The authors would like to thank Prof. Sze-Bi Hsu and Ms. Zhenzhen for useful discussions and help in the theoretical analysis and numerical simulation. Y. T. Y. would like to acknowledge funding support from the Ministry of Science and Technology under grant numbers MOST 103-2220-E-007-026 and MOST 104-2220-E-007-011, and from the National Tsing Hua University under grant numbers 103N2042E1, 104N2042E1, and 105N518CE1.

1. Assembly and Pretesting of the Morbidostat Device
<ol>
	<li>Assembly of the Morbidostat
	<ol>
		<li>Punch 3 holes on the cap of the culture vial with an 18 G syringe needle. Cut three pieces of polyethylene tubing ~7 cm in length. Insert these three pieces of polyethylene tubing on the cap.</li>
		<li>Use tape to wrap the edge of the cap to serve as the cast for the polydimethylsiloxane (PDMS) mixture. Mix 5 g of A component and 0.5 g of B component of the PDMS in a 150 ml plastic container by stirring manually with...

<ol>
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Evidence that dihydrofolate reductase interacts with another essential gene product.</a> Mol. Gen. Genet. 187, 72-78 (1982).</li><li>Okumus, B., Yildiz, S., Toprak, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluidic+and+microfluidic+tools+for+quantitative+systems+biology.">Fluidic and microfluidic tools for quantitative systems biology.</a> Curr Opin Biotech. 25, 30-38 (2014).</li><li>Cho, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+rapid+antimicrobial+susceptibility+test+based+on+single-cell+morphological+analysis.">A rapid antimicrobial susceptibility test based on single-cell morphological analysis.</a> Sci. Transl. Med. 17, 267 (2014).</li><li>Hsu, S. B., Waltman, P. 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A low-footprint morbidostat device from low-cost components is demonstrated. The increases in drug resistance level registered by the device are consistent with those of previous reports5. Designed for evolutionary studies of drug resistance, the device is potentially applicable to many other experiments. First, a comprehensive database of drug-induced mutations can be established for a large set of clinically relevant antibiotics. For example, the evolutionary pathway of multiple drug resistance can be studie...

Since the introduction of the first antibiotic drug penicillin, microbial antibiotic resistance has developed into a global health problem1. Although the acquisition of antibiotic resistance can be retrospectively studied in vivo, the conditions of these experiments are often not controlled throughout the entire evolution2. Alternatively, adaptive laboratory evolution can reveal the molecular evolution of a microbial species under environmental stresses or selection pressure from an antibiotic drug3. Recently, many well-controlled evolutionary experiments of antibiotic drug resistance have elucidated the emergence of antibiotic drug resistance. For example, Austin&#39;s group demonstrated rapid emergence in a properly engineered microfluidic compartmented environment4. The recently developed morbidostat induces systematic mutations under drug selection pressure5,6. The morbidostat, a microbial selection device that continuously adjusts the antibiotic concentration to maintain a nearly constant population, is a major advance from the fluctuation test used in microbiology7,8. In the fluctuation test, an antibiotic drug is injected at high concentration, and the surviving mutants are screened and counted. Instead, microbes in a morbidostat are constantly challenged and acquire multiple mutations.
The morbidostat operates similarly to the chemostat, a culture device invented by Novick and Szliard in 1950 that maintains a constant population by continuously supplying nutrients while diluting the microbial population9. Since its introduction, the chemostat has been advanced and improved. Current microfluidic chemostats have reached nanoliter and single-cell capacities. However, these devices are unsuitable for adaptive evolution experiments, which require a large cell population with many mutation events10,11. Recently, mini-chemostats with working volumes of ~10 ml have also been developed to fill in the gap between liter scale bioreactors and the microfluidic chemostat12,13.
Here we present the design and use of a low-cost, automated morbidostat for an antibiotic drug resistance study. The proposed module can be employed in a shaker incubator in a microbiology laboratory with minimal hardware requirement. The open-source firmware is also easily tailored to specific applications of adaptive evolution, such as metabolic engineering3. Finally, the morbidostat is integrated into a multiplexed microfluidic platform for antibiotic susceptibility testing14.

