1. 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

2. 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.

3. 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

4. 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)

5. Problem Motivation Problems: A new interference screw is needed that:
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

6. Design Constraints The screw must be: Bioactive Biocompatible Biphasic
Easily sterilized or autoclaved
Structurally sound

7. Design Materials Alginate Hydrogel:
Can be doped with growth factors, nutrients, metabolites, etc.
Provides three dimensional scaffolding
Promotes cell proliferation and tissue growth

8. Mold Investigations Plastic
Transition temperature must be larger then melting point of thermoplastic
Data:
Plastic Tm(oC) Tg(oC)
PLGA
PLA
PGA
Paper
Will burn when thermoplastic is added
Metal
May be only alternative that can handle the temperature of thermoplastic

9. 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
Alginate
PLGA

10. Hexagon Core Design

11. Triangle Core Design

12. Alginate Calculations
Shear stress at point M:
Where B varies with a/r over the range r a M
For four grooves:
For two grooves:
Maximum Shear Stress of PLGA: ~14 MPa
Insertion Torque: 1.5 N*m
Maximum Radius of Screw: 5mm

13. Alginate Radius = 0.5mm
2% of total area can be alginate

14. Torque Analysis

15. Torque Analysis T r F
Combining the two equations gives:

16. Future Work Find thermoplastic with:
Adequate melting point
Structural integrity
FDA approval
Investigate further alginate addition
Quantitatively analyze designs
Mold Development
Prototype Development
Documentation