There are many devices disclosed or proposed in the art for the application of medical materials by spraying. A particular field of spray application is for multi-part reactive materials, particularly for two-part medical materials, in which one part (“A”) is reactive with another part (“B”) either directly on contact, or upon passage of time, or upon activation, such as by heat or light. An important subfield of such applicators is dedicated to the application of fibrin sealant, in which part A contains fibrinogen, part B contains thrombin, and at least one part contains a calcium salt. On contact between the solutions, the fibrinogen is cleaved by the calcium-activated thrombin, and fibrin is formed. The fibrin self-assembles into a rigid structure, as occurs in blood clotting. This system is used to apply sealing coatings to the body, and to adhere tissue together where the mechanical stress is low. To achieve the desired effect, the two parts of the system must be intimately mixed during application to the tissue, but must be kept separate until that time. Exemplary devices for delivery of two separate fluids to a tissue surface are described in U.S. Pat. No. 5,582,596 to Fukunaga et. al., and U.S. Pat. No. 5,665,067 to Linder et. al. Linder describes a delivery device with a pair of fluid outlets surrounded by a single air annulus for spraying. Fukunaga describes a device with outlets with separate annuli, designed specifically for application of biocompatible adhesive containing human or animal protein, such as fibrin sealant, to a surgical site. The device of Fukunaga includes liquid outlets that extend distally beyond gas nozzles that surround the outlets, which Fukunaga states ensures that solutions ejected from the outlets will be sprayed uniformly by gas emitted form the nozzles.
Fibrin sealant systems can have numerous limitations, including the possible presence of viruses and prions, and newer all-synthetic systems have been devised which can alleviate these and other problems. It is easier and more reliable to tailor the mechanical properties of a synthetic system, and each of strong adherence to tissue, biocompatibility and flexibility of a coating can be achieved. An example of such a system is described in U.S. Pat. Nos. 5,749,968 and 5,800,373 and in international patent publication no. WO 96/29370. In this system, a solution of a reactive water-soluble macromer, such as a polyethylene glycol molecule extended with biodegradable groups such as lactide and made reactive by end capping with acrylate, is reacted with light in the presence of a photoinitiator or photosensitizer, and covalently polymerizes into a hydrogel. As disclosed in U.S. Pat. No. 5,748,968, it has been found that such a prior art hydrogel will adhere more strongly to tissue if the tissue is first coated with at least a part of an initiation system (herein, a “primer” or priming solution.) During polymerization, the tissue-adherent initiator assures satisfactory reaction and mechanical bonding at the tissue surface. In U.S. Pat. No. 5,800,373, it is demonstrated that this system can be further enhanced by incorporating a chemically reactive (“redox”) initiation system along with a photoinitiation system. Then one component of the redox system is used in the primer, and the other in the bulk, macromer-containing solution.
In these systems, and with other chemistries (e.g. as discussed in U.S. Pat. No. 5,874,500 and international patent publication no. WO 99/34833) it is often important to apply two or more fluids independently, and in some cases sequentially, to a tissue surface. Even where only one fluid is applied, it can be important to apply the fluid evenly, conveniently, and cleanly. It can also be desirable to apply the solutions in variable ratios. It can also be important to prevent any reaction of the two components in the device before the application is completed, to prevent having to clean or replace the application device during a medical procedure. It is an object of the invention to provide improved medical fluid delivery devices to address these and other needs.