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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. Problem Statement. - PowerPoint PPT Presentation
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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
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.
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
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
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
Design ConstraintsThe screw must be: Bioactive Biocompatible Biphasic Easily sterilized or autoclaved Structurally sound
Design Materials Alginate Hydrogel:
Can be doped with growth factors, nutrients, metabolites, etc.
Provides three dimensional scaffolding Promotes cell proliferation and tissue growth
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
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
Hexagon Core Design
Triangle Core Design
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:
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
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
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:
Future Work Find thermoplastic with:
Adequate melting point Structural integrity FDA approval
Investigate further alginate addition Quantitatively analyze designs Mold Development Prototype Development Documentation