1 ENGINEERING THE BIOINTERFACE FOR ENHANCED 2 BIOELECTRODE AND BIOSENSOR PERFORMANCE 3 BY BUDDY D. RATNER 4 5 THE MODERATOR: I'D AGAIN LIKE TO WELCOME 6 YOU TO THE SECOND OF THE SERIES OF TUTORIAL SESSIONS 7 FOR THE NATIONAL ACADEMIES KECK FUTURES INITIATIVE ON 8 SMART PROSTHETICS. IT'S MY PLEASURE TO INTRODUCE OUR 9 SECOND SPEAKER, DR. BUDDY RATNER. HE'S THE DIRECTOR OF 10 THE UNIVERSITY OF WASHINGTON ENGINEERED BIOMATERIALS 11 AND PROFESSOR OF BIOENGINEERING AND CHEMICAL 12 ENGINEERING AT THE UNIVERSITY OF WASHINGTON. HE'LL BE 13 SPEAKING ABOUT ENGINEERING THE BIOINTERFACE FOR 14 ENHANCED BIOELECTRODE AND BIOSENSOR PERFORMANCE. 15 DR. RATNER: GOOD MORNING. PLEASURE TO BE 16 ABLE TO PRESENT SOME PERSPECTIVES, I THINK, FROM COMING 17 IN THE DIRECTION, PERHAPS, THE WAY A BIOENGINEER MIGHT 18 THINK ABOUT THIS INTERFACE. 19 AND LET'S SEE. SO WHAT WE SOMETIMES REFER TO 20 AS THE BIOINTERFACE, IF THIS GREEN DEVICE IN THE CENTER 21 OF THE SLIDE IS SOME EITHER SENSOR OR ELECTRODE AND IT 22 EXISTS IN SOME BIOLOGICAL ENVIRONMENT, I'VE DRAWN IT IN 23 AN AQUEOUS, MAYBE AN OCEANIC ENVIRONMENT, BUT IT COULD 24 JUST AS WELL BE IN A BRAIN OR IN A SOFT TISSUE. AT THE 25 INTERFACE THERE'S SOME VERY INTERESTING EVENTS THAT

1 1 TAKE PLACE. 2 AND THIS SLIDE, IT'S A RATHER LENGTHY SLIDE, 3 BUT IT COVERS, I THINK, THE MAJORITY OF THE WAYS THIS 4 INTERESTING ENVIRONMENT, THE BIOENVIRONMENT, CAN IMPACT 5 SYNTHETIC MATERIALS WE PUT INTO THE BODY. I'M NOT 6 GOING TO ACTUALLY READ EVERY ONE OF THEM. SOME OF THEM 7 ARE FAIRLY OBVIOUS THINGS LIKE WATER ABSORPTION, ALMOST 8 LIKE A SPONGE SWELLING, OR LIPIDS ABSORPTION OR SOME OF 9 THEM OXIDIZE OR HYDROLYZE OR CATALYTICALLY BREAK DOWN. 10 BUT AS WE GET DOWN TOWARDS THE BOTTOM OF THIS LIST, 11 WHERE WE HAVE THINGS LIKE RELEASED MATERIAL STIMULATES 12 INTENSIFIED INFLAMMATORY REACTION, CALCIFICATION AND 13 MINERALIZATION AND ENCAPSULATION, IT'S A MORE COMPLEX 14 BIOLOGICAL PROCESS. THESE ARE GOING TO BE THE ONES 15 THAT I'M GOING TO MAINLY FOCUS ON. 16 THE ITEMS MORE TOWARDS THE TOP OF THE LIST 17 ARE ACTUALLY FAIRLY WELL DEALT WITH FROM THE 18 UNDERSTANDING OF THE MATERIAL -- SCIENCE OF THE 19 MATERIALS, BUT THESE THAT SORT OF TAKE US INTO COMPLEX 20 BIOLOGICAL PROCESSES ARE GOING TO NEED A BIT MORE 21 THOUGHT AND INTRODUCTION. 22 SO THE ELECTRODES AND DEVICES IN THE BODY, BE 23 THEY BIOSENSORS OR IN SOME CASES MEDICAL DEVICES, I 24 THINK, FIT A CATEGORY THAT'S VERY LOOSELY BEEN CALLED 25 BIOMATERIALS. AND IF ONE LOOKS AT THE ORIGIN OF THIS

2 1 MODERN FIELD OF BIOMATERIALS, YOU CAN FIND EXAMPLES OF 2 THE EGYPTIANS HAVING USED MATERIALS IN MEDICINE 3,000 3 YEARS AGO, BUT THE MORE MODERN FIELD, ENZYMES ATTRIBUTE 4 TO THIS EVENT THAT'S SORT OF BEEN ILLUSTRATED IN THIS 5 PARTICULAR PAINTING. THE INDIVIDUAL WHO'S ON THE SLIDE 6 IS DR. HAROLD RIDLEY OR SIR HAROLD RIDLEY. AND RIDLEY 7 WAS AN OPHTHALMOLOGIC SURGEON WHO DEALT WITH A NUMBER 8 OF AVIATORS AFTER WORLD WAR II. AND AN INTERESTING 9 SORT OF MEDICAL EVENT OCCURRED. 10 THE WINDSHIELDS OF THESE FIGHTER PLANES WERE 11 MADE OF A PLASTIC. AND THE MACHINE GUN FIRE IN THE 12 THEATER OVER EUROPE, THE WAR SPACE OVER EUROPE, OFTEN 13 SHATTERED THOSE WINDSHIELDS, AND THE CONSEQUENCE OF 14 THAT SHATTERING WAS, LET'S CALL IT, UNINTENTIONAL 15 IMPLANTATIONS OF SHARDS OF PLASTIC IN THE EYES OF THESE 16 AVIATORS. 17 WELL, YEARS AFTER THE WAR, DR. RIDLEY WAS 18 EXAMINING THE EYES OF THESE AVIATORS, AND HE NOTED 19 SOMETHING THAT WAS QUITE INTERESTING FOR THE TIME. HE 20 NOTICED THE SHARDS SEEMED TO RESIDE IN THE EYE WITHOUT 21 ANY FURTHER REACTION. THEY JUST SEEMED TO BE RATHER 22 INERTLY SITTING THERE. NOW, THE CONVENTIONAL WISDOM AT 23 THE TIME IS IF YOU GOT A SPLINTER IN YOU, YOU'D GET 24 REDNESS, SWELLING, INFECTION, AND RELATED UNPLEASANT 25 CONSEQUENCES, AND YET HERE WERE SHARDS OF MATERIAL IN

3 1 THE EYE THAT SAT THERE FOR YEARS. AND HE CONCLUDED, 2 WELL, PERHAPS THIS MATERIAL THAT THIS WINDSHIELD WAS 3 MADE OF WAS, AND THE WORD -- I DON'T KNOW IF HE USED 4 EXACTLY THIS WORD, BUT I'M SURE THE SORT OF GENERAL 5 THOUGHT WENT THROUGH HIS MIND -- PERHAPS THIS IS 6 BIOCOMPATIBLE. 7 AND PROFESSOR OR DR. RIDLEY ACTUALLY WENT OUT 8 AND PURCHASED A SHEET OF THE SAME MATERIAL THE 9 WINDSHIELDS WERE MADE OUT OF, FABRICATED THE FIRST 10 INTRAOCULAR LENSES THAT ARE USED TO REPLACE THE NATURAL 11 LENS OF THE EYE WHEN IT BECOMES CATARACTOUS, AND REALLY 12 STARTED AN INDUSTRY AND A MEDICAL OR THERAPEUTIC 13 PRACTICE THAT IS IMPACTING ABOUT 10 MILLION EYES PER 14 YEAR AT THE PRESENT TIME. SO JUST BASED UPON THIS 15 CHANCE, BUT CLEVER OBSERVATION, I THINK OUR WHOLE FIELD 16 REALLY MAY HAVE BEEN LAUNCHED. 17 THERE ARE OTHER INDICATIONS TOO, SO JUST 18 POINT OUT THAT THE INTRAOCULAR LENS SHOWN IN THE SLIDE 19 IS FROM A WINDSHIELD. THIS HAS SORT OF LED TO OUR 20 MODERN BIOMATERIALS AND MEDICAL IMPLANT FIELD. AND, 21 AGAIN, I HAVE JUST A FEW DEVICES LISTED HERE. I'M NOT 22 GOING TO DWELL ON THEM, BUT I THINK THE IMPORTANT THING 23 TO NOTE IS THE LARGE NUMBERS PER YEAR. THESE ARE VERY 24 WIDELY USED IN MEDICINE, SURGERY, AND IMPACT MANY 25 PEOPLE. THEY SAVE LIVES AND IMPROVE THE QUALITY OF

4 1 LIFE FOR MILLIONS. 2 SO ALL THESE MATERIALS HAVE A COMMON 3 PROPERTY, AND A WORD THAT'S VERY WIDELY USED, THE WORD 4 IS BIOCOMPATIBILITY AND, IN FACT, THERE WAS A CONSENSUS 5 CONFERENCE THAT TOOK PLACE TO ATTEMPT TO DEFINE THIS 6 WORD "BIOCOMPATIBILITY." AND THE DEFINITION THAT CAME 7 UP FROM THREE DAYS OF SCIENTISTS WRANGLING WITH EACH 8 OTHER OVER THE MEANING OF WORDS WAS THE ABILITY OF A 9 MATERIAL TO PERFORM WITH AN APPROPRIATE HOST RESPONSE 10 IN A SPECIFIC APPLICATION. IT'S ACTUALLY A PERFECTLY 11 ACCURATE DEFINITION AND REALLY DOES DESCRIBE TWO 12 ASPECTS OF THIS, THE FACT WE USE THESE MATERIALS IN SO 13 MANY DIFFERENT APPLICATIONS IN THE BODY AND THEY HAVE 14 TO PERFORM WITH AN APPROPRIATE HOST RESPONSE, THE 15 RESPONSE OF THE BODY. 16 THE PROBLEM WITH THE DEFINITION IS IT REALLY 17 GIVES US NO INSIGHTS INTO WHAT IS BIOCOMPATIBLE. HOW 18 CAN WE TEST IT? HOW CAN WE OPTIMIZE IT? AND, IN FACT, 19 THE WORD HAS BEEN A BIT OVERUSED. THERE WAS A PAPER 20 THAT CAME OUT RECENTLY ON THE BIOCOMPATIBILITY OF 21 SWEETPOTATO AND PEANUT IN HYDROPONIC SYSTEMS. DOESN'T 22 SEEM TO TOO WELL RELATE TO OUR THINKING. AND THEN A 23 COMPANY IS SELLING BIOCOMPATIBLE CHROMATOGRAPHY 24 FITTINGS. SO THERE'S A VERY WIDE SPAN IN THE 25 UNDERSTANDING OF THIS WORD "BIOCOMPATIBILITY."

