Verlaagde zwaartekracht Milieu Hardware Demonstraties van een Prototype Geminiaturiseerde doorstroomcytometer en Companion Microfluïdische Mixing Technology

Summary

Spaceflight blood diagnostics need innovation. Few demonstrations have been published illustrating in-flight, reduced-gravity health diagnostic technology. Here we present a method for construction and operation of a parabolic flight test rig for a prototype point-of-care flow-cytometry design, with components and preparation strategies adaptable to other setups.

Abstract

Until recently, astronaut blood samples were collected in-flight, transported to earth on the Space Shuttle, and analyzed in terrestrial laboratories. If humans are to travel beyond low Earth orbit, a transition towards space-ready, point-of-care (POC) testing is required. Such testing needs to be comprehensive, easy to perform in a reduced-gravity environment, and unaffected by the stresses of launch and spaceflight. Countless POC devices have been developed to mimic laboratory scale counterparts, but most have narrow applications and few have demonstrable use in an in-flight, reduced-gravity environment. In fact, demonstrations of biomedical diagnostics in reduced gravity are limited altogether, making component choice and certain logistical challenges difficult to approach when seeking to test new technology. To help fill the void, we are presenting a modular method for the construction and operation of a prototype blood diagnostic device and its associated parabolic flight test rig that meet the standards for flight-testing onboard a parabolic flight, reduced-gravity aircraft. The method first focuses on rig assembly for in-flight, reduced-gravity testing of a flow cytometer and a companion microfluidic mixing chip. Components are adaptable to other designs and some custom components, such as a microvolume sample loader and the micromixer may be of particular interest. The method then shifts focus to flight preparation, by offering guidelines and suggestions to prepare for a successful flight test with regard to user training, development of a standard operating procedure (SOP), and other issues. Finally, in-flight experimental procedures specific to our demonstrations are described.

Introduction

The inadequacy of current space-ready health diagnostics presents a limiting factor to deeper manned space exploration. Diagnostics need to be comprehensive, easy to use in reduced gravity, and relatively unaffected by the stresses of launch and spaceflight (e.g., high g-forces, vibration, radiation, temperature changes, and cabin pressure changes). Developments in point-of-care testing (POCT) may translate to effective spaceflight solutions through the use of smaller patient specimens (e.g., a finger prick), simpler and smaller fluidics (i.e., microfluidics), and reduced electrical power requirements, among other advantages. Flow cytometry is one attractive approach for in-space POC because of the broad utility of the technology, including toward cell counting and biomarker quantification, as well as significant miniaturization potential. Previous space-relevant flow cytometers include the ‘nuclear packing efficiency’ (NPE) instrument that utilized simultaneous arc-lamp induced fluorescence and electronic volume (Coulter volume) measurement ^1-4, a relatively small benchtop flow cytometer representing the ‘first generation of real-time flow cytometry data during zero gravity’ ⁵, a ‘sheathless microflow cytometer’ capable of 4- and 5-part white blood cell (WBC) differential count using pretreated 5 µl whole blood samples ^6-9, and a ‘fiber-optic-based’ flow cytometer recently tested onboard in the International Space Station ¹⁰.

Evaluating diagnostic technology for potential space applications is typically performed onboard reduced-gravity aircraft that use an approximately parabolic flight trajectory to simulate a chosen level of weightlessness (e.g., zero-gravity, martian-gravity) ¹¹. Evaluation is challenging because flight opportunities are limited, repetitive short windows of microgravity can make it difficult to assess methodologies or processes that normally require uninterrupted periods longer than 20-40 sec, and demonstrations may require additional equipment not easily utilized in-flight ^12-15. Furthermore, previous demonstrations of in vitro diagnostic (IVD) technologies used in, or designed for, reduced gravity are limited and much work remains unpublished. In addition to the above flow cytometers, other space-relevant IVD-technologies described in the literature include a whole blood staining device for immunophenotyping applications ¹⁶, an automated camera-based cytometer ¹², a handheld clinical analyzer for integrated potentiometry, amperometry, and conductometry ^12,17, a microfluidic ‘T-sensor’ device for analyte quantitation that relies on diffusion-based mixing and separation ¹⁸, and a rotating ‘lab on a CD’ diagnostics platform ^19,20. Newcomers to reduced gravity testing may also look to parabolic flight demonstrations unrelated to in vitro diagnostics when attempting to make device evaluation possible (or figuring out what is possible). Demonstrations from other previous medical or biological experimentation with well-documented flight preparation, in-flight strategies, and flight test equipment are included in Table 1^{15, 21-35}. These may be informative due to inclusion of manual in-flight tasks, use of specialized equipment, and experimental containment.