<table border="0" cellpadding="0" cellspacing="0" width="797">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Environmental Shaker Incubator</td>
			<td style="width:135px;">BioSan</td>
			<td style="width:163px;">ES-20</td>
			<td style="width:227px;"></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Arduino Leonardo board</td>
			<td style="width:135px;">Arduino</td>
			<td style="width:163px;">Leonardo</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">680 Ohm Carbon Resistor</td>
			<td style="width:135px;">Digikey</td>
			<td style="width:163px;"></td>
			<td>Bias resistor for LED</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">100k Ohm Carbon resistor</td>
			<td style="width:135px;">Digikey</td>
			<td style="width:163px;"></td>
			<td>Bias resistor for phototransistor</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:275px;">940 nm light emitting diode</td>
			<td style="width:135px;">Bright LED Electronic</td>
			<td style="width:163px;">BIR-BM13E4G-2</td>
			<td>Optical density measurement</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:275px;">940 nm phototransistor</td>
			<td style="width:135px;">Kodenshi&#160;</td>
			<td style="width:163px;">ST-2L2B</td>
			<td>Optical density measurement</td>
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			<td height="57" style="height:57px;">Darlington pair IC Toshiba</td>
			<td style="width:135px;">Mouser</td>
			<td style="width:163px;">ULN2803APG</td>
			<td style="width:227px;">&#160;this IC drives micropumps and magnetic stirring unit</td>
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			<td height="41" style="height:41px;width:275px;">5V DC brushless fan&#160;</td>
			<td style="width:135px;">ADDA</td>
			<td style="width:163px;">AD0405LX-G70</td>
			<td style="width:227px;">spec: 5V supply voltage and 80mA available www.jameco.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Piezoelectric micropump</td>
			<td style="width:135px;">CurieJet</td>
			<td style="width:163px;">PS15I-FT-5L</td>
			<td>Pressure &#62;3kPa&#160; Flow rate &#62;5 ml/min</td>
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			<td height="21" style="height:21px;width:275px;">Tygon 3350 Tuning</td>
			<td style="width:135px;">Saint Gobain</td>
			<td style="width:163px;">ABW00001</td>
			<td>ID: 1/32&#34; OD: 3/32&#34; L:50&#39;&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Magnetic Stir bar</td>
			<td style="width:135px;">COWIE</td>
			<td style="width:163px;"></td>
			<td>tapered shape dim: 10 mm x 4mm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:275px;">Glass scintillation 20ml vial</td>
			<td style="width:135px;">DGS</td>
			<td style="width:163px;"></td>
			<td>Pyrex glass 28mm(dia.)x 61 mm(h)</td>
		</tr>
		<tr height="48">
			<td height="48" style="height:48px;width:275px;">Culture vial holder</td>
			<td style="width:135px;"></td>
			<td style="width:163px;"></td>
			<td>Custom made from Polyformaldehyde&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Silicone&#160;</td>
			<td style="width:135px;">Dow Corning</td>
			<td style="width:163px;">Sylgald 184</td>
			<td>used to seal the glass vial</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Medium bottle</td>
			<td style="width:135px;">VWR</td>
			<td style="width:163px;">66022-065</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Difco M9 minimal salt 5x</td>
			<td style="width:135px;">BD</td>
			<td style="width:163px;"></td>
			<td>Medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Cadamino Acid</td>
			<td style="width:135px;">BD</td>
			<td style="width:163px;"></td>
			<td>Medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">glucose</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Agar Bateriological</td>
			<td style="width:135px;">Oxoid</td>
			<td style="width:163px;"></td>
			<td>for agar plate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Luria Bertani medium</td>
			<td style="width:135px;"></td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:275px;">Inverted microscope</td>
			<td style="width:135px;">Leica Microsystems</td>
			<td style="width:163px;">Leica DMI-LED</td>
