Piezo Micro-Injection System for ICSI

Intra cytoplasmic sperm injection (ICSI) is a human-assisted method for animal or human reproduction, which was first introduced by Palermo in 1992, and has since been used throughout the world. However, the survival and fertilization rates of oocytes from the ICSI process are still widely varying among practicing hospitals and institutions. Reported survival rates have ranged from 80 to 90%, and fertilization rates of intact oocytes have ranged from 45 to 70%.

There are two main factors affecting the success rate. One of these is due to the specific medical processes used in the actual processing of oocytes and spermatozoa. The other is due to the method used in the insertion of the needle into the ooplasm, and the impact caused to the oocytes during the insertion process. In this research, we are mainly concerned with addressing the latter cause. It is possible that the initial orientation of oocytes and spermatozoa can be carried out using a fixed procedure before the actual micromanipulation. Thus, the actual placement of the spermatozoa within the oocytes constitutes a very important factor for the survival and fertilization rates of ICSI. Traditionally, a successful ICSI mostly relies on the manual operation of experienced doctors. But, it is still very difficult, even for a highly experienced doctor, to be able to repeat the process precisely and consistently, inevitably resulting in undue trauma and damage caused to the oocyte.

A systematic and operator friendly, yet sophisticated method was developed to assist the operator execute the ICSI process at a high oocyte survival rate. The method is based on the use of a precisely-guided piezo actuator. Piezoelectric actuators are innovative manipulators which have shown a high potential in applications requiring manipulation within the sub-micrometer or even nanometer range. There are two main classes of linear piezoelectric motors (LCM), classified according to their structures and driving principles. The first class works on the direct-drive principle. Deformations of a piezoelectric element are directly used to drive the load for precise positioning. The second class of LPM operates instead on an indirect-drive principle. Several direct-drive piezoelectric actuators work in synchronization to produce a resultant linear motion of the load. 

The peizo actuator employed in this research offers the operator highly repeatable motion at both very high speed and ultra-fine resolution. These contradictory yet desirable end objectives are unachievable with the manual approach. A library of basic piezo movements is developed to enable the operator to experiment and construct a sequence of optimal mechanical movements for the ICSI operation. Investigation results are documented on the construction of an optimal injection profile to execute the ICSI process at minimal trauma and damage to the oocyte. The injection system comprises of a piezo manipulator mounted on an existing microscope setup. It is controlled via a dSPACE card mounted within a PC.

A photograph of the piezo injection system is shown in Figure 1, and a schematic diagram of the manipulator is shown in Figure 2. 

Figure 1: Photograph of the piezo injection system.

Figure 2: Schematic diagram.