Abstract:
An implantable bioartificial active secretion system for providing a physiological secretion such as insulin necessary for functionality of a physiologic activity such as glucose metabolism of a living-being host. The system includes a housing implantable within the host in fluidic communication with tissue fluid indicative of secretion need. A chamber within the housing contains a plurality of physiologically active, autonomously functioning, live secretory cells for producing the physiological secretion. A periodically operating pump apparatus moves tissue fluid into contact with the secretory cells for pick up of the regulating physiological secretion for subsequent physiologically-effective dispensing into the host while avoiding immunorejection of the host body or of the host to the secretory cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not Applicable). 
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     (Not Applicable). 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to implantable devices for providing medically required treatment regimens over a period of time, and in particular to an implantable bioartificial active secretion system comprising live secretory cells providing a physiologically-required secretion to a living-being host patient in response to specific respective needs of the patient as determined by the live secretory cells in response to physiological make-up of host tissue fluid in contact with the secretory cells. 
     Natural production of numerous agents, metabolites, enzymes, and other secretions occur within a living being host as physiological events take place. One such event is the metabolism of carbohydrates which is controlled mainly by insulin which is produced by beta cells of the islets of Langerhans within the pancreas. In addition to its principal role in carbohydrate metabolism, insulin also significantly affects lipid, protein, and mineral metabolism in addition to the metabolism of carbohydrates prior to their ultimate break-down to glucose. When efficient insulin production by the pancreas is inhibited or terminated and therefore insufficient, as occurs substantially in Type I diabetes, for example, where immune cells of the host infiltrate the islets of Langerhans and eventually destroy the beta cells by T-cell-mediated mechanisms, insulin from another source must be provided or the affected individual will suffer from many severe consequences of diabetes mellitus. 
     Prior-art approaches for providing insulin to maintain proper plasma glucose concentrations are numerous. One of the most commonly employed is the injection of insulin into the patient a plurality of times daily in response to plasma-glucose monitoring. Subcutaneous injection is a usual insulin introduction route, but is flawed and/or dis-favored for several reasons. In particular, injection administration is limited because there is no direct feedback between blood glucose level and the dosage of insulin. In addition, there is poor patient acceptance, significant absorption variability among patients, potential overdosing resulting in hyperinsulinemia/hypoglycemia, potential underdosing resulting in hypoinsulinemia/hyperglycemia, formation of anti-insulin antibodies, hypersensitivity reactions due to insulin formulations, and other untoward occurrences. Relatively new jet injector devices, as opposed to traditional syringes, do not appreciably avoid syringe-injection limitations as noted above. Orally administered insulin finds poor effectiveness because of the vast variability found in digestive processes and digestion states among patients. 
     Another prior art approach for providing insulin to patients is the provision of wearable or implantable insulin pumps which are pre-programmed and pre-loaded with insulin, therefore there is no direct feedback of optimal dosage. Unfortunately, however, these pumps can cause both mechanical and physiological problems for the patient. With respect to the former problem, these pumps can experience catheter blockage, infection, skin inflammation, erosion, local fluid accumulation, dislocation due to patient physical activity, and required regular refills of insulin usually at monthly or bimonthly intervals. With respect to the latter problem, presently available insulin pumps do not have reliable glucose sensors and therefore are unable to precisely dispense a needed insulin quantity for proper plasma-glucose level maintenance. 
     Yet another prior art approach for treating insulin deficiency is the transplantation of pancreatic beta cells to the pancreas, liver, muscles, or peritoneal cavity of the patient, or the transplantation of an entire donor-pancreas as a replacement. Such an approach, however, many times is not practical because of recipient immune-rejection, limited availability of donor organs, and other restraints on patient acceptance. 
     In view of the above inability of prior art approaches to artificially provide a natural imitation of a physiological secretion, it is apparent that a highly important need is present first for sensing an in vivo need for a secretory product, and second for fulfilling that need by providing an appropriate quantity of secretory product. Accordingly, a primary object of the present invention is to provide an implantable bioartificial active secretion system for providing, in vivo, a physiological secretion necessary for functionality of a physiologic activity dependent upon that secretion. 
     Another object of the present invention is to provide an implantable bioartificial active secretion system wherein physiologically active, autonomously functioning, live secretory cells for producing the physiological secretion are protected from immune destruction by the host while sensing and responding to functional need. 
