System for and method of processing bone material using supercritical fluids

A method of processing bone material using supercritical fluids is disclosed. The method comprises placing the bone material in a processing chamber, adding supercritical fluid to the processing chamber, pulsing the supercritical fluid in the processing chamber, and rinsing the bone material. A processing system for processing bone material using supercritical fluids in accordance with the present invention comprises a processing chamber for housing the bone material, a vat for storing a processing fluid, a pump, a heating element, a flow path, a tank, and a solvent port.

FIELD OF THE INVENTION

The present invention relates generally to the field of processing organic donor material. More specifically, the present invention relates to a system for and a method of processing bone material using supercritical fluids.

BACKGROUND OF THE DISCLOSURE

The treating and processing of bone material is becoming increasingly important as the demand for bone implants and grafts (hereinafter “bone grafts” or “grafts”) rises. Bone material must be processed properly; otherwise, disastrous consequences may result from implants of improperly processed bone material into a host. Such disastrous consequences include but are not limited to: a host's immunogenic response to the graft, a host's rejection of the bone graft altogether, the possible transfer of diseases and infectious agents from the donor to the host due to unclear bone grafts, prolonged recovery time for the host, and multiple avoidable operations on the host to remove an improperly processed bone graft. To avoid such problems, bone material must be properly processed to selectively eliminate fats, proteins, donor cells, viruses, bacteria, and the like, before the bone material can be successfully implanted into the host.

Conventionally, the processing of bone material includes a number of steps.FIG. 1shows a flow chart100of the steps using the conventional method of processing bone material as disclosed in the prior art. In the step101, the bone material is obtained from a donor. In the step110, the bone material is degreased by placing it into a container of acid or acetone. In the step120, the bone material is rinsed using a rinse medium, such as a water bath. Next, in the step130the bone material is oxidized, where the bone material is sterilized from viruses and the like. Usually, this oxidizing step requires the bone to be treated with hydrogen peroxide. In the step140the bone material is rinsed again. In the step150, the bone material is treated with a base for protein removal. In the step160, the bone material undergoes yet another rinse. Then, in the step170, the bone material is dried using some type of alcohol or acetone. Optionally, in the step180, the bone material is treated with gamma radiation. In the step190, the final product resulting from the conventional method is a white, bleached sterile demineralized bone matrix, which oftentimes has denatured collagen and lacks bone morphogenic proteins (BMPs), which are growth factors key to bone osteoconductivity and osteoinductivity.

The conventional method falls short in providing the ideal bone graft. The ideal bone graft is one that is both osteoconductive and osteoinductive. Osteoconductivity and osteoinductivity are two vital mechanisms for the regeneration and rebuilding of bone. Osteoinductivity refers to the ability to build, heal and regenerate bone in humans, and this is realized through active recruitment of host stem cells from surrounding tissue, which differentiate into bone-forming osteoblasts. Growth factors, particularly BMPs, aid and stimulate bone osteoinductivity. Collagen found inside the bone material provides an exceptional osteoinductive substrate for bone formation. To be osteoinductive, the ideal bone graft must contain undamaged BMPs and collagen. In contrast with osteoinductivity, osteoconductivity refers to the ability of a bone graft to form a scaffold or a structure on which the host's cells are able to form new bone. Thus, the ideal bone graft is both osteoinductive and osteoconductive, since such a graft allows for new bone to form at the implant site and further provides structural support for the formation and incorporation of the new bone.

The disadvantages of the conventional method are several-fold. First, the conventional method requires several separate processing chambers for the bone material to be processed, using a multitude of chemicals, some of which are toxic. For instance, acetone can be used for the degreasing step, step110, and the drying step, step170, of the conventional method, and yet in some countries, acetone is a prohibited processing agent due to its toxicity. Second, the conventional method can be expensive, labor-intensive, and time-consuming, given the numerous steps and various processing agents that are required. Also, the number of steps required by the conventional method increases the likelihood that some type of error will occur and the bone material will be improperly processed. Further, the oxidizing step, step130, of the conventional method destroys the BMPs in the bone, leaving a sterile mineral matrix. Finally, the base step of the conventional method, step150, can denature collagen and destroy BMPs. By denaturing collagen and killing growth factors, such as the BMPs, the conventional method unfortunately can result in a decrease of both the osteoconductivity and osteoinductivity of the bone material, which translates into a longer time for the bone material to incorporate properly into the host body or a complete rejection of the bone material.

