉 ∼ t1/2) at short time scales since their motion is affected by subsections of polymer chains. At long time scales the motion of these particles is diffusive, and their diffusion coefficient is determined by the effective viscosity of a polymer liquid with chains of size comparable to the particle diameter d. The motion of particles larger than the tube diameter a at time scales shorter than the relaxation time τe of an entanglement strand is similar to the motion of particles of intermediate size. At longer time scales (t > τe) large particles (d > a) are trapped by entanglement mesh, and to move further they have to wait for the surrounding polymer chains to relax at the reptation time scale τrep. At longer times t > τrep, the motion of such large particles (d > a) is diffusive with diffusion coefficient determined by the bulk viscosity of the entangled polymer liquids. Our predictions are in agreement with the results of experiments and computer simulations. © 2011 American Chemical Society.},

keywords = {Polymers and Soft Matter, Theory},

pubstate = {published},

tppubtype = {article}

}

@article{Zhou2007,

title = {Template synthesis and magnetic behavior of FeNi alloy nanotube arrays},

author = {Dong Zhou and Li-Heng Cai and Fu Shen Wen and Fa Shen Li},

doi = {10.1088/1674-0068/20/06/821-825},

year  = {2007},

date = {2007-12-01},

urldate = {2007-12-01},

journal = {Chinese Journal of Chemical Physics},

volume = {20},

number = {6},

pages = {821–825},

publisher = {IOP Publishing},

abstract = {FeNi nanotubes were successfully prepared in pores of anodic aluminium oxide templates by the wetting template method. By varying the deposition conditions and the parameters of the templates, the lengths and the outer as well as the inner diameters of the tubes can be tailored. The FeNi nanotubes and their arrays were characterized by transmission and scanning electron microscopy. Macroscopic magnetic measurements show the FeNi nanotube arrays to have obvious anisotropy, and the easy axis is parallel to the nanotube axis. The magnetic moment distributions in the tube walls and the magnetization reversal mechanism are discussed. Magnetic moments of the FeNi nanotube preferentially lie in the nanotube wall, but the distribution is spatially isotropic. These magnetic behaviours are due to the unique shape of the nanotube. © 2007 Chinese Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}