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Building a Bioartificial Kidney: From Silicon Chips to 

Renal Clearance

Paul Brakeman, MD, PhDMedical Director, Pediatric Dialysis Unit

Assistant ProfessorDepartment of Pediatrics

UCSF 

Currently There Are > 540,000 Patients with End Stage Renal Disease in the United States

USRDS Annual Report, 2009

Surv

ival

Pro

babi

lity

Months

Currently There Are > 540,000 Patients with End Stage Renal Disease in the United States

USRDS Annual Report, 2009

Surv

ival

Pro

babi

lity

> 350,000 patients receive dialysis

Months

Currently There Are > 540,000 Patients with End Stage Renal Disease in the United States

USRDS Annual Report, 2009

Surv

ival

Pro

babi

lity

> 350,000 patients receive dialysis

> 70,000 patients waiting for a renal transplant

Months

Currently There Are > 540,000 Patients with End Stage Renal Disease in the United States

USRDS Annual Report, 2009

Surv

ival

Pro

babi

lity

> 350,000 patients receive dialysis

> 70,000 patients waiting for a renal transplant

Only 18,000 transplants per yearMonths

Strategies to Increase Numbers of Available Organs

• Publicity campaigns to increase organ donation• Extended criteria for identifying usable organs (Audard Trans Int 2007)

• Desensitized patients so they are more likely to be able to find a compatible kidney (Montgomery NEJM 2011)

Strategies to Increase Numbers of Available Organs

• Publicity campaigns to increase organ donation• Extended criteria for identifying usable organs (Audard Trans Int 2007)

• Desensitized patients so they are more likely to be able to find a compatible kidney (Montgomery NEJM 2011)

• Engineer replacement organs

Strategies for Engineering Replacement Organs

• Generate humanized animals and use them as a source for organs

• Grow an organ using stem cells• Use human kidney cells to reconstitute renal tissue 

Strategies for Engineering Replacement Organs

• Generate humanized animals and use them as a source for organs

• Grow an organ using stem cells• Use human kidney cells to reconstitute renal tissue • Engineer a bioartificial organ using novel technology for hemofiltration and renal cells to provide cellular function

The Bioartificial Kidney Project

The Bioartificial Kidney Project

Frank Partridge 2009 Johnson Research

The Bioartificial Kidney Project

The Renal Filter Unit: the Nephron

Peritubular Capillary

ProximalTubule

Loop of Henle

DistalTubule

CollectingDuct

Glomerulus

Peritubular Capillary

ProximalTubule

Loop of Henle

DistalTubule

CollectingDuct

Glomerulus~500,000-1,000,000 per kidneyGenerate ~150L of filtrate per day

The Renal Filter Unit: the Nephron

Peritubular Capillary

Loop of Henle

DistalTubule

CollectingDuct

GlomerulusProximal TubuleSelectively reabsorbs ~80% of most solutesReabsorbs ~80% of filtered water1,25-(OH)2-Vit D3 activation

The Renal Filter Unit: the Nephron

Peritubular Capillary

ProximalTubule

Loop of Henle

Distal TubuleFine tunes solute excretionFurther water excretion

CollectingDuct

Glomerulus

The Renal Filter Unit: the Nephron

H2O

Schematic of the Bioartificial Kidney

Blood

Filtrate

H2O Na+

Na+

Urea

Urea

Waste

H2O Na+ Urea

H2O Na+ Urea

H2O

Blood H2O Na+

Na+ Urea

H2O Na+

H2O Na+ Urea

H2O

Blood

Filtrate

H2O Na+

Na+

Urea

Urea

WasteHemofilter

H2O Na+ Urea

H2O Na+ Urea

H2O

Blood H2O Na+

Na+ Urea

H2O Na+

H2O Na+ Urea

Schematic of the Bioartificial Kidney

H2O

Blood

Filtrate

H2O Na+

Na+

Urea

Urea

Waste

H2O Na+ Urea

H2O Na+ Urea

H2O

Blood H2O Na+

Na+ Urea

H2O Na+

H2O Na+ Urea

o Based on hemofiltration to eliminate need for dialysateo Implantable to allow for continuous blood cleansing o Incorporate of renal cells to reabsorb solutes and exclude toxinso Renal cells provide some metabolic and hormonal functions

Bioreactor - Human renal tubular cells

Schematic of the Bioartificial Kidney

Innovations Required for  Implantation of the RAD

Humes et al., Univ. of Michigan

Innovations Required for  Implantation of the RAD

Humes et al., Univ. of Michigan

o Elimination of high pressure pumps

o Miniaturization of the hemofilter

o Better biocompatibility of the filter and blood path

o Intrinsic feedback to monitor patient‘s homeostasis

o Stable function for months to years

o Adequate reabsorptionof salt and water

• Targets– Hemofiltration‐

• 30 liters per day of filtrate produced

Design Targets for the Bioartificial Kidney

• Targets– Hemofiltration‐

• 30 liters per day of filtrate produced – why?