Category	Examples
Emergency medical care	Tracheal intubation (laryngoscope-guided, on manikin) 21, cardiac life support (anesthetized pigs) 22
Surgical care	Laparoscopic surgery (video simulated 23, on anesthetized pigs 24,25)
Medical imaging or physiology assessment	Ultrasound with lower body negative pressure chamber 26, Doppler flowmeter (head mounted) 27, central venous pressure monitor 28
Specialized biological equipment	Microplate reader (and in-flight glove box) 29, temperature control system for cell cycle experiments 30, microscope (brightfield, phase contrast, and multi-channel fluorescence capable) 15, capillary electrophoresis unit coupled to video microscope 31
Altro	Plant harvesting with forceps 32, contained rats 33,34 and fish 35 for observation

Table 1. Parabolic Flight Demonstration Examples with Well Described Methods/Experiments

To expand on previous examples and provide greater insight into successful in-flight demonstrations, we are presenting a modular and adaptable procedure for construction and operation of a prototype flow cytometer with related microfluidic mixing technology as part of a parabolic flight test rig. The rig enables demonstrations of sample loading, microfluidic mixing, and fluorescent particle detection, and was tested onboard the 2010 NASA Facilitated Access to the Space Environment (FAST) parabolic flights, flown from September 29 to October 1, 2010. These demonstrations pull from the beginning, middle, and end, respectively of a potential device workflow in which fingerstick-sized blood samples are loaded, diluted or mixed with reagents, and analyzed via optical detection. Scaling a flow cytometer into a compact unit requires innovation and careful part selection. Custom and off-the-shelf components are used here, chosen as best early approximations of final component choices, and may be adaptable to the designs of other innovators. Following an outline of prototype component choices, setup is described on a support structure serving as a skeleton for rig assembly. Prototype components are assigned locations, secured, and accompanied by additional components necessary for successful experimentation. Attention then shifts to more abstract procedures involving standard operating procedure (SOP) development, training, and other logistics. Finally, demonstration-specific procedures are described. The strategies described here and the choices of supporting rig components (e.g., microscope, acrylic box, etc.), although implemented here for specific prototype, speak to the general issues and challenges relevant to testing any blood diagnostic equipment in a reduced-gravity environment.

In the 2010 flights, two lunar-gravity (achieving approximately 1/6 earth gravity)and two micro-gravity flights were scheduled across 4 days, although ultimately these were rescheduled across 3 days. Demonstrations were performed onboard a modified privately operated, narrow-body jet airliner ³⁶. Each flight provided 30-40 parabolas, each yielding about 20 sec of high-gravitation (roughly 1.8 g) followed by 20-25 sec of reduced-gravity conditions. After half of the parabolas were executed, the plane paused for a period of about 5-10 min in level flight to enable the plane to turn around and head back toward the landing site while performing the remainder of the parabolas.

Protocol

The human blood samples used in this protocol were collected with IRB approval using minimally invasive protocols (see Acknowledgements). 1. Rig Assembly Assemble prototype components (fluidics, optical, control/data acquisition electronics) for a simple flow cytometry system to be used in reduced gravity conditions Prepare a pressure system with minimal weight and power needs to drive system fluidics Connect a miniaturized air pump to a differential press…

Representative Results

Representative results for the micromixer demonstration appear in Figure 7, as viewed by the CCD camera fitted to the stereomicroscope. Mixing can be visually assessed at any point along the spiral, as well as in the Exit channel for experiments involving two sets of fluids: blood/saline and blue/yellow dye. Quantitative analysis of the two-dimensional images can include determination of shade uniformity across the channel width in different regions, as shown in other publications 38-40. See <…

Discussion

The method described here enabled effective demonstration of the major technology components (sample loading, microfluidic mixing, and optical detection) during the 2010 FAST parabolic flights, with comparable results to ground testing. Training and SOP methods described here were particularly effective, and helped to illuminate tools and other ‘crutches’ being relied on for practice demonstrations that would not be available onboard the parabolic flight.

