WO1994015557A2

WO1994015557A2 - Barrier for protection during laser use

Info

Publication number: WO1994015557A2
Application number: PCT/US1994/000268
Authority: WO
Inventors: Peter P. Policastro
Original assignee: Med-Genesis, Inc.
Priority date: 1993-01-11
Filing date: 1994-01-10
Publication date: 1994-07-21
Also published as: AU6121494A; WO1994015557A3

Abstract

A 'gas blown' silicone foam (10) is used as a barrier or shield for protecting people and equipment from the harmful effects of laser beams. A reflecting means (2) or fire retardant material (7) and/or surgical dressing (6) can be used in combination with the silicone foam (10). The reflecting means (2) can be reinforced with a foil (3). The barrier can take various forms such as rigid barriers or flexible shields, for use as drapes, eye covers, adhesive tape, etc.

Description

BARRIER FOR PROTECTION DURING LASER USE

TECHNICAL FIELD

A shield or barrier for preventing damage from stray or reflected or misdirected laser beams is provided that includes a "gas blown" porous silicone foam that can also be provided or used with light reflection, absorption, dispersion and/or heat resistant means. The barrier can take the form of drapes, eye covers, tapes, etc., for equipment and personnel shielding.

BACKGROUND

Laser usage has greatly proliferated over the past decade because of the many advantages the laser offers over cutting means such as the scalpel. The laser beam can be controlled with pin-point accuracy; it cuts without pressure; and when used to perform surgery, it seals off blood vessels upon cutting reducing the quantity of blood lost. The laser also introduces safety problems that must be dealt with effectively in the shop or clinical setting. Safety has become a major concern when working with lasers. Numerous accounts of accidents with laser procedures, especially in the medical field, leading to serious injury and death have been reported by the FDA and other government organizations over the past ten years. Injuries to the eye, which can cause blindness, are the most frequent accidents. Damage to the skin and other body organs is also a recurring problem. Laser beams that are accidentally reflected off smooth metallic surfaces, typical of surgical instruments and other objects in the operating environment, are also a problem that has resulted in impaired vision and permanent blindness. The present invention addresses this safety problem, and in particular safety in the operating room, where the undesired contact of equipment and living tissue with a laser beam might occur.

The most common method of protecting the patient from exposure to laser radiation during operations is surgical drapes made from towels or gauze pads that are saturated with water or other suitable aqueous solutions, such as saline solutions. The wetted towels or gauze pads are applied to surround the wound site adjacent the area the surgeon intends to direct the laser beam. Only the area to be operated on is exposed. Additionally, when surgical procedures are performed in the region of the head or neck, or whenever the patient undergoes general anesthesia, the patient's eyes are protected by draping the eyes with wetted towels or gauze pads. The time that wetted towels or gauze pads provide protection depends on the type and power of the laser. In many cases the protection is only for a very short time. In the use of carbon dioxide lasers at typical power densities used for surgical procedures, the water in the towels can evaporate within several seconds, after which the drape is no longer effective to protect the underlying tissue. During lengthy operating procedures water may evaporate from the wetted gauze or towel dressings, reducing the level of protection that was initially provided. In the case of shorter wavelength lasers, the radiation is not effectively blocked or absorbed by the wet towel or gauze pad and can be transmitted to the tissue. The unprotected tissue is subject to being damaged by the laser beam. In the special case of the eye, blindness can result after even a very short exposure.

It is evident that better protection from errant laser radiation is needed for the patient and other persons present. Because of this need, protective articles have been described in the prior art in an effort to improve levels of safety. None of these articles are widely employed due to their limitations and disadvantages. U.S. Patent 4,616,641, issued 14 Oct. 1986 to E. Teeple, describes a surgical shield for use during surgical procedures in which lasers are utilized. It comprises a fabric sheet interposed between a pair of coextensive metal foil sheets. The preferred fabric for the inner sheet is cotton gauze and for the outer sheets is aluminum foil. U.S. Patent 4,635,625, issued 13 Jan. 1987 to E. Teeple, has an outer surface of a mask made of a "highly reflective" metal foil, preferably aluminum. Eye pads are used with cotton gauze pads wetted with water or saline as is common in the art. Although these articles do provide a greater level of protection to the underlying eye or tissue, the articles have significant limitations that have prevented their widespread use, because the outerlying metal foil of these articles is reflective. Laser beams reflected from their surface can be just as dangerous as the original incident beam. Reflected beams have been known to cause harm to both patient's and operating room personnel and equipment. U.S. Patent 4,597,382, issued 1 July 1086 to R. Perez Jr. , teaches covering an instrument to prevent laser beam reflection. A matte finish surface can be provided on the aluminum to disperse the laser energy and avoid a total unidirectional reflection. The laser energy that is not reflected is "absorbed" and converted into heat. Since aluminum is a very good conductor of heat, the heat generated can burn the patient either by ignition of a gauze interliner of the article or, if the interliner is not present or is very thin, by direct contact of the aluminum with human tissue. Another disadvantage of attempting to disperse laser energy from the surface of aluminum, by providing a matte finish on the surface, is that the laser energy may be absorbed and the heat generated may be sufficient to create a temperature high enough to melt the aluminum. For these reasons, an outer layer of aluminum that is directly exposed to the laser beam, whether of a smooth highly reflective surface or a "matte" finish surface, is not desirable as a laser barrier.

