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Biocompatible Hydrogels for Microarray Cell Printing and Encapsulation.

Datar A, Joshi P, Lee MY - Biosensors (Basel) (2015)

Bottom Line: Conventional drug screening processes are a time-consuming and expensive endeavor, but highly rewarding when they are successful.These two-dimensional (2D) cell monolayers are physiologically irrelevant, thus, often providing false-positive or false-negative results, when compared to cells grown in three-dimensional (3D) structures such as hydrogel droplets.In this review, several hydrogels that are compatible to microarray printing robots are discussed for miniaturized 3D cell cultures.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical & Biomedical Engineering, Cleveland State University, 1960 East 24th Street Cleveland, OH 44115-2214, USA. a.datar17@vikes.csuohio.edu.

ABSTRACT
Conventional drug screening processes are a time-consuming and expensive endeavor, but highly rewarding when they are successful. To identify promising lead compounds, millions of compounds are traditionally screened against therapeutic targets on human cells grown on the surface of 96-wells. These two-dimensional (2D) cell monolayers are physiologically irrelevant, thus, often providing false-positive or false-negative results, when compared to cells grown in three-dimensional (3D) structures such as hydrogel droplets. However, 3D cell culture systems are not easily amenable to high-throughput screening (HTS), thus inherently low throughput, and requiring relatively large volume for cell-based assays. In addition, it is difficult to control cellular microenvironments and hard to obtain reliable cell images due to focus position and transparency issues. To overcome these problems, miniaturized 3D cell cultures in hydrogels were developed via cell printing techniques where cell spots in hydrogels can be arrayed on the surface of glass slides or plastic chips by microarray spotters and cultured in growth media to form cells encapsulated 3D droplets for various cell-based assays. These approaches can dramatically reduce assay volume, provide accurate control over cellular microenvironments, and allow us to obtain clear 3D cell images for high-content imaging (HCI). In this review, several hydrogels that are compatible to microarray printing robots are discussed for miniaturized 3D cell cultures.

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Various mechanisms for printing biological samples: (A) Micro-solenoid valve using electromagnetic induction; (B) Piezoelectric nozzle using piezoelectric vibration; (C) Laser-induced forward transfer (LIFT) using a laser beam to propel cell spots [13], and (D) Acoustic wave generator using ultrasound to produce acoustic waves for cell printing (Reproduced from Reference [23] with permission of The Royal Society of Chemistry).
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biosensors-05-00647-f001: Various mechanisms for printing biological samples: (A) Micro-solenoid valve using electromagnetic induction; (B) Piezoelectric nozzle using piezoelectric vibration; (C) Laser-induced forward transfer (LIFT) using a laser beam to propel cell spots [13], and (D) Acoustic wave generator using ultrasound to produce acoustic waves for cell printing (Reproduced from Reference [23] with permission of The Royal Society of Chemistry).

