Microscale hydrogels of controlled sizes and shapes are useful for cell-based screening, in vitro diagnostics, tissue engineering, and drug delivery. However, the rapid cross-linking of many chemically and pH cross-linkable hydrogel materials prevents the application of existing micromolding techniques. In this work we present a method for fabricating micromolded calcium alginate and chitosan structures through controlled release of the gelling agent from a hydrogel mold. Replica molding was employed to generate patterned membranes, whereas microtransfer molding was used to produce microparticles of controlled shapes. To explore the viability of this technique for producing complex tissue engineering micro-architectures, this approach was used to generate cell-laden size- and shape-controlled 3D microgels as well as composite hydrogels with well-defined spatially segregated regions. In addition, shape-controlled microstructures that can exhibit differential release properties were loaded with macromolecules to verify the potential of this approach for drug delivery applications.

No abstract

Microscale hydrogels with dimensions of 200 µm or less are powerful tools for various biomedical applications such as tissue engineering, drug delivery, and biosensors, due to their size, biocompatibility, and their controllable biological, chemical, and mechanical properties. In this review, we provide a broad overview of the approaches used to synthesize and characterize microgels, as well as their applications. We discuss the various methods used to fabricate microgels, such as emulsification, micromolding, microfluidics, and photolithography. Furthermore, we discuss the effects of porosity and crosslinking density on the mechanical and biological properties of hydrogels. In addition, we give specific examples of the use of hydrogels, such as scaffolds and cell encapsulation for tissue engineering, controlled release materials for drug delivery, and environmentally sensitive sensors for microdevices. Finally, we will discuss the future applications of this technology.

No abstract

Abstract-Network coding is known to improve throughput by mixing information from different flows and conveying more information in each transmission. Recently some proposals have demonstrated the benefits of applying network coding to wireless networks with broadcast transmissions. It is expected that the opportunities for coding and the corresponding gains depend on the bit-rate chosen for determining routes and transmitting packets. However, the previous work on wireless network coding assumed a fixed rate and did not explicitly account for the interaction between rate selection and coding gain. In this paper, we define a new metric, expected coded time (ECT), that measures the total time needed by a node to deliver two packets to their receivers given the bit-rate for transmitting coded packets. We then investigate how the optimal bit-rate for coded packets differs from that for transmission of native packets individually. We also study the performance of network coding under different fixed bit-rates for the whole network. Our evaluation shows that 11 Mbps is the best default fixed rate for MIT Roofnet and 5.5 Mbps is mostly the optimal rate to transmit coded packets when the ideal individual bit-rate for each receiver is different.

Two-dimensional polyfluorenes bearing thienylenevinylene-bridged malononitrile (PF-BTDCN) or diethylthiobarbituric acid accepting side chains (PF-BTDTA) have been successfully prepared. The polymers were fully characterized for their physicochemical, electrochemical, and photovoltaic properties. These polymers exhibited greatly changed properties with the introduction of π-conjugated accepting side chains. The enhancement of current density for the bulk-heterojunction solar cells was observed when replacing the PEDOT:PSS interfacial layer with molybdenum oxide (MoO 3 ). Photovoltaic solar cells with the configuration ITO/MoO 3 /polymer:PCBM/Al exhibited an efficiency of 3.13% and 1.72% for PF-BTDCN and PF-BTDTA, respectively. A morphology study revealed the existence of nanoscale phase separation with interpenetration networks between polymer and PCBM domains.

Three novel dithieno[3,2‐b:2′,3′‐d]thiophene‐based low‐bandgap polymers are synthesized by a Suzuki–Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26–32 kDa) and narrow polydiversity (1.3–1.7). With a highest occupied molecular orbital (HOMO) energy level around −5.20 eV, these polymers exhibit a narrow bandgap of 1.75–1.87 eV. All the polymers display strong absorption in the range of 350–700 nm. Bulk‐heterojunction (BHJ) solar cells are further fabricated by blending the as‐prepared polymer with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm−2).

No abstract