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Research Papers

Fractional Skin Harvesting: Device Operational Principles and Deployment Evaluation

[+] Author and Article Information
Walfre Franco

Wellman Center for Photomedicine,
Massachusetts General Hospital,
Department of Dermatology,
Harvard Medical School,
Boston, MA 02114
e-mail: wfranco@mgh.harvard.edu

Joel N. Jimenez-Lozano, Joshua Tam, Martin Purschke, Ying Wang, Fernanda H. Sakamoto, William A. Farinelli, Apostolos G. Doukas, R. Rox Anderson

Wellman Center for Photomedicine,
Massachusetts General Hospital,
Department of Dermatology,
Harvard Medical School,
Boston, MA 02114

1Corresponding author.

2Present address: ZELTIQ Aesthetics Inc.

Manuscript received September 30, 2013; final manuscript received March 13, 2014; published online xx xx, xxxx. Assoc. Editor: Rafael V. Davalos.

J. Med. Devices 8(4), 041005 (Aug 19, 2014) (9 pages) Paper No: MED-13-1244; doi: 10.1115/1.4027427 History: Received September 30, 2013; Revised March 13, 2014

As an alternative method to conventional split-thickness skin grafts (STSGs), we recently proposed fractional skin grafting (FSG), which consists in harvesting hundreds of microscopic skin tissue columns (MSTCs) to place them directly into the skin wound (Tam et al., 2013, “Fractional Skin Harvesting: Autologous Skin Graft Without Donor Site Morbidity,” Plast. Reconstructive Surgery–Global Open, 1(6)). This paper (i) introduces the concept and operational principles of a simple but robust fractional skin harvesting (FSH) device and (ii) presents the quantitative evaluation of the deployment of the FSH device with respect to different harvesting-needle sizes. The device utilizes a hypodermic needle with a specific cutting-geometry to core skin tissue mechanically. The tissue core is removed from the donor site into a collecting basket by air and fluid flows. The air flow transports the tissue core, while the fluid flow serves the purpose of lubrication for tissue transport and wetting for tissue preservation. The design and functionality of the device were validated in an animal study conducted to establish preclinical feasibility, safety and efficacy of the proposed FSH device and FSG method. The FSH device, operating at 55.16 kPa (8 psi) gauge pressure and 208 ml/min saline flow rate, cored 800 μm diameter × 2.5 mm length skin columns using a 1.05/0.81 mm outer/inner diameter needle. The MSTC harvesting rate was established by the user at 1 column/sec. For this columns size, about 50 MSTCs are required to cover a 1.5 cm × 1.5 cm wound. In comparison to STSGs, the proposed FSG method results in superior healing outcomes on the donor and wound sites. Most important, the donor site heals without morbidity by remodeling tissue, as opposed to scarring. The FSH device has the capability of extracting full-thickness skin columns while preserving its viability and eliminating the donor site morbidity associated with skin grafting.

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Figures

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Fig. 1

Fractional skin harvesting device concept: a harvesting needle cuts the skin creating a full-thickness microscopic skin tissue column (MSTC) that is removed from the donor site and deposited into a repository by air and fluid flows

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Fig. 2

(a) Schematic of FSH device prototype, (b) cross-sectional view. (c) Geometry dimensions and inner channels zones: (A) harvesting needle, (B) needle hub, (C) transport channel, (D) repository.

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Fig. 3

Schematic of custom-shaped harvesting needle with (a) two blades as cutting front and made out of 304 stainless steel by (b) two flat grinds at 12 deg bevel angle, α, each. In general, the tissue around any needle tip is compressed during insertion. For this geometry, the resistant force against compression is symmetrically balanced preventing deflection and minimizing buckling of the harvesting needle.

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Fig. 4

Representative measurement of the force applied during manual harvesting of MSTC: the force increases steadily before penetration (prepuncture), drops sharply when the needle cuts the skin (puncture) and increases after puncture until needle insertion stops

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Fig. 5

Needle motion mechanics: 0. Placement, needle initial position. 1. Deformation, needle cutting-front compresses skin. 2. Penetration, needle cuts into the skin. 3. Relaxation, needle motion stops. 4. Extraction, loaded needle retracts coring the skin. 5. Transport, tissue core is ready for transfer.

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Fig. 6

Velocity and pressure profiles along the longitudinal axis of inner channels of FSH device with 19, 22 and 25G needles: needle (light blue), hub (orange), tube (yellow), and collector (light gray)

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Fig. 7

Inner channels cross section of FSH device with 19G needle: (a) streamlines and velocity (m/s) map; (b) velocity (m/s) map and field; and (c) pressure map (Pa)

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Fig. 8

Fractional skin (FS) grafting overview: (a) donor site after harvesting MSTCs with FSH device, black horizontal lines represent 1 cm and 1 mm reference scales; (b) harvested MSTCs grafted into wound, the ruler on the left spans 2.5 cm; (c) donor site 5 weeks postharvesting, the ruler on the left spans 2.5 cm; (d) wound site 5 weeks postfractional grafting, the ruler on the top (out of focus) spans 2.5 cm

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Fig. 9

Split-thickness skin (STS) grafting overview: (a) donor site after harvesting MSTCs with FSH device; (b) harvested MSTCs grafted into wound, the ruler on the left spans 2.5 cm; (c) donor site 5 weeks postharvesting, the ruler on the left spans 2.5 cm; (d) wound site 5 weeks postfractional grafting, the ruler on the top (out of focus) spans 2.5 cm

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Fig. 10

Partial-thickness MSTC cut with a 19G harvesting needle

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