Hydrogels for Coating Medical Devices



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Hydrogels for Coating Medical Devices

  • University of Wisconsin
  • BME 400

Our Team

  • Benjamin Roedl – Team Leader
  • Patrick Schenk – Communicator
  • Darshan Patel – BWIG
  • Brett Mulawka - BSAC

Client & Advisor

  • Client: Arthur J. Coury, Ph.D.
    • Vice President Biomaterials Research Genzyme Corporation
  • Advisor: William Murphy, Professor of Biomedical Engineering

Problem Statement

  • To form PEG based hydrogels on biomaterial surfaces in an interfacial photopolymerization process and to screen the coatings for interactions with cells and media that mimic physiologic fluids. It is hypothesized that these coatings will resist fouling and may be useful for implantable devices.

Genzyme Corporation

  • One of world’s foremost biotechnology companies with the goal of applying the most advanced technologies to address unmet medical needs.

Motivation

  • Development of blood compatible hydrogel could have many applications
    • Orthopedic applications
    • Urinary Catheter
    • Tissue Repair
  • Create a hydrogel application procedure that results in accurate and reproducible results

Background-Hydrogels

  • Polymeric structures that absorbs water
    • Crosslinks, Polymer, Liquid (Water)

Crosslinking

  • Covalent Bonds Linking One Polymer Chain to Another
  • Can be Caused by Heat, Pressure, Chemicals
    • Form free radicals
    • We use a chemical that is light initiated
  • By Crosslinking, Hydrogels are Capable of Remarkable Water Retention/Adsorption

Polyethylene Glycol (PEG)

  • Properties
    • Clear, viscous, odorless, miscible in water, non-toxic
  • Uses
    • Wound dressing, soft tissue replacement, drug delivery.

Eosin Y

  • One Part of a Two Part Photoinitiator System
  • Maximum Adsorption at 514 nm (visible)
  • Passes Free Radical to Triethanolamine
  • Taken from OLMC.Ogi.edu

Triethanolamine

  • Accepts Free Radical from Eosin Y
  • Combines with Macromer to polymerize reaction

Procedure

  • Stain specimen with Eosin Solution
  • Immerse stained specimen in macromer solution
  • Apply visible light
  • An adherent, thin, hydrogel forms by polymerization of the macromer (PEG)
  • Expose specimen to cells to test for fouling

Testing

  • Thickness
    • Need to maintain consistent thickness for reliable test data / Toughness
  • Adherence
    • Durability through many cycles
  • Fouling Resistance
    • Biocompatibility
    • Most important

Thickness

  • Place fully swollen coated substrate on edge under optical microscope
    • Microscope with camera would be ideal
  • Hydrogel thickness goal: 25 – 100 microns
  • Alternate method:
    • Peel/slice piece of gel off at interface, cut to straight edge and measure with optical microscope

Adherence

  • Using a pointed spatula or needle, one person (control) will estimate adherence on a specific scale
    • 0 = Has fallen off
    • 1 = Lifts off almost intact with mild force
    • 2 = Lifts off in large chunks with some force
    • 3 = Lifts off in small pieces with some force
    • 4 = Does not delaminate even by destroying gel with pushing force

Fouling Resistance

  • Expose to proteins found in blood in solution
  • Stain with appropriate dye to view adhered proteins

Future Work: Protein Adsorption

  • Determine the concentration of proteins we must measure
  • Establish the best protein assay method to use
    • Acceptable resolution
    • Ease of procedure
      • UV adsorption, BCA assay… etc

References

  • Arthur J. Coury, Ph.D.
  • Kenneth Messier
  • McNair, Andrew M. "Using Hydrogel Polymers for Drug Delivery." Medical Device Technology (1996).
  • Kizilel, Seda, Victor H. Perez-Luna, and Fouad Teymour. "Photopolymerization of Poly(Ethylene Glycol) Diacrylate on Eosin-Functionalized Surfaces." Langmuir (2004).

Thank you

  • Questions?

Hydrogel Preparation

  • Radical chain reaction used to form cross links
    • Initiated using electrons, gamma-rays, x-rays, UV light to excite polymer chain and form radicals
      • (We will use visible light 514nm for eosin)
  • Crosslinkers
    • Acrylate, double bond forms radical

Polyethylene Glycol (PEG)

  • Non-toxic
  • Laxatives, Skin Creams, Lubricants

Light Source

  • Using a xenon light source
  • Applied to sample for 40 Seconds at a Distance of One Inch
  • Light Source Supplies Energy to Remove Electron from Eosin Y
    • Leads to a propagation of crosslinking between the macromer and triethanolamine


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