Combined Use of an Alkaline Earth Metal Compound and a Sterilizing Agent to Maintain Osteoinduction Properties of a Demineralized Bone Matrix

(12) United States Patent Christopher et al. IJS007771652B2 US 7,771,652 B2 Aug. 10, 2010 (10) Patent No.: (45) Date of Patent: (54) COMBINED USE OF AN ALKALINE EARTH METAL COMPOUND AND A STERILIZING AGENT TO MAINTAIN OSTEOINDUCTION PROPERTIES OF A DEMINERALIZED BONE MATRIX (75) Inventors: Renee A. Christopher, Dryden, NY (US); J. Anastasia Nichols, Ithaca, NY (US) (73) Assignee: Novasterilis, Inc., Lansing, NY (US) ( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 214 days. (21) Appl.No.: 12/101,489 (22) Filed: Apr. 11, 2008 (65) Prior Publication Data US 2009/0257914 A1 Oct. 15, 2009 (51) Int. Cl. A61L 2/20 (2006.01) (52) U.s. Cl. ...................................................... .. 422/33 C02 Cylinder Valve C02 Booster Compressor (58) Field of Classification Search ................. .. 422/28, 422/31, 33 See application file for complete search history. (56) References Cited U.S. PATENT DOCUMENTS 7,108,832 B2 * * cited by examiner Primary Examiner—Walter D Griffin Assistant Examiner—Timothy Cleveland (74) Attorney, Agent, or Firm—Welsh & Flaxman LLC 9/2006 Christensen et al. ........ .. 422/33 (57) ABSTRACT A method is disclosed that produces allografts from matrices typically containing demineralized bone matrix (DBM) pow- der, demineralized bone matrix gel, demineralized bone matrix paste, bone cement, cancellous bone, or cortical bone and mixtures thereof. The matrices are sterilized utilizing supercritical CO2 in the presence of a sterilizing additive and an entrainer such as an alkaline earth metal compound, pref- erably CaCO3. The resultant allograft materials have a reduced rate of rejection when used in allograft procedures including, bone, cartilage, tendon, and ligament grafting pro- cedures. 10 Claims, 2 Drawing Sheets U.S. Patent Aug. 10, 2010 Sheet 1 012 US 7,771,652 B2 N mm H E 8 8 S we ow 8 av _ 4 > > 1%,“. - 8 mm mm 26> Eam mm E H mm \/o_ smmuaeou ._< Emocm 3 3 mm Nag _%____»o %> N8 I w R mm U.S. Patent Aug. 10, 2010 Sheet 2 of2 US 7,771,652 B2 Percentsunnval U1 0'! o o c o C: c: 30.00 1 - — 20.00 —— -—*~—~—~— - ~—-~ —~»- 1000 -—-~h~—— 0.00 ~ f~——w 0 —-——. 0 50 100 150 200 250 300 Time (mins) Fig. 3 US 7,771,652 B2 1 COMBINED USE OF AN ALKALINE EARTH METAL COMPOUND AND A STERILIZING AGENT TO MAINTAIN OSTEOINDUCTION PROPERTIES OF A DEMINERALIZED BONE MATRIX FIELD OF THE INVENTION The present invention relates to methods of reducing rejec- tion in allograft procedures including, bone, cartilage, ten- don, and ligament grafting procedures. BACKGROUND OF THE INVENTION Allograft bone is a graft substitute readily available from cadavers and avoids the surgical complications and subject morbidity associated with harvesting autologous bone. Allograft bone is essentially a load-bearing matrix comprised of cross-linked collagen, hydroxyapatite, and osteoinductive Bone Morphogenetic Proteins (BMP). Human allograft tis- sue is widely used in orthopedic surgery. Allograft tissue is strong, integrates with the recipient host bone, and can be shaped either by the surgeon to fit the specific defect or shaped commercially by a manufacturing process. Allograft bone is available in two basic forms: cancellous and cortical. Cortical bone is a highly dense structure comprised of triple helix strands of collagen fiber reinforced with hydroxyapa- tite. The hydroxyapatite component is responsible for the high compressive strength and stiffness of bone while the collagen fiber component contributes to its elastic nature, as well as torsional, shear, and tensile strength. Cortical bone is the main load-bearing component of long bones in the human body. Use of allograft material is often a preferred treatment option for musculoskeletal related injuries. Significant prob- lems associated with the use of allografts are recipient rejec- tion of the tissue due to the presence of donor related antigens still present in the allograft, allograft inability to incorporate into the host, and contaminated tissue used in transplant. Numerous methodologies have been employed to reduce the level of antigenic compounds present in allografts and per- form low-level disinfection and sterilization. These methods generally include numerous washes with a variety of chemi- cals. These methods have extreme drawbacks to the extent that they utilize reactive chemicals that alter the structural components of the allograft or denature and/ or remove com- pounds that facilitate integration of the allograft by the recipi- ent. It therefore would be highly desirable if a sterilization method could be provided leading to improved clincal out- comes of bone grafting. Recently, in U.S. Pat. No. 6,149,864 to Dillow et al and U.S. Pat. No. 7,108,832 to Christensen et al. (the entire con- tent of both are expressly incorporated herein by reference), the use of supercritical CO2 was disclosed as an altemative to existing technologies for sterilizing a wide range of products for the healthcare industry with little or no adverse effects on the material treated. SUMMARY OF THE INVENTION The present invention fills the foregoing need by providing devices, systems and methods for repairing bone and soft tissue defects in a subject, wherein the bone and soft tissue defects are repairable by a bone or soft tissue graft procedure. The present invention contemplates the use of allografts that have been produced from matrices typically containing dem- 10 15 20 25 30 35 40 45 50 55 60 65 2 ineralized bone matrix (DBM) powder, demineralized bone matrix gel, demineralized bone matrix paste, bone cement, cancellous bone or cortical bone sterilized utilizing super- critical CO2 in the presence of a sterilizing additive and an alkaline earth metal compound such as CaCO3. These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Reference will hereinafter be made to the accompanying drawings, wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein; FIG. 1 is a schematic view of a presently preferred steril- ization apparatus in accordance with the present invention; FIG. 2 is a detailed schematic view of the pressure vessel employed in the apparatus of FIG. 1; and FIG. 3 is a graph that relates the survival percentage of endospores to processing time in the apparatus of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION The present invention contemplates the production of allografts from matrices typically containing one or more material of: demineralized bone matrix (DBM) powder, dem- ineralized bone matrix gel, demineralized bone matrix paste, bone cement, cancerous bone, cortical bone, or mixtures thereof and the like; that are sterilized utilizing supercritical CO2 in the presence of a sterilizing additive and an entrainer such as an alkaline earth metal compound, preferably CaCO3. The resultant allograft materials display a reduced rate of rejection when used in bone allograft. The sterilization appa- ratus and methods of the present invention are usefully employed to sterilize a variety of materials to produce allografts including but not limited to demineralized bone matrix powder, demineralized bone matrix gel, demineral- ized bone matrix paste, bone cement, cancellous bone and cortical bone and the like. The instant invention can be prac- ticed with different bone structures. For example, suitable bone graft structures may include cartilage, cortical bone, cancellous bone, subchondral bone, and any combination of the various bone tissue types. In addition, bone-tendon-bone allografts used for ACL reconstruction and structures employed for long bone allograft tumor reconstruction can also be used. The graft structure may comprise a composite bone that includes a polymer and a demineralized bone, and, optionally, a bone powder. These compounds may be used in different ratios that can be determined by a person of ordinary skill in the art. A non-limiting example of the suitable com- posite bone includes 50% polylactide (PLA), 30% deminer- alized bone (