Poly(p-phenylenediamine) (PpPD)/carboxylic acid-functionalized multiwalled carbon nanotubes (c-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K 2 S 2 O 8 ) as an oxidant. Field-emission scanning electron microscopy (FE-SEM) and field-emission transmission electron microscopy (FE-TEM) showed that a tubular layer of PpPD was coated on the surface of carbon nanotubes with a thickness of 10-20 nm. FT-IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of c-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of PpPD was not affected much by the addition of c-MWCNTs. As the content of c-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.

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Three-dimensional (3D) bioprinting has become mainstream for precise and repeatable high-throughput fabrication of complex cell cultures and tissue constructs in drug testing and regenerative medicine, food products, dental and medical implants, biosensors, and so forth. Due to this tremendous growth in demand, an overwhelming amount of hardware manufacturers have recently flooded the market with different types of low-cost bioprinter models—a price segment that is most affordable to typical-sized laboratories. These machines range in sophistication, type of the underlying printing technology, and possible add-ons/features, which makes the selection process rather daunting (especially for a nonexpert customer). Yet, the review articles available in the literature mostly focus on the technical aspects of the printer technologies under development, as opposed to explaining the differences in what is already on the market. In contrast, this paper provides a snapshot of the fast-evolving low-cost bioprinter niche, as well as reputation profiles (relevant to delivery time, part quality, adherence to specifications, warranty, maintenance, etc.) of the companies selling these machines. Specifically, models spanning three dominant technologies—microextrusion, droplet-based/inkjet, and light-based/crosslinking—are reviewed. Additionally, representative examples of high-end competitors (including up-and-coming microfluidics-based bioprinters) are discussed to highlight their major differences and advantages relative to the low-cost models. Finally, forecasts are made based on the trends observed during this survey, as to the anticipated trickling down of the high-end technologies to the low-cost printers. Overall, this paper provides insight for guiding buyers on a limited budget toward making informed purchasing decisions in this fast-paced market.

Limb regeneration is a frontier in biomedical science. Identifying triggers of innate morphogenetic responses in vivo to induce the growth of healthy patterned tissue would address the needs of millions of patients, from diabetics to victims of trauma. Organisms such as Xenopus laevis —whose limited regenerative capacities in adulthood mirror those of humans—are important models with which to test interventions that can restore form and function. Here, we demonstrate long-term (18 months) regrowth, marked tissue repatterning, and functional restoration of an amputated X. laevis hindlimb following a 24-hour exposure to a multidrug, pro-regenerative treatment delivered by a wearable bioreactor. Regenerated tissues composed of skin, bone, vasculature, and nerves significantly exceeded the complexity and sensorimotor capacities of untreated and control animals’ hypomorphic spikes. RNA sequencing of early tissue buds revealed activation of developmental pathways such as Wnt/β-catenin, TGF-β, hedgehog, and Notch. These data demonstrate the successful “kickstarting” of endogenous regenerative pathways in a vertebrate model.

Computational modeling has been promulgated as a means of optimizing artificial bone tissue culturing ex vivo. In the present report, we show, as a proof-of-concept, that it is possible to model the exact microenvironment within the scaffolds while accounting for their architectural complexities and the presence of cells/tissues in their pores. Our results clearly indicate that image-based modeling has the potential to be a powerful tool for computer-assisted tissue engineering.

According to the U.S. Department of Health & Human Services, nearly 115,000 people in the U.S needed a lifesaving organ transplant in 2018, while only ~10% of them have received it. Yet, almost no artificial FDA-approved products are commercially available today -three decades after the inception of tissue engineering. It is hypothesized here that the major bottlenecks restricting its progress stem from lack of access to the inner pore space of the scaffolds. Specifically, the inability to deliver nutrients to, and clear waste from, the center of the scaffolds limits the size of the products that can be cultured. Likewise, the inability to monitor, and control, the cells after seeding them into the scaffold results in nonviable tissue, with an unacceptable product variability. To resolve these bottlenecks, we present a prototype addressable microfluidics device capable of minimally disruptive fluid and cell manipulations within living cultures. As proof-of-concept, we demonstrate its ability to perform additive manufacturing by seeding cells in spatial patterns (including co-culturing multiple cell types); and subtractive manufacturing by removing surface adherent cells via focused flow of trypsin. Additionally, we show that the device can sample fluids and perform cell "biopsies" (which can be subsequently sent for ex-situ analysis), from any location within its Culture Chamber. Finally, the on-chip plumbing is completely automated using external electronics. This opens the possibility to perform long-term computer-driven tissue engineering experiments, where the cell behavior is modulated in response to the minimally disruptive observations (e.g. fluid sampling and cell biopsies) throughout the entire duration of the cultures. It is expected that the proof-of-concept technology will eventually be scaled up to 3D addressable microfluidic scaffolds, capable of overcoming the limitations bottlenecking the transition of tissue engineering technologies to the clinical setting.

A custom-built mask aligner (CBMA), which fundamentally covers all the key features of a commercial mask aligner, while being low cost and light weight and having low power consumption and high accuracy, is constructed. The CBMA is composed of a custom high fidelity light emitting diode light source, a vacuum chuck, a mask holder, high-precision translation and rotation stages, and high resolution digital microscopes. The total cost of the system is under $7500, which is over ten times cheaper than a comparable commercial system. It produces a collimated ultraviolet illumination of 1.8-2.0 mW cm over an area of a standard 4-in. wafer, at the plane of photoresist exposure, and the alignment accuracy is characterized to be <3 m, which is sufficient for most microfluidic applications. Moreover, this manuscript provides detailed descriptions of the procedures needed to fabricate multilayered master molds using our CBMA. Finally, the capabilities of the CBMA are demonstrated by fabricating two- and three-layer masters for micro-scale devices, commonly encountered in biomicrofluidic applications. The former is a flow-free chemical gradient generator, and the latter is an addressable microfluidic stencil. Scanning electron microscopy is used to confirm that the master molds contain the intended features of different heights.

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