by: sara anam, garni tatikian
TRANSCRIPT
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By: Sara Anam, Garni Tatikian
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Thousands of people die every year waiting for organs from a donor
Mechanical solutions (kidney dialysis, heart-lung bypass machines, etc.) and synthetic solutions (blood vessels, joint replacements) are not as efficient and don’t last as long as the real organ◦
There’s also a risk of infection, rejection, etc.
The ideal solution is to be able to grow our own organs
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Overview of Tissue Engineering ◦
Role of Scaffolds
Anatomy and Physiology of the Bladder
Approaches to Scaffold Design
Introduction to Dr. Anthony Atala’s artificial bladder project
The Process of Decellularization
The Process of Making Pre-Made Porous Scaffolds
Results of Dr. Atala’s Experiment
The Future of Scaffolds and Artificial Bladders
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Function◦
Collect and store urine from kidneys◦
Holds about two cups of urine for 2-5 hours◦
Releases it out to urethra when it is full
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Location◦
Part of the urinary system◦
Inside pelvis behind the pelvic bone
Other Components of the Urinary System◦
Ureters: Tube that allows urine to run from the kidney to the bladder◦
Urethra: Tube that allows the urine to run from the neck of bladder to the exterior of the body◦
Sphincters: Valves that control flow from the urethra
Internal Sphincter/External Sphincter: Regulate storage and emptying of bladder
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Resembles a balloon
Empty Bladder: Small, like a deflated balloon
Filled Bladder: Rounded shape that rises to the abdominal cavity
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Three Layers of the Bladder1. Mucosa
-composed of transitional epithelium (urothelial cells) -contains no blood vessels -lines bladder and ureters -stretches as bladder fills up
2. Submucosa -composed of connective tissue -contains blood vessels, nerves and glands -supplies mucosa with nutrients
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3. Detrusor Muscle◦
Composed of smooth muscle
◦
Expands to store urine and contracts to expel urine
◦
Contraction activated by release of transmitters from motor nerves
◦
Normally remains relaxed to allow bladder to fill
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• Nerves in the spinal cord carry information between bladder and brain
• When a certain amount of urine is in the bladder, internal pressure becomes strong
• Stretch receptors in the bladder wall become activated and send signals to the brain
• This results in the desire to urinate
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• The brain sends a signal to the spine• The spine forwards the signal to the bladder• Small contractile waves occur in the detrusor muscle,
causing the internal sphincter to loosen• The external sphincter will then loosen as well, and the
bladder empties
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Things can go wrong when there is tissue damage
Tissue damage can be caused by trauma, birth defects, neurological diseases and cancer
It usually results in low volume and high pressure in the bladder
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Birth Defects1) Exstrophy
Rare
Abdominal wall fails to close during fetal development
Posterior bladder sticks out of lower abdominal wall
Part of urinary bladder present outside the body
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Birth Defects
2) Myelomeningocele (Neurological Disorder)
Caused in pregnancy when two sides of spinal cord don’t join together
Incomplete development of lower part of the spinal cord and its coverings
Nerves of spinal cord damaged
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Bladder Cancer
Cells multiply and form an area of abnormal cells
Doctors will try to surgically remove the tumour (this will damage bladder wall)
Advanced stages of cancer: Part or all of the bladder will be removed
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Augmentation Cystoplasty◦
Involves tissue grafts
◦
Can use tissue from any organ attached to the bladder ex. intestine, stomach
◦
Can also use synthetic materials
◦
Result: Larger storage capacity and reduced amount of pressure on the bladder wall
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Enterocystoplasty
◦
Most widely used form of cystoplasty
◦
Patch of small intestine is used
◦
Bladder is cut open◦
Patch of intestine used to augment bladder
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The Extra-Cellular Matrix (ECM) is a protein filled structure that surrounds cells
Most cells secrete their own ECM and are anchored in them
ECM varies based on the tissue it’s in
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Provides a physical environment in which cells grow, migrate, and function
Influences the structural and mechanical properties of the cells that grow in it◦
Consider: Bladders must be elastic since they are constantly expanding and retracting
Provides bioactive signals that regulate the activities of the cell
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Acts as both a resevoir and a deliverer of growth factors
Is biodegradable in the event that changes in vascularization and remodeling of the tissue is required
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To develop an organ that’s identical to the one we want to mimic, we should build it in a
scaffold that’s just like the ECM of its tissue!