U.S. Patents 4,558,093, issued 10 Dec. 1985 to J. Hatzenbubler et al and 4,735,623, issued 5 Apr. 1988 to J. Hatzenbubler et al, teach encapsulated spherical glass beads or water packed within a matrix of silicone. They teach laser shields formed into articles such as surgical drapes, surgical sponges and as covers for articles, such as an endotracheal tube. A fabric sheet can be attached to the laser terminating material for comfort or aesthetic appearance. These articles are described as being effective against the 10.6 micron wavelength of a carbon dioxide laser beam. The patents review the fact that ablation or penetration of the laser shield occurs upon exposure to the laser beam over a period of time. U.S. Patent 4,901,738, issued 20 Feb. 1990 to R. Brink et al, describes a laser shield comprised of an opaque, flexible, fabric sheet bonded to a metal foil. U.S. Patent 4,604,998, issued 12 Aug 1986 to J. Bellina, describes a laser surgery drape having at least one metallic layer adhered to at least one non- metallic fabric-like layer, and a reflective surface means positioned to reflect laser radiation toward the metallic and non-metallic layers. U.S. Patent 5,103,816, issued 14 Apr. 1992 to . Kirschbaum, describes a composite of an adhesive backed foil, a layer of fire retardant fabric bonded to the foil on the side opposite the adhesive, and an insulative layer laminated to the fabric for use in making protective articles for use in laser surgery. U.S. Patent 4,728,567, issued 1 Mar. 1988 to J. Razzano et al, entitled "Silicone Foam Backed Polyimide Film" discloses a silicone foam backed film, where the film can be a metallic foil that does not flake away with oxidation. In addition to these references, U.S. Patent 4,570,626, issued 18 Feb. 1986 to J. Norris, et al, teaches a plastic silicone sheet used to protect the eyes during laser surgery. The use of porous materials in combination with metallic layers is common with U.S. Patent 5,022,389, issued 11 June 1991 to L. Brennan, U.S. Patent 5,014,723, issued 14 May 1991 to J. Kaufman, and U.S. Patent 4,603,076, issued 29 July 1986 to . Bowditch, et al, examples. Foams have been used as light barriers as a back-up to a metallic covering, U.S. Patent 4,979,811, issued 25 Dec. to W. Boyer, and as a means to disperse laser energy with U.S. Patent 5,033,479, issued 23 July 1991 to G. Tanny, teaching the use of porous laser barriers with the pore geometry related to the beam wavelength.

Although heat and fire barrier resistance are desirable properties of a laser barrier, they are only two of the many considerations that are necessary for an effective laser barrier. Optical, biological, and mechanical properties are examples of other considerations that must be satisfied for the invention to be useful as a laser barrier that will provide protection during, for example, laser surgery. Further, the relative importance of heat and fire barrier properties, as compared with other properties, will depend on the nature of the laser radiation. Heat and fire resistance do not have the same importance for all wavelengths of laser light that may be employed.

The "gas blown" silicone foam useful in this invention can be described as any silicone foam that is primarily formed through the blowing of gas through a mixture of silicone monomers and/or polymers that are participating in reactions, that simultaneous to the blowing of the gas, leads to a substantially gelled or crosslinked state. The blowing gas may be introduced from an external source, either as a gas or as a blowing agent which decomposes to form a gas, or the blowing gas may be generated internally as a byproduct of the polymerization reaction of the silicone materials. These foaming processes are well known in the art. The following are examples of patents that disclose and describe many of the various types of silicone foams that can be used to form the silicone foams utilized in this invention. U.S. Patents, 3,923,705, issued 2 Dec. 1975 to S. Smith, 4,189,545, issued 19 Feb. 1980 to F. Modic, and 4,418,157, issued 29 Nov. 1983 to F. Modic, disclose various silicone foams which are formed through generation of a blowing gas (hydrogen) as a byproduct of silicone polymerization reactions. U.S. Patents 3,425,967, issued 4 Feb. 1969 to F. Modic and 3,730,931, issued 1 May 1973 to E. Simoneau, describes silicone foams that are formed by the addition of external blowing agents. Other disclosures of silicone foams which contain descriptions that fall within the scope of the "gas blown" silicone foams of the present invention are: U.S. Patent Nos. 3,070,555, issued 25 Dec 1962 to L. Bruner, Jr.; 3,338,847, issued 29 Aug. 1967 to S. Nitzsche et al; 3,677,981, issued 18 July 1972 to T. Wade et al. It should be noted that the foams of the above patents include a great many compositional variations. The articles of the present invention can utilize these variations but is not limited to them.

