Generation of micro-blood droplets and their impact on various surfaces

In this paper, an experimental setup for successful generation of single micro blood droplets is reported and preliminary investigations on the formation of micro droplets and micro droplet impact dynamics are presented. An optimal operating range is identified for the stable generation of single blood droplet in the droplet-on-demand (DoD) mode. By raising the local relative humidity around the tip of the piezoelectric dispensing nozzle, a single blood droplet can be generated in the DoD mode without clogging for a long operation time. The influence of pulse width on the generation of micro blood droplets has been studied and an optimal operation region for generating single micro blood droplet has also been identified. The surface wettability is found to affect the maximum spread factor and post-impact oscillation of an impacting micro blood droplet. The influence of the surface wettability becomes weaker with an increasing Weber number, We. The variation of the maximum spread factor for a millimeter-sized blood droplet follows a trend similar to that for a micro blood droplet on silicon and Teflon surfaces (advancing contact angle θa > 90°) but not on the glass surface (θa < 90°). Micro bloodstains on the glass surface exhibit zonal characteristics similar to the macro-sized bloodstains. The blood cells can be clearly identified in the central part of the micro bloodstain. The bloodstain on the Plain Woven fabric surface basically stays on the top of a yarn without saturating too much space within it due to the tiny amount of the micro blood droplet and the comparable size of the yarn.