5 1 SO I'D LIKE TO EXAMINE IT A LITTLE BIT MORE 2 IN CERTAIN DETAIL, AND I HAVE THIS DIAGRAM. AGAIN, 3 IT'S A BIT COMPLICATED, BUT I THINK IT OUTLINES IN A 4 TUTORIAL SENSE THE KEY ELEMENTS THAT WE SEE WHEN A 5 BIOCOMPATIBLE DEVICE OR BIOMATERIAL, AND THAT'S SORT OF 6 INDICATED BY THIS BLUE-GREEN-LIKE STRUCTURE HERE, IS 7 IMPLANTED IN THE BODY. 8 THE IMPLANTATION, OF COURSE, IS IN ITSELF AN 9 INJURY. AND THE FIRST EVENT WE SEE IN SECONDS WHEN 10 THIS IS IMPLANTED IS PROTEIN ADSORPTION. PROTEINS 11 OVERCOAT THE OUTSIDE OF THE MATERIAL. VERY SHORTLY 12 AFTER THAT WE FIND NEUTROPHILS PRESENT AROUND THE 13 MATERIAL. THE NEUTROPHILS ARE BELIEVED TO BE PRIMARILY 14 SEARCHING FOR BACTERIA. IF THIS IS DONE IN A STERILE 15 FIELD, THEY DON'T FIND BACTERIA, THEY'RE PRETTY QUICKLY 16 GONE. BUT SOMEWHAT AFTER THAT, PROBABLY WITHIN MAYBE 17 24 TO 48 HOURS, ONE STARTS SEEING MACROPHAGES AT THE 18 BIOMATERIAL INTERFACE. AND THE MACROPHAGES ATTACH TO 19 THE BIOMATERIAL, AS SEEN DOWN IN NO. 4 HERE. AND WHAT 20 THEY'RE REALLY TRYING TO DO IS BASICALLY INTERROGATE 21 AND DIGEST THIS FOREIGN OBJECT. 22 WHEN THEY FIND THAT THIS IS QUITE 23 INDIGESTIBLE, THEY FUSE AND BEGIN TO SPREAD OVER THE 24 SURFACE OF THE BIOMATERIAL. AND WHAT THEY'RE TRYING TO 25 DO, AGAIN, IS TO ENGULF IT, AND THEY STILL FIND THAT

6 1 THEY'RE INCAPABLE OF BECOMING LARGE ENOUGH TO EAT THE 2 WHOLE BIOMATERIAL, SO THEY CALL IN PERHAPS ANOTHER CELL 3 TYPE, FIBROBLASTS, THAT MAY COME IN. AND THE 4 FIBROBLASTS WILL GENERATE A COLLAGENOUS CAPSULE, A BAG. 5 AND WE CALL IT THE FOREIGN BODY REACTION, AND THAT'S 6 PRETTY UNIVERSALLY SEEN WITH BIOCOMPATIBLE 7 BIOMATERIALS. 8 HERE'S THE REALITY OF THIS. THIS IS A SLIDE 9 FROM ONE OF THE COMPANIES THAT PARTNER WITH OUR 10 NSF-FUNDED ENGINEERING RESEARCH CENTER. THE COMPANY IS 11 CALLED ISENSE, AND THEY'RE INVOLVED IN THE DEVELOPMENT 12 OF A GLUCOSE SENSOR. AND THIS TEFLON DEVICE WE SEE 13 HERE IS A GLUCOSE SENSOR. AND THIS HAS BEEN IMPLANTED 14 SIX WEEKS SUBCUTANEOUSLY IN A RAT. AND WHAT DO WE FIND 15 AT THE END OF SIX WEEKS? IN THIS SCANNING ELECTRON 16 MICROSCOPE VIEW, WE FIND A DENSE FOREIGN BODY CAPSULE. 17 REMEMBER, THIS TEFLON DEVICE HERE IS A GLUCOSE SENSOR. 18 AND GLUCOSE WOULD HAVE TO PENETRATE THROUGH THIS DENSE 19 CAPSULE. IT'S RATHER CHALLENGING TO GET GOOD DIFFUSION 20 THROUGH SUCH A DENSE CAPSULE. 21 THIS IS MORE LIKE WHAT NORMAL TISSUE SHOULD 22 LOOK LIKE. IT CERTAINLY HAS COLLAGEN IN IT, BUT IT'S A 23 MORE OPEN SORT OF STRUCTURE. SO THAT'S WHAT THE 24 REACTION LOOKS LIKE. AND ONE OF THE THINGS WE DID IN 25 OUR UWEB PROGRAM, OUR NSF ENGINEERING RESEARCH CENTER

7 1 PROGRAM, IS TO JUST TAKE A WHOLE RANGE OF MATERIALS. 2 NOW, I'M NOT GOING TO GO OVER WHAT ALL THESE MATERIALS 3 ARE, BUT EACH OF THESE BLUE BARS IS A DIFFERENT 4 SYNTHETIC MATERIAL. SOME OF THEM DO HAVE PROTEINS 5 IMMOBILIZED THROUGH THEM. THEY WERE ALL IMPLANTED FOUR 6 WEEKS SUBCUTANEOUSLY IN A MOUSE. 7 AND WHAT DID WE GET AT THE END OF FOUR WEEKS? 8 EVERY ONE OF THEM WAS ENCAPSULATED IN THIS CAPSULE, AND 9 THIS IS CAPSULE THICKNESS. AND THE CAPSULE THICKNESS 10 WAS BASICALLY IDENTICAL. IF YOU START DOING SOME 11 STATISTICS ON THIS DATASET, YOU WILL FIND THEY'RE ALL 12 QUITE SIMILAR, EVEN THOUGH THE MATERIALS THEMSELVES 13 WERE VERY WIDELY DIFFERENT. WE HAVE THINGS LIKE 14 TITANIUMS, WE HAD HYDROXYAPATITE, WE HAD POLYETHYLENES, 15 AND THEY ALL JUST HEALED THE SAME. THE BODY FOUND THEM 16 ALL AS FOREIGN MATERIALS AND JUST WALLED THEM OFF. SO 17 THAT'S THE REACTION WE GET WITH THE FOREIGN BODY 18 REACTION. 19 AND, OF COURSE, IF WE WANT TO USE ELECTRODES 20 IN THE BODY TO RECORD OR TO STIMULATE, WHAT WE FIND IS 21 THE BODY DOES THE EXACT SAME THING TO A BIOELECTRODE, 22 WALLS IT OFF. AND THERE RESIDES PART OF OUR PROBLEM. 23 THE BIOELECTRODES, PARTICULARLY THE RECORDING 24 ELECTRODES, MIGHT HAVE TO BE VERY SENSITIVE. AND THIS 25 TOUGH COLLAGENOUS SCAR INHIBITS THE SPATIALLY LOCALIZED

8 1 TRANSMISSION OF ELECTRICAL SIGNALS THAT IS SO CRITICAL 2 TO THIS PROCESS. 3 SO HERE'S SORT OF A CONTROVERSIAL THOUGHT. 4 SINCE WE MAKE ALL OUR ELECTRODES, ALL OUR MEDICAL 5 DEVICES, OUT OF BIOCOMPATIBLE BIOMATERIALS, THE BODY 6 DOESN'T INTEGRATE THE BIOCOMPATIBLE DEVICE OR MATERIAL. 7 IT ISOLATES IT. WELL, PERHAPS OUR BIOCOMPATIBLE 8 MATERIALS ARE NOT BIOCOMPATIBLE, A BIT OF A HERETICAL 9 THOUGHT. 10 PROFESSOR JAMES ANDERSON OF CASE WESTERN HAS 11 ACTUALLY HELPED US UNDERSTAND THIS PROCESS, THE FOREIGN 12 BODY REACTION, VERY NICELY. IN TERMS OF A TEMPORAL 13 SEQUENCE, GOING FROM DAYS TO WEEKS TO MONTHS, AND ONE 14 CAN WATCH THESE VARIOUS CELL TYPES, THE 15 POLYMORPHONUCLEAR LEUKOCYTES AT FIRST COMING IN AND 16 LEAVING, MACROPHAGES COMING IN, EVENTUALLY GOING DOWN 17 IN NUMBER, BUT THE FOREIGN BODY GIANT CELLS GOING UP A 18 NUMBER, FIBROBLASTS, THE FIBROSIS, SO THIS IS KIND OF A 19 NICE CARTOON TO ASSIST US IN APPRECIATING THE STEPS IN 20 THIS REACTION. 21 NOW, LET ME JUST CONTRAST THIS FOREIGN BODY 22 REACTION WITH SOMETHING CALLED INFLAMMATION. THE 23 NORMAL RESPONSE OF THE BODY TO INJURY IN VASCULARIZED 24 TISSUE IS CALLED INFLAMMATION. IT'S A MEDICAL TEXTBOOK 25 DEFINITION. WHEN THE INJURY IS HEALED, THE

9 1 INFLAMMATORY PROCESS CEASES. ON THE OTHER HAND, WE 2 HAVE THE FOREIGN BODY REACTION. WHAT WE HAVE HERE IS A 3 SIMILAR INFLAMMATORY REACTION ASSOCIATED WITH THE 4 INJURY, BUT THE BODY CAN'T HEAL THE INJURY. IT CAN'T 5 GET RID OF THE IMPLANTED FOREIGN OBJECT, AND THEN THIS 6 FOREIGN BODY REACTION IS OBSERVED. 7 THE REACTION IS CHARACTERIZED BY THE GIANT 8 CELLS, THE FIBROUS CAPSULE, AND MILDLY ACTIVE 9 INFLAMMATORY CELLS, INTERESTINGLY, EVEN YEARS AFTER THE 10 DEVICE HAS BEEN IMPLANTED. SO THE INFLAMMATION IS THE 11 NORMAL PROCESS. WHAT WE'RE SEEING WITH THIS FOREIGN 12 BODY REACTION IS A RATHER ABNORMAL PROCESS. IT KIND OF 13 LEADS TO WHAT WE MIGHT CALL THE OPERATIONAL DEFINITION 14 OF BIOCOMPATIBILITY. AGAIN, CERTAINLY MILLIONS OF 15 DEVICES ARE GOING INTO HUMANS. THEY BASICALLY SORT OF 16 FUNCTION, BUT THE OPERATIONAL DEFINITION WOULD SAY THE 17 IMPLANT AFTER APPROXIMATELY ONE MONTH IS FOUND WITHIN A 18 THIN RELATIVELY ACELLULAR COLLAGENOUS SAC. THE 19 REACTION SITE IS QUIESCENT. THE SURGEON WOULD PROBABLY 20 SAY THIS IS A SUCCESSFUL IMPLANT, AND IN MOST CASES WE 21 CAN FUNCTIONALLY USE THE IMPLANT, BUT IN THE CASE OF 22 RECORDING ELECTRODE, INDEED, WE MAY BE -- OR BIOSENSOR, 23 THIS THIN WALL CAPSULE MAY BE INHIBITORY. 24 SO LET'S SEE. THE CLASSICAL FOREIGN BODY 25 REACTION. THE COLLAGENOUS CAPSULE IS OBSERVED UPON

