bioactive interference screws for acl reconstruction
DESCRIPTION
Bioactive Interference Screws for ACL Reconstruction. Dana Nadler – Communicator Cole Kreofsky – BSAC Katherine Davis – BSAC Aaron Huser – BWIG Joe Poblocki – Team Leader. Client – Professor William Murphy Advisor – Professor Kristyn Masters. Problem Statement. - PowerPoint PPT PresentationTRANSCRIPT
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Bioactive Interference Screws for ACL Reconstruction
Dana Nadler – Communicator
Cole Kreofsky – BSAC
Katherine Davis – BSAC
Aaron Huser – BWIG
Joe Poblocki – Team Leader
Client – Professor William Murphy
Advisor – Professor Kristyn Masters
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Problem Statement The primary objective of this project is to
design an interference screw for ACL reconstruction that will simultaneously promote the growth of tissue while the screw degrades.
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Background Information - ACL 90,000 annual ACL reconstruction surgeries worldwide Reconstructions use patellar or hamstring tendon grafts Grafts are implanted in the femur and tibia Grafts secured with interference screws
http://miranda.ingentaselect.com/vl=2967323/cl=12/nw=1/fm=docpdf/rpsv/cw/pep/09544119/v217n1/s9/p59
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Background Information - Screws Titanium:
Extremely strong Biocompatible Reliable Second surgery may be
necessary Degradable Plastics:
Strength and shape Degradable Multiple polymers used
Poly(L-Lactic) Acid (PLLA)
Poly(Lactic-co-Glycolic) Acid (PLGA)
http://www.arthrotek.com/products/aclpcl_interference.cfm
http://www.jnjgateway.com/home.jhtml?loc=USENG&page=viewContent&contentId=09008b9880a6f43e&parentId=09008b9880a6f43e
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Problem Motivation Problems:
Current screw may cause unwanted debris in the knee
Current material does not promote tissue growth
A new interference screw is needed that: Mimics bone scaffold structure Promotes tissue growth
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Design ConstraintsThe screw must be: Bioactive Biocompatible Biphasic Easily sterilized or autoclaved Structurally sound
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Design Materials Alginate Hydrogel:
Can be doped with growth factors, nutrients, metabolites, etc.
Provides three dimensional scaffolding Promotes cell proliferation and tissue growth
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Mold InvestigationsPlastic
Transition temperature must be larger then melting point of thermoplastic
Data:Plastic Tm(oC) Tg(oC)PLGA 210 37PLA 185 57PGA 225 40
PaperWill burn when thermoplastic is added
MetalMay be only alternative that can handle the temperature of thermoplastic
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Design Evolution Limitations with
mechanical properties of mineralized hydrogel
Change geometry of thermoplastic to increase structural strength
Minimize stress on mineralized hydrogel portions of screw
PLGA
Alginate
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Hexagon Core Design
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Triangle Core Design
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Shear stress at point M:
Where B varies with a/r over the range
Alginate Calculations3r
TB
432
49.130506.99713.339697.22135.1
r
a
r
a
r
a
r
aB
ra 5.01.0
r
a
M
Maximum Shear Stress of PLGA: ~14 MPa
Insertion Torque: 1.5 N*m
Maximum Radius of Screw: 5mm
32
0534.79501.25427.10055.1
r
a
r
a
r
aB
For two grooves:
For four grooves:
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Alginate Radius = 0.5mm 2% of total area can be alginate
For 4 Grooves: r=5mm
a/ r BRadius of
Alginate (mm)Shear Stress (MPa)
0.5 3.874275 2.5 46.50.3 1.72 1.5 20.640.1 1.167 0.5 14.01
For 2 Grooves: r=5mm
a/ r BRadius of
Alginate (mm)Shear Stress (MPa)
0.5 1.921 2.5 23.010.3 1.393 1.5 16.70.1 1.137 0.5 13.64
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Torque Analysis
BL
BLL
AA
BA
LLA
HT
H
T
45.22
33)4/3)((2/1
2
33
)4/3)((2/1
2
2
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Torque AnalysisT
rr
F
F
F
F
F
F
F
F
F
T
L
BFF
BFLF
BFTM
LFTM
HT
HT
HH
TT
2
)6)(2/()3)(2/(
)6)(2/(0
)3)(2/(0
HT
HT
FF
BLL
BFF
)225.1(
45.2;2
Combining the two equations gives:
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Future Work Find thermoplastic with:
Adequate melting point Structural integrity FDA approval
Investigate further alginate addition Quantitatively analyze designs Mold Development Prototype Development Documentation