Design Targets for the Bioartificial Kidney

Improvement in Survival with Intensive Daily Dialysis

Johansen K, Kidney Int, 2009

Conventional hemodialysis

Nocturnal hemodialysis

• Targets– Hemofiltration‐

• 30 liters per day of filtrate produced – how?

Design Targets for the Bioartificial Kidney

Improved Membrane Technology is Critical for Miniaturizing the Bioartificial Kidney

Standard dialysis membrane Silicon nanopore membrane

William Fissell and Shuvo Roy, J Memb Sci, 2010

• Very consistent pore sizes create highly selective pores and allow for exclusion of antibodies and medium to large size proteins for better biocompatibility

• High hydraulic permeability• Smooth surface allows for coating 

the membranes to allow for low bioreactivity

Silicon nanopore membrane after 48 hours of in vitroexposure to whole blood

Fissell, J Memb Sci, 2010

Improved Membrane Technology is Critical for Miniaturizing the Bioartificial Kidney

• Very consistent pore sizes create highly selective pores and allow for exclusion of antibodies and medium to large size proteins for better biocompatibility

• High hydraulic permeability• Smooth surface allows for coating 

the membranes to allow for low bioreactivity

Silicon nanopore membrane after 48 hours of in vitroexposure to whole blood

Fissell, J Memb Sci, 2010

Improved Membrane Technology is Critical for Miniaturizing the Bioartificial Kidney

3‐Dimensional CAD Rendering of the Bioartificial Kidney

Hemofilterblood in blood out

ultrafiltrate

Membrane chips bondedback-to-back

}

ultrafiltrateblood

membranesilicon substratebonding layer

Bioreactor Current hydraulic 

permeability of the silicon membrane is 10 l/cm2/min/PSI. 

At this porosity the hemofilter requires 380 cm2 of filter area to generate 30L per day of filtrate – About the size of two decks of cards

Ex‐vivo Hemofilter Design Testing

Computer Assisted Design

ManufacturingPrototype

TestingPrototype

• Targets– Hemofiltration‐

• 30 liters per day of filtrate produced• Biocompatibility of the filter and blood path

– Bioreactor‐• Barrier function to prevent reabsorption of toxins• 25 liters of water reabsorption• 3500 mM of sodium reabsorption• Metabolic function

Design Targets for the Bioartificial Kidney

Properties of an Ideal Renal Cell for the Bioreactor

o Barrier to reabsorption of toxinso Adequate reabsorption of sodium, potassium,

phosphorus and watero Provides metabolic function including 1,25 OH

Vitamin D productiono Stable for 3-4 monthso Non-immunogenic

Analysis of Cells in a LaminarFlow Bioreactor

Standard Tissue Culture Tissue Culture Under Flow Conditions

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

OK LLC-PK1

CreatinineRetention

Urea Retention

Barrier Function of Commercially Available Proximal Tubule Cell Lines

n = 6 n = 6 n = 6 n = 6

Water Transport of Proximal Tubule Cell Lines

Tran

sport R

ate L

/cm

2 /day

Ferrell et al. 2011, submitted

0

10

20

30

40

50

60

OK LLC-PK1 HCTC

n = 4 n = 4

Immortalized Human Proximal Tubule Cells ‐ RPTEC/TERT1 Cells

Primary human proximal tubule cells were transfected with human telomerase and clones were selected and characterized

Green = Acetylated Tubulin Green = -catenin

Wieser, Grillari, AJPR, 2008

Barrier Function of RPTEC/TERT1 Cells

n = 6 n = 6 n = 6 n = 697.0%

97.5%

98.0%

98.5%

99.0%

One Month Two Months Three Months

Perc

ent r

etai

ned

crea

tinin

e

Salt Reabsorption of RPTEC/TERT1 CellsTran

sport R

ate 

mEq

/cm

2 /day

n = 6 n = 6

20181614121086420

Salt Reabsorption of RPTEC/TERT1 Cells

n = 6

25 kD

20 kD

-tubulin

ZO-1

10uM

Water Transport of Other Immortalized Human Renal Proximal Tubule Cells

n = 4 n = 4

Sanechika, NDT, 2011

Water Transport of Other Immortalized Human Renal Proximal Tubule Cells

n = 4 n = 4

** Actual reabsorption 17 uL/cm2/day

Sanechika, NDT, 2011

Salt and Water Transport in Renal Proximal Tubule Cells

Bioartificial Kidney Project

Silicon Nanofabrication Cell Engineering

UCSF Bioartificial Kidney Team

• UCSF Team memberso Brakeman Lab

o Chao‐Zong Leeo Natalie Spivako Daniel Kaplan

o Shuvo Roy Labo Rishi Kanto Alex Hellero Peter Solero Torin Yeager

o Mark Wilson Labo Steven Hettso Loi Doo Mathem Saeedo Jeremy Durack

Bioartificial Kidney

• Non‐UCSF Team memberso William Fissell Lab (Vanderbilt School of Medicine)

o Nicholas Ferrell, PhDo David Humes, MD (University of Michigan)

Project Team

Bioartificial Kidney Project

Silicon Nanofabrication Cell Engineering