10 1 IMPLANTATION OF THE FOREIGN OBJECT IN SOFT TISSUE, BUT 2 I THINK THERE MIGHT BE SUBTLE MANIFESTATIONS OF THIS 3 FOREIGN BODY REACTION THAT GO WELL BEYOND, FOR EXAMPLE, 4 THE ELECTRODE CASE. I DO HAVE FAILURE OF IMPLANT 5 ELECTRODES, BUT THINGS LIKE THE POOR HEALING OF 6 VASCULAR PROSTHESES, POSTERIOR CAPSULAR OPACIFICATION 7 IN INTRAOCULAR LENSES, EXTRUSION OF PERCUTANEOUS 8 DEVICES, BIOSENSOR FAILURE. MAYBE EVEN SOMETHING LIKE 9 THE COMFORT OF CONTACT LENSES MAY BE ASSOCIATED WITH 10 THIS SORT OF CHRONIC INFLAMMATORY REACTION THAT WE GET 11 WITH BIOMATERIALS. 12 SO HOW CAN WE GET AROUND THE FOREIGN BODY 13 REACTION? WELL, I'VE MADE A BUNCH OF STATEMENTS HERE 14 THAT IMPLY PERHAPS WHAT'S GOING ON HERE. IT DOES SEEM 15 TO OR POSSIBLY BE TRIGGERED BY THOSE NONSPECIFIC 16 PROTEINS THAT ADSORB VERY EARLY ON WHEN AN IMPLANT IS 17 PLACED IN THE BODY. THE MACROPHAGE CELL CERTAINLY 18 SEEMS TO BE INVOLVED IN THE PROCESS, AND NORMAL WOUND 19 HEALING, NORMAL INFLAMMATORY WOUND HEALING, FOLLOWS A 20 VERY DIFFERENT COURSE. THE INFLAMMATION IS RESOLVED ON 21 HEALING. SO CAN WE ENGINEER THE INTERFACE OF AN 22 ELECTRODE OR A SENSOR OR A MEDICAL DEVICE TO CONTROL 23 THIS BIOLOGICAL REACTION USING SOME OF THESE IDEAS? 24 LET'S EXAMINE THAT. LET'S MAYBE START WITH 25 TRIGGERED BY NONSPECIFIC PROTEINS. WELL, LET ME, FIRST

11 1 OF ALL, MENTION THAT THERE IS A COMMUNITY, A FIELD, OF 2 PEOPLE THAT ARE EXPLORING THE BIOINTERFACE, WHAT GOES 3 ON AT THE BIOINTERFACE, AND WAYS TO MANIPULATE IT. AND 4 WE HAVE OVER THE YEARS ACCUMULATED WHAT I SORT OF CALL 5 THE TOOL CHEST OF METHODS. AND, AGAIN, THERE'S KIND OF 6 A LONG LIST HERE, AND I EVEN USED THIS SORT OF LIST TO 7 GUIDE ME THROUGH ONE OF MY GRADUATE COURSES. 8 IN ANY EVENT, WHAT I AM GOING TO DO IN THIS 9 CONTEXT, I'M GOING TO TALK ABOUT A NUMBER OF THESE; BUT 10 INSTEAD OF JUST READING THE LIST, WE'LL JUST GO DOWN 11 SOME EXAMPLES OF THE TOOLS WE USE. 12 SO WE'RE GOING TO APPLY SOME TOOLS, AND 13 STARTING WITH THE IDEA OF THE FOREIGN BODY REACTION 14 MIGHT BE TRIGGERED BY THESE NONSPECIFIC INTERFACIAL 15 PROTEINS. WELL, MAYBE WE CAN ELIMINATE THE PROTEINS AT 16 THE INTERFACE. LET'S SEE WHAT WE CAN DO HERE. ONE 17 STRATEGY THAT MIGHT HELP US ELIMINATE THOSE PROTEINS AT 18 THE INTERFACE IS A MOLECULE CALLED POLYETHYLENE GLYCOL 19 OR POLYETHYLENE OXIDE. THE CHEMICAL STRUCTURE IS SHOWN 20 HERE. YOU CAN SEE IT'S A RATHER SIMPLE MOLECULE. AND 21 POLYETHYLENE OXIDE SURFACES HAVE BEEN FOUND SINCE ABOUT 22 1983 TO RESIST PROTEIN IN CELL PICKUP. WITHIN OUR OWN 23 GROUP WE SAID THIS WAS AN EXTREMELY INTERESTING 24 OBSERVATION, AND WE WORKED ON FINDING A, LET'S SEE, A 25 FACILE METHOD TO DEPOSIT THIS PARTICULAR SUBSTANCE ON,

12 1 FOR EXAMPLE, A REAL MEDICAL DEVICE. HOW COULD WE PUT 2 IT ON A FULLY FABRICATED MEDICAL DEVICE OR A SPECIFIC 3 BIOMATERIAL? 4 WELL, WE STARTED WITH A MONOMER, CHEMICAL, 5 WHICH WE CALL TETRAGLYME. THE STRUCTURE IS SHOWN DOWN 6 HERE. IT HAS THIS ETHYLENE GLYCOL MOTIF REPEATED FOUR 7 TIMES, METHOXY-ETHER TERMINATIONS. IT'S ACTUALLY A 8 CLEANING SOLVENT. YOU CAN GET IT IN TANK TRUCKLOADS IF 9 YOU WANT IT. BUT WE TAKE THIS MATERIAL, AND WHAT WE DO 10 IS WE VOLATILIZE IT INTO A GLOW DISCHARGE, INTO A 11 GLOWING IONIZED GAS ENVIRONMENT. AND WE CAN USE THIS 12 GLOWING IONIZED GAS ENVIRONMENT TO DEPOSIT A THIN LAYER 13 ONTO OUR MEDICAL DEVICES, WHICH IS SORT OF IN THIS 14 DIAGRAM INDICATED BY THAT SORT OF ORANGE-ISH STRUCTURE. 15 ONE OF THE THINGS WE DO TO ENSURE THAT OUR 16 COATINGS ARE WHAT WE THINK THEY ARE IS WE USE A 17 TECHNOLOGY CALLED X RAY PHOTOELECTRON SPECTROSCOPY. 18 THIS IS A PICTURE OF SORT OF THE MACHINE. IT COSTS 19 ROUGHLY A MILLION DOLLARS FOR ONE OF THOSE MACHINES, 20 BUT THEY'RE KIND OF MAINSTAYS OF THE MICROELECTRONICS 21 INDUSTRY, AND, IN FACT, THERE'S EVEN A NATIONAL CENTER 22 CALLED NASEC FUNDED BY THE NIH THAT MAKES THIS 23 INSTRUMENTATION AVAILABLE FOR BIOMEDICAL RESEARCH. AND 24 USING THE XPS METHOD, WE CAN PROVE, BASED UPON THIS 25 286.5 ELECTRON VOLT PEAK THAT, IN FACT, THERE'S A LOT

13 1 OF THIS ETHYLENE GLYCOL-LIKE STRUCTURE ON THE SURFACE. 2 SO IT SAYS OUR PLASMA DEPOSIT GAVE US THE CHEMISTRY WE 3 THOUGHT IT DID. 4 WELL, LET'S SEE HOW IT WORKS. I'M GOING TO 5 SHOW SOME NEW DATA THAT COMES FROM A RECENT GRADUATE OF 6 OUR GROUP, DR. LAN CAO, MY COLLEAGUE, TOM HORBETT. AND 7 WHAT WE'RE DOING HERE IS LOOKING AT TWO MATERIALS, ONE 8 UNTREATED, ONE TREATED WITH THIS TETRAGLYME IN THE 9 PLASMA REACTOR. AND WHAT WE HAVE HERE ON THE Y AXIS IS 10 FIBRINOGEN ADSORPTION. WE HAVE THREE DIFFERENT 11 MATERIALS: A POLYURETHANE, THE TYPE OF MATERIAL THAT 12 MIGHT BE USED IN A PUMPING BLADDER OF AN ARTIFICIAL 13 HEART, GLASS, POLYETHYLENE, AND THE DARK BAR INDICATES 14 HOW MUCH PROTEIN IS PICKED UP WHEN WE TREAT IT WITH 15 TETRAGLYME. 16 IT'S PRETTY OBVIOUS THE PROTEIN IS GREATLY 17 DIMINISHED WHEN WE TAKE THAT SAME SURFACE AND TREAT IT 18 WITH TETRAGLYME. AND THERE'S AN INTERESTING 19 IMPLICATION. IF YOU KEEP THE PROTEINS OFF, YOU CAN 20 ALSO KEEP CELLS FROM INTERACTING. FOR EXAMPLE, THIS IS 21 HUMAN BLOOD PLATELETS. AND, AGAIN, THE DARK BARS ARE 22 TETRAGLYME TREATED, AND IT'S PRETTY OBVIOUS THAT WE 23 HAVE GREATLY INHIBITED THE ABILITY OF BLOOD PLATELETS 24 TO STICK TO THAT SURFACE. THIS IDEA WORKS WITH MOST 25 ANY CELLS AND, IN FACT, EVEN WORKS WITH BACTERIA. IN

