This is being reported as a large advance in the field of organ/ tissue transplantation. USing increasing concnetration of cryoprotectant solutions apprently allows deep freeze without crystalization and without protectant damage to the tissues. What is it's applicability for larger organism preservation?
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=P... Partial text follows United States Patent 6,740,484 Khirabadi , et al. May 25, 2004 Method of cryopreservation of tissues by vitrification Abstract A method for vitrification of a tissue or organ includes immersing the tissue or organ in increasing concentrations of cryoprotectant solution at a temperature greater than -15.degree. C. to a cryoprotectant concentration sufficient for vitrification; cooling the tissue or organ at an average rate of from 2.5-100.degree. C. per minute to a temperature between -80.degree. C. and the glass transition temperature; and further cooling the tissue or organ at an average rate less than 30.degree. C. per minute to a temperature below the glass transition temperature to vitrify the tissue or organ. After the vitrified tissue or organ has been stored, the tissue or organ may be removed from vitrification by warming the tissue or organ at an average rate of from 20-40.degree. C. per minute to a temperature between -80.degree. C. and the glass transition temperature; further warming the tissue or organ at a rate of from 200-300.degree. C. per minute to a temperature above -75.degree. C.; and reducing the concentration of the cryoprotectant. Tissues or organs treated in this manner exhibit near normal functions, for example, blood vessels exhibit near normal smooth muscle contractility and normal graft functions. BACKGROUND OF THE INVENTION The supply of viable tissues and cells for autologous implantation and heterologous transplantation (hereinafter jointly referred to as transplantation) and study is limited in part by the time a tissue or organ can be maintained in a viable state. Increasing the length of time that a tissue or organ remains viable may drastically increase the likelihood that a particular tissue or organ reaches a recipient or researcher in a viable state. The transplantation of tissues, natural or engineered, including vascularized tissues and avascular tissues, including, but not limited to, vascular tissue, such as blood vessels, musculoskeletal tissue, such as cartilage, menisci, muscles, ligaments and tendons, skin, cardiovascular tissue, such as heart valves and myocardium, neuronal tissue, periodontal tissue, glandular tissue, organ tissue, islets of Langerhans, cornea, ureter, urethra, breast tissue, and organs, intact or sections thereof, such as pancreas, bladder, kidney, liver, intestine and heart, may all be benefited by increasing the length of time that such tissues and organs remain viable. In the present era of arterial replacement, at least 345,000-485,000 autologous coronary grafts (either arteries or veins) and over 200,000 autogenous vein grafts into peripheral arteries are performed each year. Report of a working party of the British Cardiac Society: Coronary Angioplasty in the United Kingdom. Br Heart J. 66:325-331, 1991; Heart and Stroke Facts: Statistical Supplement, American Heart Association, 1996; and Callow AD. Historical overview of experimental and clinical development of vascular grafts, In: Biologic and Synthetic Vascular Prosthesis, Stanley J (Ed), Grune and Stratton, New York, 11, 1983. A recent marketing report indicated that at least 300,000 coronary artery bypass procedures are performed annually in the United States involving in excess of 1 million vascular grafts. World Cell Therapy Markets, Frost & Sullivan, 5413-43 Revision #1, ISBN 0-7889-0693-3, 1997. Many of these patients do not have autologous veins suitable for grafts due to pre-existing vascular disease, vein stripping or use in prior vascular procedures. It has been estimated that as many as 30% of the patients who require arterial bypass procedures will have saphenous veins unsuitable for use in vascular reconstruction. Edwards W S, Holdefer W F, Motashemi, M, The importance of proper caliber of lumen in femoral popliteal artery reconstruction, Surg Gynecol Obstet. 