In U.S. Pat. No. 5,725,579, issued to Fages et al, entitled “Process for Treating Bone Tissue and Corresponding Implantable Biomaterials,” issued Mar. 10, 1998, it was disclosed that the degreasing step, step110, and the rinse step, step120, of the conventional method (FIG. 1) can be replaced by a single step of treating a bone material with supercritical fluid. However, under Fages, the remainder of the conventional method steps, namely, the steps130,140,150,160, and170(FIG. 1), must follow after treating the bone material with supercritical fluid, for the cleaning process to be completed.

SUMMARY OF THE DISCLOSURE

In accordance with the present invention, a method and apparatus for processing organic donor material is disclosed. In some embodiments of the present invention, a method of processing bone material using supercritical fluid comprises four steps. In the first step, the bone material is placed in a processing chamber. In the second step, supercritical degreasing is performed. In the third step, supercritical pulsing is performed. In the fourth step, a supercritical drying step is performed. The resulting bone material is both osteoinductive and osteoconductive, making it an ideal bone graft for implantation. All these steps are performed in situ in the processing chamber. The steps can be performed automatically, thus, dramatically reducing labor costs.

In some embodiments, a supercritical pulsing step, alone, presents useful improvements to the field of organic donor material processing. In other embodiments of the present invention, a supercritical drying step, alone, presents useful improvements to the field of organic donor material processing. In yet other embodiments, a step of exposing organic donor material to high energy radiation, such as gamma-ray radiation, is performed.

The present invention also includes a processing system for processing bone material using supercritical fluid. The processing system comprises a processing chamber, a vat, a pump, a heating element, a flow path, a tank, and a solvent port. The processing chamber houses the bone material to be processed. The vat is coupled to the processing chamber through a flow path. In operation of the system, a processing fluid flows through the flow path from the vat to the processing chamber. According to the preferred embodiment, once the processing fluid successfully enters the processing chamber, the processing fluid undergoes pressure pulsing and temperature pulsing with the help of the pump and the heating element, respectively. The processing fluid can thus fluctuate from its supercritical and nonsupercritical states based on the effects of the pulsing. Finally, the bone material is rinsed to dry it properly. The rinsing agent in the preferred embodiment is a mixture of CO2and alcohol, which is added to the processing chamber through the flow path. The alcohol enters the flow path from the tank through the solvent port. Optionally, gamma radiation can also be applied to the bone material.

DETAILED DESCRIPTION

The present invention discloses a method of and a system for processing organic donor material using supercritical fluids, such as supercritical CO2. In the preferred embodiment of the present invention, the organic donor material is bone material. Supercritical fluids have surprisingly efficient extraction and cleaning capabilities, particularly with bone material. Supercritical fluids are superior to most chemicals used in the conventional bone material processing method, because supercritical fluids can infuse bone material like a gas and dissolve undesirable substances, such as fat, bacteria, and viruses, like a liquid. Furthermore, supercritical fluid extraction and processing can be controlled by adjusting certain variables, such as pressure and temperature, so that selected contaminants can be extracted, while leaving desired bone components (such as collagen and growth proteins) unharmed in the final matrix product of the material.

FIG. 2Aillustrates a processing sequence200for processing organic donor material in accordance with the preferred embodiment of the invention. At the start step201, bone material is provided. In some embodiments of the present invention autografts are provided. In other embodiments of the present invention, allografts, isografts, or xenografts are provided. In the preferred embodiment, the bone material is an allograft, from a human donor or a cadaver, intended for implantation into a human host. At the step210, the bone material to be processed is placed in a processing chamber. In the preferred embodiment of the present invention, a single processing chamber is used throughout the processing sequence200.

Next, a supercritical degreasing step220is performed. The degreasing step220involves delivering a supercritical fluid along with a degreasing chemistry to the processing chamber that holds the bone material. The degreasing chemistry aides in bone degreasing and in extracting liquids from the bone matrix. Preferably, the supercritical fluid is supercritical CO, and the degreasing chemistry is an alcohol, such as acetone. It is well known that CO2reaches its supercritical state when the temperature is above 30.5 degrees Centigrade and the pressure is above 1070.4 psi. The degreasing step220concludes with flushing the supercritical fluid and degreasing chemistry from the processing chamber.