14 1 ANOTHER STUDY THAT WAS DONE WITH SOME OF MY COLLEAGUES, 2 JAMES BRYERS, DR. ERICA JOHNSTON, AND THIS WAS DONE AT 3 THE BIOFILM ENGINEERING CENTER AT BOZEMAN, MONTANA. 4 WE COMPARED A BUNCH OF DIFFERENT MATERIALS. 5 THAT'S ALL THESE BARS AGAIN. I'M NOT GOING TO GO INTO 6 ALL THE DETAILS, BUT THE TETRAGLYMES HAD AMONG THE 7 LOWEST PICKUP. THIS IS PSEUDOMONAS AERUGINOSA 8 ATTACHMENT. SO, AGAIN, THIS IDEA OF INHIBITING THE 9 PROTEINS AT THE INTERFACE INHIBITS THE CELLS FROM 10 ATTACHING, AND WE HAVE DATA WITH MANY OTHER DIFFERENT 11 TYPES OF CELLS. 12 THIS IS STILL ANOTHER STUDY. ACTUALLY, FOR 13 THE SAKE OF TIME, I'M GOING TO PASS BY THIS, BUT WE 14 SHOW THAT THE BACTERIA ONLY ADHERE ON GLASS AND NOT ON 15 THE TETRAGLYME, WHICH IS THE SPACE BETWEEN THESE DOTTED 16 LINE PATTERNS. 17 SO IF THIS IDEA LOOKS SO ATTRACTIVE, LET'S 18 IMPLANT A TETRAGLYME-COATED BIOMATERIAL INTO SOFT 19 TISSUE AND SEE WHAT HAPPENS. SO WE TOOK A PIECE OF 20 TEFLON, IMPLANTED IT. THIS IS FROM DR. MENSHOU SHEN. 21 TOOK A PIECE OF TEFLON, IMPLANTED IT, AND WE COATED 22 THAT TEFLON WITH THE TETRAGLYME, IMPLANTED IT; AND IF 23 WE LOOK AT THE FIBROUS CAPSULE THICKNESS ON BOTH THE 24 SKIN SIDE AND MUSCLE SIDE OF THIS IMPLANT, THE TEFLON 25 IS YELLOW, AND THE GREEN IS THE TETRAGLYME,

15 1 INDISTINGUISHABLE. SO THIS IS VERY CONFUSING. WE'VE 2 MADE A MATERIAL THAT SEEMS TO GREATLY RESIST THE PICKUP 3 OF JUST ABOUT ANY CELL WE'VE LOOKED AT. IT RESISTS THE 4 PICKUP OF BACTERIA, AND YET IT HEALS INDISTINGUISHABLY 5 FROM EVERYTHING ELSE. IT COULD MEAN THE HYPOTHESIS IS 6 WRONG, BUT THERE'S ANOTHER POSSIBLE EXPLANATION TOO. 7 THESE TETRAGLYME MATERIALS ARE POLYETHYLENE 8 GLYCOL-LIKE SURFACES. AND POLYETHYLENE GLYCOL IS VERY 9 SUBJECT TO BREAKDOWN BY OXIDATION. MACROPHAGES MAKE 10 STRONG OXIDANTS. SO MAYBE IN THE FOREIGN BODY 11 REACTION, THESE MATERIALS ARE BROKEN DOWN, AND WE DON'T 12 HAVE THE TETRAGLYME THERE ANYMORE. SO ONE OF THE 13 THINGS WE'RE THINKING ABOUT, MAYBE THIS NON-FOULING 14 WOULD BE NECESSARY, BUT NOT SUFFICIENT, BUT WE WANT TO 15 TEST THIS FURTHER. AND WE'RE ACTUALLY WORKING WITH 16 SOME MOLECULES LIKE TAURINE, WHICH WHEN PLACED AS THE 17 HEAD GROUP ON A MONOLAYER, FOR EXAMPLE, HAS ALSO BEEN 18 SHOWN TO BE VERY EXCELLENT IN REDUCING PROTEIN PICKUP 19 ON SURFACES. AND TAURINE SHOULD BE RESISTANT TO 20 OXIDATION. SO LOOKS LIKE A GOOD APPROACH, BUT IT'S NOT 21 TESTED YET IN VIVO. 22 HERE'S ANOTHER WAY WE MIGHT PERTURB THIS 23 CLASSIC FOREIGN BODY REACTION. AND WE CALL THIS 24 GEOMETRIC CONTROL OF THE MACROPHAGE PHENOTYPE. THE 25 CONCEPT CAME FROM AN EXPERIMENT THAT WAS PUBLISHED IN

16 1 1995. JAMES BRAUKER WAS THE LEAD AUTHOR. AND ACTUALLY 2 THE DATA WE HAVE HERE, THOUGH IS, NOT DR. BRAUKER'S 3 DATA. WE FOUND THE PAPER, THE 1995 PAPER, SO 4 REMARKABLE, WE THOUGHT WE MIGHT TRY AND REPLICATE IT IN 5 OUR LABORATORY, AND WE DID. SO THIS IS OUR OWN 6 DATASET. 7 SO WE IMPLANTED TWO MATERIALS. THEY WERE 8 IMPLANTED FOR ONE MONTH SUBCUTANEOUSLY IN A MOUSE. AND 9 ONE OF THE -- THE MATERIALS ARE CALLED MIXED ESTERS OF 10 CELLULOSE. ONE HAD SMALL PORES, .2 MICRONS, ONE HAD 11 LARGE PORES, 5 MICRONS. AFTER A MONTH WE LOOKED AT THE 12 HISTOLOGY. THE .2 MICRON MIXED ESTER OF CELLULOSE HAD 13 A DENSE FOREIGN BODY CAPSULE. IT HAD ACTIVATED 14 MACROPHAGES IN GIANT CELLS AT THE INTERFACE. IN THE 15 SAME ANIMAL IN THE SAME TYPE OF IMPLANTATION SITE, THE 16 5 MICRON MIXED ESTER OF CELLULOSE HAD A VERY DIFFERENT 17 RESPONSE. IT HAD A VERY OPEN COLLAGENOUS STRUCTURE 18 RATHER THAN THIS DENSE COLLAGEN STRUCTURE. THERE WERE 19 NO MACROPHAGES AT THE INTERFACE, AND THERE WERE MANY 20 BLOOD VESSELS THAT PERMEATE THROUGH THIS CAPSULE. 21 SO HOW DID WE CHANGE, RADICALLY CHANGE, THE 22 NATURE OF THE FOREIGN BODY RESPONSE? ALL WE DID WAS 23 CHANGE THE PORE SIZE OF THE MATERIAL. AND THAT LED US 24 ON AN INTERESTING EXPLANATION. THE PROBLEM WITH THE 25 MATERIALS, SUCH AS THOSE MIXED ESTER OF CELLULOSE

17 1 FILTERS THAT WERE USED IN THAT EXPERIMENT, IS THEY HAVE 2 VERY HETEROGENEOUS PORE SIZE DISTRIBUTION. THEY HAVE 3 SMALL, LARGE, AND MEDIUM SIZE PORES. THERE'S REALLY NO 4 PRECISE CONTROL. SO IF ONE PORE SIZE WAS IMPORTANT FOR 5 HEALING, IT MIGHT GET DROWNED IN THE NEGATIVE SIGNAL 6 FROM SMALL OR LARGE PORES WHERE, LET'S SAY, THE MEDIUM 7 PORE WAS THE ONE WE WANTED. 8 SO WE EMBARKED ON A PROJECT, AND THIS WAS 9 RECENTLY COMPLETED BY DR. ANDREW MARSHALL IN WHICH WE 10 FRACTIONATED MICROSPHERES. AND THIS JUST SHOWS SOME OF 11 THE MICROSPHERES. IT'S A DEVICE CALLED A SONIC SIEVE, 12 JUST SCREENS THAT WE CAN SHAKE DOWN AND GET THESE VERY 13 NICE PRECISE CUTS OF MICROSPHERES. AND WE USED THESE 14 IN AN INTERESTING PROCESS. 15 WE TOOK OUR MICROSPHERES AND WE SIEVED THEM 16 TO A UNIFORM SIZE. AND THEN WE SHOOK THEM SO THEY 17 SETTLED DOWN INTO ALMOST A CLOSE-PACKED CRYSTAL-LIKE 18 FORM. AND THEN WE GENTLY HEATED THEM SO THE SPHERES 19 FUSED OR CENTERED WITH EACH OTHER INTO A CENTERED CAKE 20 OF MICROSPHERES. AND THEN WE SURROUNDED THEM WITH A 21 MONOMER LIQUID, AND THEN WE SOLIDIFIED OR POLYMERIZED 22 THAT MONOMER TO MAKE A GEL SURROUNDING THEM. AND THEN 23 FINALLY, WE USED A STRONG SOLVENT TO SOLUBILIZE OUT THE 24 MICROSPHERES FROM THESE MATERIALS. 25 SO WHAT WE'RE LEFT IS INTERCONNECTING

18 1 SPHERICAL PORES ALL OF IDENTICAL SIZE. AND SO WE CALL 2 THIS PROCESS SIEVE -- CAN WE GO BACK ONE SLIDE? THANK 3 YOU. SO WE CALL THIS PROCESS SIEVE, SHAKE, SINTER, 4 SURROUND, SOLIDIFY, SOLUBILIZE. WE CALL IT THE 6 S 5 PROCESS, AND IT HAS LED TO SOME SUCCESS. 6 SO HERE'S OUR -- THE MATERIALS THAT WE MAKE 7 WITH THE 6 S PROCESS. AND YOU CAN SEE THEY KIND OF 8 HAVE A VERY NICE AESTHETIC TO THEM, VERY UNIFORM PORE 9 SIZES. THESE BLACK AREAS ARE THE INTERCONNECTS BETWEEN 10 THE PORES. AND THEY WERE IMPLANTED SUBCUTANEOUSLY IN A 11 MOUSE FOR ONE MONTH. AND ANDREW MARSHALL USED A GRID 12 SUCH AS THIS TO DO COUNTING STATISTICS. AND WE FOUND 13 AN ABSOLUTELY REMARKABLE RESULT, THAT THE PORE SIZE WAS 14 CORRECT, AND IN THIS CASE IT CAME OUT ROUGHLY 35 15 MICRONS. WE HAD A HUGE INCREASE IN VASCULARITY. IF 16 THE PORE SIZE WAS MUCH LARGER, ALMOST NO BLOOD VESSELS, 17 THE PORE SIZE WAS MUCH SMALLER. THE DATA ISN'T HERE, 18 BUT SOLID MATERIALS WITH ZERO PORE SIZE GIVE ALMOST 19 LIKE THIS, 160. SO PLOTTED WITH ERROR BARS, YOU CAN 20 SEE THERE'S A DISTINCT MAXIMUM TO VASCULARITY, BUT ALSO 21 THERE WAS A CHANGE IN THE CAPSULE. AND I'LL SHOW SOME 22 DATA ON THAT. 23 THIS JUST SHOWED THE VASCULAR DENSITY 24 SURROUNDING THE TISSUE, AND IT'S ALSO LINKED TO THE 25 INTRA-PORE VASCULAR DENSITY TO ATTRACT EACH OTHER.