Various surgical dressings that are suitable for use with the present invention are described in the prior art. Collagen based hydrogel sheets are discussed in U.S. Patents 3,471,598 issued 7 Oct. 1969 to O. A. Battista and 3,632,361 issued 4 June 1972 to O. A. Battista. U.S. Patent No. 5,076,265 issued 31 Dec. 1991 to H. okalek, discusses examples of polysaccharide containing hydrogels. Additional U.S. Patents that disclose hydrogel surgical dressings are 4,743,399 issued 10 May 1988 to R. A. Kirchhoff et al 5,115,801 issued 26 May 1992 to J. V. Cartmell et al and 5,116,921 issued 26 May 1992 to H. L. Hsieh. DISCLOSURE OF THE INVENTION

Articles prepared from "gas blown" silicone foam and composite laminates which contain a layer of "gas blown" silicone, form superior laser barriers. Some of the laser energy contacting the laser barrier can be dissipated by conversion to heat and some of the energy can be dissipated through the light scattering and diffraction processes. Precise relationships of power to thickness, and power to laminate construction, in the many combinations that are possible, can be controlled. The addition of light absorbing additives enables the user of the invention to adjust the various material characteristics to better meet specific needs.

The object of the invention is to provide a laser barrier that can be formed into surgical drapes, eye shields, tapes, or equipment/personnel shields, to provide protection against exposure to laser beam radiation in the work place or clinical setting. The laser barrier in the form of a surgical drape eye shield, protects the patient's underlying tissue by preventing contact of the underlying tissue with laser beams. The barrier can be used in an industrial/or manufacturing setting to protect equipment and people from exposure to laser radiation. Electronic and photonic devices that contain lasers may also benefit from beam shielding. Sensitive electronic components within the devices can be protected. The laser barriers are substantially nonreflective of coherent light and do not have an outer metallic foil layer that can reflect the laser beam to create a safety hazard. The laser barrier provides for a single, universally applicable laser barrier providing protection against most common laser wavelengths encountered in the work place and in particular the clinic. Protection is provided against laser wavelengths that range from the ultraviolet to the far infrared portion of the spectrum. The vapor barrier, when incorporated, retains moisture in a tissue or gauze dressings that may lie beneath it.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1-7 are sectional views of preferred embodiments of the invention.

Figure 8 is a bottom plan view of a barrier in the shaped of an eye protector.

BEST MODES FOR CARRYING OUT THE INVENTION

The "gas blown" silicone foams in sheet-like form have been found to demonstrate a remarkable ability to function as a laser barrier. The remarkable ability of

"gas blown" silicone foam laser barrier to protect underlying objects from laser radiation is not fully understood, but it is thought to be due in part to the intricate and unique cellular foam structure that results when the foam is formed by the gas blowing process.

The characteristics of light are well known. When light of a given wavelength strikes or impinges on the surface of an object it is either reflected from or transmitted into the object. If it is transmitted into the object it either passes through the object, when the object is transparent to that particular light wavelength, or it is absorbed by the object, when the object is opaque to that particular light wavelength. As a practical matter, few objects are 100% transparent or 100% opaque. Absorption is accompanied by a corresponding heat increase in the object. A given object surface may also either reflect or transmit a given light wavelength depending on the angle of incidence, i.e. whether the angle of incidence is more or less than the critical angle for the particular material involved. When the angle of incidence is not perpendicular to the object's surface, the light proceeds with an angular change in a transparent material. The angle changes are determined by the refraction of the particular materials involved. Even though a laser beam is concentrated into a relatively small area, the random size and distribution of bubbles in the "gas blown" silicone foam have a unique ability to dissipate the light and energy of the laser beam. The bulk and fine cellular structure of "gas blown" silicone foam is different and distinct from other silicone structures. In addition, silicone has a higher temperature tolerance than most plastics and is capable of having molecular structures and additives that absorb some radiation. Even when the laser, or heat generated from the laser, break down the molecular structure of the silicone into largely "silica", the resulting optical properties are still effective as a barrier.

An appreciation of how the "gas blown" silicone foam functions to protect against laser radiation when formed into the laser barriers of this invention may be suggested by considering the effect of a laser barrier comprised of an intricate, silicone, cellular foam structure on an incoming laser beam. The cellular foam structure presents an extremely large internal surface area within the structure at varying angles to disrupt the laser beam by refraction, scattering and dispersion of the beam. These internal surface areas present an almost continuously changing angle of incidence and exit to the light rays passing through the silicone and gas filled voids. By control of the molecular structure and/or use of additives, absorption can also be controlled and used to reduce the laser energy. By using these structures, at the point the laser beam exits the barrier, its overall energy is diminished through absorption and the coherency of the light is broken up and distributed over a much wider area than that of the incoming beam. This is offered as a possible explanation of why the "gas blown" silicone foam has the superior ability to act as a laser barrier. Since there are many inter-related parameters and characteristics that are operative in a laser barrier, it is likely that there are other cause and effect relationships that also contribute to the effectiveness of the "gas blown" silicone foam.