Mentions: To encapsulate cells in 3D and prevent their direct contact with the surface, polymeric substances (hydrogels) that have capacity to hold a large amount of water and show compatibility to cells have been employed in microarray bioprinting. Hydrogels can contain growth media and growth factors to support cell growth for 3D cell cultures and various other applications [11,12]. These cells in hydrogels can be dispensed on glass slides or plastic chips via several printing technologies, including micro-solenoid valves, piezoelectric nozzles, and laser-induced forward transfer (LIFT) technique, and acoustic bioprinting [13]. Among these, micro-solenoid valves (Figure 1A) working on the principle of electromagnetic induction are the most commonly used for cell printing due to their robust and reliable printing with cells in hydrogels [8]. A micro-solenoid valve consists of a metal rod within solenoid coils that moves up and down by electric voltages applied, acting as a gate to dispense cells in hydrogels. The intensity and duration of voltage applied to the micro-solenoid valve control the open time of the gate and hence determine the volume of biological samples dispensed. Certain pressure is applied to maintain the liquid sample to move forward when the gate is opened; typically syringe pumps are necessary to maintain the pressure and dispense cells in hydrogels. The solenoid valves allow us to print relatively high density of cells in hydrogels and accommodate relatively viscous samples. However, the dispensing volume is large, ranging from 20 to 1000 nL, compared to piezoelectric nozzles. The principle behind piezoelectric nozzles (Figure 1B) is very similar to the conventional inkjet printers [14]. The piezoelectric transducer in the nozzle contracts and expands with application of certain voltages, which pushes biological samples including cells in hydrogels to flow [15]. The volume dispensed depends on the voltage and frequency applied, viscosity of hydrogels, and the diameter of the nozzle, making the dispensing volume extremely small, ranging from 50 to 1000 pL. However, piezoelectric printing is significantly influenced by viscosity of the samples, and the nozzles are frequently clogged with cells. Thermal inkjet printers can be used to print cells in hydrogels in a high throughput fashion and may reduce the tip clogging issue considerably by heating polymers and making them less viscous. However, thermal inkjet printing may not be suitable for cell printing due to cell damage or death by high temperature [16]. Another printing technology that can be used for microarray bioprinting is laser-induced forward transfer (LIFT) (Figure 1C). In this technique, a donor film and an acceptor film are set in a parallel manner, where the donor film is a thin film made of cells in hydrogel to be printed. A laser beam is shone on the absorbing substrate layer, which develops laser-induced vapor bubbles, inducing deposition of cell spots on the acceptor film that is either cell culture media or biopolymer-coated glass slides [13,15,17]. Interestingly, the volume of the cell droplets dispensed using this technique is varied, depending on the temperature applied, the nature of biological samples, and the thickness of the donor film containing cells [15,18]. With appropriate optimization of laser beam intensity and focusing conditions, the LIFT technology has been applied for printing DNA, proteins, peptides, and cells in microarrays [14,19]. Although LIFT can be used to print a wide range of biological samples, cell printing in hydrogels with LIFT might be challenging due to high temperature induced by the laser beam. Therefore, maintaining high cell viability and proliferation after printing would be a concern [20,21]. As the dispensed volume depends on the thickness of the hydrogel layer, the uniformity of cell seeding and cell distribution over the glass slide have to be investigated and validated prior to data analysis with test compounds. Acoustic printers depend on ultrasound for printing cells in hydrogels (Figure 1D). A high-intensity acoustic wave is generated by focusing ultrasound beams, and this energy is used to dispense liquid droplets from air-liquid interface. This technique was initially developed for printing single cells in pico-liter droplets. However, modification and optimization have enabled the implementation of 3D cell cultures [22,23]. Characteristics of bioprinting methods are summarized in Table 1. Cell printing using acoustic printers may be questionable as cell membrane might be affected and ruptured when the cells are exposed to ultrasonic waves and, hence, this technique is considered unsuitable for this application [24].


Biocompatible Hydrogels for Microarray Cell Printing and Encapsulation.

Datar A, Joshi P, Lee MY - Biosensors (Basel) (2015)

Various mechanisms for printing biological samples: (A) Micro-solenoid valve using electromagnetic induction; (B) Piezoelectric nozzle using piezoelectric vibration; (C) Laser-induced forward transfer (LIFT) using a laser beam to propel cell spots [13], and (D) Acoustic wave generator using ultrasound to produce acoustic waves for cell printing (Reproduced from Reference [23] with permission of The Royal Society of Chemistry).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697138&req=5