19 1 THERE'S BLOOD VESSELS IN THE PORES AND BLOOD VESSELS 2 SURROUNDING THE MATERIAL. AND THIS SHOWED THE CAPSULE 3 THICKNESS, AND, INDEED, AT THE 35 MICRON PORE SIZE, WE 4 GOT THE LEAST FOREIGN BODY CAPSULE. AND SO, AGAIN, 5 THINKING ABOUT THE ELECTRODE CASE, WE HAVE MORE BLOOD 6 VESSELS, POSSIBLY MORE NERVES ASSOCIATED WITH THOSE 7 BLOOD VESSELS, AND LESS COLLAGEN TO INHIBIT BIOLOGICAL 8 SIGNALS. 9 WE'RE KIND OF CURIOUS ABOUT THE MECHANISM; 10 AND WHEN WE EXAMINED USING A MACROPHAGE MARKER STAIN, 11 THE BM8 MOUSE MACROPHAGE MARKER, WE FOUND AT THE 35 12 MICRON, THE MATERIAL WAS INTENSELY INFILTRATED BY 13 MACROPHAGES. YOU MIGHT EVEN CALL IT A CHRONIC 14 INFLAMMATORY REACTION IF YOU'RE JUST LOOKING AT THAT, 15 YET THAT REACTION SEEMS TO LEAD TO HEALING. AND, IN 16 FACT, ANDREW MARSHALL TOOK THIS A LITTLE FURTHER. HE 17 USED A DATASET ON THIS PORE SIZE VERSUS VASCULAR 18 DENSITY, AND DEVELOPED A SEMI-EMPIRICAL EQUATION THAT 19 FIT THAT DATASET, AND THEN DID AN EXTRAPOLATION, WHICH 20 SUGGESTED THAT BY OPTIMIZING THE PORE SIZE, WE MAY BE 21 ABLE TO GET TWO TO THREE TIMES MORE VASCULARITY. AND, 22 IN FACT, THESE SAMPLES HERE ARE NOW IN HISTOLOGY 23 BLOCKS, AND WE'RE ANXIOUSLY AWAITING TO SEE IF WE CAN 24 INDEED GET THAT EXCELLENT ENHANCEMENT SUGGESTED BY THIS 25 EXTRAPOLATION MODEL.

20 1 WHAT'S GOING ON THERE? WELL, I'D LIKE TO 2 CALL THIS A MECHANICAL CONTROL OF CELL PHENOTYPE. I 3 THINK IN THE LARGE PORES OUR MACROPHAGES CAN SPREAD 4 OUT. THEY'RE LIKE A BALLROOM AS FAR AS THE MACROPHAGE 5 IS CONCERNED. THE MACROPHAGE CAN SPREAD OUT AND GO 6 INTO THIS PHAGOCYTIC STATE. ON THE NONPOROUS MATERIAL 7 IT CAN CERTAINLY SPREAD OUT AND GO INTO THIS PHAGOCYTIC 8 STATE. BUT IN THE SMALL PORES, THE MACROPHAGES ARE 9 MECHANICALLY CONSTRAINED. THESE WALLS OF THESE PORES 10 PREVENT THEM FROM SPREADING OUT, AND WE THINK WE'RE 11 FORCING THEM INTO A MORE HEALING PHENOTYPE RATHER THAN 12 A FIBROTIC PHENOTYPE. 13 INTERESTINGLY, FOR THE DEFINITION, THE 14 MATERIAL IS CALLED THE POLYHEMA THAT THESE WERE MADE 15 OUT OF. IT'S THE SAME MATERIAL FOR SOFT CONTACT LENS 16 REALLY. BUT THE MATERIAL CAN BE MADE IN A POROUS FORM 17 OR A SOLID FORM, AND ONE FORM, TWO IDENTICAL MATERIALS 18 IN THE SAME APPLICATION, THE SAME SITE, ONE FORM GIVES 19 A VASCULARIZED ALMOST CAPSULE-FREE HEALING. THE OTHER 20 ONE GIVES A DENSE CAPSULE WITH NO BLOOD OR LITTLE 21 VASCULARITY. SAME MATERIAL, SAME APPLICATION. IT'S 22 INTERESTING, WE CALL BOTH REACTIONS BIOCOMPATIBLE, AND 23 THAT'S WHY SOMETIMES WE THINK THE DEFINITION MAY BE UP 24 FOR RETHINKING IN THE FUTURE. 25 WE'RE WORKING NOW WITH LEGACY HEALTH CARE

21 1 SYSTEMS WHO ARE DEVELOPING AN IMPLANTABLE GLUCOSE 2 SENSOR, AND WE'RE ACTUALLY COATING IT WITH THESE 3 SPHERE-TEMPLATED MATERIALS TO SEE IF WE CAN IMPROVE 4 BIOSENSOR LIFE. 5 AND, AGAIN, FOR THE SAKE OF, I THINK, JUST 6 THE TIMING, I'M GOING TO SKIP A FEW SLIDES HERE. BUT 7 THIS JUST SHOWS THAT THESE BIOSENSORS CAN WORK VERY 8 NICELY IN TRACKING BLOOD GLUCOSE AND THE SENSOR 9 GLUCOSE, BUT THIS IS UP TO 360 MINUTES. BY THE TIME 10 YOU GET TO ONE AND TWO MONTHS, THESE SENSORS ALMOST 11 ALWAYS FAIL DUE TO THIS ENCAPSULATION. SO IF OUR 12 SPHERE-TEMPLATED MATERIAL CAN WORK, THIS WILL BE VERY 13 EXCITING. 14 WELL, THERE'S OTHER WAYS WE CAN DO THAT TOO. 15 WE WONDER IF WE COULDN'T ENGINEER THE BIOMATERIAL WITH 16 A PRECISE PROTEIN LAYER INSTEAD OF A NONSPECIFICALLY 17 ADSORBED PROTEIN LAYER TO CONTROL THE MACROPHAGE, GET 18 IT TO SEND THE CORRECT CYTOKINES, AND, AGAIN, LEAD TO 19 THIS VERY NICE HEALING. AND WE'VE BEEN VERY INTERESTED 20 IN THE CLASS OF PROTEINS CALLED MATRICELLULAR PROTEINS 21 THAT EXIST BETWEEN THE EXTRACELLULAR MATRIX AND THE 22 CELLS, MATRICELLULAR. AND SOME OF THESE SPARK 23 OSTEOPONTIN THROMBOSPONDIN. THESE ARE NAMES OF A FEW 24 OF THESE PROTEINS THAT PRESENT IN EVERY WOUND. AND AS 25 SOON AS THE WOUND IS HEALED, THEY'RE GONE. SO WE THINK

22 1 THEY MIGHT BE VERY IMPORTANT IN THIS PROCESS. 2 AN EXCITING PIECE OF WORK THAT WAS LED BY 3 PAUL BORNSTEIN AND THEMIS KYRIAKIDES UNDER THE UWEB 4 PROGRAM. WE LOOKED AT THE PROTEIN THROMBOSPONDIN 2, 5 TSP2, AND IN THIS PARTICULAR EXPERIMENT, PROFESSOR 6 BORNSTEIN AND PROFESSOR KYRIAKIDES HAD TWO STRAINS OF 7 MOUSE. ONE WAS A WILD TYPE AND THE OTHER WAS A MOUSE 8 WITH A DOUBLE KNOCKOUT FOR THROMBOSPONDIN 2. AND WE 9 USED TWO MATERIALS, A SILICONE RUBBER AND OXIDIZED 10 SILICONE RUBBER. AND IN THE WILD-TYPE MOUSE, WE GOT 11 VERY LITTLE BLOOD VESSELS AND A DENSE FOREIGN BODY 12 CAPSULE. IN THE KNOCKOUT MOUSE, ON THE OTHER HAND, 13 WITH ABSENCE OF THROMBOSPONDIN, WE GOT TEN TIMES MORE 14 BLOOD VESSELS; AND ALTHOUGH THE CAPSULE MIGHT EVEN LOOK 15 THICKER HERE, ACTUALLY THE DATA IS SHOWN IN THE PNAS 16 PAPER, THOUGH THE CAPSULE MIGHT LOOK THICKER, IT'S 17 ACTUALLY A VERY OPEN DIFFUSE CAPSULE RATHER THAN THIS 18 DENSE TIGHT CAPSULE. SO IT LOOKS LIKE THROMBOSPONDIN 2 19 MAY BE SORT OF THE ENEMY. IF WE COULD ELIMINATE THIS, 20 IT WOULD BE GOOD. 21 SO, AGAIN, PAUL BORNSTEIN AND THEMIS 22 KYRIAKIDES TOOK THIS ONE STEP FURTHER, AND THEY USED AN 23 ANTISENSE RNA TO THE THROMBOSPONDIN 2 OR THE MESSENGER 24 RNA TO THE THROMBOSPONDIN 2. THEY APPLIED IT ON THE 25 BIOMATERIAL IN A GENE-ACTIVATED COLLAGENOUS-LIKE

23 1 MATRIX, IMPLANTED IT, AND EXAMINED WHAT HAPPENED. AND 2 THE RESULTS THAT CAME OUT OF THIS SHOWED THAT THE WILD 3 TYPE WAS THE CONTROL. THIS IS JUST AN IMPLANT WITH NO 4 ANTISENSE GENE TO THROMBOSPONDIN 2 IN IT. SHOWED VERY 5 LITTLE BLOOD VESSEL DENSITY. IF YOU USE THE WILD-TYPE 6 ANTISENSE TO THROMBOSPONDIN 2, WILD-TYPE ANIMAL, WE GOT 7 ACTUALLY GREATLY INCREASED BLOOD VESSEL DENSITY. AND 8 JUST LOOKING AT THE GENE-ACTIVATED MATRIX ALONE WITHOUT 9 THE ANTISENSE, ONE GOT, AGAIN, TYPICAL SORT OF CONTROL 10 VALUE, RATHER LOW BLOOD VESSEL DENSITIES. SO BY 11 LOCALLY WIPING OUT THE PRODUCTION OF THE THROMBOSPONDIN 12 2, WE HAVE IMPACTED THE HEALING IN A VERY NICE WAY. 13 THEMIS KYRIAKIDES HAS TAKEN THIS EVEN FURTHER 14 AND SHOWN THAT MATRIX METALLOPROTEINASE 9 IS KNOCKED 15 OUT CAN GIVE A MORE OPEN DIFFUSE COLLAGENOUS CAPSULE 16 RATHER THAN THE DENSE CAPSULE WE GOT IN A WILD-TYPE 17 ANIMAL THAT HAD THE MMP-9, AND YOU CAN SEE THIS IN THE 18 STAINING USING PICOSIRIUS RED THAT LOOKS FOR THE 19 ORGANIZATION OF COLLAGEN. SO IN THE WILD-TYPE ANIMAL, 20 THERE'S A DENSE RED STAIN CHARACTERISTIC OF DENSE 21 FIBRIL COLLAGEN WHERE IN THE MMP-9 KNOCKOUT MOUSE, 22 AROUND THE IMPLANT, WHICH IS INDICATED BY THE STAR, 23 INCIDENTALLY, WE GOT MUCH MORE OPEN DIFFUSE CAPSULE 24 RATHER THAN THIS DENSE CAPSULE. SO MMP-9 SEEMS TO BE 25 AND ACTOR.

