Controlled degradation and transiency of materials is of significant importance in the design and fabrication of degradable and transient biomedical and electronic devices and platforms. Here, the synthesis of programmable biodegradable and transient insulating polymer films is reported, which have sufficient physical and chemical properties to be used as substrates for the construction of transient electronics. The composite structure can be used as a means to control the dissolution and transiency rate of the polymer composite film. Experimental and computational studies demonstrate that the addition of gelatin or sucrose to a PVA polymer matrix can be used as a means to program and either slow or enhance the transiency of the composite. The dissolution of the polymer composites are fitted with inverse exponential functions of different time constants; the lower time constants are an indication of faster transiency of the polymer composite. The addition of gelatin results in larger time constants, whereas the addition of sucrose generally results in smaller time constants.

The first step in curing a disease is being able to detect the disease effectively. Paper-based microfluidic devices are biodegradable and can make diagnosing diseases costeffective and easy in almost all environments. We created a three-dimesnional (3D) paper device using wax printing fabrication technique and basic principles of origami. This design allows for a versatile fabrication technique over previously reported patterning of SU-8 photoresist on chromatography paper by employing a readily available wax printer. The design also utilizes multiple colorimetric assays that can accommodate one or more analytes including urine, blood, and saliva. In this case to demonstrate the functionality of the 3D paper-based microfluidic system, a urinalysis of protein and glucose assays is conducted. The amounts of glucose and protein introduced to the device are found to be proportional to the color change of each assay. This color change was quantified by use of Adobe Photoshop. Urine samples from participants with no pre-existing health conditions and one person with diabetes were collected and compared against synthetic urine samples with predetermined glucose and protein levels. Utilizing this method, we were able to confirm that both protein and glucose levels were in fact within healthy ranges for healthy participants. For the participant with diabetes, glucose was found to be above the healthy range while the protein level was in the healthy range. D iseases surround the world and being able to diagnose them is crucial in order to then cure the disease. Diagnosing diseases is not always an affordable, time-efficient, or easy task. Paper-based microfluidic devices construct a framework that leaves the level of complication and cost low while keeping the efficiency high.1−6 The application of paperbased microfluidics presents many advantages such as their cost effectiveness: they are easy to mass-produce, transport, store, implement, dispose, and they do not need excessive equipment to move liquid like other devices. There are also many disadvantages to paper-based microfluidic devices. They are relatively new, which means issues such as the control over flow rates, mixing, and interaction times between sample and reagents have not yet been perfected. 7−9A previous approach by Liu and Crooks 10 uses photolithography and origami to develop a 3D paper-based analytical device (μPAD). The inclusion of origami to the overall design of the μPAD allows for only one step of the fabrication process. The μPAD can be simply folded into multiple layers. This also eliminates the contamination and nonspecific adsorption caused by using tape in previous 3D designs. 3 Following the procedure, analysis can be done by unfolding the μPAD, revealing the colorimetric and fluorescence assays on each layer. Photolithography patterns the paper by use of a light-sensitive chemical as photoresist, creating a pattern on the paper to control fluid flow without any input of excess energy such as a pump or valve system in glass-based ...

In recent years, the exploitation of phenomena surrounding microfluidics has seen an increase in popularity, as researchers have found a way to use their unique properties to create superior design alternatives. One such application is representing the properties and functions of different organs on a microscale chip for the purpose of drug testing or tissue engineering. With the introduction of "organ-on-a-chip" systems, researchers have proposed various methods on various organ-on-a-chip systems to mimic their in vivo counterparts. In this article, a systematic approach is taken to review current technologies pertaining to organ-on-a-chip systems. Design processes with attention to the particular instruments, cells, and materials used are presented.

Fibrous scaffolds have shown promise in tissue engineering due to their ability to improve cell alignment and migration. In this paper, poly(ε-caprolactone) (PCL) fibers are fabricated in different sizes using a microfluidic platform. By using this approach, we demonstrated considerable flexibility in ability to control the size of the fibers. It was shown that the average diameter of the fibers was obtained in the range of 2.6−36.5 μm by selecting the PCL solution flow rate from 1 to 5 μL min −1 and the sheath flow rate from 20 to 400 μL min −1 in the microfluidic channel. The microfibers were used to create 3D microenvironments in order to investigate growth and differentiation of adult hippocampal stem/progenitor cells (AHPCs) in vitro. The results indicated that the 3D topography of the PCL substrates, along with chemical (extracellular matrix) guidance cues supported the adhesion, survival, and differentiation of the AHPCs. Additionally, it was found that the cell deviation angle for 44−66% of cells on different types of fibers was less than 10°. This reveals the functionality of PCL fibrous scaffolds for cell alignment important in applications such as reconnecting serious nerve injuries and guiding the direction of axon growth as well as regenerating blood vessels, tendons, and muscle tissue.

