Nov 17, 20193 min read

Design of a novel MEMS based microgripper with hybrid actuation to determine CTC progression.

Updated: Jun 1, 2020

The system is designed to evaluate cancer progression through CTCs. The micro-gripper can be further used to manipulate different biological cells for several other applications. The novelty of this design lies on the hybrid actuation mechanism and the sensing method used.

Introduction

Cancer is a major public health problem worldwide and the second leading cause of death in 2019. It's the disease caused by uncontrolled division of the abnormal cells in a part of the body. Cancer can also be referred as a tumor. The adaptation of a cancer cell within a tissue micro environment that is distance from the primary tumor is called as metastasis. The major cause of cancer-associated mortality is tumor metastasis where metastasis remains the cause of 90% of deaths from solid tumors. Cancer spread mostly occurs through the blood, mainly through circulating tumor cells (CTCs) that had been shed into the vasculature. Numerous studies in the past decade have shown that CTCs may be used as a bio marker to predict disease progression and survival in metastatic even in early-stage cancer patient. High CTC numbers correlate with aggressive disease, increased metastasis, and decreased time to relapse.

CTCs have been proposed as a tool for monitoring disease progression and response to therapy. The CTCs have different mechanical properties in comparison with red and white blood cells, and their detection may be employed to study the efficiency of medical treatments. According to most of the studies related to mechanics of normal and cancer cells showcase that cancer cells specifically CTCs are softer than normal healthy cells. More importantly the decrease in stiffness of the CTC correlates with the progression of cancer disease. Therefore, this stiffness factor is considered and featured in this research.

System Overview

The gripper is design to evaluate cancer progression through the CTC stiffness measurements. A hybrid actuation method of piezoelectric and electrostatic is used in the proposed system. This hybridization allows the gripper to grip and check the stiffness of the CTC separately. The main parts of the microgripper system is introduced in the following video.

Actuating methods

Piezoelectric actuator is used to grip the CTC. The design consists of two parallel gripper tips where both tips are integrated with a piezoresistive sensor to identify the contact between the cell and the tip. According to several research studies most of the CTCs are within the size range between 10 microns and 30 microns. Therefore, the piezoelectric actuator design parameters are optimized to generate the required tip displacement to grip CTCs within the diameter range.

Sensing elements

The gripping and squeezing operations are controlled using a sensor system. Two piezoresistive sensors are positioned below the gripper tip to identify the contact between the tip and the cell. After gripping the cell electrostatic actuator squeeze in and squeeze out the cell while the right side electrostatic comb drive sense the force change to predict the stiffness of the CTC.

Figure 1: Piezoresistive sensor (a) volumetric strain results (b) dimensional parameters

The paper "Design of a novel MEMS based microgripper with hybrid actuation to determine Circulating tumor cell (CTC) progression" was accepted to the KES InMED-20 conference which will be held in June 2020 in Croatia. This will be published as a springer book chapter. More information on results and fabrication will be added to the blog after the publication.