Examples of specific silicone foams which are useful to prepare the laser barriers of the present invention and that are commercially available fall into two general categories: (1) Bulk foams which have been formed into shapes by the manufacturer, which may be cut or shaped into an article of this invention, and (2) multicomponent systems that when mixed together form a foam upon interaction and reaction of the parts. Two commercially available silicone foams falling into the latter category, are GE Silicone foam RTF8510 and GE Silicone RTF762. Each of these consists of two parts that form foam products when mixed. Dow Corning also offers similar products. The foam components can be mixed and poured into a mold. The foam will expand and fill or replicate the mold cavity. Precast silicone foams which are commercially available in sheet stock are COHRlastic™ R10470 or F12 from the Furon Company, Laguna Niguel, CA, CHR Division and Poron™ S2000 Silicone, a preformed silicon "gas blown" foam sheet product, available from the Rogers Corporation, Rogers, CT, are suitable materials for use in this invention. Rogers refers to their product as a "cellular silicone material". Manufacturers also alternate in describing these products as "sponges" or "foams" and attempt to differentiate their products by referring to them as "open" or "closed" cell. They also describe and differentiate their products by stiffness, tensile strength, color, and through different compositions such as those containing fluorosilicones, or phenyl silicones, or methysiliconeε. For purposes of this invention, all of these are considered suitable and within the scope of "gas blown" silicone foam products that make the protective articles of this invention useful. The molded foam object can be used as it comes from the mold or further shaped by cutting, sawing or other suitable method to produce the laser barrier or a component part of the barrier. Alternatively, in forming a layer of foam attached to a substrate, the foam mixture can be directly cast on the substrate to form a layer of foam adhering to the substrate without the need of an adhesive.

A laser barrier sheet can also be formed from bulk foam which has been purchased as sheet or bun stock. The shape may be retained or altered by cutting or sawing or other suitable methods, and the foam adhered to a substrate to form a composite sheet laser barrier. Although most adhesives will be adequate for this purpose, a silicone RTV adhesive, such as silicone sealant GE 012, clear, General Household Sealant, or Dow Corning Silastic medical Adhesive, Type A, is preferred. Pressure sensitive silicone adhesives are also effective, for example, General Electric Silicones GE PSA6574 and Dow Corning Bio-PSA, Type A, can be used.

The physical and mechanical properties of the silicone foam, whether formed in place or adhered to the substrate, will vary significantly depending on the particular laser wavelength and energy and the article it will be used to form. For example, a laser barrier which is intended to be free standing and placed between the laser source and equipment, such as the anesthesia apparatus, can be made of a silicone foam that is stiff and rigid. A laser barrier which is intended for use as a surgical drape, must be flexible enough to conform to the part of the patient's body that the shield is intended to protect. Flexibility is also a requirement for an eye shield where the barrier must tightly conform to the patient's face or body contour, such as around the nose and bridge of the nose, to form a tight seal and prevent the passage of laser light. Under such circumstances, it would be required that the physical and mechanical properties of the foam allow bending at the particular thickness required. A foam which is used in a surgical drape, or eye shield, should preferably have a compression deflection of 2 to 50 psi at 25%, a tensile strength of 20 to 350 psi; and an elongation of 20 to 300 percent. The cured foam may have a thickness of from 5 mils to 1 inch, depending on the protection required and the circumstances under which the laser barrier will be used. A preferred thickness is 30 to 250 mils. The preferred range of thickness for typical carbon dioxide medical lasers with a power of 50 watts is from 40 to 250 mils. Other laser systems may have a range which is different, but generally 10 mils to 1 inch in thickness is adequate. Comparing foam thickness relative to laser power, a typical gas blown silicone foam that is 62 mils thick can substantially disperse laser beam energy exposure of a typical medical carbon dioxide, Nd:YAG, KTP or Argon laser. Going thicker than 62 mils provides an added protection but may not be necessary for many circumstances. Going thinner than 62 mils may not be suitable for many applications, but will be adequate for those applications that do not require high power densities. The silicone foams employed in this invention may have a density which varies significantly but 3.5 lbs per cubic foot to 60 lbs per cubic foot is an acceptable range with a preferred range being from 8 to 25 lbs per cubic foot. The pores may cover a broad range of cell sizes for both open and closed cell structures. The cell diameters can range from 0.25 micrometers to 500 micrometers. The pore distribution of commercially available preformed silicone foams shows them to have a very broad distribution of cell sizes. The distribution can range from approximately 0.25 micrometers to 500 micrometers. No critical relationship of pores to laser wavelength has been identified. On a practical basis, gas blown silicone foams have such great variability in the structure of any single foam sample that this relationship would be very difficult to determine. It is suspected that this variation may be one of the reasons for the laser beam dispersion.

The invention also dissipates laser energy through absorption of light as well as by diffraction and scattering of the coherent light waves. This mitigates the importance of any cause and effect relationship between precise cell geometries and laser wavelength. The use of film, foil, sheet, etc., are often considered to inherently or technically define specific dimensions. The use of these terms in this Disclosure does not limit them to any specific dimensions. Dimensions are recited where specific thicknesses are intended. The metallic foil or layer, preferably aluminum, should be from 0.2 mil to 100 mils with an optimum thickness being from 0.5 mil to 12 mils. Typically a 5 mil thick 1100 alloy aluminum foil can be employed. As an alternative to a metallic material, a metallized plastic film, such as metallized Mylar™ film, manufactured by E.I. duPont de Nemours and Co., Wilmington, Delaware, can be used. The plastic film can be from 0.2 to 30 mils thick with a metallic coating of from 0.01 to 0.2 mils.