			<td style="width:227px;">used for microfluidic measurement Use X40 objective NA=0.55</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:275px;">Microscope Incubator</td>
			<td style="width:135px;">Live Cell Instrument</td>
			<td style="width:163px;">CU-109</td>
			<td>used for microfluidic measurement</td>
		</tr>
		<tr height="49">
			<td height="49" style="height:49px;width:275px;">Solenoidal valves</td>
			<td style="width:135px;">Pneumadyne</td>
			<td style="width:163px;">S10MM-31-12-3</td>
			<td>Normally open 1.3 Watt 12 Vdc</td>
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			<td height="21" style="height:21px;">USB interface card</td>
			<td style="width:135px;">Hobby Engineering</td>
			<td>USBIO24-R Digital I/O Module&#160;</td>
			<td>for microfluidics measurement</td>
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		<tr height="45">
			<td height="45" style="height:45px;width:275px;">Air compressor</td>
			<td style="width:135px;">Rocker Scientific</td>
			<td style="width:163px;">ROCKER 440</td>
			<td style="width:227px;">Pressure source for microfluidcs Max. Pressure 80 Psi</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Male luer-lock fittings to 1/8&#34; barb</td>
			<td>ValuePlastics.com</td>
			<td style="width:163px;">MTLL230-1</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1/8&#34; barb to 10-32 threaded port</td>
			<td>ValuePlastics.com</td>
			<td style="width:163px;">B-1</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Female luer-lock fittings to 10-32 threaded port</td>
			<td>ValuePlastics.com</td>
			<td style="width:163px;">KFTL-1</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NPN darlington transistor 500mA, 40V (2N6427)</td>
			<td>DigiKey.com</td>
			<td>2N6427GOS-ND</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">10kOhm, carbon film resistor, 0.25W</td>
			<td>DigiKey.com</td>
			<td>P10KBACT-ND</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tantalum capacitor, 10uF, 25V, 10%</td>
			<td>DigiKey.com</td>
			<td>478-1841-ND</td>
			<td>used for microfluidic control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Andor CCD camera</td>
			<td style="width:135px;">Andor</td>
			<td style="width:163px;">Zyla 4.2 Plus SCMOS</td>
			<td>used for microfluidic on chip imaging</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">ELISA plate reader</td>
			<td style="width:135px;"></td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">two component Silicone&#160;</td>
			<td style="width:135px;">Momentive</td>
			<td style="width:163px;">RTV 615</td>
			<td>used for microfluidic chip fabrication</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">SU-8 photoresist</td>
			<td style="width:135px;">Micrchem</td>
			<td style="width:163px;">SU8 2015</td>
			<td>used for microfluidic chip fabrication</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">AZ4620 photoresist</td>
			<td style="width:135px;">Clariant</td>
			<td style="width:163px;">AZ 4620</td>
			<td>used for microfluidic chip fabrication</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Plasma cleaner</td>
			<td style="width:135px;">Harrick Plasma</td>
			<td style="width:163px;">PDC 32G</td>
			<td>used for microfluidic chip fabrication</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">20 Gauge Syringe Needle</td>
			<td style="width:135px;">BD</td>
			<td style="width:163px;"></td>
			<td>used for microfluidic chip fabrication</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Labcycler</td>
			<td style="width:135px;">Sensoquest</td>
			<td style="width:163px;">Labcycler</td>
			<td>PCR&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">DNA polymerase</td>
			<td style="width:135px;">Toyobo</td>
			<td style="width:163px;">KDO Plus</td>
			<td>PCR amplification</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Trimethoprim</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:163px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:275px;">Plate reader</td>
			<td style="width:135px;">Biotek</td>
			<td style="width:163px;">Synergy H1 hybrid&#160;</td>
			<td>antibiotic resistane measurement</td>
		</tr>
	</tbody>
</table>