     Still another object of the present invention is to provide an implantable bioartificial active secretion system wherein tissue fluid of the host is introduced to the live secretory cells for cell-secretion uptake and subsequent delivery for distribution within the host. 
     These and other objects of the present invention will become apparent throughout the description thereof that now follows. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an implantable bioartificial active secretion system for providing a physiological secretion necessary for functionality of a physiologic activity of a living-being host. The system first includes a housing having an inlet with an external opening thereto and an outlet with an external opening therefrom. This housing is implantable at least partially within the host such that the inlet and outlet openings are positionable in fluidic communication with tissue fluid of the host and the tissue fluid can be received into the housing and thereafter dispensed from the housing. A chamber is disposed within the housing between the inlet and outlet and in communication therewith, and contains a plurality of physiologically active, autonomously functioning, live secretory cells for producing the physiological secretion. Also disposed within the housing is a periodically-operating pump apparatus for drawing initial tissue fluid through the inlet from the host for contact with the physiologically active cells within the chamber for pick up and regulation of the physiological secretion, and for dispensing resulting tissue fluid bearing the physiological secretion through the outlet and into the host. Finally, inlet and outlet filter systems in operational communication with the external openings of the inlet and outlet have openings therethrough sized for prohibiting passage of immune system cells, immunoglobulins, and complement system components of the host. 
     The tissue fluid drawn to be in contact with the live secretory cells must generally reflect host requirements for the particular physiological secretion. Thus, in treating diabetes for example, peritoneal fluid is drawn since it is known that peritoneal fluid reflects blood glucose levels, whereby peritoneal fluid contacts secretory cells that are pancreatic beta cells which produce insulin for peritoneal-fluid uptake and return for routing to regulate such glucose levels. The secretory cells preferably are encapsulated with a permeable medium through which cellular nutrient as well as cellular metabolic waste can pass and likewise through which the physiological secretion can pass, but not through which immune system cells can pass on the off-chance that such cells passed through the inlet filter. Encapsulation increases the loading density of the cells and their surface interaction with the fluid. Depending upon the specific application, secretory-cell life span many times can be up to about two years, after which time replacement cells are introduced. 
     The pump apparatus preferably includes a plurality of sequentially disposed, peristaltic-like activated and deactivated, elasticized pump tubes for peristaltic-like moving therewithin the initial tissue fluid and the tissue fluid bearing the physiological secretion through the housing. Simultaneously, the preferred arrangement of the plurality of secretory cells is such that sub-pluralities thereof are disposed on a tray, a plurality of trays are situated into a column, and a plurality of columns are horizontally spaced from each other with respective inter-column spaces there between wherein pump tubes are situated. Peristaltic-like pumping can be accomplished electromagnetically by a programmed controller disposed with the housing and thus implanted, or by a programmed controller situated outside the patient and in proximity to the implanted housing. In either configuration, power is intermittently applied to replicate peristaltic movement of tissue fluid through the pump tubes and thus in moving contact with the live secretory cells situated within the housing. The tissue fluid must reflect whether a need is present for the particular secretion provided by the secretory cells (e.g., glucose level for insulin-secreting cells), whereby the secretory cells will naturally respond to the conveyed need and automatically produce a quantity of secretion specific to this need as sensed by the secretory cells. This secretion is picked up by the tissue fluid as it contacts the secretory cells, and thereafter is delivered within the host. Finally, when the tissue fluid indicates less need for the secretion (e.g., the required activity of the secretion has been completed for the time being), such reduced need is sensed by the secretory cells as the tissue fluid continues in contact therewith, and the secretory activity naturally ceases. 