Next, a supercritical pulsing step230is performed. The supercritical pulsing step involves delivering substantially pure supercritical fluid to the processing chamber and pulsating the fluid. Preferably, the supercritical fluid is supercritical CO2. The pulsing of the supercritical fluid inside the processing chamber involves fluctuating the pressure of the supercritical fluid, fluctuating the temperature of the supercritical fluid, or a combination thereof. Pulsing the supercritical fluid is performed to kill and extract contaminants, such as bacteria, donor cells, viruses, and the like which are present within the bone material.

In some embodiments of the present invention, supercritical CO2fluctuates in a cycle from its supercritical state to its nonsupercritical state, through the varying ranges of pressure and temperature. Alternatively, pulsing can occur from a first supercritical pressure and a second supercritical pressure. However, it will be readily apparent to those having ordinary skill in the relevant art that a number of temperature and pressure fluctuations may be used to kill the contaminants present in the bone material.

The destruction of the contaminants occurs as the supercritical fluid infuses into the undesirable contaminants. Once infused into the contaminants, the step of pulsing pressure and temperature cause the membranes of the contaminants to explode or implode. In a preferred embodiment, the pulsing step is rapid, which in turn causes the supercritical fluid to disrupt, lyse and crack the walls of bacteria, viruses, donor cells, and the like. The supercritical pulsing step present clear advantages over the bacteria killing step practiced in the prior art because, unlike the use of an oxidizer to eliminate contaminants and a base chemistry to remove proteins, using a supercritical pulsing step eliminates unwanted contaminants, but does not destroy collagen, Bone Morphogenetic Proteins (BMPs), or other growth factors.

An additional benefit of the supercritical pulsing step230includes agitating contaminants present within the bone matrix, causing the contaminants to be removed from the bone matrix. In addition to killing contaminants, it is also beneficial to the osteoconductive and osteoinductive processes to remove dead contaminants from the bone matrix.

Another benefit of the supercritical pulsing step230lies in the ability of supercritical fluid to destroy prions. Prions are misshapen proteins typically found in fat that are thought to be linked with neurodegenerative diseases, such as mad cow disease, fatal familial insomnia, Gerstmann-Straussler syndrome, and Creutzfeldt-Jakob disease, to name a few. Prions are extremely difficult to kill, and under the conventional method (FIG. 1), strong oxidizers at the step130are used to accomplish this task. However, strong oxidizers in the conventional method can be advantageously replaced by supercritical fluids in the present invention, since supercritical fluids also eliminate prions. Thus, the use of supercritical fluid as an extractor of contaminants, including prions, at the step230(FIG. 2) in accordance with the present invention, prevents the transfer of diseases from the donor to the host via a bone transplant, without the disadvantage of using a multitude of strong, sometimes toxic chemicals.

The supercritical pulsing step230ends with flushing the fluid and the contaminants from the processing chamber. In some embodiments of the present invention a recirculation loop system is utilized to reuse supercritical fluid after the contaminants and the supercritical fluid exit the processing chamber. In some embodiments of the present invention, the contaminants are filtered out from the supercritical fluid using a filter, and the remaining supercritical fluid reenters the processing chamber through a loop, for the supercritical fluid to be reused for another next cycle.

In an alternative embodiment, the supercritical fluid enters the processing chamber through a flow path. Through pulsing, the supercritical fluid extracts the contaminants, which separate from bone material without a filter or a recirculation loop. For instance, contaminants can separate from bone material through condensation, preferably in one processing chamber. Those skilled in the art will also recognize other processes for separating contaminants from bone material, without using filtration or recirculation systems.

Next, at the step240, the bone material is dried using supercritical fluid and a drying chemistry. In some embodiments of the present invention, a combination of supercritical CO2and alcohol is used for the proper rinsing of the bone material. In some embodiments of the present invention, acetone is used as the drying chemistry. The use of the supercritical drying step presents clear advantages over the prior art because using supercritical fluid for the delivery of the drying chemistry allows the drying agent to more-fully permeate the bone matrix to remove unwanted moisture. This step of drying is important due to the adverse effects of left over moisture with the bone matrix such as the prevention of cell migration through the structure (resulting in a decreased osteoconductivity) and the cracking of the bone structure as the bone material is cooled down to preserve the graft, among other negative effects. Finally, at the step250, the bone material is ready to be implanted into the host's body.