The thickness of the surgical dressing is not critical. An acceptable range is from 25 mils to 2 inches, with the optimum thickness being from 0.250 to 1 inch. Surgical dressings that are well known in the art may be used. They are generally made from nonwoven cotton or modified cellulosic material, such as Rayon, or in some cases a synthetic fiber, such as a polyester, polyethylene, polypropylene, polyurethane , polyacrylamides , polyamide or any combination thereof, or a blend of synthetic and cellulose fibers can be used. All of the absorbent dressings may be wet with water, or saline or aqueous solutions which contain typical medical additives such as disinfectants, etc. Sheets of hydrogel dressings, well known in the surgical dressing art, may also be employed in addition to or in combination with the absorbent dressings set forth above. Hydrogel dressings, without limiting the definition thereof and by way of example include those comprising polysaccharides and polypeptides such as collagen, as well as those comprised of synthetic gels.

As to absorption, methylsilicone-based materials, the most common silicone type, absorb laser light energy moderately across the entire range of laser wavelengths of interest, i.e. from approximately 488 nm for an Argon Laser and 532 nm for a KTP laser to 1064 nm for a Nd:YAG Laser and 10,600 nm for a carbon dioxide laser. As opposed to typical organic foams, such as polyesters and polyurethanes, the high thermostability of silicones enables them to withstand temperatures of approximately 900° Fahrenheit for a short period of time before they decompose significantly. The best polyurethanes typically withstand less than half this temperature. Because of this, absorption of light energy to produce heat is an acceptable mode of laser energy dissipation when using a silicone foam. As temperatures exceed approximately 900° F. , silicone foam decomposes to silica foam. Even though the organic radicals have been oxidatively cleaved, the cellular superstructure remains. The critically relevant optical properties of the silicone foam are retained in the silica foam structure, which is thermally stable to approximately 3000° F. Silica foam continues to dissipate laser energy much like that of the silicone foam, i.e. by both absorption and dispersion. Moderate changes in the way the laser energy is dissipated can be controller by the addition of additives such as dark pigments, hydrated salts and/or through alteration to the silicone molecular structure such as by the inclusion of phenyl groups. Modifiers can be added that improve thermal conductivity, so that heat generated by the beam over a small area, relative to the total area of the article, can be spread over a larger area of the article more effectively, to limit local thermal damage. Examples of good thermal conductors are graphite and kaolin clay-based ceramic fibers such as Fiberfrax™ EF-119 provided by the Carborundum Co. of Niagara Falls, N.Y.

The use of additives and fillers to modify the properties of silicone foams are well known in the art. The patents cited above under Description of Related Art address the "gas blown" silicone foams useful in this invention and are specifically incorporated herein by reference. The additives and fillers disclosed in the art are often employed to modify the physical properties of the reactive components of the foam or of the foam itself. Such modifiers are used to control viscosity, compressive strength, tensile strength and density. Additives and fillers have also been employed to increase thermal and fire resistance of the foams. These include ground quartz, carbon black, various grades of graphite i.e. natural and synthetic powders, flakes, fibers etc., mica in either or both powder or flake form, ceramic fibers such as fibrous potassium titanate and kaolin- based fibers such as those available from the Carborundum Co. as Fiberfrax™ EF-119, etc. Other additives have been specifically added to modify the absorbance of the foams with respect to specific light wavelengths. Hydrated inorganic salts, such as calcium sulfate dihydrate salts, or other inorganic sulfate, borate, aluminate, silicate, carbonates or phosphate salts, which carry one or more water of hydration, may be included as part of the composition of the present foam to improve absorption of the laser beam light. Similar results to that of adding specific absorbing materials may be accomplished by modification of the polymeric structure of the silicone foams to absorb certain light wavelengths. For example, enhanced absorption of ultraviolet wavelength light can be achieved through the incorporation of aromatic radicals on the silicone chain. The substitution of some of the dimethylsilicone resin with diphenyl or methylphenyl silicone resin is an example.

A silicone foam containing composite laser barrier laminate is disclosed in Figure 1 that comprises an outer layer of foam 10 to which is bonded an inner layer of, for example, metallic foil 2. The first side of the foam layer faces away from the laminate toward the person or object to be protected. The second side is shown attached to the metallic foil. During use, the outer silicone foam layer is positioned so as to be the first exposed to laser radiation. Metallic layer 2 is only exposed to laser radiation which has first passed through the silicone foam layer. This use of metallic foil in combination with the silicone foam sheet-like material represents the preferred embodiment of the laser barriers of this invention. As shown in Figure 2, a barrier laminate 1' is shown. The first side of the foil 2 is attached to the foam 10 and the second side of the foil has an adhesive layer 4 on it.