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Experimented with the :◦
Collagen Matrix Scaffold:
Scaffold Approach: Decellularizing
the bladder’s submucosa tissue
The resulting ECM is very rich in collagen
◦
Collagen-PGA Scaffolds:
Scaffold Approach: Pre-made porous scaffold technique
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Process: Remove the cells from an allogenic or xenogenic tissue, leaving behind the ECM
•
Advantages: Scaffold will have the closest imitation of the natural mechanical properties and composition of the ECM
•
Disadvantages:
Incomplete removal of the cells may trigger an immune response
The ECM is damaged during the production processes
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Goal:Complete this process without
negatively affecting the composition, mechanical
properties, and the biological activity of the ECM!
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1)
Obtain tissue that contains the desired ECM
2)
Physically separate the unwanted tissue structures from the ECM:
1)
Methods include:1)
Freezing and Thawing2)
Sonication-
agitation of particles using sound energy
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3) The cell remnants are removed from the ECM
4) Optional Step: Tissue is often disinfected and dehydrated
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Dehydration:◦
Loss of Water During Decellularization
Negative Results: Collapse of collagen fibers, changes in degradation rate, and less cellular attachment
Positive Results: Less leaching of growth materials, increased shelf life, and modified strength and mechanical properties
◦
Tradeoff: Sometimes processes like vacuum pressing are used to encourage dehydration despite the negative affects!
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5) The scaffold is terminally sterilized ◦
Methods of sterilization used on all of Dr. Atala’s bladders, including the pre-made porous ones, included UV light and ethylene oxide
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Process:
Uses natural and synthetic biomaterials in an attempt to create a scaffold that mimics the ECM
•
Advantages: Lots of control over the materials used and the architecture and microstructure of the scaffold
•
Disadvantages: Time consuming
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Biocompatibility with the cells being grown and the tissue it will be implanted in
Stability (before and after implantation)
Sterilizable
Eventually Dissolves ◦
Products of breakdown can’t be toxic ◦
The degradation rate upon implantation should equal the growth rate of the host tissue
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Large surface area for cells◦
Usually porous
The pores should be large enough to host cells and should be interconnected so that nutrients and wastes can be exchanged between the cells
Should include growth factors, cell adhesive lignands, and certain topography that encourages growth in a particular pattern
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Naturally existing materials such as and collagen and alginate
Concerns:◦
The properties of these material’s can’t be easily modified for specific applications◦
Can enough of this material be harvested?
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The properties of synthetic materials can be modified to suit a particular situation
They can be mass produced
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Consider the Poly (α-
hydroxyl acid) family:◦
PGA ◦
PLLA◦
PLGA
A copolymer of PGA and PLLA
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Advantages of the Poly (α-
hydroxyl acid):
They are FDA approved
They are sufficiently stable
Degradation◦
Degrade when undergoing hydrolysis ◦
Fibers can be modified to control their degradation rate◦
The product of their degradation can be metabolized and excreted by cells
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There are four main techniques for preparing these scaffolds. ◦
Fiber Bonding◦
Solvent Casting/ Particular Leaching◦
Gas Foaming◦
Phase Separation
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Scaffold fibers are immersed in a PLLA solution
The solution is evaporated leaving PLLA covered fibers
The product is heated. PLLA will melt first, filling empty spaces in the fibers.
Once the fibers melt, they won’t collapse. They’ll instead start to weld where fibers cross
The PLLA is removed
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Advantages:◦
Large surface area◦
81% porosity◦
Up to 500 micrometers pores
Disadvantages:◦
Uses toxic chemicals that must be completely removed from the scaffold using vacuum drying◦
Overheating/Toxic agents make it hard to incorporate growth factors during scaffold processing
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Dissolve fibers in chloroform or methylene chloride
Add a water soluble compound (Ex. Salt)
Evaporate the solvent
Place the resulting product in water for 2 days until the salt comes off
The salt particles will create pores in the fiber
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Advantages: ◦
High interconnectivity and biocompatibility ◦
Works well with a large range of cells◦
Amount of porosity can be controlled based on the amount of salt added
Disadvantages:◦
Use of organic materials risks adding pharmacological agents to the scaffold
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Here, gas is used as the porogen
Solid discs of the fibers are placed in chamber
They are initially exposed to CO2 at high pressures