     As is apparent, the implantable bioartificial active secretion system here defined significantly replicates natural metabolic function by employing live secretory cells as both sensor and provider of physiologic balance. Such live-cell employment eliminates external guess work with respect to quantity and timing of secretion-product injection or other type introduction since actual cells make a natural determination of need followed by a natural production and natural release of an exactly-necessary quantity of the secretory product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings in which: 
     FIG. 1 is a top plan view of an implantable bioartificial active secretion system housing; 
     FIG. 2 is a top plan cut-away view of the housing of FIG. 1; 
     FIG. 3 is an enlarged side elevation view of the secretion system; 
     FIG. 4 a  is an end elevation view in section of a first configuration of a nano-capillary filtration bundle; 
     FIG. 4 b  is an end elevation view in section of a second configuration of a nano-capillary filtration bundle; 
     FIG. 5 is a partial perspective view of a tray containing secretory cells; 
     FIG. 6 a  is an end elevation view of a peristaltic pump mechanism; 
     FIG. 6 b  is a perspective view of a portion of a memory alloy sheet; and 
     FIG. 7 is a partial side elevation view in section of an exteriorly powered secretion system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-6 a , an implantable bioartificial active secretion system housing  10  has an inlet  12  with an external inlet opening  14  thereto and an outlet  16  with an external outlet opening  18  therefrom, with each outlet  18 ,  16  having respectively therewith an inlet external filter  20  (shown in FIG.  1 ), an outlet external filter  22  (shown in FIGS.  1  and  2 ), and nano-capillary bundles  15 ,  17  therewithin (shown in FIGS.  2  and  4 ). The external filters  20 ,  22  function as prefilters that control inflow and outflow of fluids and have apertures sized to address entry of larger immune cells of the host. Liquids have generally unimpeded access through the filters  20 ,  22  while the preferred configuration of a mushroom-shape tip permits easy anchoring without tissue damage as the lower border of the mushroom configuration hooks into, for example, the wall of the peritoneal cavity of the host. Additionally, the configuration of the external filters  20 ,  22  functions to prevent clogging of the nano-capillary bundles  15 ,  17  and to provide insulin distribution. The nano-capillary bundles  15 ,  17  are constructed of glass or silica for filtration protection against entry of immune system cells, immunoglobulins, and complement system components of a host living being. As illustrated in FIGS. 4 a  and  4   b , capillaries  13  of the bundles  15  (and  17 ) can be arranged in a quadrangular configuration (FIG. 4 a ) or in triangular configuration (FIG. 4 b ) in reference to each other. The housing  10  and external filters  20 ,  22  are fabricated of a biocompatible polymer as known in the art. 
     Disposed within the housing  10  and in fluidic communication with the inlet  12  and outlet  16  is a chamber  26 . Within the chamber  26  are housed a plurality of columns  28  of trays  30  wherein each tray  30  has thereon a sub-plurality of insulin secretory cells  32  such as provided by islet of Langerhans beta-cells or by pancreatic tissue cumulative to a plurality of such secretory cells  32  disbursed among the several trays  30  throughout the chamber  26 . Situated adjacent each column  28  of trays  30  are respective elasticized pump tubes  36  preferably of rectangular cross-section as shown in FIG. 6 a , each in fluidic communication with the trays  30  of the columns  28  on either horizontal side. Between the tubes  36  are respective electromagnetically-driven peristaltic pump mechanism members  38  for moving fluid (liquid) through the housing  10 . Each member  38  includes a series of inductor coils  42  disposed above each respective tube  36  as particularly shown in FIG.  3 . Immediately below the tubes  36  are permanent magnets  48 , while immediately outside the housing  10  is a conventional battery pack  44  with standard wiring (not shown) leading to the inductor coils  42 . A standard microprocessor  46  is programmed to provide sequentially-timed, intermittent, electrical charge to the inductor coils  42  whereby, upon power application, the tubes  36  below the respective inductor coils  42  have pressure exerted thereon because of attraction of the inductor coils  42  to the permanent magnets  48  to thereby compress these tubes  36  and force fluid therein through the tubes  36  to a subsequent column  28  of trays  30  for direct contact with the secretory cells  32  of respective trays  30  so contacted. Once compression of the tubes  36  has occurred, electrical charge to the involved inductor coils  42  is discontinued and the so-compressed tubes  36  expand to their original configuration while simultaneously creating suction to draw fluid from a preceding column  28  of trays  30  therein for a subsequent repeat of the sequential pumping as above described. A sheet  40  (FIGS. 6 a  and  6   b ) of non-magnetic memory alloy (e.g. nickel-titanium) typically is situated between the inductor coils  42  and tubes  36  such that the alloy is electromagnetically forced toward the permanent magnets  48  (and therefore the capillary tubes  36 ) to accomplish uniform compression of the tubes  36  during pumping activity. Cessation of electrical power to the involved inductor coils  42  withdraws the coils  42  from movement-attraction to the permanent magnets, and the memory alloy sheet  40  returns to its original non-distorted configuration. As illustrated in FIGS. 6 a  and  6   b , the sheet  40  preferably is cross-sectionally shaped to enhance collapse against the tube  36  upon application of charge in the coils  42 . 