In Figure 3, a reflecting strata or laminate 2• is shown. The reflecting material consists of a strata of two or more plys of aluminum foil which are bonded together. A layer or layers of reinforcing means such as a fabric and/or plastic film 3 may be bonded between the individual plys of aluminum to add strength to the foil. If plastic film is used, the preferred thickness would be between 0.3 and 5 mils. A fabric or scrim of cotton, polyester, nylon, or blends, are the preferred reinforcement fabrics. A plastic film of polyester, polyurethane, or polypropylene are the preferred reinforcing plastic films. NEPTAPE™, available from NEPTCO of Pawtucket RI, is a commercially available laminate of aluminum foil and polyester film that can be used as the metallic layer, by way of example. The metallic foil strata or laminate 2', including individual plys of metallic foil 2 and reinforcing fabric scrim 3, has a preferred total thickness of from 0.7 to 60 mils.

As an example, a laser drape constructed of a 125 mil thick sheet of "gas blown" silicone foam, such as GE RTF 762, laminated to a 6 mil thick aluminum sheet employing a silicone RTV adhesive. To the side of the aluminum sheet opposite the silicone foam, a gauze pad was bonded using a silicone RTV adhesive. The gauze pad of the laser drape was then moistened with water. The beam of a 30 watt carbon dioxide laser was focused on the silicone foam side of the laser drape. After several seconds of exposure, no damage to the gauze layer was evident. A similar exposure to the aluminum side of a drape, that contained only the aluminum sheet and the moistened gauze pad, resulted in significant visible damage to the gauze pad.

The silicone foam metallic foil laser barrier laminate may be formed into any of the protective articles previously mentioned. Figure 4 shows a surgical drape l" formed from the metallic foil 2» containing a composite laminate forming the laser barrier. An absorbent surgical dressing or gauze layer 6 and a pressure sensitive adhesive layer 4 may be provided. With this arrangement, a first portion of the adhesive layer secures the surgical dressing in place and a second portion extends beyond the surgical dressing perimeter and can secure the laser barrier to the person or object to be protected. When used, the surgical dressing or absorbent fabric layer may be wet with water, saline, or other suitable aqueous solution. As an alternative, a layer or sheet of hydrogel material, which has a similar effect to that of providing moisture to underlying tissue, may be used. The silicone foam metallic foil composite accomplishes several objects. The use of the silicone foam sheet as an outer layer in combination with a metallic inner layer, allows the advantageous properties of aluminum to be incorporated into the laser barrier surgical drape. The aluminum sheet is nonflammable under normal conditions and forms a barrier to moisture. When wet dressing pads 6 are used as an underlayer for the aluminum 2 or other vapor barrier material in a drape, the moisture in the pads is kept from evaporating during the operating procedure.

Aluminum foil reflects light. Reflected laser light can be as dangerous as the incident beam and it is one object of the present invention to provide a laser barrier material which does not reflect highly energized coherent light beams back toward equipment and personnel. Aluminum readily conducts heat, and presents a safety hazard if it gets hot. It will get hot if even a small fraction of the laser light is absorbed by it. Aluminum is malleable and conformable as a drape, but only in thin sheets. Aluminum melts at a relatively low temperature and will readily melt when exposed to a carbon dioxide laser beam due to the thin gauge thickness that is required to maintain malleability.

The present invention, employing a composite structure, has better laser resistance than would be expected by simply adding the materials. The silicone foam dissipates the power or energy of the beam before it impinges on the aluminum. The light which reaches the interior interface of the aluminum has a greatly reduced coherency. Because of exposure to the lower energy, there is less tendency for the aluminum to heat and melt. This permits maintaining an optical barrier to virtually all laser wavelengths. This lower energy scattered light, once reflected by the aluminum, then travels back through the cellular foam matrix, and the energy and coherence is further reduced and dissipated through absorption, dispersion and scattering in the silicon foam. This further reduces the possibility of harm by reflection as the light re-emerges from the barrier means back out into the work area. The silicone foam containing-metallic foil allows all of the advantages of the aluminum layer reflection, temperature resistance, sealing and heat conduction.

Optionally a surgical dressing sheet 6 can be attached to the foam 10. The preferred surgical dressing is cotton gauze fabric, as is commonly employed in the operating room. Such dressing or gauze 6 can be wet with water or saline to further improve the laser resistance of the surgical drape and protect the underlying tissue from any heat that may be developed. The gauze may be applied to the foam sheet by an adhesive bond 11 as shown in Figure 4. Alternatively, the mixed foam components may be coated directly onto the surface of the gauze and the foam allowed to form in place or in situ 9 as shown in Figure 6. This is the preferred method from the standpoint of economy. The foam 10 may be allowed to extend over an area greater than the gauze as shown in Figures 4 and 6, thereby creating a perimeter of foam surrounding the gauze. Pressure sensitive adhesive 4 may be applied to the perimeter foam surface that is free of gauze. A release liner 5, typically a film of resin coated paper or a plastic film, can be applied over the pressure sensitive adhesive. The release liner 5 may be removed prior to use of the drape to expose the pressure sensitive adhesive 4 used to secure the drape into position.

Although metallic foil, and specifically aluminum foil, is the preferred interlayer between the silicone foam layer and the gauze layer, other materials can be used as a substitute for the metallic foil to provide a laser barrier which can be formed into protective articles that offer advantages over employing the silicone foam sheet alone. The advantages of these other materials are usually limited to specific laser exposure.

