technology is its very low cost as compared to a laser as well as its small size. In the following, we shall present an confirmation of the expected ex vivo results of crater vaporization in tissue with an oscil- lating thermo-mechanical element.

their oscillatory journey depends on the initial com- pression loading force (spring constant loading × ~0.1–5 amplitude) and can be practically set to mil- liseconds. This implies that the vaporizing rods stay in the skin for that time duration. As a result, an array of vaporized craters (Figure 1C) is formed in the skin ~0.1–5 within milliseconds, which is similar to craters formed by a many pulsed ‘Fraxel’ CO2 laser of same pulse duration (6).

## The The ‘ThermiXel’

The new tissue ablation technology is based on the supply of vaporization heat from an extremely hot (~350–400°C) array of miniature rods down to a pre- selected depth (50–250 microns) in tissue within ~0.1–5 milliseconds, thus mimicking the pulsed CO2 laser action. As is shown below, this can be practically realized in a small device due to exploitation of a fortunate coincidence of thermal characteristics of some metals and tissue.

####### Theoretical analysis – selection of operational parameters

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The following conditions are prerequisites for the high temperature rods to practically mimic high quality CO2 (as well as Erbium) lasers operation as describes above:

(a)

The thermal energy, which is stored in the distal end of each rod, should be equal to (or higher than) the latent heat of vaporization of tissue for a volume equal to the vaporized crater volume. The thermal energy should be delivered within ~0.1–5 milliseconds (depending on depth), namely: the thermal relaxation time of the thermal energy storage section of the rod ~0.1–5 should be shorter than milliseconds. Rods (as well as copper block) should attain ~350–400°C a temperature of in order to mimic pulsed CO2 laser action (5) as well as avoid sticking of tissue to the metallic rods and, as shown below, provide the necessary vaporizing energy. Treatment repetition rate should be high enough – at least 1 Hz as achievable by most pulsed CO2 lasers with treatment spot size mm2, ~10 10 for an unlimited number of × treatment spots. This implies temperature rise of rods distal tip within 1 second fol- < lowing each treatment ‘flick’ and movement to the next treatment spot, without gradual decrease of distal end temperature. Initial heating up of the fixed metallic block 400°C to a temperature of prior to a treat- ment session should practically take only a few minutes. On the other hand, the pre- heated block should be large enough since it serves as a passive energy reservoir for the vaporizing rods. Yet, it should be small enough to be integrated in of a small hand held treatment handpiece. The treatment device should be hand held and only few centimetres in size.

####### Operating principles

The operating principles of the ‘ThermiXel’ technol- ogy are schematically presented in Figures 1A–C. A high thermal conductive copper block with an inte- grated array of copper rods is located inside a hand held treatment handpiece and is heated by a high (~100 power W) miniature electric heater cartridge to 350–400°C. a temperature of The high temperature block is held in a loaded position by a compressed spring. A thermally isolated protective plate (which ~10°C) may be chilled to a temperature of with a cor- responding array of holes serves as the distal end of the treatment handpiece and is placed on the skin to be treated. Once the handpiece is placed on the treat- ment site and a treatment command is given by the operator, the high temperature block/rods unit is released and allowed to move forward and perform a single harmonic oscillation (with the aid of the attached ~30 spring) of milliseconds duration, with an ampli- tude which is set to allow all rods penetrate a prese- lected distance (of 50 – 250 micron) into the skin (Figure 1B). A thermally insulating spacer provides additional assurance of penetration depth accuracy. Since the rods penetration into the skin occurs when the spring is fully stretched and copper block velocity is decelerated to zero, there is no mechanical impact on patient. Once the vaporizing rods have ‘flicked’ a thermal impact into the skin, the stretched spring returns the oscillating element back to its original retained position where it is reheated and gets ready for the next treatment command. We note here that the rods do not affect tissue at all if not heated, as opposed to mechanical needles. An analysis of the copper block movement reveals that the dwelling time of the rods in their distal 50–250 micron section of

(b)

(c)

(d)

(e)

(f)

- i) Adjustment of dwelling time duration in tissue

In the process of vaporizing tissue craters of depth H, the copper block and rods array (of total mass M)

1Note: The ‘ThermiXel’ technology is patent pending.