Shockwaves have been extensively used for various medical procedures with extracorporeal lithotripsy being the most celebrated application. Other applications of shockwaves in the medical field include use of shockwaves for the treatment of avascular necrosis, accelerated bone fracture healing, angiogenesis and tendinitis. In the field of genetic engineering, shockwaves have been successfully used to enable transformation of bacteria and fungi. Researchers have also harnessed the energy associated with shockwaves to deliver vaccines in the animals. These methods involve the conventional approach like the use of compressed gases, use of explosive material use of piezoelectric crystals etc. to generate shock waves. In the long run these methods have a negative impact on the environment e.g.: the use of explosive material generated by products of combustion which may contribute to the global warming.
This article highlights a device that has evolved by the interweaving of all the concepts aforementioned. The convergence of various scientific disciplines bring with them multifaceted benefits. A renewable energy source is used to drive water electrolysis. The mixture generated by electrolysis is in situ thus eliminating the need for storage of combustible gases. The mixture is in stoichiometric ratio and hence can facilitate spontaneous combustion. There is no problem of mixing the gases which is a routine problem in many combustion scenarios. The combustion of this mixture gives just water vapor. The strength of the shock wave generated by the combustion can be varied. The shock wave duration can also be varied by varying the length of the different section according to the specific application.
The various configurations of shock wave pressure duration and amplitude have been used to understand the response of different bacterial strains. Bacterial viability has been evaluated for three different bacterial strains at different shock wave pressures. The same device is also being used to delivery vaccines in mice. The device is used in a different configuration as compared to the configuration for bacterial transformation.
Description of the device
Solar powered miniature shock tube
The device comprises of three main components – solar panels, an electrochemical cell and the miniature shock tube assembly with provisions for bacterial transformation and vaccine delivery. All components, expect for the solar panels have been built in-house. Two 150 Watt solar panels have been used to tap the required solar power to drive the system. The renewable electricity from the solar panels is fed as input to an alkaline water electrolysis cell. The electrochemical cell consists of electrodes made of stainless steel (SS304 grade) and has 6M concentration alkaline KOH solution as an electrolyte. The cathode and anode reactions generate hydrogen and oxygen gas respectively in a stoichiometric ratio.
The stoichiometric mixture of hydrogen-oxygen gas is filled in the driver section of the shock tube. A spark plug is used to ignite the mixture in the driver section. Tracing paper (95 GSM) is used as diaphragm in the shock tube for all the fill pressures. The diameter of the shock tube is maintained as 6mm throughout. The length of the driver section and the driven section are chosen specifically to match the requirements of bacterial transformation and vaccine delivery. The lengths have been varied to obtain two specific configurations as portrayed in the figure. The use of a tri-clover clamp assembly at the junction of the various sections makes the length variation effortless.
Towards the end of the driven section of the shock tube provision has been made to accommodate the biological samples in a cavity of diameter 6mm and depth 5mm. The optimization of the dimension of the cavity has already been reported. For vaccination experiments, the end of the cavity has a 300 micron hole as shown in figure 3c unlike the case of bacterial transformation experiments. The biological sample inside the cavity is held by the surface tension of the liquid. When the shock wave passes through the liquid, it breaks the surface tension and gives sufficient momentum to the particles that the liquid ejects out of the hole in the form of a jet. A silicone rubber is used as material for energy transfer between the shock tube and the cavity. Silicone rubber is biocompatible and non-reactive material resistant to temperature of up to 300 C and having good tensile strength. These properties make it ideal for our application as there is no necessity of frequent replacement.
This shockwave generator has been used to perform bacterial transformation as well as needleless vaccine injections. Preliminary data suggests that the shockwaves generated by this device does not affect the viability of the bacteria which are used for transformation as well as vaccination.
Figure (a), (b) and (c): Viability assays of E.coli, Pseudomoas aeruginosa and Salmonella Typhimurium when exposed to shockwaves. (d) DNA integrity when exposed to shockwaves.