One class of materials that can act as an interlayer are burn and/or fire retardant fabric materials 7 as shown in the laminate 8 of Figure 7. Several of these useful materials are made from fibers of polyamides which contain aromatic rings in their polymer backbone. These are referred to as polyaramids as a class, Kevlar and Nomex are two such fiber materials produced by Dupont that can be woven into fire resistant fabrics either alone or in combination with other fibers such as cotton. The fire retardancy is reduced as the polyaramid content is reduced. Fibers made of polybenzi idazole or PBI, as it is referred to by its manufacturer Hoechst-Celanese Corporation, can be woven into fabric or blended with Kevlar or Nomex to produce highly flame retardant fabrics which exhibit a high degree of strength even after charring. When these fire retardant fabrics are employed in place of aluminum, they provide an improved reinforcement to the foam if it is converted from its semi-organic to inorganic state by action of the laser beam. They also provide added protection as a fire barrier when flammable cotton gauze is used. Another fabric which may be substituted is bonded or woven fiberglass filaments. This fabric is made by PPG Industries under the trade name Hercuflex. The resulting silicone foam containing-fire retardant fabrics can be formed into any of the previously mentioned protective articles.

All of the laser barriers, silicone foam, silicone foam containing-metallic foil and the silicone foam containing-fire retardant fabric composites may be formed into eye shields. Figure 8 shows an eye shield 12 with pressure sensitive adhesive 4 and gauze pads 6. h e object of the eye shields is to protect the patient from being exposed to unintended laser radiation. Even short exposures to such radiation have been known to cause blindness and so there is a great need in the field for improved patient eye protection. The eye shield of Figure 8 can be formed from the laser barrier embodiments using the silicone foam metallic foil containing composite laminate shown in Figure 4 or without the metallic foil as shown in Figure 6. Cotton gauze eye pads, or other suitably aqueous absorbent material 6 can be attached with an adhesive 4 to the foil 2 opposite to the side of the foil which has the silicone foam sheet 10 attached as shown in Figure 4. Such eye pads may be moistened in a manner similar to those used with surgical drapes. A space free from gauze pad is left over the bridge of the nose 13 to allow the eye pads to properly seat in the ocular wells of the patient to obtain a tight fit. A perimeter seal of pressure sensitive adhesive can be provided to fasten the eye shield tightly to the face to prevent the laser beam from entering the ocular well through voids or spaces that might occur around the nose or cheeks. Similar eye shields may be formed from the other laser drape materials described. A monocular eye shield, which is intended to protect only one eye, is also contemplated.

Figure 6 represents a laminate 14• with the incipient foam product being coated directly on the gauze layer. After coating, the silicone rises to become a foam. This creates a better bond between the foam 10 and gauze layer 6 than can be achieved through use of a separate adhesive. The pressure sensitive adhesive 4 and the release liner 5 do not extend under the gauze, but only extend along the perimeter of the foam that is not bonded to the gauze. Although effective, the structure of Figure 6, is not as desirable as structures which include the metallic layer.

In Figure 4 the adhesive layer is entirely coextensive with the aluminum foil layer. The release liner layer 5 is coextensive with the adhesive layer that extends beyond the gauze 6. At the areas the pressure sensitive adhesive serves to bond the gauze to the article to be protected, no release liner is necessary.

The laser barriers of the present invention can be formed into a protective tape article as shown in Figures 2 and 5, as 2' and 14 respectfully. Tape is useful for protecting patient, operating room staff, equipment and supplies from damage by laser beams. The tape may be used for wrapping metallic instruments that can reflect a laser beam, endotracheal tubes that are otherwise flammable, anesthesia circuits and other equipment, supplies, and areas of the body of a patient or operating room staff where protection from laser beams may be needed. The tape can be formed by adding a layer of pressure sensitive adhesive 4 to the side of the foil 2 opposite the side the silicone sheet 10 is bonded to. The pressure sensitive adhesive is in turn covered with a release liner of coated paper or plastic 5. The tape may also be formed by replacing the foil with the fire retardant fabrics 7 previously mentioned, or the interlayer may be eliminated completely. The tape may consist of the silicone sheet 10 alone to which is coated a layer of pressure sensitive adhesive 4 with a sheet of release liner 5 applied over the pressure sensitive adhesive as shown in Figure 5.

It is believed that the construction, operation and advantages of these devices and procedures will be apparent to those skilled in the art. It is to be understood that the present disclosure is illustrative only and that changes, variations, substitutions, modifications and equivalents will be readily apparent to one skilled in the art and that such may be made without departing from the spirit of the invention as defined by the following claims.

Claims

Claims :

1. A method of preventing laser damage to persons or objects: providing a "gas blown" silicone foam (10) ; positioning said "gas blown" silicone foam (10) between a laser source and said person or object to be protected to dissipate the energy of said laser.

2. A method of preventing laser damage to persons or objects as described in Claim 1 including: providing a light reflecting means (2) ; positioning said light reflecting means (2) between said silicone foam (10) and said person or object to be protected so that said laser must pass through said "gas blown" silicone foam (10) , be reflected by said light reflecting means (2) , then pass back through said "gas blown" silicone foam (10) to further dissipate the energy of said laser.

