Surgery – Instruments – Light application
Reexamination Certificate
1999-01-15
2001-04-24
Leubecker, John P. (Department: 3737)
Surgery
Instruments
Light application
C606S003000, C606S009000, C606S010000, C606S014000, C128S898000, C607S089000
Reexamination Certificate
active
06221068
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to tissue welding, more particularly, to a method by which tissue may be welded reliably under controlled conditions. Lasers of various types have long been used in various medical applications. In a wide variety of surgical techniques, laser light is used to cut tissue, and to coagulate simultaneously along the cut. Some progress has been made previously, in the use of laser energy for joining tissue, commonly termed tissue welding. The ultimate goal is to facilitate the joining of tissues with a minimum of scar tissue formation, and high tensile strength at the joined edges. Progress in the field of laser tissue welding has been slow due, in part, to the large number of laser parameters that need to be considered in the welding process. These parameters include wavelength, radiant exposure, irradiance, pulse duration, pulse repetition rate, irradiation time, spot size, dye selection, and adhesive selection. Past tissue welding studies have used a wide range of values for these welding parameters, making the interpretation of results and comparison between studies difficult.
The majority of previous tissue welding studies have used a laser operated in either continuous wave (CW) mode or quasi-CW mode with constant surface temperature control. During CW and temperature-controlled welding, heat diffuses from the weld site into surrounding healthy tissue, typically resulting in a large zone of thermal damage. A zone of thermal damage greater than ~200 &mgr;m extending laterally from the weld site may inhibit wound healing and result in excessive scarring. For some applications, such as skin welding, too much scar tissue may be clinically unacceptable even if strong welds can be achieved.
SUMMARY OF THE INVENTION
The method of the subject invention involves the use of pulsed delivery of radiation in combination with a dye, to initiate healing by producing strong welds in tissue that contain proteins, most significantly collagen, with strong adhesive properties when denatured, while limiting the thermal damage zone to the immediate area of the weld site. The radiation is delivered in pulses of short duration to achieve confinement of the temperature rise to the immediate area of the weld site. A pulse of radiation may be achieved by interrupting the radiation source or by passing radiation over the weld site. A series of multiple pulses of up to approximately 250 ms in duration are delivered to the weld site to achieve cumulative thermal denaturation over time, resulting in the formation of a weld with high tensile strength. Sufficient active or passive cooling is allowed between successive pulses to maintain the temperature in the tissue adjacent to the weld site below denaturation temperatures. A dye is applied to the tissue edges to act as a selective absorber of the radiation. The wavelength of the radiation is selected such that there is strong absorption by the dye and minimal absorption in the native tissue. Thus, heating and denaturation occur readily along the weld edges where the dye is located but not in the adjacent native tissue where absorption is minimal. The radiation is incident over a region of the surface that is sufficient for deep penetration of the radiation; thus each pulse of radiation heats a significant thickness of the weld site. Using this technique, it is possible to produce both strong welds and minimize thermal damage to surrounding healthy tissue, that would otherwise result in delayed wound healing and excessive scarring.
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Fried Nathaniel
Walsh, Jr. Joseph T.
Farah Ahmed
Leubecker John P.
Northwestern University
Welsh & Katz Ltd.
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