1.  Field of the Invention
The invention relates to systems and methods for mixing therapeutic cells before and/or during localized delivery, preferably to a biological lumen. 
2.  Description of the Related Art
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in biological conduits, e.g., without limitation, blood vessels and similar body passageways.  A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries.  Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels.  Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque.  Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material.  If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes, leg pain and the like. 
Rotational atherectomy procedures have become a common technique for removing such stenotic material.  Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries.  Most often the rotational atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patency of the opened artery.  For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patency of the opened artery.  Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience stent restenosis—i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent.  In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patency of the artery. 
Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material.  In one type of device, such as that shown in U.S. Pat.  No.  4,990,134 (Auth), a burr covered with an abrasive abrading material such as diamond particles is carried at the distal end of a flexible drive shaft.  The burr is rotated at high speeds (typically, e.g., in the range of about 150,000-190,000 rpm) while it is advanced across the stenosis.  As the burr is removing stenotic tissue, however, it blocks blood flow.  Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr.  Frequently more than one size burr must be utilized to open an artery to the desired diameter. 
U.S. Pat.  No.  5,314,438 (Shturman) discloses another atherectomy device having a drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged surface being covered with an abrasive material to define an abrasive segment of the drive shaft.  When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. 
U.S. Pat.  No.  6,494,890 (Shturman) discloses an atherectomy device having a drive shaft with an enlarged eccentric section, wherein at least a segment of this enlarged section is covered with an abrasive material.  When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.  The device is capable of opening an artery to a diameter that is larger than the resting diameter of the enlarged eccentric section due, in part, to the orbital rotational motion during high speed operation.  The disclosure of U.S. Pat.  No.  6,494,890 is hereby incorporated by reference in its entirety. 
Another method of treatment of occluded biological lumens, e.g., vessels, may include the use of stents.  Stents may be placed at the site of a stenosis and expanded to widen the lumen, remaining in position as an implant. 
No matter the technique used to open an occluded biological lumen, e.g., blood vessel, and restore normal fluid flow therethrough, one problem remains: restenosis.  A certain percentage of the treated conduits and vessels will reocclude (restenose) after a period of time; occurring in as many as 40-50% of the cases.  When restenosis does occur, the original procedure may be repeated or an alternative method may be used to reestablish fluid, e.g., blood, flow. 
The relevant commonality shared by each of the above treatment methods is that each one results in some trauma to the biological lumen wall.  Restenosis occurs for a variety of reasons; each involving trauma.  Small clots may form on the wall.  Small tears in the wall expose the blood to foreign material and proteins which are highly thrombogenic.  Resulting clots may grow gradually and may even contain growth hormones released by platelets within the clot.  Moreover, growth hormones released by other cells, e.g., macrophages, may cause smooth muscle cells and fibroblasts in the affected region to multiply in an abnormal fashion.  There may be an injury in the biological lumen wall due to the above methods that results in inflammation which may result in the growth of new tissue. 
It is known that certain therapeutic agents may have a positive effect on prevention and/or inhibition of restenosis However, intravenous medications are delivered systemically by vein, or regionally, e.g., through intra-lumen infusion without targeting the subject region.  Such unnecessary systemic exposure results with unknown and unnecessary adverse results in regions, tissue, and/or organs that are distant from the region of interest.  Clearly, systemic delivery and exposure is not well suited to treatment of diseases or conditions having a single intra-lumen region of interest. 
The potential utility of mixing therapeutic agents before or during localized application of a therapeutic dose of the therapeutic agent(s) is not limited to treatment of coronary arteries and may comprise any biological lumen.  For example, beyond coronary artery delivery, other sites of atherosclerosis, e.g., renal, iliac, femoral, distal leg and carotid arteries, as well as saphenous vein grafts, synthetic grafts and arterio-venous shunts used for hemodialysis would be appropriate biological conduits for a localized therapeutic substance delivery method and mechanism.  Nor is the potential utility limited to blood vessels; any biological lumen having a region of interest amenable to treatment may benefit from such a treatment method and mechanism.  Finally, the utility of the various embodiments of the present invention are not limited to application to a biologic lumen or conduit.  The present invention may be used in virtually any application whereby mixing of therapeutic agent(s) is desired. 
One particular problem with one form of therapeutic agent or substance is the tendency for therapeutic cells, e.g., stem cells, to not remain dispersed within a carrier fluid.  This results in a failure to provide a continuous dosing strength as the therapeutic agent comprising cells is administered; some regions will receive relatively small doses of the cells, while other regions may receive a super dosing of the cells.  In either case, the therapeutic benefit is not maximized and may be harmful to the patient.  The present invention is not, however, limited to the mixing of cells.  Other therapeutic agents, including but not limited to mixtures of two or more therapeutic agents, may benefit from the present invention. 
The present invention overcomes these deficiencies.