     While the embodiment described above with respect to FIGS. 1-6 has an integral power source, a second embodiment, illustrated in FIG. 7, provides for an externally-disposed, wearable power source  58  operating an internally-disposed system substantially identical to the system of the first embodiment except for non-presence of an implanted electrical power source and for construction of the pump assembly. In particular, with respect to the latter, FIG. 7 illustrates construction of one version of the pump tube  60  which includes a series of dielectric arms  62  extending from the floor  64  of the tube  60 , with each such arm  62  having applied at its distal end a magnetic alloy or permalloy coating  66 . When the power source  58  is activated, the magnetic flux thereby generated causes the dielectric arms  62  within the tube  60  to move toward the flux. Subsequently, when flux generation is discontinued, the arms  62  return to their original positions. Control circuitry of the power source  58  is such that sequential arm movements occur and thereby move fluid with a sweeping action through the tube  60  for contact with secretory cells as earlier described in connection with the first embodiment. 
     Operability is here non-limitedly exemplified in the physiologically beneficial delivery-on-demand of insulin for glucose metabolism within a patient suffering from Type I diabetes. Particularly, the system housing  10  functions in the capacity of an artificial pancreas and is implanted at a site within the peritoneal cavity such that peritoneal fluid can enter the housing  10 . The housing  10  can be located subcutaneously and be anchored to the anterolateral region of the iliac crest bone by a bone anchor system as known in the art with catheter penetration through the peritoneal fascia and into the peritoneal cavity. This placement permits relatively easy, rapid, and complete retrieval in the event of any implant failure or malfunction. Implantation into the anterolateral subcutane abdominal region is carried out under local anesthesia. It is to be noted that peritoneal fluid is chosen for insulin-need determination because a change of glucose concentration in peritoneal fluid is in the same direction, same amount, and relatively same time factor as in blood. The peritoneal fluid travels through the inlet filter  20 , inlet opening  14 , and nano-capillary bundle  15  within the inlet  12  to the chamber  26  for entry into a first row  34  of pump tubes  36  and subsequent periodic pumping action that provides continuous microcirculation and drives the fluid to a first column  28  of trays  30  for contact with insulin secretory cells  32  which can be present as beta-cells or as tissue as described above. 
     In the preferred embodiment, groups of cells  32  are gelled-alginate encapsulated in bead configurations each having a diameter from about 50 to about 200 microns, with total count for the entire chamber  26  of at least about 1,000,000 cells. Each tray  30  preferably is fabricated of silicon or quartz material with wells etched into the surface for housing the secretory cells  32 . The trays  30  preferably are clamped into stack configurations and are removable and replaceable as secretory cell life eventually expires. Movement of the peritoneal fluid continues through the chamber  26  for contact with each successive column  28  of trays  30  bearing the insulin secretory cells  32 , as these secretory cells  32  naturally react to the glucose level of the peritoneal fluid and naturally secrete insulin into the peritoneal fluid as determined by the secretory cells  32  to be needed for proper glucose metabolism. Additionally, oxygen and nutrients are passed to the secretory cells  32  while metabolic waste from the secretory cells  32  passes into the peritoneal fluid. Upon completion of travel through the chamber  26 , the peritoneal fluid moves to the outlet  16 , through the nano-capillary bundle  17 , external outlet opening  18  and outlet filter  22  for final reintroduction into the peritoneal cavity and final delivery to the circulatory system through normal and on-going routing for insulin delivery and use as well as elimination of secretory-cell waste products. Secretory-cell life spans are, of course, dependent upon a number of factors including proper nutrition and oxygen delivery, waste product removal, and extent of secretion called for by the host being. When cell effectiveness diminishes or ceases, however, the housing  10  is relatively easily retrieved and the columns  28  of trays  30  are easily removed and replaced by fresh units, with the housing  10  then returned to its implanted site. 
     As is apparent from the above description, the secretion system here defined bioartificially emulates a naturally occurring secretion system by providing live secretion-producing cells for sensing and producing secretions at levels naturally determined because of such live authenticity. In addition to such implantation of secretion-producing cells, other media, including drugs, medicines, and/or enzymes, for treating or preventing diseases in accord with physiological demands, can likewise be administered by employing the system here described and within which the chosen media is placed. Thus, while these illustrative and presently preferred embodiments of the invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.