design and use of a low cost, automated morbidostat for adaptive evolution of bacteria under antibiotic drug selection

We describe a low cost, configurable morbidostat for characterizing the evolutionary pathway of antibiotic resistance. The morbidostat is a bacterial culture device that continuously monitors bacterial growth and dynamically adjusts the drug concentration to constantly challenge the bacteria as they evolve to acquire drug resistance. The device features a working volume of ~10 ml and is fully automated and equipped with optical density measurement and micro-pumps for medium and drug delivery. To validate the platform, we measured the stepwise acquisition of trimethoprim resistance in Escherichia coli MG 1655, and integrated the device with a multiplexed microfluidic platform to investigate cell morphology and antibiotic susceptibility. The approach can be up-scaled to laboratory studies of antibiotic drug resistance, and is extendible to adaptive evolution for strain improvements in metabolic engineering and other bacterial culture experiments.

The above-described morbidostat is schematized in Figure 1. The common morbidostat operations, including experimental evolution, antibiotic susceptibility test and cell morphology checking, were validated in an E. coli MG1655 culture exposed to trimethoprim (TMP), a commonly used antibiotic drug5,6. TMP induces very distinctive stepwise increases in drug resistance, and the mutations are clustered around the dihydrofolate reductase (DHFR) gene. Therefo...

Watch this Scientific Journal Video about Design and Use of a Low Cost, Automated Morbidostat for Adaptive Evolution of Bacteria Under Antibiotic Drug Selection at JoVE.com

Design and Use of a Low Cost, Automated Morbidostat for Adaptive Evolution of Bacteria Under Antibiotic Drug Selection

We describe a low cost, configurable morbidostat that enables the characterization of antibiotic drug resistance by dynamically adjusting the drug concentration. The device can be integrated with a multiplexed microfluidic platform. The approach can be scaled up for laboratory antibiotic drug resistance studies.

We describe a low cost, configurable morbidostat for characterizing the evolutionary pathway of antibiotic resistance. The morbidostat is a bacterial ...