24 1 ALSO, THIS IS A SIMILAR DATASET LOOKING AT 2 FOREIGN BODY GIANT CELL FORMATION AND SHOWN THAT THE 3 MACROPHAGE CHEMOTACTIC PROTEIN 1 KNOCKOUT ANIMAL CAN 4 GREATLY REDUCE THESE FOREIGN BODY GIANT CELLS. SO, 5 AGAIN, WE HAVE ANOTHER POTENTIAL THERAPEUTIC MODALITY 6 TO ADDRESS THIS FOREIGN BODY CAPSULE. 7 AND THEMIS, AGAIN, HAS PUT TOGETHER A VERY 8 EXCELLENT LITTLE CARTOON THAT SORT OF SHOWS ALL THE 9 DIFFERENT APPROACHES WE CAN TAKE TO ADDRESS THIS 10 PROBLEM: BIOMATERIAL WITH THE GIANT CELLS, THE DENSE 11 CAPSULE, THE BLOOD VESSELS. THIS IS SORT OF THE WILD 12 TYPE. BUT IF WE USE THROMBOSPONDIN KNOCKOUT, WE CAN 13 GET A MUCH LESS DENSE CAPSULE WITH BLOOD VESSELS IN IT. 14 SPARC GIVES A MUCH THINNER CAPSULE. THE MATRIX OR THE 15 MACROPHAGE CHEMOTACTIC PROTEIN 1 GIVES NO GIANT CELLS. 16 AND SO WHAT WE'RE GETTING, AS WE START 17 LOOKING AT THIS WHOLE SET OF IDEAS IS A POTENTIAL 18 MULTIPLE PARAMETER THERAPEUTIC APPROACH THAT CAN LEAD 19 TO BEING ABLE TO IMPLANT THINGS, SYNTHETIC MATERIALS, 20 IN THE BODY WITHOUT GETTING THAT DENSE FOREIGN BODY 21 REACTION. THAT'S THE PATH WE'RE HEADING ON. 22 ONE MORE INTERESTING PROTEIN IS OSTEOPONTIN, 23 ANOTHER ONE OF THESE PROTEINS THAT'S PRESENT IN WOUNDS 24 ALL THE TIME. AND IT MAY INHIBIT FOREIGN BODY GIANT 25 CELL FUSION, MAYBE HAVE AN ASSOCIATION WITH

25 1 ANGIOGENESIS. IT'S SOMETHING WE CALL A MULTIFACED 2 PROTEIN. AND ONE OF THE PROBLEMS WITH THIS IS THERE 3 ARE 14 LYSINES, I BELIEVE, ON THE SURFACE OF 4 OSTEOPONTIN. IT MEANS IF WE WANTED TO IMMOBILIZE IT ON 5 THE SURFACE AND WE WANTED ONE OF THE ACTIVE FACES TO BE 6 UP, WE'D HAVE VERY LITTLE CONTROL OF IT. SO WHEN WE 7 IMMOBILIZE OSTEOPONTIN ON A SURFACE TO MAYBE MANIPULATE 8 HEALING, WE CAN GET UP, DOWN, SIDEWAYS AND WE DON'T 9 KNOW WHICH ACTIVE REGION IS UP. NATURE NEVER USES THIS 10 KIND OF IMMOBILIZATION, BUT THE KINDS OF THE 11 TECHNOLOGIES WE HAVE NOW FOR MOST IMMOBILIZATIONS LEAD 12 TO THIS IRRATIONAL IMMOBILIZATION. 13 SO WE'VE BEEN WORKING ON AN INTERESTING IDEA 14 WHERE WE TAKE OUR BIOMATERIAL. AGAIN, IF WE JUST 15 ADSORB OSTEOPONTIN UP, DOWN, SIDEWAYS; BUT WHAT IF WE 16 COAT THE BIOMATERIAL WITH TYPE 1 COLLAGEN WHICH HAS A 17 NATURAL AFFINITY FOR THE OSTEOPONTIN AND ALWAYS BINDS 18 IT IN THE CORRECT WAY? MAYBE THEN WE COULD GET ORDERED 19 OSTEOPONTIN ON THE BIOMATERIAL. AND, IN FACT, THE 20 RESULTS HAVE BEEN VERY PROFOUND, THAT IF WE -- THIS IS 21 AN IN VITRO CELL ADHESION ASSAY WITH BOVONIC 22 ENDOTHELIAL CELLS, BUT THE POLYHEMA MATERIAL, THE 23 HYDROXLATED CONTROL HAS NO CELLS ON IT. WE USE THIS 24 IMMOBILIZATION AGENT, CDI, CARBONEAL DIAMTHAZOLE, WE 25 GET A FEW CELLS AND WE JUST LOOK AT THIS CONTROL. IF

26 1 WE USE THE CDI TO IMMOBILIZE OSTEOPONTIN, WE SEE SOME 2 CELLS. IF WE USE THE CDI TO IMMOBILIZE COLLAGEN, WE 3 SEE SOME CELLS. BUT IF WE TAKE THE POLYHEMA, ACTIVATE 4 IT WITH THE CDI, IMMOBILIZE COLLAGEN, AND THEN DIP IT 5 IN OSTEOPONTIN, WE GET PROLIFIC CELL ATTACHMENT AND 6 GROWTH. 7 WHY DO WE GET THAT? BECAUSE WE HAVE 8 DELIVERED THE OSTEOPONTIN SIGNAL WITH PRECISION MAYBE 9 THE WAY THE BODY HAD INTENDED THAT TO OCCUR; AND, 10 THEREFORE, WE GOT THIS VERY GOOD HEALING. 11 MY COLLEAGUE, CECI GIACHELLI, HAS SHOWN A 12 WONDERFUL EXAMPLE WORKING WITH STEPHANIE MARTIN AND 13 SOME OF THE OTHER STUDENTS IN THE LAB. CECI HAS A 14 MOUSE MODEL THAT VERY RAPIDLY CALCIFIES. AND IN 15 LOOKING AT HEART VALVES, WE FIND THERE'S A COUPLE OF 16 CONTROLS HERE, BUT THE HEART VALVES RAPIDLY CALCIFY. 17 IF WE TAKE THE HEART VALVE LEAFLETS, THESE ARE TISSUE 18 HEART VALVE LEAFLETS, IMMOBILIZE TO THEM COLLAGEN, AND 19 THEN DIP IT IN THIS PHOSPHORYLATED OSTEOPONTIN, WE CAN 20 GET GREATLY REDUCED VALVE CALCIFICATION IN VIVO, 21 SHOWING, AGAIN, WE CAN MANIPULATE THE COURSE OF THESE 22 LONG-TERM HEALING REACTIONS. 23 THIS IS JUST STILL ANOTHER EXAMPLE SHOWING 24 THAT -- I'M JUST GOING TO CLICK TO THE NEXT DIAGRAM. 25 WE'RE USING SURFACES THAT ARE AMINE SURFACES, A

27 1 CARBOXYLIC ACID SURFACE. WE THINK THE MULTIFACE NATURE 2 OF OSTEOPONTIN MAY ALLOW US TO DIRECT IT JUST BY PH OR 3 BY ISOELECTRIC POINT WOULD BE A BETTER WAY TO PUT IT 4 WHERE THE, FOR EXAMPLE, THE RGD SITE IS. AND SO, FOR 5 EXAMPLE, IF WE ADSORB OSTEOPONTIN TO AN AMINE SURFACE, 6 AND THIS IS SOME WORK THAT'S BEEN DONE WITH MY 7 COLLEAGUE, SHAOYI JIANG, AGAIN CECI GIACHELLI, AND SOME 8 OF OUR PH.D. STUDENTS. THE OSTEOPONTIN IS IMMOBILIZED 9 TO AN AMINE SURFACE OR CARBOXYLIC ACID SURFACE. WE MAY 10 DIRECT THE RGD SITE UP OR DOWN; AND WE SEE, ALTHOUGH 11 IT'S THE SAME AMOUNT OF PROTEIN, OSTEOPONTIN EXACTLY ON 12 THIS SURFACE AND ON THIS SURFACE, HUGELY MORE CELLS ON 13 THE AMINE SURFACE BECAUSE WE THINK WE'RE DIRECTING THE 14 PROTEIN CORRECTLY, PRECISION CONTROL. 15 SO LET ME WRAP THIS UP A LITTLE BIT HERE. 16 THIS CARTOON CAME FROM THE INTERNATIONAL HERALD 17 TRIBUNE . IT'S A RATHER GLIB CARTOON ILLUSTRATING SOME 18 WORK THAT HAS BEEN DONE IN PLACING AN ELECTRODE ARRAY 19 IN THE BRAIN OF A MONKEY. AND THE MONKEY CAN SIT AND 20 OPERATE THE CURSOR ON A COMPUTER SCREEN USING JUST ITS 21 MIND. ACTUALLY TOTALLY REMARKABLE EXPERIMENT, BUT THE 22 PROBLEM IS THAT ELECTRODE PERFORMANCE WILL NOT PERSIST 23 FOR CERTAINLY NOT THE LIFETIME OF A MONKEY OR AN 24 INDIVIDUAL PROBABLY DUE TO THIS FOREIGN BODY REACTION. 25 SO THE STUDIES WE'RE DOING, I THINK, TO GET AROUND THE