Areas for improvement incl…

Materials

Name of Material/ Equipment	Company	Catalog Number	Comments/Description
Micro air pump	Smart Products, Inc.	AP-2P02A	Max pressure = 6.76 psi; 1.301” x 0.394” x 0.650” , 0.28 oz (8 g); available direct from Smart Products
Differential pressure sensor	Honeywell International, Inc.	ASDX015D44R	Range  of  0-15psi; 0.974" x 0.550" x 0.440", 0.09 oz (2.565 g); suppliers include Digi-Key and Mouser Electronics
Rigid plastic vial (small size)	Loritz & Associates, Inc.	55-05	Polystyrene; ID 0.81" (20.6 mm), IH 2.06" (52.4 mm); available direct from LA Container Inc.; similar product available from Dynalab Corp.
Rigid plastic vial (larger size)	Loritz & Associates, Inc.	55-140	Polystyrene; ID 1.88" (47.6 mm), IH 3.31" (84.1 mm); available direct from LA Container Inc.; similar product available from Dynalab Corp.
latex examination gloves	dynarex corporation	2337	Middle finger used for latex diaphragm in fluid source vial.  Other brands (e.g., Aurelia ®  Vibrant ™) acceptable.
Optical glue	Norland Products	NOA 88	Low outgassing adhesive; available direct from Norland; Also available from Edmund Optics Inc.
3-way solenoid valves	The LEE Company	LHDA0531115H	Gas valves, but can function with liquid; 1.29 " L, 0.28 " D.  Discontinued product.  Similar products available from The LEE Company.
Volumetric water flowmeter	OMEGA Engineering inc.	FLR-1602A	Non-contacting flow rate meter strongly preferred.  We recommend SENSIRION LG16 OEM Liquid Flow Sensor for flow rates from nl/min up to 5 ml/min.
PCD-mini photon detector	Sensl	PCDMini-00100	For fluorescence detection; available direct from Sensl
Accelerometer	Crossbow Technology, Inc.	CXL02LF3	3-demensional force detection.  Supplied to DMI by NASA.  Similar product available from Vernier Software & Technology, LLC.
Stereomicroscope	AmScope	SE305R-AZ-E
CCD Camera	Thorlabs	DCU223C	1024 x 768 Resolution, Color, USB 2.0; available direct from Thorlabs
USB and Trigger Cable (In/Out) for CCD Camera	Thorlabs	CAB-DCU-T1	Available direct from Thorlabs
Microbore tubing	Saint-Gobain Corporation	AAD04103	Tygon®; ID 0.02", OD 0.06", 500ft, 0.02" wall. Suppliers: VWR, Thermo Fisher Scientific Inc.
Hollow steel pins	New England Small Tube	(Custom)	0.025" OD, 0.017" ID, 0.500” L, stainless steel tube, type 304, cut, deburred, passivated; enable microbore tubing connections, chip tubing connections
Slide clamp	World Precision Instruments, Inc.	14042	Available direct from World Precision Instruments
Leur adaptor pieces	World Precision Instruments, Inc.	14011	Available direct from World Precision Instruments
Silicon wafer	Addison Engineering, Inc.		6" diameter; for SU-8 mold fabrication
Polydimethylsiloxane (PDMS) elastomer base	Dow Corning	3097366-1004	Supplier: Global Industrial SLP, LLC
Polydimethylsiloxane (PDMS) elastomer curing agent	Dow Corning	3097358-1004	Supplier: Global Industrial SLP, LLC
Needle (23 gauge), bevel tip	Terumo Medical Corporation	NN-2338R	Ultra thin wall; 23G x 1.5"; 22G also usable; suppliers: Careforde, Inc.,  Port City Medical
Dispensing needle (23 gauge), blunt tip	CML Supply	901-23-100	23Gx 1";  available from CML Supply
Rotary tool	Robert Bosch Tool Corporation	1100-01	Dremel® 1100-01 Stylus™
