A Bioactive Interference Screw for ACL Reconstruction

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A Bioactive Interference Screw for ACL
Reconstruction
Team Members Aaron Huser, Cole Kreofsky, Dana
Nadler, Joe Poblocki Advisor Prof. Mitchell
Tyler, Ph.D Client Dr. William Murphy,
Ph.D Dept. of Biomedical Engineering
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(No Transcript)
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Problem Statement

• The purpose of this project is to design an
  interference screw for ACL reconstruction that
  will promote and foster the growth of tissue and
  secure the graft.

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Problem Motivation

• Currently, the majority of interference screws
  are made of titanium or partially bio-degradable
  material. These materials may inhibit tissue
  growth or cause unwanted debris in the patellar
  region of the body.
• A minority of interference screws are composed of
  a mixture of bioactive materials and polymers.
  These screws only promote tissue growth of small
  magnitudes.

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Design Constraints

• The screw must be
• bioactive
• biocompatible
• easily sterilized or autoclaved
• biodegradable as tissue re-grows
• able to withstand the stresses involved in
  surgery and limited postoperative activity

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Background ACL Reconstruction

• 90,000 annual ACL reconstruction surgeries
  worldwide
• Reconstructions use patellar or hamstring tendon
  grafts
• Grafts are implanted in the femur and tibia
• Grafts are secured with interference screws

http//www.orthoohio.com/OIO_services_surgeries.ht
ml

• http//miranda.ingentaselect.com/vl2967323/cl12/
  nw1/fmdocpdf/rpsv/cw/pep/09544119/v217n1/s9/p59

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Background Current Screws

• Most interference screws are titanium
• Bioactive interference screws are starting to be
  utilized
• Current bioactive screws degrade incompletely and
  asynchronously with tissue formation
• Both types have varying geometries and sizes
• Multiple companies produce these types of screws

http//www.arthrotek.com/products/aclpcl_interfere
nce.cfm
http//www.jnjgateway.com/home.jhtml?locUSENGpag
eviewContentcontentId09008b9880a6f43eparentId
09008b9880a6f43e
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Background Hydrogel Templates

• Water-based scaffolds used to mimic extracellular
  fluid
• Promote cell proliferation and tissue growth
• Can be differentiated with growth factors,
  nutrients, metabolites, etc.
• A mineralization process calcifies the hydrogel
  to meet mechanical demands
• Ultimate degradation replaces hydrogel with
  tissue

http//www.sciencedirect.com/cache/MiamiImageURL/B
6TWB-4D4PS12-2-1/0?wchpdGLbVzz-zSkzk
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Hollow Screw Shaft

• Why?
• Maximize torque
• Minimize possible surgical damage
• Provides increased surface area for tissue growth

http//www.stryker.co.uk/ms_pic_interference-wedge
-screw-2.jpg
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Producing The Hollow Screw Shaft

• A modular screwdriver is place inside mold
• The screwdriver is coated with a non-
  sticking agent
• A thermoplastic is poured into the mold and
  allowed to cool
• Upon setting, the screw is removed from the
  mold

http//www.sulzerorthoeu.ch/images/product/sm-11.g
if
http//www.aclstudygroup.com/Powerpoint-pdf02/bios
crews-hamstrings-johnson.pdf
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Technique Alternative 1Diffusive Membrane
Application

• Mold is split into two halves
• Shaft-fitting semi-permeable membrane
• Hydrogel monomer injected into threads

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Technique Alternative 1Diffusive Membrane
Application

• Crosslinker poured onto membrane
• Induces gel state
• Re-attach mold halves
• Mineralization hardens gel (i.e. Ca2)
• Remove membrane after setting
• Apply thermoplastic
• Hollow shaft

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Technique Alternative 2 Static UV Application

• Tube inserted into mold
• UV-activated crosslinker/hydrogel mixture
• UV light activates crosslinker
• Tube removed, mineralization occurs
• Thermoplastic application is carried out
• Mold is unhinged and screw is removed

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Technique Alternative 3Rotational Application

• Hydrogel and UV-activated crosslinker
• The mold is rotated allowing solution to fill
  threads
• UV light polymerizes hydrogel
• Mineralization and thermoplastic application

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Technique Matrix
Scale of 1 10 10 being the best 1 being the
worst
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Future Work

• Research methods for fabricating molds
• Continue researching the hydrogel process
• Develop a prototype mold
• Test various facets of molded interference screws
• Biocompatibility
• Degradation
• Structural Integrity
• Ease of development

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?QUESTIONS?