The CO2 pressures drop to atmospheric level over three days
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Advantages: ◦
93% porosity ◦
Pore sizes of up to 100 micrometers◦
No organic solvents involved
Disadvantages:◦
Not enough interconnectivity ◦
Extreme processing conditions prevent incorporation of growth factors into the scaffold during processing
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Technique 1: Liquid-
Liquid Phase Separation◦
Fibers are dissolved in a liquid with a low melting point◦
They are then cooled and vacuum dried
Technique 2: Freeze-
Drying◦
Fibers are placed in a solution of methylene oxide and water
◦
They then undergo freeze-drying
Advantages:
90-95 % porosity
Disadvantages:◦
Use of harsh organic solvents (Technique 1 hasn’t even been tested for biocompatibility)
◦
Technique 2’s pores are too small for effective use, but it’s believed this can be improved
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The Candidates
7 Patients, ranging from 4-19 years of age, were given bladder transplants
All had myelomeningocele
They had poor bladder compliance
Had not responded to other medical treatments
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A bladder biospy sample of 1-2 cm^2 was taken
The urothelial cells and the smooth muscle cells were separated and cultured independently
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Number of bladders
Collagen Matrix
PGA- Collagen Matrix
Omental Covering
3 Yes No No
1 Yes No Yes
3 No Yes Yes
Omental-membrane that lines the abdominal cavity
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Smooth cell muscles were used to line the exterior of the scaffold
The urothelial cells were added to the interior of the scaffold
After being placed in a container with a growth medium, the scaffold was placed in an incubator for 3-4 days
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An incision is made into the midsection of the patients
Dr. Atala augmented the artificial bladder with the native bladder using polyglycolitic sutures and fibrin glue
The omental membrane was added after the suturing process
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Follow up: Ranging from 22 to 61 months
The frequency of urination leakage post-surgery was:◦
1.5 to 3.5 hours for patients with the collagen bladder◦
2.5 to 4 hours for the patient the collagen bladder that was covered with omental wrap
◦
3 to 7 hours for the patients implanted with the collagen-
PGA bladders with omental wraps
The collagen-PGA bladders were deemed the best option
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The patients did not experience metabolic problems
The new bladder performed better than the other surgical options, without all of the negative side effects (ex. mucous production and absorbing material)
Biopsies that the bladder had the proper triple layer structure
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Neo-bladders for Patients With Neurogenic Bladders
Dr. Atala is conducting phase II of his study
Recruited 10 patients with spinal cord injuries and failing bladders◦
The patients are between 3 to 21 years of age◦
Haven’t responded to other medical treatments◦
Haven’t had any other augmenting procedures
Using their neo-bladders to further study and improve this treatment
Objective: ◦
To measure the safety and efficiency◦
To improve the compliance (pressure vs. volume)
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Nanofibers
Fibres within the diameter on the order of nanometers
Has ultrafine continuous fibers and high porosity
Being explored for scaffold building
Similar properties to that of ECM
Better at regenerating tissues
Need to improve mechanical properties to match preferred tissue properties
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(2010). Bladder Problems. November 6, 2010. [http://biomed.brown.edu/Courses/BI108/BI108_2007_Groups/group10/problems.html]
(2010) Bladder Cancer. November 5, 2010. [http://www.emedicinehealth.com/bladder_cancer/page3_em.htm#Bladder Cancer Symptoms]
Bladder Augmentation. November 5, 2010. [http://www.surgeryencyclopedia.com/A-Ce/Bladder-
Augmentation.html]
(2010). Spina Bifida. November 5, 2010. [http://kidshealth.org/parent/system/ill/spina_bifida.html#]
Bladder Augmentation and Incontinence Surgery. November 7, 2010. [http://www.med.wayne.edu/urology/DISEASES/bladderaug.html]
National Cancer Institute: Bladder Cancer. November 8, 2010. [http://training.seer.cancer.gov/bladder/anatomy/layers.html]
Bladder Anatomy and Physiology. November 8, 2010. [http://www.wellbladder.com/bladder_anatomy__physiology]
Bladder. (2000). Bladder. November 07, 2010. [http://www.mamashealth.com/organs/bladder.asp]
The bladder. November 07, 2010. [http://www.cancerhelp.org.uk/type/bladder-cancer/about/the-bladder]
(2009). The Urinary Bladder. November 06, 2010. [http://education.yahoo.com/reference/gray/subjects/subject/255]
S. G. Kumbar. (September 2008). Electrospun nanofiber scaffolds: engineering soft tissues. (November 6, 2010). [http://iopscience.iop.org/1748-605X/3/3/034002/]
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Dolly, Brandon. Emrich, Adam. Groothuis, Sarah. Halenda, Greg. Jankowski, Tito.
Tissue Engineering.http://biomed.brown.edu/Courses/BI108/BI108_2007_Groups/group10/tissue_engineering.html
The Lancet. (April 15, 2006).
Tissue-engineered autologous bladders for patients needing cystoplasty. November 4, 2010.http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T1B-
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