Cover glass	Thermo Fisher Scientific, Inc.	12-518-105E	Gold Seal™ noncorrosive borosilicate glass; for PDMS chip cover; 24×60 mm; available from Thermo Fisher Scientific, Inc.
Vacuum pump	Mountain	MTN8407	For degassing PDMS; supplier:  Ryder System, Inc.
Vacuum chamber	Thermo Fisher Scientific, Inc.	5311-0250	Nalgene™ Transparent Polycarbonate; available from Thermo Fisher Scientific, Inc.
Plasma cleaner	Harrick Plasma	PDC-32G
Hand magnifier	Mitutoyo	183-131	Use in reverse direction to enable viewing at ~15".
Ethanol	CAROLINA	861283	For chip cleaning. Dilute to 70% using millipore water.
Water purification system	Thermo Fisher Scientific, Inc.	D11901	Available direct from Thermo Fisher Scientific, Inc.
Optomechanical translation mounts	Thorlabs	K6X	6-Axis Kinematic Optic Mount; discontinued product; new product (K6XS) available direct from Thorlabs
Laptop	Hewlett-Packard	VP209AV	HP Pavilion Laptop running Windows 7
Laptop tray (spring loaded)	National Products, INC.	RAM-234-3	RAM Tough-Tray™. Can accommodate 10 to 16 inch wide laptops.
USB splitter	Connectland Technology Limited	3401167
USB Data Acquisition Cards (8 analog input, 12 digital I/O)	National Instruments	NI USB-6008	12-Bit, 10 kS/s Low-Cost Multifunction DAQ
USB Data Acquisition Cards (16 analog input, 32 digital I/O)	National Instruments	NI USB-6216	16-Bit, 400 kS/s Isolated M Series MIO DAQ, Bus-Powered
Control/acquisition Software	National Instruments	LabVIEW 2009	Custom coded National Instruments (NI) LabVIEW
3D Solid Modeling Software	Dassault Systèmes SolidWorks Corp.	SolidWorks 2011
2D Modeling Software	AUTODESK	AutoCAD LT 2008
Vertical equipment rack	(NASA provided)	N/A
Solid aluminum optical breadboard	Thorlabs	MB2424	24" x 24" x 1/2", 1/4"-20 Taps; available direct from Thorlabs
Industrial grade steel and hardener	The J-B Weld Company		J-B Weld Steel Reinforced Epoxy Glue
Micro-hematocrit capillary	Fisher Scientific	22-362-574	inner diamter 1.1 to 1.2 mm
1 mL syringes	Henke-Sass, Wolf	4010.200V0	NORM-JECT®; supplier: Grainger, Inc.
Human red blood cells	Innovative Research	IPLA-WB3	Tested and found negative by supplier for: HBsAg, HCV, HIV-1, HIV-2, HIV-1Ag or HIV 1-NAT, ALT, and syphilis by FDA-Approved Methods.  Because no test methods can guarantee with 100% certainty the absence of an infectious agent, human derived products should be handled as suggested in the U.S. Department of Health and Human Services Manual on BIOSAFETY IN MICROBIOLOGICAL AND BIOMEDICAL LABORATORIES, FOR POTENTIALLY INFECTIOUS HUMAN SERUM OR BLOOD SPECIMENS
Phosphate buffered saline concentrate	P5493	SIGMA	10x; diluted to 1x
Tween	P9416	SIGMA	TWEEN® 20
Centrifuge	LW Scientific	STRAIGHT8-5K	Swing-Out 8-place Centrifuge.  Available through authorized dealers.  Other centrifuges available direct from LW Scientific.
HD video recorder	Sony	MHS-CM5
Orange fluorescent nucleic acid stain	Invitrogen	S-11364	SYTO® 83 Orange Fluorescent Nucleic Acid Stain.  Stored in DMSO solvent. Always wear reccommended Personal Protective Equipment. No special handling advice required.
Fluorescent counting beads	Invitrogen	MP 36950	CountBright™ Absolute Counting Beads.  Always wear reccommended Personal Protective Equipment. No special handling advice required.