Due to the particular structure and functionality of the placenta, most current human placenta drug testing methods are limited to animal models, conventional cell testing, and cohort/controlled testing. Previous studies have produced inconsistent results due to physiological differences between humans and animals and limited availability of human and/or animal models for controlled testing. To overcome these challenges, a placenta‐on‐a‐chip system is developed for studying the exchange of substances to and from the placenta. Caffeine transport across the placental barrier is studied because caffeine is a xenobiotic widely consumed on a daily basis. Since a fetus does not carry the enzymes that inactivate caffeine, when it crosses a placental barrier, high caffeine intake may harm the fetus, so it is important to quantify the rate of caffeine transport across the placenta. In this study, a caffeine concentration of 0.25 mg mL −1 is introduced into the maternal channel, and the resulting changes are observed over a span of 7.5 h. A steady caffeine concentration of 0.1513 mg mL −1 is reached on the maternal side after 6.5 h, and a 0.0033 mg mL −1 concentration on the fetal side is achieved after 5 h.

We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross-sections. Uniform gelatin microfibers with various morphologies and cross-sections (round and square) are fabricated by increasing the gelatin concentration of the core solution from 8% to 12%. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Young's modulus and tensile stress at break of gelatin (12%) fibers are raised about 2.2 and 1.9 times as those of gelatin (8%) fibers. The COMSOL simulations indicate that the sizes and cross-sections of the gelatin fibers can be tuned by using a microfluidic device with four-chevron grooves. The experimental results demonstrate that the decrease of the sheath-to-core flow-rate ratio from 150 : 1 to 30 : 1 can increase the aspect ratio and size of ribbon-shaped fibers from 35 μm × 60 μm to 47 μm × 282 μm, which is consistent with the simulation results. The increased size and shape evolution of the cross-section can not only strengthen the Young's modulus and tensile stress at break, but also significantly enhance the tensile strain at break. Disciplines Applied Mechanics | Biology and Biomimetic Materials | Biomechanical Engineering | Polymer and Organic MaterialsComments This is a manuscript of an article published as Bai, Zhenhua, Janet M. Mendoza Reyes, Reza Montazami, and Nastaran Hashemi. "On-chip development of hydrogel microfibers from round to square/ribbon shape."We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross sections. Uniform gelatin microfibers with various morphologies and cross sections (round and square) are fabricated by increasing the gelatin concentration of core solution from 8 % to 12 %. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Young's modulus and tensile stress at break of gelatin (12 %) fiber are raised about 2.2 and 1.9 times as those of gelatin (8 %) fiber. The COMSOL simulations indicate that the size and cross section of gelatin fiber can be tuned by microfluidic device with four-chevron grooves. The experiment results demonstrate that the decrease of sheath-to-core flow-rate ratio from 150:1 to 30:1 can increase the aspect ratio and size of ribbon-shaped fiber from 35 µm × 60 µm to 47 µm × 282 µm, which consists well with the simulation results. The increased size and shape evolution of cross section can not only strengthen the Young's modulus and tensile stress at break, and also significantly enhance tensile strain at break.

The effects of global warming, pollution in river effluents, and changing ocean currents can be studied by characterizing variations in phytoplankton populations. We demonstrate the design and fabrication of a Microflow Cytometer for characterization of phytoplankton. Guided by chevron-shaped grooves on the top and bottom of a microfluidic channel, two symmetric sheath streams wrap around a central sample stream and hydrodynamically focus it in the center of the channel. The lasers are carefully chosen to provide excitation light close to the maximum absorbance wavelengths for the intrinsic fluorophores chlorophyll and phycoerythrin, and the excitation light is coupled to the flow cytometer through the use of an optical fiber. Fluorescence and light scatter are collected using two multimode optical fibers placed at 90-degree angles with respect to the excitation fiber. Light emerging from these collection fibers is directed through optical bandpass filters into photomultiplier tubes. The cytometer measured the optical and side scatter properties of Karenia b., Synechococcus sp., Pseudo-Nitzchia, and Alexandrium. The effect of the sheath-tosample flow-rate ratio on the light scatter and fluorescence of these marine microorganisms was investigated. Reducing the sample flow rate from 200 lL/min to 10 lL/min produced a more tightly focused sample stream and less heterogeneous signals.

Microfibers have received much attention due to their promise for creating flexible and highly relevant tissue models for use in biomedical applications such as 3D cell culture, tissue modeling, and clinical treatments. A generated tissue or implanted material should mimic the natural microenvironment in terms of structural and mechanical properties as well as cell adhesion, differentiation, and growth rate. Therefore, the mechanical and biological properties of the fibers are of importance. This paper briefly introduces common fiber fabrication approaches, provides examples of polymers used in biomedical applications, and then reviews the methods applied to modify the mechanical and biological properties of fibers fabricated using different approaches for creating a highly controlled microenvironment for cell culturing. It is shown that microfibers are a highly tunable and versatile tool with great promise for creating 3D cell cultures with specific properties.