Compact Phantom with embedded 3-dimensional capillary pumping network using sacrificial sugar structures for use in Biomedical and Biometric Applications

E. Breloff, L. Christie, K.W. Oh
SUNY at Buffalo,
United States

Keywords: phantom, cotton candy, capillary network, ultrasonic sensing, biometrics

Summary:

Prior Work: Three dimensional micro vascular networks have many potential applications spanning from consumer markets to medical diagnostic testing. The ability to design artificial tissue constructs that have their own inherent vascular network remains a critical limiting step [1]. Research has proven that using cotton candy as sacrificial sugar structures, the 3D network can closely resemble the dimensions of natural microvascular beds [2]. Expanded upon by Schneider et al, improvements were made to both miniaturize the device into dimensions resembling a finger and developing further techniques to remove the sacrificial sugar material [3]. Methods: The phantom was developed in a series of layers inside of a standard petri dish. Figure 1 shows the steps taken to create each layer chronologically. Sylgard 184 was added to act as the dermis layer in the finger. A spacer material was used to create a cavity so the cotton candy structure could be suspended to ensure structural integrity. Once removed, the remaining substrate consisted of Ecoflex-00-30 to act as the subcutaneous fat layer in the finger. Once the phantom was cut and the paperclip removed, the remaining sugar was dissolved away in an ultrasonic cleaner. The most challenging part of the design was ensuring reproducible geometric dimensions for the cotton candy structure. This was achieved by using a standard paperclip as the frame as shown in Figure 2 which provided improved rigidity. The paperclip was coated in melted sugar so the cotton candy would adhere. Experiments: The dermis layer (Sylgard 184) was carefully measured and calculated using the volume of the cylinder. Ultrasonic pitch-catch analysis was performed using a 2.25MHz Olympus non-focused transducer shown in Figure 3. The timing of the echo returns validated the location and thickness (depth) levels of the various interfaces by using the known speed of sound for both substrate materials of Sylgard 184 and Ecoflex-00-30. Colored water was pumped through the phantom as a blood simulate. Microscope images were collected to validate the diameter of the cotton candy vascular network and to also observe the natural chaotic arrangement shown in Figure 4. Measurements of various channels validated that diameters ranged between 10-30um which agrees with microvasculature vessel diameters located in the human body. Anti-spoofing detection test platforms are growing in demand with the increase in biometric authentication sensors located in commercial smartphone devices such as Qualcomm’s SenseID ultrasonic fingerprint sensor. These companies need to develop next generation algorithms to determine whether a presented finger is genuine or an imposter. This research aims to develop a test phantom to perform such anti-spoofing testing with the ability to pump fluid through an embedded vascular network to simulate a heartbeat. This feature may help distinguish live fingers from spoof fingers. Future improvements can be made such as matching the physiological properties of the finger better and potentially adding more features to distinguish live fingers such as sweat pores. References: 1. Nat Rev Drug Discov, 2002. 1(3): p. 177-86. 2. Soft Matter, 2009. 5(7). 3. Schneider, P. 2018.