KryptoniteTM Bone Void Filler – Biocompatibility and Osseointegration

The bone cement and bone void filler market is crowded with new materials that broadly claim osteoconductive properties. However, the manner in which these materials balance structure, resorption, strength and biochemical factors is varied and all fall short of universal application. Evidence is provided demonstrating that the KryptoniteTMmaterial provides a biochemical and structural environment suitable for osseous applications. A series of experiments are reviewed, including standardized biocompatibility tests defined by ISO 10993 and tests designed to assess the materials performance in clinically relevant models. Collectively these experiments demonstrate that the material is well tolerated by the body and presents no acute or long term risks to the recipient. Additionally, in some models the porous structure of the material lends itself to infiltration of new bone that persists through late time points and integrates with existing anatomy. Motivated by the limitations of allografts,including finite supply, inadequate strength and concerns regarding disease transmission, numerous bone-graft substitutes that curein situhave been developed in the lab and brought forward for clinical use. Although some success has been noted, no product has achieved universal acceptance as a substitute for allograft. Polymethyl-methacrylate materials have been used as bone replacement material because of their excellent mechanical strength. However, these materials are not conducive to regeneration of bone, are not resorbable, and impose chemical and thermal challenges to local tissue at the time of implantation. Tri-calcium phosphates and similar cements have received attention due to theirbioabsorption, biocompatibility, and isothermicproperties. These materials; however, do not perform as well as native bone in many loading configurations and cannot be used as a standalone remedy in load bearing applications. Rapid rates of resorption may in some instances exceed the rate of proper bone ingrowth that results in an overall weakened construct. Product failures, generally associated with tensile loads or material fatigue, have limited widespread acceptance and prevented these materials from supplanting autograft as the standard of care for procedures requiring bone regeneration. The KryptoniteTM material is apolymer comprised of castor oil based polyols, a reactive isocyanateand calcium carbonate powder that curesin situ. Three component parts are mixed intraoperatively to form a viscous liquid, which polymerizes over approximately 20 minutes, transformingfrom an injectable state, through an adhesive taffy-like paste, to a moldable putty (Figure 1). Over the next 24 hours polymerization continues, ultimatelyformingarigid polymer. One of the chemical reactions generates carbon dioxide gas, which remains entrapped within the viscous material and forms a porous networkresembling human cancellous bone. Figure 1: As it polymerizes the Kryptonite material transitions from an injectable viscous liquid to a sticky taffy-like consistency, to a moldable putty and ultimately to a rigid solid. The KryptoniteTM material is manufactured by Doctors Research Group, Inc. (Southbury, CT) and was first used in Europe in 2006. Through 2009,the material has been used in more than 3000 clinical cases and no adverse events related to biocompatibility have been reported. The material has received FDA marketing authorizationfor cranial applications and is CE marked (see the package insert for market specific Indications for Use). Figure 2 depicts use of the material for filling a cranial defect that resulted from a motor vehicle accident. In this case the material was applied in the sticky, taffy-like state and contoured to fit the surrounding bone. A description of the surgical technique and reports on early clinical experience in cranioplasty applications are available from Doctors Research Group. Figure 2: The Kryptonite material can be applied to defects of the skull. To be effective, a bone void filling device must exhibit two key features; a favorable chemical environment and an appropriate structure. This article presents evidence that the Kryptonite material meets both criteria from several sources of scrutiny. First, a reviewof published literature pertaining to implantable castor oil polymers reveals the high potential for this class of material to serveas a biocompatible bone filler.