Microencapsulation of cells

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Microencapsulation of cells

• Team
• Bryan Baxter
• Tim Eng
• April Zehm
• Joe Zechlinski
• BME 301
• February 18, 2005

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ClientDr. Craig AtwoodDr. Sivan
VadakkadathMiguel GallegoVA HospitalAdvisor
Assistant Professor William MurphyDepartment of
Biomedical Engineering
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Overview

• Problem Statement
• Background
• Design Specifications
• Design Solutions
• Future Work

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Problem Statement

• Develop method of encapsulating cells to allow
  hormone release while providing a physical
  barrier to the hosts immune system
• Motivation
• Potential alternative to less desirable
  treatments
• Organ transplant
• Hormone injections
• Cellular grafts

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Microcapsules

• Provide physical barrier to immune system
• Semi-permeable membrane
• Consist of hydrogels
• Cells suspended
• Polymer crosslinked
• Implanted subcutaneously or in intra-peritoneal
  cavity
• Time-released drug therapy

(Uludag et al., 2000)
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Client Research

• Microencapsulation applications
• Anti-aging therapy
• Reproductive disorders
• Cells and hormones of interest
• Leydig and Sertoli cells
• Hormone transfer including testosterone,
  inhibin, activin, FSH, LH

(Ownby, 1999)
(Machluf, 2003)
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Design Specifications

• Biocompatibility
• In vivo
• Crosslinking
• Degradation
• Mechanical
• Biological
• Immunoprotection
• Controlled pore size (MWCO)
• Repeatability of results
• Hypoxia

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Design Solutions

• Alginate/PLL system
• Polyethylene glycol (PEG)
• Glycosaminoglycans

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Alginate/PLL

• Alginate Natural polymer
• Mannuronic (M) and guluronic (G) acids
  crosslinked using divalent cation
• Poly-L-lysine (PLL)
• Used to coat alginate core
• Provides membrane for capsule
• Capsules re-coated in alginate to bind charged
  residues

Poly-guluronic acid (G)
Poly-mannuronic acid (M)
http//www.cybercolloids.net/library/alginate/stru
cture.php
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Alginate/PLL

• Advantages
• Most studied system
• Simple crosslinking
• Inert material
• Biocompatible
• Non-toxic

• Disadvantages
• Uncontrollable, unpredictable degradation
• Source variability (natural polymer)
• Exposed PLL causes inflammatory response
• Expensive to thoroughly purify alginate

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Polyethylene Glycol (PEG)

• Synthetic polymer
• Polymerization
• Bulk
• Interfacial (conformal)
• Crosslinking at polymer terminals
• Light (UV or visible)
• Chemical

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Polyethylene Glycol

• Advantages
• Repeatable results (synthetic polymer)
• Properties controlled by changing M.W.
• Degradation
• Mechanical strength
• Pore size
• Biocompatible
• Non-toxic
• Low protein adhesion
• Rapid polymerization

• Disadvantages
• Cross-linking
• Potentially harmful to cells

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Glycosaminoglycans (GAGs)

• Components in natural extracellular matrices
• Negatively charged disaccharides repeating units
  ? linked to core proteins
• Covalent or photo crosslinking
• Examples
• Hyaluronic acid
• Proteoglycans
• Heparin

Hyaluronate
http//web.indstate.edu/thcme/mwking/glycans.html
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Glycosaminoglycans (GAGs)

• Advantages
• Naturally derived
• Biocompatible
• Non-toxic

• Disadvantages
• Purification required
• Poor mechanical properties
• Short-lived

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Design Matrix
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Future Work

• Hybridization of materials
• Determine MWCO for pore size
• Crosslinking methods
• Droplet generator

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References

• http//chemfinder.cambridgesoft.com
• http//web.indstate.edu/thcme/mwking/glycans.html
• http//www.cybercolloids.net/library/alginate/stru
  cture.php
• Machluf M, Orsola A, Boorjian S, Kershen R, and
  Atala A. 2003. Microencapsulation of leydig
  cells a system for testosterone supplementation.
  Endocrinology 1444975-4979.
• Ownby. 1999. Histology male reproductive
  system. http//www.cvm.okstate.edu/instruction/mm_
  curr/histology/MR/HiMRp3.htm. Accessed February
  12, 2005.
• Uludag H, De Vos P, and Tresco PA. 2000.
  Technology of mammalian cell encapsulation.
  Advanced Drug Delivery Reviews 4229-64.