3. A method of preventing laser damage to persons or objects as described in Claim 2 including: providing a surgical dressing (6) ; positioning said surgical dressing (6) between said light reflecting means (2) and said person or object to be protected to insulate and separate said person or object from said light reflecting means (2) .

4. A method of preventing laser damage to persons or objects as described in Claim 1 including: providing a burn and flame retardant material (7) ; positioning said burn and flame retardant material (7) between said silicone foam (10) and said person or object to be protected.

5. A method of preventing laser damage to persons or objects as described in Claim 1 including: providing an adhesive means (4) ; positioning said adhesive means (4) on said silicone foam (10) ; securing said silicone foam (10) to said person or object to be protected by using said adhesive means (4) .

6. A method of preventing laser damage to persons or objects as described in Claim 3 including: providing an adhesive means (4) ; positioning said adhesive means (4) on said silicone foam (10) adjacent to said surgical dressing (6) ; wetting said surgical dressing (6) with an aqueous solution; securing said silicone foam (10) and said surgical dressing (6) to said person or object to be protected by using said adhesive means (4) .

7. A method of preventing laser damage to persons or objects as described in Claim 3 including: providing an adhesive means (4) ; positioning said adhesive means (4) on said light reflecting means (2) between said surgical dressing (6) and said silicone foam (10) and on said reflecting means

(2) adjacent to said surgical dressing (6) ; using said adhesive means (4) to secure said surgical dressing (6) to said light reflecting means (2) and to secure said surgical dressing (6) and said silicone foam (10) onto said person or object to be protected.

8. A method of preventing laser damage to persons or objects as described in Claim 4 including: providing an adhesive means (4) ; positioning said adhesive means (4) between said burn and flame retardant material (7) and said person or object to be protected; securing said silicone foam (10) to said burn and flame retardant material (7) and to said person or object to be protected by use of said adhesive means (4) .

9. A method of preventing laser damage to persons or objects as described in Claim 2 including: making said light reflective means (2) of two light reflecting foils with a plastic film reinforcement means

(3) positioned between said two light reflecting foils (2).

10. A laser shield for dissipation of a laser beam for preventing damage to persons or objects including: a "gas blown" silicone foam layer (10) for dissipation of laser light; a light reflecting means (2) having a first side and a second side; said first side of a light reflecting means (2) secured to one side of said "gas blown" silicone layer (10) for reflecting laser light coming through said "gas blown" silicone foam (10) back into said "gas blown" silicone foam (10) for further dissipation; an adhesive means (4) on said second side of said light reflecting means (2) to secure said light reflecting means (2) and said silicone foam to said person or object to be protected.

11. A laser shield for dissipation of a laser beam for preventing damage to persons or objects as described in Claim 10 wherein: said light reflecting means (2) includes two layers of aluminum foil having a reinforcement means (3) secured between said two layers of aluminum foil (2) .

12. A laser shield for dissipation of a laser beam for preventing damage to persons or objects as described in Claim 10 wherein: a hydrogel material is secured to a portion of said adhesive means for separating said light reflecting means (2) from said person or object to be protected.

13. A laser barrier shield for preventing damage to persons or objects by a laser beam including: a "gas blown" silicone foam layer (10) having a first side and a second side and having pore diameters between 0.25 and 500 micrometers and a density of between 8 and 25 pounds per cubic foot and a thickness of between 30 and 250 mils; an adhesive means (4) on said second side of said "gas blown" silicone foam layer (10) for attaching said "gas blown" silicone foam layer (10) to said person or object to be protected.

14. A laser barrier shield for preventing damage to person or objects by a laser beam as described in Claim 13 including: a surgical dressing (6) attached to a portion of said second side of said "gas blown" silicone foam layer (10) , for additional protection of said person or object to be protected.

15. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 13 including: a burn and flame retarding layer (7) attached to said second side of said "gas blown" silicone foam (10) and to said adhesive means (4) ; said adhesive means (4) being attached to said "gas blown" silicone foam (10) by way of said burn and flame retarding layer (7) .

16. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 13 including: a release layer (5) removably attached to said adhesive means (4) for protecting said adhesive means (4) until said laser barrier shield is applied to said person or object to be protected.

17. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 13 wherein: said "gas blown" silicone foam (10) is modified with a select amount of light absorbent material to control the amount of laser energy converted into heat and the temperature of said laser barrier shield during use.

18. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 13 wherein: an aluminum foil (2) having a thickness between 0.5 and 100 mils is positioned between said "gas blown" silicone foam (10) and said adhesive means (4) .

19. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 18 wherein: said laser barrier shield (10) is shaped (12) to shield the eyes of said person; a surgical dressing (6) secured to a portion of said adhesive means (4) to cover, protect and insulate said eyes of said person.

20. A laser barrier shield for preventing damage to persons or objects by a laser beam as described in Claim 13 including: an surgical dressing (6) attached to one portion of said adhesive means (4) such that a second portion of said adhesive means (4) is available to attach said laser barrier shield to said person or object to be protected.