biosensors-05-00647-f001: Various mechanisms for printing biological samples: (A) Micro-solenoid valve using electromagnetic induction; (B) Piezoelectric nozzle using piezoelectric vibration; (C) Laser-induced forward transfer (LIFT) using a laser beam to propel cell spots [13], and (D) Acoustic wave generator using ultrasound to produce acoustic waves for cell printing (Reproduced from Reference [23] with permission of The Royal Society of Chemistry).
Mentions: To encapsulate cells in 3D and prevent their direct contact with the surface, polymeric substances (hydrogels) that have capacity to hold a large amount of water and show compatibility to cells have been employed in microarray bioprinting. Hydrogels can contain growth media and growth factors to support cell growth for 3D cell cultures and various other applications [11,12]. These cells in hydrogels can be dispensed on glass slides or plastic chips via several printing technologies, including micro-solenoid valves, piezoelectric nozzles, and laser-induced forward transfer (LIFT) technique, and acoustic bioprinting [13]. Among these, micro-solenoid valves (Figure 1A) working on the principle of electromagnetic induction are the most commonly used for cell printing due to their robust and reliable printing with cells in hydrogels [8]. A micro-solenoid valve consists of a metal rod within solenoid coils that moves up and down by electric voltages applied, acting as a gate to dispense cells in hydrogels. The intensity and duration of voltage applied to the micro-solenoid valve control the open time of the gate and hence determine the volume of biological samples dispensed. Certain pressure is applied to maintain the liquid sample to move forward when the gate is opened; typically syringe pumps are necessary to maintain the pressure and dispense cells in hydrogels. The solenoid valves allow us to print relatively high density of cells in hydrogels and accommodate relatively viscous samples. However, the dispensing volume is large, ranging from 20 to 1000 nL, compared to piezoelectric nozzles. The principle behind piezoelectric nozzles (Figure 1B) is very similar to the conventional inkjet printers [14]. The piezoelectric transducer in the nozzle contracts and expands with application of certain voltages, which pushes biological samples including cells in hydrogels to flow [15]. The volume dispensed depends on the voltage and frequency applied, viscosity of hydrogels, and the diameter of the nozzle, making the dispensing volume extremely small, ranging from 50 to 1000 pL. However, piezoelectric printing is significantly influenced by viscosity of the samples, and the nozzles are frequently clogged with cells. Thermal inkjet printers can be used to print cells in hydrogels in a high throughput fashion and may reduce the tip clogging issue considerably by heating polymers and making them less viscous. However, thermal inkjet printing may not be suitable for cell printing due to cell damage or death by high temperature [16]. Another printing technology that can be used for microarray bioprinting is laser-induced forward transfer (LIFT) (Figure 1C). In this technique, a donor film and an acceptor film are set in a parallel manner, where the donor film is a thin film made of cells in hydrogel to be printed. A laser beam is shone on the absorbing substrate layer, which develops laser-induced vapor bubbles, inducing deposition of cell spots on the acceptor film that is either cell culture media or biopolymer-coated glass slides [13,15,17]. Interestingly, the volume of the cell droplets dispensed using this technique is varied, depending on the temperature applied, the nature of biological samples, and the thickness of the donor film containing cells [15,18]. With appropriate optimization of laser beam intensity and focusing conditions, the LIFT technology has been applied for printing DNA, proteins, peptides, and cells in microarrays [14,19]. Although LIFT can be used to print a wide range of biological samples, cell printing in hydrogels with LIFT might be challenging due to high temperature induced by the laser beam. Therefore, maintaining high cell viability and proliferation after printing would be a concern [20,21]. As the dispensed volume depends on the thickness of the hydrogel layer, the uniformity of cell seeding and cell distribution over the glass slide have to be investigated and validated prior to data analysis with test compounds. Acoustic printers depend on ultrasound for printing cells in hydrogels (Figure 1D). A high-intensity acoustic wave is generated by focusing ultrasound beams, and this energy is used to dispense liquid droplets from air-liquid interface. This technique was initially developed for printing single cells in pico-liter droplets. However, modification and optimization have enabled the implementation of 3D cell cultures [22,23]. Characteristics of bioprinting methods are summarized in Table 1. Cell printing using acoustic printers may be questionable as cell membrane might be affected and ruptured when the cells are exposed to ultrasonic waves and, hence, this technique is considered unsuitable for this application [24].

Bottom Line: Conventional drug screening processes are a time-consuming and expensive endeavor, but highly rewarding when they are successful.These two-dimensional (2D) cell monolayers are physiologically irrelevant, thus, often providing false-positive or false-negative results, when compared to cells grown in three-dimensional (3D) structures such as hydrogel droplets.In this review, several hydrogels that are compatible to microarray printing robots are discussed for miniaturized 3D cell cultures.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical & Biomedical Engineering, Cleveland State University, 1960 East 24th Street Cleveland, OH 44115-2214, USA. a.datar17@vikes.csuohio.edu.

ABSTRACT
Conventional drug screening processes are a time-consuming and expensive endeavor, but highly rewarding when they are successful. To identify promising lead compounds, millions of compounds are traditionally screened against therapeutic targets on human cells grown on the surface of 96-wells. These two-dimensional (2D) cell monolayers are physiologically irrelevant, thus, often providing false-positive or false-negative results, when compared to cells grown in three-dimensional (3D) structures such as hydrogel droplets. However, 3D cell culture systems are not easily amenable to high-throughput screening (HTS), thus inherently low throughput, and requiring relatively large volume for cell-based assays. In addition, it is difficult to control cellular microenvironments and hard to obtain reliable cell images due to focus position and transparency issues. To overcome these problems, miniaturized 3D cell cultures in hydrogels were developed via cell printing techniques where cell spots in hydrogels can be arrayed on the surface of glass slides or plastic chips by microarray spotters and cultured in growth media to form cells encapsulated 3D droplets for various cell-based assays. These approaches can dramatically reduce assay volume, provide accurate control over cellular microenvironments, and allow us to obtain clear 3D cell images for high-content imaging (HCI). In this review, several hydrogels that are compatible to microarray printing robots are discussed for miniaturized 3D cell cultures.

Show MeSH
Related in: MedlinePlus