1666 wileyonlinelibrary.com Artifi cial micro-/nanoswimmers have various potential applications including minimally invasive diagnosis and targeted therapies, environmental sensing and monitoring, cell manipulation and analysis, and lab-on-a-chip devices. Inspired by natural motile bacteria such as E. Coli , artifi cial bacterial fl agella (ABFs) are one kind of magnetic helical microswimmers. ABFs can perform 3D navigation in a controllable fashion with micrometer precision under low-strength rotating magnetic fi elds (<10 mT) and are promising tools for targeted drug delivery in vitro and in vivo. In this work, the successful wirelessly targeted and single-cell gene delivery to human embryonic kidney (HEK 293) cells using ABFs loaded with plasmid DNA (pDNA) in vitro is demonstrated for the fi rst time. The ABFs are functionalized with lipoplexes containing pDNA to generate functionalized ABFs (f-ABFs). The f-ABFs are steered wirelessly by low-strength rotating magnetic fi elds and deliver the loaded pDNA into targeted cells. The cells targeted by f-ABFs are successfully transfected by the transported pDNA and expressed the encoding protein. These f-ABFs may also be useful for in vivo gene delivery and other applications such as sensors, actuators, cell biology, and lab-on-a-chip environments.

An approach for batch preparation of liposome‐functionalized microdevices is demonstrated for remotely controlled single‐cell drug delivery. The liposome functionalized artificial bacterial flagella exhibit corkscrew swimming in 3D with micrometer positioning precision by applying an external rotating magnetic field. The devices are also capable of delivering water‐soluble drugs to single cells in vitro.

The loss of expression of chondrogenic markers during monolayer expansion remains a stumbling block for cell-based treatment of cartilage lesions. Here, we introduce sulfated alginate hydrogels as a cartilage biomimetic biomaterial that induces cell proliferation while maintaining the chondrogenic phenotype of encapsulated chondrocytes. Hydroxyl groups of alginate were converted to sulfates by incubation with sulfur trioxidepyridine complex (SO 3 /pyridine), yielding a sulfated material cross-linkable with calcium chloride. Passage 3 bovine chondrocytes were encapsulated in alginate and alginate sulfate hydrogels for up to 35 days. Cell proliferation was five-fold higher in alginate sulfate compared with alginate ( p = 0.038). Blocking beta1 integrins in chondrocytes within alginate sulfate hydrogels significantly inhibited proliferation ( p = 0.002). Sulfated alginate increased the RhoA activity of chondrocytes compared with unmodified alginate, an increase that was blocked by b1 blocking antibodies ( p = 0.017). Expression and synthesis of type II collagen, type I collagen, and proteoglycan was not significantly affected by the encapsulation material evidenced by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry. Alginate sulfate constructs showed an opaque appearance in culture, whereas the unmodified alginate samples remained translucent. In conclusion, alginate sulfate provides a three dimensional microenvironment that promotes both chondrocyte proliferation and maintenance of the chondrogenic phenotype and represents an important advance for chondrocyte-based cartilage repair therapies providing a material in which cell expansion can be done in situ.

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The layer-by-layer (LbL) technique has been widely used to produce nanofilms for biomedical applications. Naturally occurring polymers such as ECM macromolecules are attractive candidates for LbL film preparation. In this study, we assessed the build-up of type I collagen (Col1)/chondroitin sulfate (CS) or Col1/Heparin (HN) on polydimethylsiloxane (PDMS) substrates. The build-up was assessed by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). Integrin-mediated cell adhesion was assessed by studying the cytoskeletal organization of mammalian primary cells (chondrocytes) seeded on different end layers and number of layers. Data generated from the QCM-D observations showed a consistent build-up of films with more adsorption in the case of Col1/HN. Col1/CS films were stable in media, whereas Col1/HN films were not. AFM analysis showed that the layers were fibrillar in structure for both systems and between 20 and 30 nm thick. The films promoted cell adhesion when compared with tissue culture plastic in serum-free media with cycloheximide. Crosslinking of the films resulted in constrained cell spreading and a ruffled morphology. Finally, beta1 integrin blocking antibodies prevented cell spreading, suggesting that cell adhesion and spreading were mediated mainly by interaction with the collagen fibrils. The ability to construct stable ECM-based films on PDMS has particular relevance in mechanobiology, microfluidics, and other biomedical applications.