Advanced Techniques for Pore Structure Characterization of Biomedical Materials

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Advanced Techniques for Pore Structure
Characterization of Biomedical Materials

• Akshaya Jena and Krishna Gupta
• Porous Materials, Inc.20 Dutch Mill Road
• Ithaca, NY 14850

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Topics

• Need For Structure Characterization of Biomedical
  Materials

• Important Pore Structure Characteristics
• Innovative Extrusion Techniques for
  Characterization
• Examples of Applications
• Advantages of the Techniques
• Summary and Conclusion

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Need For Structure Characterization of Biomedical
Materials

• Many modern biomedical materials are porous

• Performance is determined by pore structure
  characteristics.

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Need for Pore Structure Characterization of
Biomedical Materials
Examples

• Powder drugs
• Drug delivery system
• Hydrophobic/hydrophilic mixtures
• Dialysis membranes

• Synthetic Skin
• Hydrogels
• Substrate for tissue growth
• Dialysis membranes

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Need for Pore Structure Characterization of
Biomedical Materials
Examples

• Cosmetic powders
• Blood clotting material

• Arterial grafts
• Blood deliverysystems

• and many more

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Important Pore Structure Characteristics

• Pore throat diameter Pore Volume(Barrier
  properties) (Holding capacity)
• Largest diameter Pore distribution (Barrier
  properties) (Barrier flow)

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Important Pore Structure Characteristics
Mean diameter Surface area(Barrier
flow) (Barrier, rate flow) Liquid
permeability Gas permeability(Rate of
process) (Rate of process)
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Innovative Extrusion Techniques for
Characterization
Principle

• Pores of sample spontaneously filled with a
  wetting liquid g sample/liquid ltg sample/gas

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Innovative Extrusion Techniques for
Characterization

• Differential pressure, p of gas on one side of
  sample increased to displace liquid from porep
  4 g cos q/D
• g liquid surface tension
• q liquid contact angle
• D Diameter of pore such that (dS/dV)pore
  (dS/dV)cylindrical opening of diameter, D
• S gas/solid surface area in pore
• V volume of gas in pore

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Innovative Extrusion Techniques for
Characterization

• Differential pressure and gas flow rates through
  wet and dry samples measured ? Extrusion flow
  porometry (Capillary Flow Porometry)

• Differential pressure and flow rate of liquid
  displaced from pores measured ? Extrusion
  porosimetry (Liquid Extrusion Porosimetry)

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Innovative Extrusion Techniques for
Characterization
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Instrument

• Fully automated computer controlled

• Highly accurate, reliable objective

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Examples of Applications
Dialysis membrane

• Primary function Filtration
• Important requirements
• The largest pore diameter
• Mean pore diameter
• Pore distribution
• Flow Rate

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Dialysis membrane Test results using Capillary
Flow Porometry
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Dialysis membrane Pore Structure Characteristics

• The largest pore diameter ? From pressure for
  flow initiation 1.023 mm

• Mean flow pore diameter ? From mean flow pressure
  0.458 mm
• Pore distribution ? Distribution function f
  -d(fw/fd)x100/dD fw wet flow fd dry flow

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Dialysis membrane Pore Structure Characteristics

• Area in a pore size range Flow through pores
  in the range. Almost 80 flow is through
  0.2-0.7mm pores

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Dialysis membrane Pore Structure Characteristics

• Dry curve yields gas permeability

• Liquid permeability computed from measured liquid
  flow rates

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Dialysis membrane Pore Structure Characteristics

• All required characteristics including very small
  pore diameters were measured by capillary flow
  porometry

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Hydrogels

• Primary function
• Hormone drug delivery

• Promotes healing of wounds burns when used as
  dressings
• Requirements
• Pore volume for holding capacity
• Pore size distribution for barrier
• High permeability to promote healing of wounds

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Hydrogels Test results using Water Extrusion
Porosimetry
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Hydrogels Pore Structure Characteristics

• Pore Volume
• Total pore volume ? 0.421 cm3/g

• Porosity ? 67.12
• Pore Volume Distribution ? Distribution function,
  fv -(dV/dD) V pore volume D pore
  diameter

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Hydrogels Pore Structure Characteristics

• Pores have a narrow range ? 5-20 mmFor a given
  range Area pore volume

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Hydrogels Pore Structure Characteristics

• Liquid flow rate yields permeability

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Hydrogels Pore Structure Characteristics

• Pore volume, pore volume distribution and liquid
  permeability were successfully measured in a
  water extrusion porosimeter. No other technique
  can measure these properties.

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Artificial Skin

• Primary function
• Promotes and allows growth of blood vessels

• Be breathable
• Requirements
• Pore size distribution to promote blood vessel
  growth
• Gas and vapor permeability to be breathable

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Artificial Skin Test results using Capillary
Flow Porometry
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Artificial Skin Pore Structure Characteristics

• The largest pore diameter ? From pressure for
  flow initiation 4.932 mm

• Mean flow pore diameter ? From mean flow pressure
  31.489 mm
• Pore distribution ? Distribution function f
  -d(fw/fd)x100/dD fw wet flow fd dry
  flow

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Artificial Skin Pore Structure Characteristics
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Artificial Skin Pore Structure Characteristics

• A board uniform distibution About 5 to 70 mm

• Dry flow rate yields permeability
• Largest constricted pore diameters, broad
  distribution and high permeability were measured
  by capillary flow porometry

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Nanofiber Mats for Tissue and Organ Culture

• Primary function
• Sufficient pore volume to supply adequate
  nutrients

• Suitable pore diameter in x, y z directions
• Ability to be shaped in desired manner

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Nanofiber Mats for Tissue and Organ Culture

• Requirements
• Pore volume

• Pore size distribution
• x, y z direction pore structure

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Techniques measurable Characteristics
Nanofiber Mats for Tissue and Organ Culture

• Extrusion porosimetry
• Pore volume

• Pore diameter
• Extrusion Flow Porometry
• Constricted pore diameter
• Pore distribution
• Extrusion Flow Porometry (In-plane)
• x y direction pore diameter
• x y direction pore distribution

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Advantages of the Techniques

• No toxic material is used No heath hazard, No
  environmental pollution

• Samples not contaminated, reusable and can be
  saved
• Low test pressures
• Small test duration
• Only through pores measured

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Summary and Conclusion

• Performance of many pharmaceutical and biotech
  products depend upon their pore structure
  characteristics

• An innovative extrusion technique was used for
  characterization. Two variations of the technique
  were employed
• Extrusion flow porometry
• Extrusion porosimetry

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Summary and Conclusion

• The technique was successfully used to measure
  pore structure characteristics including
  constricted pore diameter, the largest pore
  diameter, mean flow pore diameter, flow
  distribution, pore volume and permeability

• A variety of products including dialysis
  membranes, artificial skins, hydrogels, were
  successfully tested

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Summary and Conclusion

• The technique had a number of advantages
  including absence of the need for use of any
  toxic material, ability for the sample to be
  reused or saved, use of low pressures and small
  test duration.

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Thank You