All surgical disciplines are concerned with the repair of damaged tissues and vessels. Damage can be the result of direct trauma to the body or as part of a surgical procedure in which there is a separation of normally continuous tissue such as in vein or artery anastomoses. Regardless of the cause, proper repair of the tissue or blood vessel is an essential step in the positive outcome of surgery.
The joining of separated tissues has principally been performed by suturing or stapling in which the skilled hands of the surgeon stitch or staple the separated tissues together. This procedure not only requires significant skill but also is a slow, tedious process, particularly if extensive repair is required.
Suturing suffers from several other drawbacks which have complicated surgical procedures. First, leaks often develop at the ends of the joined tissues which can require resuturing. In addition, suturing itself is a trauma to the tissue which can cause additional damage and extend the healing period. Further there are occurrences of inflammation in vicinity of the sutures which can result in late failure of a repair or anastomosis.
As a result, efforts have focused on overcoming the difficulties associated with suturing by the development of sutureless repairs using surgical adhesives or glues which adhere to tissue surfaces and form a bond therebetween.
The most common tissue adhesive is fibrin adhesive or glue typically containing a concentrate of fibrinogen and thrombin. Immediately prior to application these agents are mixed together and react in a manner similar to the last stages of the clotting cascade to form a fibrin clot. The clot fills the space between the separated tissues until the tissue regenerates eliminating the space. Fibrin adhesive has been used in a variety of surgical procedures because it forms a strong bond between the tissues and is generally biocompatible. (See, for example, Dennis F. Thompson et al., "Fibrin Glue: A Review of its Preparation, Efficacy and Adverse Effects as a Topical Hemostat", Drug Intell. Clin. Pharm. vol. 22, pp. 946-952 (1988); and Richard L. Burleson et al., "Fibrin Adherence to Biologic Tissues", J. Surg. Res. vol. 25, pp. 523-529 (1978).
Fibrin adhesive, however, has significant drawbacks which has prevented its commercial use in the United States. In order to prepare commercial quantities of fibrin adhesive the components must be obtained from pooled human blood. There is therefore the possibility of infection from agents such as Hepatitis "B", HIV virus and others. Particularly in the United States, the threat of infection has outweighed the benefits of obtaining commercial quantities of fibrin adhesive. As a result, the production of fibrin adhesive has been limited to quantities obtained from a patient's own blood to reduce the risk of infection. (See, for example, Karl H. Siedentop et al., "Autologous Fibrin Tissue Adhesive", Laryngoscope vol. 95, pp. 1074-1076 (September, 1985) Gidon F. Gestring et al., "Autologous Fibrinogen for Tissue-Adhesion, Hemostasis and Embolization", Vasc. Surg. vol. 17 pp. 294-304 (1983) and D. Jackson Coleman et al., "A Biologic Tissue Adhesive for Vitreoretinal Surgery", Retina vol. 8 no. 4, pp. 250-256 (1988). These autologous procedures make the use of fibrin adhesive costly and time consuming and therefore of limited value.
Non-biological materials have been tried as surgical adhesives in an effort to reduce the risk of infection over adhesives obtained from pooled blood. Isobutyl-2-cyanoacrylate has been applied to separated tissues and has formed a solid watertight seal shortly after contact with the tissue. Khalid J. Awan et al., "Use of Isobutyl-2-Cyanoacrylate Tissue Adhesive in the Repair of Conjunctional Fistula in Filtering Procedures for Glaucoma", Annals of Ophth. pp. 851-853 (August, 1974). However, such adhesives have been criticized because they are irritating to tissues, difficult to apply and fail to form a permanent closure. Andrew Henrick et al., "Organic Tissue Glue in the Closure of Cataract Incisions", J. CATARACT REFRACT. SURG. vol. 13 pp. 551-553 (September, 1987).
Thus, surgical adhesives have not been successful in replacing the suture as the primary means of tissue and vessel repair.