Although the preferred embodiment of the present invention comprises a process including a supercritical degreasing step, a supercritical pulsing step and a supercritical drying step; it will be clear to those having ordinary skill in the art that the pulsing step, alone, presents useful improvements over the prior art. As explained, utilizing a process of pulsing a supercritical fluid to kill contaminants provides a clear improvement over the prior art in that the final product is the ideal bone graft material; that is, it is not only osteoinductive and osteoconductive (since its collagen and BMPs are still intact), but it is also clean of contaminants, such as viruses, bacteria, donor cells and the like.

Furthermore, it will be clear that the supercritical drying step also stands on its own and provides useful improvements over the prior art. Utilizing a supercritical fluid along with a drying agent allows the drying chemistry to more fully permeate the bone structure to remove unwanted moisture from the bone matrix.

FIG. 2Billustrates an alternative processing sequence299for processing bone material in accordance with the preferred embodiment of the invention. The alternative processing sequence299is substantially similar to the processing sequence200with one additional step. Specifically, the alternative processing sequence involves: the start step201′ of obtaining bone material, a step210′ of placing bone material into a processing chamber, a supercritical degreasing step220′, a supercritical pulsing step230′, and a supercritical drying step240′. Furthermore, after the supercritical drying step240′, a gamma radiation step245′ occurs as the bone material is bombarded with gamma radiation. At the step250′, the bone material is ready to be implanted into the host's body.

FIG. 3Aillustrates a processing system300for processing bone material310using a processing fluid320, in accordance with some embodiments of the present invention. The processing system300comprises a processing chamber330, a vat340, a pump350, a heating element360, a flow path370, a tank380, and a solvent port390. The processing chamber330is coupled to the vat340through the flow path370. The pump350and the heating element360are coupled to the processing system300. The tank380is coupled to the flow path370through a solvent port390.

Initially, the processing chamber330houses the bone material310to be processed. In the preferred embodiment, the bone material310is an allograft from a human donor intended for a human host. WhileFIG. 3illustrates a processing system300having a single processing chamber330, it will be apparent to those skilled in the art that the processing system300can comprise any number of processing chambers for performing multiple processes on bone material or for concurrently processing multiple bone materials.

Processing fluid320is directed to the processing chamber330through the flow path370. In some embodiments of the present invention an agent is added to the processing fluid320before entering the processing chamber. According to the preferred process200, an agent400is added to a portion of processing fluid320from the tank380through the solvent port390. In some embodiments of the present invention, the agent is a degreasing agent such as acetone, however, those having ordinary skill in the relevant art will appreciate that any degreasing agent is similarly applicable. The degreasing agent is mixed with the supercritical fluid320to form a degreasing chemistry. The degreasing chemistry is directed into the processing chamber330to achieve the supercritical degreasing step220.

Also, according to the preferred process200, the degreasing agent is flushed from the processing chamber330and the supercritical pulsing step230begins. According to this step, supercritical fluid320flows from the vat340through the flow path370and into the processing chamber330. Once the processing fluid320successfully enters the processing chamber330, the processing fluid320undergoes pulsing to begin the extraction of the contaminants contained on or within the bone material310.

The term “pulsing” in reference to the processing system300refers to the fluctuation of the processing fluid320, such as CO2, between its nonsupercritical state and its supercritical state or from one supercritical pressure and another supercritical pressure. As a result of pulsing the processing fluid320, undesirable contaminants are extracted. Pulsing can be done any number of ways. Preferably, pulsing can be accomplished by fluctuating the pressure of the processing fluid320with the help of the pump350. Alternatively, temperature pulsing can be applied to the processing fluid320with the heating element360. In yet another alternative embodiment, both pressure pulsing and temperature pulsing can be accomplished with the help of the pump350and alternatively the heating element360, respectively.

In the preferred embodiment, the processing fluid320infuses into the undesirable contaminants and, if necessary, lyses those contaminants. Such contaminants include but are not limited to viruses, bacteria, donor cells, prions and the like.

