High speed imaging of solid needle and liquid micro-jet injections

Abstract

High speed imaging was used to capture the fast dynamics of two injection methods. The first one and perhaps the oldest known, is based on solid needles and used for dermal pigmentation, or tattooing. The second, is a novel needle-free micro-jet injector based on thermocavitation. We performed injections in agarose gel skin surrogates, and studied both methods using ink formulations with different fluidic properties to understand better the end-point injection. Both methods were used to inject water and a glycerin-water mixture. Commercial inks were used with the tattoo machine and compared with the other liquids injected. The agarose gel was kept stationary or in motion at a constant speed, along a plane perpendicular to the needle. The agarose deformation process due to the solid needle injection was also studied. The advantages and limitations of both methods are discussed, and we conclude that micro-jet injection has better performance than solid injection when comparing several quantities for three different liquids, such as the energy and volumetric delivery efficiencies per injection, depth and width of penetrations. A newly defined dimensionless quantity, the penetration strength, is used to indicate potential excessive damage to skin surrogates. Needle-free methods, such as the micro-jet injector here presented, could reduce the environmental impact of used needles, and benefit the health of millions of people that use needles on a daily basis for medical and cosmetic use. arXiv:1811.00510v1 [physics.app-ph] 1 Nov 2018

A Comparison of Drug Delivery into Skin Using Topical Solutions, Needle Injections and Jet Injections

“…37 The needle pressure value ( = 2400 ), taken from a similar experiment with agarose, is assumed to be within the same order of magnitude for porcine skin. 27 Both solutions in the NFI experiments resulted in a nine times lower penetration strength than the solid needle ( = 4.8). Despite their low and thus, values ( < 1), which theoretically implies no penetration, the bright-field and fluorescence images confirm the jets entered the skin.…”

“…The methods used to obtain these values are described in more detail elsewhere. 27 In real-life conditions, repeatability or reproducibility of multiple injections may require that the jet injection frequency is increased to larger values than possible with the current experimental setup. For future in -vivo studies, we consider that the temperature of the liquid jets has to be measured to assess any probable burn injuries of the skin.…”

“…15 As measured elsewhere, both solutions behave as Newtonian fluids with measured constant viscosity η aqueous = 0.9 and η glyc10% = 1.2 . 27 The absorption was measured for both solutions in the spectral range of [300-1000] (UV-Visible Spectrophotometer UV-2600, Shimadzu).…”

“…16,17 From the different energy sources used to power NFIs, a recent example is based on continuous wave (CW) lasers that cause a phenomenon known as thermocavitation to create liquid jets by heating the injectate above its boiling point with an explosive phase transition. 8,9,27,28,35 This work evaluates a CW-based needle-free micro-jet injector as a possible transdermal delivery alternative with minimal damage to the skin structure. For the purpose of this study, the topical solution delivery will be primarily associated with diffusion processes.…”

Drug delivery via tattooing: Effect of needle and fluid properties

“…As far as the physics of the process, very few literature exists that detail the intricacies of the process [19,20] and more rigorous descriptions of the physics behind the tattooing procedure is lacking despite the wealth of literature on the immunological response of the process.…”