Another approach to sutureless tissue repair is tissue welding. Tissue welding involves the bonding of tissues together using an energy source such as a laser beam. Several types of lasers have been found useful for tissue welding including Nd:YAG, CO.sub.2, THC:YAG and Argon. Julian E. Bailes et al., "Review of Tissue Welding Applications in Neurosurgery", Microsurgery vol. 8 pp. 242-244 (1987); Rodney A. White et al., "Mechanism of Tissue Fusion in Argon Laser-Welded Vein-Artery Anastomoses", Lasers in Surgery and Medicine vol 8. pp. 83-89 (1988); Lawrence S. Bass et al., "Sutureless Microvascular Anastomoses using the THC:YAG Laser: A Preliminary Report", Microsurgery vol. 10 pp. 189-193 (1989), Masame Suzuki et al., U.S. Pat. No. 4,625,724, Jude S Sauer U.S. Pat. No. 4,633,870; Douglas Dew, U.S. Pat. Nos. 4,672,969 and 4,854,320, each incorporated herein by reference.
Tissue welding has been performed on a variety of tissues. For example, a carbon dioxide laser has been used in nerve tissue repair as described in Julian E. Bailes et al., Microsurgery. Tissue welding has successfully repaired intestinal tissue. Semion Rochkind et al., "Low-Energy Co.sub.2 Laser Intestinal Anastomsis: An Experimental Study" Lasers in Surgery and Medicine vol. 8 pp. 579-583 (1988).
The use of lasers to directly weld tissues can eliminate about two-thirds of the time needed to repair damaged tissues or blood vessels. However, histological analysis of direct laser welds has shown transmural thermal injury at the site of the weld which adds to the trauma of the injury and surgery. In vascular anastomosis, this can lead to complicating aneurysm formation at the weld site which presents a threat to the healing process and in some cases may lead to internal bleeding and complications associated therewith. Furthermore, the welds produced by direct laser contact have been characterized by marginal strength. The welds are prone to leakage and can burst in some cases.
To overcome the problems of direct tissue welding efforts have been made to employ organic agents which improve weld strength and at least minimize trauma to the tissue brought on by direct contact with laser energy. Typically, these agents known as laser adhesives or glues absorb laser energy forming a weld which bonds separated tissues together. In some cases, the laser adhesive selectively absorbs the laser energy thereby reducing the risk of transmural thermal injury. For example, blood has been used as a welding agent in laser repair surgery to improve bond strength and arterial healing through early fibrin cross-linking. Su Wang et al, "Effect of Blood Bonding on Bursting Strength of Laser-Assisted Microvascular Anastomoses", Microsurgery vol 9 pp. 10-13 (1988). Egg white albumin has also been used as a laser glue. Dix P. Poppas et al., "Laser Welding in Urethral Surgery: Improved Results with a Protein Solder", J. Urology vol. 139 pp. 415-417 (February, 1988) and George S. Ganesan et al., "Urethral Reconstruction Using The Carbon Dioxide Laser: An Experimental Evaluation", J. Urology vol. 142 pp. 1139-1141 (October, 1989).
Despite these efforts, laser adhesives still suffer from deficiencies which make their universal application problematical. In particular, laser adhesives are difficult to apply to separated tissues. They are either in the form of semi-solids (e.g. fibrinogen) or liquid (e.g. albumin or blood). As a semi-solid, the product must be cut into strips and placed at the weld site. Quite often the solid strip will move during application requiring time consuming repositioning. Additionally, the strip may shrink when exposed to the laser beam and weld only a portion of the tissue. The unwelded portion may be large enough to permit the passage of blood. This requires the use of additional strips of welding material and time consuming repeat operations.
Liquid laser adhesives are disadvantageous because they can run off of the weld site and thus may also require repeat applications. In addition, conventional laser adhesives made of protein materials, such as fibrinogen, often form rigid welds which reduce the flexibility of the welded tissues, particularly welded blood vessels. If the vessel is subjected to normal pressure fluctuations which occur during the cardiac cycle, the unclamping of the blood vessel or when the patient moves suddenly, the weld can rupture causing internal bleeding and related complications.
It is therefore an object of the present invention to provide a composition which can form a strong, flexible biologically compatible bond between separated tissues preferably upon the application of energy such as a laser beam.
It is another object of the invention to provide a composition which can form a watertight, flexible seal in tissues or prosthetic materials.
It is still another object of the invention to provide a laser adhesive whose viscosity can be modified according to the desired application to facilitate placement of the composition at the tissue site.
It is still another object of the invention to provide a method of bonding separated tissues or coating tissues to form a watertight seal using a composition which is easy to handle, particularly during surgical procedures.