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Advanced Biotechnology
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
A relatively new class of micromachining is based on printing, molding, and embossing elastomeric materials and is collectively referred to as soft lithography (Qin et al. 2010). The most common soft lithography process is illustrated in Fig. 5. A thick layer of photoresist, up to several hundred microns, is spin coated on a silicon wafer and exposed through a photomask. After development, the thick features form the master mold for creating multiple molded parts. Poly(dimethylsiloxane) (PDMS) is a common elastomer for that purpose. The two precursors are mixed thoroughly and then poured onto the wafer with the thick features and cured at 60° to 80°C for several hours. It is then peeled off the master with negative features imprinted on the underside, forming fluidic chambers and channels of different sizes and shapes. Openings for fluidic injection and extraction are punched into the PDMS piece. The finishing step is to bond the piece onto a glass substrate. The advantages of forming a platform with PDMS is that it is cost effective, easy to mold, flexible, permeable to gas but not to liquid, biocompatible, and optically transparent to allow examination of the fluids and materials inside the device. Microfluidic devices fabricated with this technique have been used to perform cell sorting, capturing, tagging, and studied under various chemical or physical stimuli (Whitesides et al. 2001). It greatly enhances our ability to probe the physiological responses of single cells for the purpose of understanding both the natural and pathological implications of cell development.
Body-on-a-Chip for Pharmacology and Toxicology
Published in Brian J. Lukey, James A. Romano, Salem Harry, Chemical Warfare Agents, 2019
Anthony Atala, Mahesh Devarasetty, Steven. D. Forsythe, Russell. M. Dorsey, Harry Salem, Thomas. D. Shupe, Aleksander Skardal, Shay Soker
Microfluidic devices are produced in several main steps. First is the deposition of molding material or resist, typically polymethylmethacrylate (PMMA) or SU-8, onto a glass substrate. This material should be light reactive and thus, is called a photoresist. Next, a photomask is used to isolate areas of interest (or exclude areas of interest in the case of negative photoresists) before a UV light is shone over the photomask. The UV light crosslinks the material in positive photoresists (PMMA) or degrades the material in negative photoresists (SU-8). Afterward, the unneeded photoresist material is discarded from the substrate, and the result should be a thin structure that matches the photomask. This structure is a negative mold of the desired microfluidic device. Finally, a curable silicone can be poured over the negative mold, allowed to cure, and removed to produce the final microfluidic channel or system molded in silicone (Qin et al., 2010).
Innovative industrial technology starts with iodine
Published in Tatsuo Kaiho, Iodine Made Simple, 2017
A photoacid generator is a photosensitizer which generates acid by exposure to light. It is used as a photoresist (photosensitive composition) during the photolithography process in the production of semiconductor devices, printed circuit boards, and LCD (Liquid-Crystal Display) panels. The upper diagram shows the basic lithography process. The photoresist consists of either a negative type, where the pattern of the irradiated area remains, or a positive type where the irradiated area is removed after the development process.
Microfluidics in drug delivery: review of methods and applications
Published in Pharmaceutical Development and Technology, 2023
Mutasem Rawas-Qalaji, Roberta Cagliani, Noor Al-hashimi, Rahma Al-Dabbagh, Amena Al-Dabbagh, Zahid Hussain
Photoresists are fundamental materials related to photolithography. They are light-sensitive materials, composed of a polymer, a sensitizer, and a solvent. The polymer is able to change its structure when it is exposed to radiations. The solvent allows the photoresist to be spun and to form thin layers over the wafer surface. Finally, the sensitizer is able to control the photochemical reaction in the polymer phase (Nihtianov and Luque 2014). Photoresists can be classified as positive or negative. In the positive photoresists, the photochemical reaction occurs during exposure to light and make the polymer more soluble to the developer (Nihtianov and Luque 2014). In the case of negative photoresists, exposure to light causes the polymerization of the photoresist, the negative resist remains on the surface of the substrate where it is exposed, and the developer solution removes only the unexposed areas. The advantages of negative photoresists are good adhesion to silicon, lower cost, and a shorter processing time. The advantages of positive photoresists are better resolution and thermal stability.
Light mediated drug delivery systems: a review
Published in Journal of Drug Targeting, 2022
Biomimetic materials, such as peptide sequences in combination with NIR light are efficient in drug-releasing for therapeutic purposes and can be used for monitoring the progression of cancer. Chen et al. fabricated a TiO2 substrate and coupled it with an NGR (asparagine-glycine-arginine) peptide sequence [79]. They engineered TiO2 nanofibers by electrospinning and modified the surface with bovine serum albumin (BSA) to inhibit the attachment of non-target cells. The BSA modified TiO2-NGR conjugate showed higher sensitivity and selectivity towards capturing circulating tumour cells (CTC’s). Similarly, a microfluidic platform was created by integrating it with streptavidin functionalised PLGA nanofibers for isolating CTC’s [80]. In this study, they utilised a negative photoresist to fabricate the microfluidic device. Blood lyzed with red blood cells from healthy patients pre-treated with biotin anti-CD45 anti-body and stained with DAPI (4′,6-diamidino-2-phenylindole) were passed through the microfluidic chip. The capture efficiency of the white blood cells by the protein functionalised substrate was 97%. This efficiency was further reproduced in the clinic by isolating the CTC’s from 20 patients suffering from non-small cell lung cancer (NSCLC). They were able to successfully sort the cells into stage I, stage II, and stage III NSCLC.
Single-molecule measurements in microwells for clinical applications
Published in Critical Reviews in Clinical Laboratory Sciences, 2020
Connie Wu, Adam M. Maley, David R. Walt
Currently, microwells are commonly prepared via microfabrication, a technique widely used in the microelectronics industry. Various microfabrication strategies have been used to prepare microwells, including photolithography, block copolymer lithography, microcontact printing, capillary force lithography, and electrochemical micromachining [48–53]. Microwell arrays can be composed of diverse materials, such as glass, silicon, polydimethylsiloxane (PDMS), or other polymers. PDMS is a silicone elastomer widely used for fabrication due to its optical transparency, biocompatibility, chemical inertness, flexibility, and thermal stability [54]. In a typical microfabrication process, a photoresist layer and mask are deposited onto a silicon wafer, followed by ultraviolet light exposure and dissolution of exposed photoresist areas with organic solvent or base. Microwell arrays made of PDMS are then obtained by pouring PDMS onto the resulting master, followed by thermal curing and peeling off of the PDMS layer. Microwells with diameters of 1–1000 µm can be fabricated via photolithography methods [50].