Unlike other ultrasonically assisted machining methods, ultrasonically assited microtomy has had very little attention and therefore very little literature is availale to reference. Therefore, this work has been generated to understand whether ultrasonically assisted cutting (UAC) within microtomy is a viable alternative of conventional microtomy. With the key outcome being whether UAC can be used to reduce blade wear and therefore increase balde life. As this was found to be true in ultrasonically assited drilling, turning, milling, grinding and etc. [1,2,3,4,5,6].
In order to understand UAC within microtomy, it’s important to note that the microtome has become a universal tool in the creation of sample slides from tissue embedded paraffin wax blocks for histology. Being a widely used tool, few changes have been made to the operation of the microtome itself over the years. However, incremental changes have been made to the ergonomics and design of the microtome, these changes have not been made to improve the quality of the sections and blade life [7]. Although efforts have been made in increasing the ease of changing the cutting blade, this process is still the most time consuming and costly operation. This is mainly because the time required to “cut in” a new blade as well as the cost of the new blade itself. The most significant change in the industry is the move from reusable blades, which are usually diamond reinforced and could therefore be sharpened after use. The use of reusable blades has become less common mainly due to the significant reduction in the cost of disposable blades and the increased labour cost in the sharpening of reusable blades. Although it was found that the reusable blades tended to have a greater blade life compared to their disposable counterpart, the cost savings in the use of disposable blades strongly outweighed the higher blade life benefits of the reusable blades. Due to the transition to disposable blades, the environmental impact and time associated with changing the blades has also increased. This increase could therefore be offset by increasing the blade life and thus decerase the amount of blades used per histologist per hour. This would in turn decerase the overall environmental impact of single use baldes but would increase the output of each histologist by spending less time changing blades and more time cutting samples.
During conventional microtomy as the blade completes a pass over the sample, brittle fragmentation of the blade edge occurs causing the blade to lose its sharp edge. The fragmentation of the blade causes an increase in the contact area which increases the cutting force required. This effect was also seen in various studies, which showed that the radius of the cutting edge was directly related to the cutting force required and that this effective radius increased with an increase in wear [8]. This increase in blade tip radii has also been shown to increase localised heating of the material as well as induced stress at the blade tip, all these factors can be categorised as directly related to blade wear.
In order to increase blade life, the blade could be vibrated ultrasonically. Ultrasonic cutting usually operates between 20 and 100 kHz with a vibration amplitude between 2 and 25 µm. The frequency at which the piezoelectric elements are excited at is dependent on the natural frequency of the blade holder. The ultrasonic vibration causes localised plastic deformation at the blade tip. This localised plastic deformation is caused by the high strain rates [9] along with this the pulsating effect of the vibration causes a reduction in contact time between the blade and the sample [10]. The pulsating effect of the blade causes an accumulation of damage to appear in front of the blade, thus decreasing the cutting force required. Although no study has been completed on the effect of blade life within microtomy, studies have been completed on the effect of tool wear on the diamond cutting of optical glass [11] and turning of low alloy steel [10]. Both these studies showed that the introduction of an ultrasonically assisted cutting tool increased tool life due to the decrease in the cutting force required.