28 1 FOREIGN BODY REACTION TO ADVANCE BEYOND THIS WILL BE 2 VERY IMPORTANT, I THINK, IN TERMS OF FUTURE 3 DEVELOPMENTS IN USING ELECTRODE AND SENSOR DEVICES IN 4 THE BRAIN AND NEURONAL TISSUE. 5 I'VE ALLUDED TO THE PROBLEMS WITH 6 BIOCOMPATIBILITY, AND SO I KEEP ON THINKING ABOUT 7 DEFINITIONS. AND I'VE SAID MAYBE WE NEED A NEW ONE. 8 SO THESE ARE SOME NEW DEFINITIONS I'VE THROWN OUT. I 9 THINK WHAT WE CALL TODAY BIOCOMPATIBILITY MIGHT BE THE 10 ABILITY OF MATERIALS TO LOCALLY TRIGGER AND GUIDE 11 NORMAL WOUND HEALING, RECONSTRUCTION, AND TISSUE 12 INTEGRATION. THIS IS THE BIOCOMPATIBILITY THAT MAYBE 13 WE SEE WITH THESE SPHERE-TEMPLATED MATERIALS, A VERY 14 DIFFERENT SORT OF ALMOST NORMAL HEALING. 15 I THINK WHAT WE'RE GETTING TODAY WITH ALL OUR 16 SO-CALLED BIOCOMPATIBLE MATERIALS MIGHT BETTER BE 17 DEFINED AS BIOTOLERABILITY. IT'S THE ABILITY OF 18 MATERIALS TO RESIDE IN THE BODY FOR LONG PERIODS OF 19 TIME WITH ONLY LOW DEGREES OF INFLAMMATORY REACTION, 20 BUT CERTAINLY INFLAMMATORY REACTION AND CERTAINLY 21 ENCAPSULATION IS SEEN. SO I'M HOPING WE CAN SOMEDAY 22 SHIFT THE DEFINITION OF BIOCOMPATIBILITY TO ADDRESS 23 THIS IDEA OF HEALING, RECONSTRUCTION, AND TISSUE 24 INTEGRATION. 25 WELL, LET ME SORT OF WRAP THIS UP. I

29 1 MENTIONED THE UWEB PROGRAM A NUMBER OF TIMES. UWEB IS 2 UNIVERSITY OF WASHINGTON ENGINEERED BIOMATERIALS. AND 3 HAVE TO THANK OUR NATIONAL SCIENCE FOUNDATION SPONSORS 4 VERY MUCH FOR MAKING THESE HEALING STUDIES FOCUSED ON 5 ADVANCING THE WAYS MATERIAL INTEGRATED INTO THE BODY 6 MAKING THEM POSSIBLE. UWEB IS A LOT OF DIFFERENT 7 PEOPLE. THIS IS ABOUT HALF THE GROUP, BUT I'M VERY 8 PROUD OF OUR TEAM AND THE WAY I THINK WE'VE ENTERED 9 SOME NEW TERRITORY THAT HAS NOT BEEN EXPLORED BEFORE IN 10 BIOMATERIALS. 11 AND WE HAVE -- SOME OF THIS WORK WAS FUNDED 12 BY THE GOVERNMENT OF SINGAPORE AND THE SUWA PROGRAM, 13 SOME BY THE NIH, BUT MOSTLY THANKS TO STUDENTS, STAFF, 14 AND COLLEAGUES WHO HAVE CONTRIBUTED TO THIS RESEARCH. 15 THANK YOU FOR LISTENING. 16 THE MODERATOR: ONE CHALLENGE ASSOCIATED WITH 17 USING RECORDING ELECTRODES IN THE CENTRAL NERVOUS 18 SYSTEM IS MOVEMENT. COULD YOU COMMENT ON HOW MOVEMENT 19 OF IMPLANTED ELECTRODES IMPACTS THE BIOLOGICAL 20 RESPONSE? 21 DR. RATNER: YEAH. ABSOLUTELY. THAT'S AN 22 EXTREMELY GOOD POINT, AND IT'S MAYBE ALMOST OBVIOUS IF 23 SOMETHING IS RUBBING, ERODING, SCRATCHING, WE'RE GOING 24 TO GET INCREASED ENHANCED LOCAL INFLAMMATION THAT WILL 25 PROBABLY LEAD TO AN UNDESIRABLE OUTCOME. SO, AGAIN, I

30 1 BELIEVE ONE OF THE HORIZONS IN BIOMATERIALS RESEARCH IS 2 GOING TO BE THE ABILITY TO TREAT THE SURFACE OF THE 3 ELECTRODES SO WE CAN ELIMINATE OR MINIMIZE MICRON 4 MOVEMENT AT THE SURFACE OF ELECTRODES AND DEVICES AND 5 ELIMINATE THIS IRRITATION. AND, IN FACT, WE ARE OUT 6 WORKING TRYING TO DEVELOP METHODOLOGIES TO DO THIS 7 BECAUSE I THINK IT'S A CRITICAL PART OF THE EQUATION. 8 THE MODERATOR: IF ANGIOGENESIS IS AN 9 INDICATOR OF HEALING, HOW CAN WE QUANTIFY ANGIOGENESIS? 10 DR. RATNER: YEAH. THAT'S ALSO A VERY 11 IMPORTANT QUESTION. WE'VE DEALT WITH THIS IN A NUMBER 12 OF WAYS. WE'VE ACTUALLY WITHIN THE UWEB PROGRAM 13 DEVELOPED SOME SOFTWARE TO LOOK AT, IN A FRACTAL 14 MANNER, THE BRANCHING OF BLOOD VESSELS. FORTUNATELY 15 THESE DAYS WE'RE QUITE LUCKY TO HAVE A WIDE RANGE OF 16 IMMUNOSTAINS THAT WE CAN DIRECT TO VERY SPECIFIC 17 COMPONENTS ASSOCIATED WITH ANGIOGENESIS AND 18 VASCULOGENESIS. SO WE CAN USE SOME OF THE IMAGE 19 ANALYSIS TECHNIQUES. WE CAN USE SOME OF THE NEWER 20 SOFTWARE. WE CAN USE THINGS LIKE MICRO-CT AND WE CAN 21 START A CONFOCAL MICROSCOPY, AND I THINK WE CAN START 22 TO BUILD QUANTITATIVE MODELS NOW OF ANGIOGENESIS. AND 23 WE HAVE PEOPLE WITHIN OUR PROGRAM, AGAIN, WHO HAVE BEEN 24 THINKING AND WORKING ALONG THOSE LINES. 25 THE MODERATOR: WHAT IS THE DOMINANT

31 1 MECHANISM OF GLUCOSE SENSOR FAILURE? IS IT THAT THE 2 GLUCOSE MOLECULE IS TOO LARGE TO DIFFUSE THROUGH THE 3 FOREIGN BODY CAPSULE? 4 DR. RATNER: I BELIEVE THAT'S ALMOST EXACTLY 5 WHAT'S HAPPENING. WHEN ONE EXAMINES THE SENSORS, TAKES 6 THEM OUT AFTER LONG PERIODS OF TIME AND CLEANS THEM, 7 ONE CAN GET BACK ALMOST THE INITIAL PERFORMANCE OF 8 THOSE SENSORS. SO THE SENSORS AREN'T BEING 9 ELECTRONICALLY OR CHEMICALLY WIPED OUT. WHAT'S 10 HAPPENING IS YOU'RE LOSING THE ABILITY TO RAPIDLY 11 DETECT GLUCOSE CHANGES. 12 AND IT HAS BEEN DEMONSTRATED THAT IF WE CAN 13 ACCURATELY TRACK GLUCOSE LEVELS, WE CAN HAVE A STRONG 14 THERAPEUTIC IMPACT IN REDUCING DIABETIC COMPLICATIONS. 15 SO I THINK THE LONG LAG TIME ASSOCIATED WITH DIFFUSION, 16 THE LONG LAG TIME ASSOCIATED WITH DIFFUSION OF THE 17 GLUCOSE MOLECULES THROUGH THE CAPSULE REALLY SETS US 18 BACK, AND SO, AGAIN, OUR APPROACH TO ELIMINATE THE 19 CAPSULE AND INCREASE THE VASCULARITY LOCALLY. 20 THE MODERATOR: IS SIZE A CONTRIBUTING FACTOR 21 TO DETERMINING THE FOREIGN BODY RESPONSE? WOULD YOU 22 EXPECT THE SAME RESPONSE TO A MATERIAL AT MILLIMETER 23 MICROMETER AND NANOMETER DIMENSIONS? 24 DR. RATNER: WELL, IT'S ACTUALLY A FAIRLY 25 COMPLICATED QUESTION. SPEAKING OF SIZE, ONE VERY LARGE

32 1 SURFACE AREA IMPLANTED IN THE BODY IS A BREAST IMPLANT. 2 AND BREAST IMPLANTS HAVE A TERRIBLE PROBLEM WITH 3 FOREIGN BODY CAPSULE AND CAPSULAR CONTRACTURE, A MAJOR 4 MEDICAL PROBLEM. 5 IF WE GO DOWN ALL THE WAY TO THE OTHER 6 EXTREME, TO THE NANOSCALE, ONE OF OUR INVESTIGATORS IN 7 THE UWEB PROGRAM, PROFESSOR JOAN SANDERS, HAS LOOKED AT 8 MICRO AND NANOFIBERS, AND THEY FIND THAT WHEN THE FIBER 9 DIAMETERS GET BELOW ABOUT 5 MICRONS OR SO, THE BODY 10 FAILS TO EVEN DETECT THEM. SO IT SUGGESTS STRATEGIES 11 WITH MICRO GOING INTO NANO RANGE OF VERY FINE FIBERS. 12 IF WE GO INTO THE MIDDLE RANGE THAT WE JUST MENTIONED, 13 THE MICRO RANGE, I THINK WE'VE JUST SHOWN SOME PRETTY 14 COMPELLING EVIDENCE THAT A MICRO SCALE POROSITY CAN 15 INDEED ALTER, CAN CHANGE THE FOREIGN BODY REACTION. 16 AND SO WE'RE FOCUSING VERY MUCH, AGAIN, ON 17 METHODS TO CAPITALIZE ON THAT MICRON RANGE. SO THAT IS 18 AN INTERESTING QUESTION BECAUSE THERE ARE PARTS OF THE 19 ANSWER THAT COVER MACRO, MICRO, AND NANO ISSUES. 20 THE MODERATOR: A RELATED QUESTION. IS THERE 21 A SIZE LIMIT TO BIOMATERIALS THAT WILL PREVENT THEM 22 FROM BEING EATEN BY MACROPHAGES OR MULTINUCLEAR GIANT 23 CELLS? 24 DR. RATNER: SIZE LIMIT. THAT'S KIND OF 25 A -- SO TO RECAPITULATE THIS IDEA THAT NANOFIBERS DO

