Minimally invasive automated de-epithelization by precise ArF excimer laser ablation

OBJECTIVE

Development of a robotic ArF excimer laser device with a three-dimensional (3D) pattern scanning sensor for the controlled de-epithelization of live mouse and xenografted epidermis.

SIGNIFICANCE

The animal model could be adapted to humans for automated, minimally invasive de-epithelization of cutaneous areas and therefore is of interest for cutaneous gene therapy research.

MATERIALS AND METHODS

Ablation thresholds of mouse, porcine, and human skin were measured by acoustic detection methods. These ablation thresholds were used as initial parameters for dosimetry measurements. De-epithelization of live mouse and xenografted epidermis was performed by laser ablation (ArF excimer laser, λ = 193 nm, t(p) = 20 nsec). The rectangular shape of the laser spot and a robotic arm displacement incorporating a three-dimensional patter scanning sensor allowed a polygonal tile floor irradiation of a 2-cm-diameter area. Ablated epidermis was subjected to histology.

RESULTS

SCID and nude mouse skin did not entirely reflect the de-epithelization of human skin because abundant pockets of dermal keratinocytes persist in the outer root sheath of hair and cysts providing competitive foci of re-epithelization. Automated de-epithelization of human and porcine skin xenografts resulted in precise removal of keratinocytes with subcellular precision, providing a smooth live surface where epidermal transplants might engraft with little endogenous competition from residual outer root sheath from rare hairs.

CONCLUSIONS

The displacement of the ArF excimer laser devices allows reproducible, smooth, and damage-free ablation of epidermal areas in the animal model.

Silicon oxide cluster formation and stability in the laser ablation of SiO targets

The formation mechanism and stability of silicon oxide clusters observed in the ablation of SiO targets at 266 nm were investigated by time-of-flight mass spectrometry, laser-induced fluorescence (LIF), and DFT calculations. Neutral and positively charged Si(n)(+/0) and Si(n)O(m)H(0,1)(+) clusters were identified in the plume, but neutral Si(n)O(m) could not be observed. The time distribution of SiO in the plume measured by postionization with an ArF laser (Delta lambda approximately 1 nm, tau approximately 14 ns) and mass spectrometric detection was compared with that obtained by LIF with narrowband dye laser selective excitation of one specific rovibronic transition in SiO. Postionization leads to a multicomponent distribution that extends up to times near 100 micros after ablation, whereas LIF measurements obtain time distributions shorter than 20 micros. DFT calculations of several Si(n)O(m)(0/+) were performed, showing that one photon absorption of the postionization laser makes available low-energy dissociation channels of the neutrals, whereas two photon absorption is required for ionization. DFT calculations were carried out for stoichiometric H-containing clusters Si(n)O(n)H(+) (n = 1-4). For n = 1,2, the optimized geometries involve bonding of hydrogen to one oxygen atom in the clusters; for n = 3 and 4, the structures containing H-Si bonds are more stable.