122:37, 1966. More recently it has been demonstrated that 2-5% of saphenous veins considered for bypass procedures were unusable on the basis of gross pathology and that up to 12% were subsequently classified as diseased. These diseased veins had patency rates less than half that of non-diseased veins. Panetta T F, Marin M L, Veith F J, et al., Unsuspected pre-existing saphenous vein disease: an unrecognized cause of vein bypass failure, J Vasc Surg. 15:102-112, 1992. However, we estimate that if all arterial grafts and alternative veins are utilized according to current surgical practice, the maximum number of potential allograft recipients is probably closer to 10%. Vitrified arterial grafts may also have a market as a scaffold for the seeding and adhesion of autologous endothelial cells or genetically modified endothelial cells. Prosthetic grafts are currently employed for large diameter (greater than 6 mm internal diameter) non-coronary applications. Between 1985 and 1990, approximately 1,200 allogeneic vein segments were employed for arterial bypass. Brockbank K G M, McNally R T, Walsh K A, Cryopreserved vein transplantation, J Cardiac Surg. 7:170-176, 1992. The demand for allogeneic veins is growing despite the well documented immune response to these grafts and the low clinical patency rates. In 1991 alone, at least 1,400 allograft saphenous vein segments were transplanted. McNally R T, Walsh K, Richardson W, Early clinical evaluation of cryopreserved allograft vein, Proceedings of the 29.sup.th meeting of the Society for Cryobiology, Cryobio., Abstract #4, 1992. Conservatively, the market potential for vitrified vascular grafts may be 50,000 units per year, or 10% of all vascular grafting procedures in the United States. Blood vessels are also a ubiquitous component of vascularized tissues and organs, both human and animal, which may one day be successfully stored by vitrification for transplantation. Providing that significant immunological issues can be overcome, animal-derived grafts may, one day, provide an unlimited supply of blood vessels and vascularized tissues and organs that could be stored in a vitrified state prior to transplantation. Avascular tissues may also be used for transplantation. For example, on average, an orthopedic surgeon specializing in knee surgery will treat between 10-20 patients per year who have sustained traumatic, full-thickness articular cartilage injuries. These patients may all be candidates for cartilage implantation. Approximately 30% of all Anterior Cruciate Ligament (ACL) tears have an associated full-thickness cartilage defect that often is undetected, even after surgery. For example, it was estimated that 20.4% of the 392,568 patients who received cartilage repairs in 1996 were candidates for a cartilage implant. Over time, most full-thickness defects deteriorate and cause significant joint impairment. Since cartilage is avascular, the recruitment of cells to aid healing of partial thickness defects is difficult. In contrast, full-thickness defects have the potential for partial healing when techniques such as abrasion arthroplasty are employed. Unfortunately, however, these procedures generally result in mechanically inferior fibrous scars. Fresh osteochondral allografts have proven to be effective and functional for transplantation. The limited availability of fresh allograft tissues, however, necessitates the use of osteoarticular allograft banking for long-term storage. Although cryopreservation involving freezing is a preferred method for storing tissue until needed, conventional protocols result in death of 80-100% of the chondrocytes and damage to the extracellular matrix due to ice formation. These detrimental effects are the main obstacles preventing successful clinical outcome. Various studies using animal articular cartilage models and human cartilage biopsies have revealed no more than 20% chondrocyte viability following conventional cryopreservation procedures employing either dimethyl sulfoxide (DMSO) or glycerol as cryoprotectants. Such results greatly limit the possibilities for transplantation or grafting harvested cartilage. Low temperature preservation of biological tissues and organs, i.e., cryopreservation, has been the subject of much research effort. Cryopreservation can be approached by freezing or by vitrification. If the organ or tissue is frozen, ice crystals may form within the organ or tissue that may mechanically disrupt its structure and thus damage its ability to function correctly when it is transplanted into a recipient. Organized tissues and organs are particularly susceptible to mechanical damage from ice crystals formed during freezing. Even when all cryopreservation variables are controlled, there is a limit, which is largely a function of tissue volume and geometry (including any associated fluids and packaging), beyond which traditional cryopreservation methods do not consistently work. For example, in cryopreserved allograft heart valves, the leaflet fibroblasts survive well (70-90%), but neither the endothelial cells nor the smooth muscle cells of the aortic tissue associated with the valve survive. Cryopreservation can also be effective for isolated islets of Langerhans, but preservation of islets in bioengineered capsules can be technically difficult. Skin is relatively easy to preserve because of the thin, flat structure of the tissue. It appears that thawing of skin-like products, however, can be technically difficult due to the narrow window for error during warming, outside of which ice growth
... więcej ť
Favoured: 0