33 1 NOT SEEM TO INDUCE A FOREIGN BODY REACTION SUGGESTS 2 THAT MAYBE AT THE NANOSIZE SCALE, ONE CAN TRICK THE 3 BODY INTO NOT SEEING MATERIALS. AT LARGER SCALES, I 4 THINK, PARTICULARLY OVER, LET'S SAY, 5 MICRONS, TO 5 THROW OUT A NUMBER, THE BODY WILL SEE IT. MACROPHAGES 6 WILL GLOM DOWN ON THESE MATERIALS. AND THEN THE 7 MACROPHAGE WILL TRY AND DIGEST THE MATERIAL. 8 NOW, ANOTHER PART OF THAT IS SOME MATERIALS 9 ARE MADE TO BE DEGRADED OR BROKEN DOWN. AND DIGESTIVE 10 ENZYMES AND THE OXIDANTS PRODUCED BY THE MACROPHAGES 11 CAN BE USED FOR BREAKING DOWN MATERIALS IF YOU ENGINEER 12 OR DESIGN IT TO DO SO. BUT FOR LARGER MATERIALS, THE 13 MACROPHAGES JUST SIMPLY CAN'T DO IT AND SIMPLY LEADS TO 14 THIS ENCAPSULATION PROCESS. 15 THE MODERATOR: THE CENTRAL NERVOUS SYSTEM IS 16 SURROUNDED BY THE BLOOD BRAIN OR BLOOD NERVE BARRIER 17 AND CREATES AN IMMUNOPROTECTED ENVIRONMENT. CAN YOU 18 COMMENT ON HOW THE FOREIGN BODY REACTIONS THAT YOU 19 DESCRIBED MIGHT DIFFER FROM THOSE THAT ARE OBSERVED IN 20 THE BRAIN? 21 DR. RATNER: YEAH. AGAIN, A VERY GOOD 22 QUESTION. THERE ARE SUBTLE DIFFERENCES IN DIFFERENT 23 SITES IN THE BODY OR SOMETIMES NOT EVEN SO SUBTLE 24 DIFFERENCES IN DIFFERENT SITES OF THE BODY IN THE 25 MAGNITUDE OF THIS FOREIGN BODY REACTION. I THINK IT'S

34 1 BEEN REPORTED THAT WITHIN THE BRAIN, ON THE FAR SIDE OF 2 THE BLOOD BRAIN BARRIER, ONE GETS LESS OF THIS REACTION 3 OVERALL, BUT STILL THE REACTION IS SEEN. 4 THE EYE IS ANOTHER SORT OF SEMIPRIVILEGED 5 SITE, LET'S CALL IT, AND PEOPLE SEE LESS REACTION. BUT 6 YOU DO SEE STILL REACTION IN THE EYE. THE EYE 7 REPRESENTS AN INTERESTING CASE. FOR YEARS PEOPLE SAID 8 THERE WOULD BE NO REACTION IN THE EYE BECAUSE IT'S 9 PRIVILEGED, AND THEN PEOPLE STARTED LOOKING AT IMPLANT 10 DEVICES JUST LOOKING, USING AN OPHTHALMOLOGIC 11 MICROSCOPE RIGHT THROUGH THE CORNEA. AND WHAT THEY SEE 12 IS NEUTROPHILS IN THE EARLIEST STAGES, MACROPHAGES, 13 FOREIGN BODY GIANT CELLS, AND FINALLY FIBROBLASTS. SO 14 THE EXACT SAME SEQUENCE IN THE EYE. 15 THE SAME SEQUENCE HAS ALSO BEEN NOTED IN THE 16 BRAIN. SO, AGAIN, THERE MAY BE DIFFERENCES IN 17 MAGNITUDE OF THE EFFECT; BUT ON THE OTHER HAND, I THINK 18 THE GENERAL PATHWAY SEEMS TO BE QUITE SIMILAR IN ALL 19 TISSUES IN THE BODY. 20 THE MODERATOR: YOU SHOWED THE COATINGS, 21 ADHESION, AND POROSITY INFLUENCED THE TISSUE RESPONSE. 22 HOW IS THE TISSUE RESPONSE INFLUENCED BY THE MODULES OF 23 THE MATERIAL AND ESPECIALLY THE RELATIVE MODULI OR 24 MECHANICAL IMPEDANCES OF THE MATERIAL AND THE TISSUE? 25 DR. RATNER: VERY IMPORTANT QUESTION.

35 1 ACTUALLY RELATES TO THE FIRST QUESTION I ANSWERED. 2 FIRST OF ALL, I THINK IT'S PRETTY CLEAR THAT SOFTER, 3 LOW MODULUS MATERIALS PROBABLY WILL INDUCE, AS YOU 4 MIGHT IMAGINE, LESS IRRITATION, SCRATCHING, DISTURBANCE 5 AT THE INTERFACE AND, THEREFORE, PROBABLY WILL HEAL 6 BETTER. A HARD, RIGID MATERIAL, ESPECIALLY WHEN PLACED 7 IN A SOFT MATERIAL, LEADS TO A RATHER SEVERE 8 INTERFACIAL REACTION PROBABLY DUE TO THE MECHANICS. 9 AND SO I BELIEVE THE FUTURE RESIDES IN 10 LEARNING HOW TO STABILIZE AT A MICRO LEVEL THESE 11 IMPLANT DEVICES WITH THE TISSUE. 12 THE MODERATOR: YOU DEMONSTRATED THAT 13 COATINGS ON DEVICES CAN INFLUENCE BOTH THE THICKNESS 14 AND CONSTITUTION OF THE FOREIGN BODY REACTION. TO 15 THESE COATINGS HAVE A FINITE LIFETIME AND EVENTUALLY 16 THEY'RE DEGRADED AND THE REACTION REVERTS TO THAT OF 17 THE UNDERLYING BASE MATERIAL? 18 DR. RATNER: IT'S A NICE QUESTION. WE'RE 19 ACTUALLY DEVELOPING, FOR EXAMPLE, THOSE 20 SPHERE-TEMPLATED MATERIALS THAT SEEM TO BE ABLE TO 21 IMPACT THE MAGNITUDE OF THE FOREIGN BODY REACTION. 22 WE'RE DEVELOPING THEM OUT OF BOTH BIOSTABLE AND 23 BIODEGRADABLE FORMS. FOR EXAMPLE, WE MAKE THEM OUT OF 24 SILICONE RUBBER, AND THESE WILL PERSIST IN THE BODY 25 PRETTY MUCH FOREVER SINCE THE BODY CAN'T REALLY BREAK

36 1 DOWN SILICONE RUBBER. 2 AND SO ONE OF THE QUESTIONS WE HAVE TO ASK IS 3 IN A VERY LONG TERM HOW WILL THAT EXCELLENT TISSUE THAT 4 IS BEING RESTORED IN THAT SPHERICAL STRUCTURE, HOW WILL 5 THAT TISSUE PERSIST? ON THE OTHER HAND, WE'RE ALSO 6 DEVELOPING THESE MATERIALS OUT OF BIODEGRADABLE FORMS, 7 SO AFTER THE TISSUE IS HEALED AND RESTORED, PRESUMABLY 8 DUE TO THE SPECIAL GEOMETRIC EFFECT OF THE 9 SPHERE-TEMPLATED MATERIAL, THEN WE HAVE THIS NEW TISSUE 10 THAT'S FORMED, WE ASK THE QUESTION IF THE BIODEGRADABLE 11 MATERIAL GOES AWAY, AGAIN, WILL THAT NICE TISSUE 12 HEALING WE GOT REMAIN? AND THESE ARE QUESTIONS WE 13 DON'T QUITE HAVE THE ANSWER TO, BUT WE DO HAVE TWO 14 INTERESTING PROBES, THE BIOSTABLE FORM AND THE 15 BIODEGRADABLE FORM OF THESE MATERIALS. 16 THE MODERATOR: YOU ILLUSTRATED THE IMPACT OF 17 PORE SIZE ON THE TISSUE RESPONSE TO A BIOMATERIAL. CAN 18 YOU COMMENT ON THE PORE DENSITY OR PORE SIZE 19 PERIODICITY TO THE RESPONSE OF A MATERIAL? 20 DR. RATNER: THESE ARE VERY GOOD QUESTIONS. 21 WE'RE PRETTY COMMITTED TO THE IDEA THAT THE HIGHEST 22 PORE DENSITY WE CAN GET; NAMELY, THE MOST VOID SPACE, 23 WILL BE BEST. OBVIOUSLY THE PORE SIZE IS CRITICAL. 24 WE'RE NOT SURE ABOUT THE PERIODICITY ISSUE, BUT ONE CAN 25 GET THE HIGHEST DENSITY BY PACKING THESE MICROSPHERES

37 1 MOST TIGHTLY AND, THEREFORE, GIVES US BOTH THE HIGHEST 2 DENSITY AND VERY GOOD PERIODICITY. SO THE TWO ARE KIND 3 OF INTERCONNECTED. 4 THE MODERATOR: CAN YOU COMMENT ON POTENTIAL 5 MECHANISMS TO ENHANCE THE STABILITY OF MICROELECTRODES 6 IMPLANTED IN THE BRAIN AND PREVENT THE MICROMOTION THAT 7 WE DISCUSSED EARLIER? 8 DR. RATNER: LET'S SEE. WE ARE AT THE MOMENT 9 WORKING ON SOME STRATEGIES, AND I REALLY AM NOT FREE TO 10 TALK ABOUT THE PRECISE NATURE OF THE STRATEGIES. IT'S 11 WORK IN PROGRESS, BUT WE'RE COLLABORATING WITH 12 PROFESSOR MARK HAMAYAN, WHO'S ALSO SPOKEN IN THIS 13 SERIES FROM THE DOHENY EYE INSTITUTE, AND ALSO FROM 14 ANOTHER ONE OF OUR ENGINEERING RESEARCH CENTERS, AND 15 WORKING ON EXACTLY THIS ISSUE OF HOW WE CAN MICROAFFIX 16 THESE ELECTRODES TO INHIBIT MICROMOTION AT THE TISSUE 17 LEVEL. SO I'M NOT FREE TO GO INTO DETAILS AT THE 18 MOMENT, BUT WORK IS IN PROGRESS. 19 THE MODERATOR: THAT'S THE LAST QUESTION. 20 THANK YOU VERY MUCH, DR. RATNER. 21 DR. RATNER: YOU'RE WELCOME. 22 23 24 25

38