Also, according to the preferred process200, the supercritical fluid320used in the supercritical pulsing step230is flushed from the processing chamber330and bone material310is subjected to a supercritical drying step240to dry it properly. The drying agent in the preferred embodiment is a mixture of the processing fluid320and an alcohol. Preferably, the processing fluid320is CO2. The processing fluid320flows from the vat340through the flow path370to the processing chamber330. An agent400, such as an alcohol, flows from a tank380through a solvent port390to the flow path370. Once it reaches the flow path370, the agent400mixes with the CO2, and the mixture of the agent400and CO2finally reaches the processing chamber330. It will be apparent to those skilled in the art that the rinsing agents can be any agents that cleanse the bone material310and leave it dry for proper implantation into the host.

In some embodiments, the agent400is the same agent used in the degreasing step. In the preferred embodiment, the agent400is acetone. In some embodiments, multiple agents are utilized and are delivered to the flow path370via multiple tanks (not shown) and solvent ports (not shown).

In some embodiments of the present invention, following the application of the rinsing agents, gamma radiation can also be applied to the bone material310. After its processing through the processing system, the final product is a bone material that is both osteoinductive and osteoconductive, making it an ideal bone graft for implantation. Such an ideal bone graft translates to a shorter healing time for the host, fewer post-implant operations, shorter hospital stays, and less expense for the host.

It will be readily apparent to one skilled in the art that various modifications may be made to the embodiments without departing from the spirit and scope of the invention. For instance, a recirculation loop, additional chemistry vats, or the like can be optionally added to the processing system.

FIG. 3Billustrates a processing system300′ for processing bone material310′ using a processing fluid320′ in accordance with some embodiments of the present invention. The processing system300′ comprises a processing chamber330′, a vat340′, a pump350′, a flow path370′, a valve371′, a first chemistry tank380′, a second chemistry tank382′, a mixer385′, a recirculation loop375′, and components395′ and396′.

As shown inFIG. 3B, the vat340′, the first chemistry tank380′ and the second chemistry tank382′ are coupled to the mixer385′. A valve381′ is provided between the first chemistry tank380′ and the mixer385′ to optionally ensure that fluid delivered to the mixer385′ from the first chemistry tank380′ possesses some prerequisite pressure. Likewise, a valve383′ is provided between the second chemistry tank382′ and the mixer385′. In some embodiments of the present invention, heaters (not shown) heat the chemistry contained within the chemistry tanks to heat the chemistries to some prerequisite temperature.

The mixer385′ is configured to receive and mix processing fluid320′ from the vat340′ and one or more chemistries from the first chemistry tank380′ and/or the second chemistry tank382′. The mixed fluid is delivered via the flow path370′ to the processing chamber330′. A valve331′ is positioned between the mixer385′ and the processing chamber330′ to optionally ensure that fluid delivered from the mixer385′ to the processing chamber330′ possesses some prerequisite pressure. In some embodiments of the present invention, the valve331′ is dynamically controllable to vary the pressure of the fluid delivered to the processing chamber in order to accomplish the pulsing step, as explained above. Likewise, a heating element360′ is coupled to the processing chamber330′ and the heating element360′ is dynamically controllable to vary the temperature of the fluid delivered to the processing chamber in order to accomplish the pulsing step, as explained above.

According toFIG. 3B, the fluid in the processing chamber330′ exits the processing chamber330′ into a recirculation loop375′. A number of valves376′ are positioned within the recirculation loop375′ to control pressure. Also contained within the recirculation loop375′ are components395′ and396′. Components395′ and396′ can include, but are not limited to separator, filters or the like. In some embodiments of the present invention, outlet lines398′ and399′ are coupled to the components395′ and396′, respectively.

In some embodiments of the present invention, contaminants are filtered out from the processing fluid, leaving remaining fluid. The recirculation loop375′ is configured such that the remaining fluid reenters the flow path370′ to be reused for the next processing cycle. Any number of cycles and types of filters necessary to extract undesirable contaminants of bone material can be used, based on the application at hand.

Reference has been made in detail to the preferred and alternative embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention has been described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention. Furthermore, in the detailed description of the present invention, numerous specific details have been set forth in order to provide a thorough understanding of the present invention. However, it should be noted that the present invention may be practiced without these specific details. In other instances, well known methods, procedures and components have not been described in detail as not to unnecessarily obscure aspects of the present invention.