The overall goal of this experiment is to characterize the evolutionary pathway of antibiotic resistance using a Morbidostat that continuously monitors bacterial growth and dynamically adjusts the antibiotic concentration as bacteria acquire drug resistance. The main advantage of this technique is that the set up is made of low cost easily available electronic components and can be easily reconfigured for specific means. Demonstrating the procedures will be Po Cheng Liu and Yi Tai Lee, both are grad students of my laboratory.To assemble the Morbidostat, begin by using an 18 gauge needle to punch three holes into the cap of the culture vial. Cut three pieces of polyethylene tubing approximately seven centimeters in length and insert them into the holes in the cap. Use tape to wrap the edge of the cap to serve as the cast for the Polydimethylsiloxane, or PDMS, mixture.Then add five grams of component A and 0.5 grams of component B of the PDMS in a 150 milliliter plastic container and use a toothpick to manually stir it. Load the mixture into a 10 milliliter syringe. Then, with the syringe, inject the PDMS mixture onto the cap.Bake the entire cap at 70 degrees Celsius for eight hours to cure the PDMS. Next, using a soldering iron, solder the LED anode with the 24 gauge wire and the LED cathode with the carbon resistor. Then solder a 680 Ohm carbon resistor with a 24 gauge wire.Use electrical tape to insulate the wire connection. Solder the collector of the photo detector with the 24 gauge wire and the emitter of the photo detector with a 100 Ohm carbon resistor. Then use electrical tape to insulate the wire connection.Place the light emitting diode in the culture vial holder. By following the circuit diagram shown here, connect the light emitting diode and use a five volt power supply to power it. Ensure that the LED works by using a digital camera that can detect IR.Now place the photo detector in the culture vial holder.Then following the diagram, connect the photo detector and use a five volt power supply to power it. Connect the wire to both sides of the photo detector resistors o measure the voltage across the electronic control board. Glue a magnet on the shaft of the cooling fan which serves as the magnetic stirrer unit.Because the magnetic stirring unit is formed from the magnet and the cooling fan, it's crucial to align the shelf of the fan to culture vial. Also the distance between the culture vial and the magnet is very critical to ensure the stable operation. Connect each piece of polyethylene tubing of the culture vial into the corresponding piece of silicone tubing for the micro pumps, medium bottles, and waste bottle.Turn on the pump for one hour and measure the total volume being pumped from the medium bottle to the culture vial to determine the pump rate. The typical pumping rate should be approximately four milliliters per hour, which corresponds to the dilution rate of D equals 0.33 per hour for a 12 milliliter working volume of the culture vial. When the set up is complete, place the entire assembly on a mid sized shaking incubator.To pre test the Morbidostat, set the power supply voltage of the cooling fan to five volts to start its motor to test the magnetic stir bar. After preparing a series of E-coli samples and plotting a calibration curve according to the text protocol, prepare the culture vial with three seven centimeter lengths of ultra chemical resistant Tygon tubing with an inner diameter of 132nd of an inch and an outer diameter of 332nds of an inch for inlets to form the device. Prepare M9 minimal medium with 0.2%glucose and M9 containing the drug Trimethoprim or TMP.Then sterilize the medium, medium bottle, the drug medium bottle, the waste bottle, and the culture vial in an autoclave at 121 degrees Celsius. On the first day of the experiment, thaw one milliliter of frozen wild type E-coli MG1655 cells at room temperature for five minutes and transfer 120 microliters of the cells to a culture vial containing approximately 12 milliliters of M9 growth medium. Turn on the shaking incubator and set the temperature to 30 degrees Celsius with no shaking.Start the Morbidostat operation by turning on the micro pump, the magnetic stirring unit, and the optical density measurement. After approximately 23 hours, stop the micro pump by turning off its supply voltage and take out the culture vial. Add 15%glycerol into the culture vial and freeze the samples at negative 80 degrees Celsius for storage.Switching to a new culture vial in the beginning of each of these experiments is also important to avoid biotin formations. Otherwise the biotin formation can occur within two or three days. After thawing the daily frozen sample at room temperature for five minutes, inoculate a new test tube with fresh M9 medium.Place the sample in a shaking incubator at 37 degrees Celsius overnight. The following day, use M9 medium to dilute the microbial sample tenfold and load it into the microfluidic device by pressuring the microbial sample container at five PSI. Then load the TMP containing medium into the chip by pressuring the M9 with TMP container at five PSI.Execute the mixing between the microbe and drug by actuating the micro mechanical valve between the two chambers on the microfluidic chip for 15 minutes. Finally place the microfluidic chip in the microscope incubator mounted on the inverted microscope. With a CCD camera, acquire cell images in the growth chamber every hour for eight hours.Calculate cell number data according to the text protocol. The common Morbidostat operations including experimental evolution, antibiotic susceptibility test, and cell morphology checking were invalidated using an E-coli MG1655 culture exposed to the antibiotic TMP, which induces a distinctive step wise increase in drug resistance with mutations clustered around the dihydrofolate reductase, or DHFR, gene. Each day, the microbe is expected to grow above the pre set optical density threshold and trigger the drug injection as shown here.The drug injection is expected to inhibit the growth, and as a result, decrease the optical density. This plot shows the temporal increase in the antibiotic drug resistance in an experiment to determine the IC50. The drug resistance increased approximately 1500 fold to 1, 000 micrograms per milliliter over about 12 days.Consistent with previous findings. The DHFR point mutations in the last day mutant were measured by Sanger sequencing and are listed in this table. The acquisition of drug resistance with multiple mutations proves the usefulness of the Morbidostat.As the selection on drug containing agar plates tends to confer only the single mutation. This figure displays the on chip growth curves at various concentrations of TMP. The mutant samples shows a significant increase in antibiotic drug resistance.After its develop, this technique paved the way for the researchers to study the position of antibiotic drug resistance in a real control laboratory environment. Following this procedure, other measure like microfluidic single cell measurement can be performed in order to answer additional questions like it still morphology to change due to the exposure of antibiotic drugs. Once mastered, this device can be easily reconfigured for all the bacterial culture experiment such as the cultivation of a sign of bacteria or increasing the costing tolerance level of a bacterial strain.After watching this video, you should have a good understanding of how to study the acquisition of antibiotic drug resistance in a real control adaptive laboratory evolutionary experiment. Don't forget to handle the drug resistant bacteria according to the bio safety rules for microbiological practice. Special permission may be required for an experiment involving basic training of bacteria.

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JoVE Journal

Genetics

9.5K vistas.  National Tsing Hua University. The overall goal of this experiment is to characterize the evolutionary pathway of antibiotic resistance using a Morbidostat that continuously monitors bacterial growth and dynamically adjusts the antibiotic concentration as bacteria acquire drug resistance. The main advantage of this technique is that the set up is made of low cost easily available electronic components and can be easily reconfigured for specific means. Demonstrating the procedures will be Po Cheng Liu and Yi Tai Lee, both a...