A bone...

T E M P L A T E

Bao-Yi Chang Elissa Robbins

Elizabeth Immen Lisa Scoppettuolo

3.082

FINAL PRESENTATION

May 17, 2001

Injection Molding

Thank you to Speed of Light for the Casting photograph

www.biomet.com

Iron or Stainless SteelPolymers:

PLLA or PCL

• To fabricate a bioresorbable bone plate

• To fabricate a bone plate with a modulus close to that of bone through selection of materials and processing conditions

Mission/Goals

Injection Molding

•Used to fabricate plastic objects

-CD cases, water bottles, toys

•Easy one step process

•Ideal for mass production

Injection Molding Machine

Battenfeld 250

Mold Chamber

Hopper

Plasticating Unit

Control System

Max Clamp Force 250 kNMax Mold Opening Force 28 kNMax Nozzle Contact Force 35 kNMax Injection Pressure 125 MPaMax Injection Rate 74 cc/sMax Shot Volume 39 ccMax Ejector Rate 26.2 kN

Equipment Specifications

Injection Mold Process

2. End Plastication

3. Close Mold 4. Begin Injection Mold

5. Eject Part

1. Begin Plastication

screw nozzle

Mold-Obtaining Mold Blank

-Design Process

-Machining

-Adjustments

Length 6.5Width 0.5Hole Spacing 1Hole Diameter 0.25

Plate Dimensions(in)

Experimental Runs

Establishing Ideal IM Conditions Varying Parameters

T0 220 CT1 220 CT2 220 CP 40%V1 20%V2 15%S1 30%S2 37%

Run V(%) P(%)1 25 252 25 1003 100 254 100 100

Product Testing….

Instron Tensile Testing

Results: Instron Testing

SampleYoung’sModulus(GPa)

Cortical bone 3-30PCL (expected) 0.280PCL (as-received) 0.270PCL (IM 1: v=25%, p=25%) 0.453PCL (IM 2: v=25%, p=100%) 0.410PCL (IM 3: v=100%, p=25%) 0.437PCL (IM 4: v=100%, p=100%) 0.415

IM1: low screw speed, low pressure

IM Parameters Mechanics

Bone plate, not shaped for tensile testing

IM2: low screw speed, high pressure

IM3: high screw speed, low pressure

IM4: high screw speed, high pressure

Gel Permeation Chromatography

DegradationPeriod (days)

MolecularWeight (g/mol)

0 123,29222 117,097

• PCL degrades by hydrolysis

• PCL was placed in water to simulate the body’s aqueous environment

• Hydrolytic cleavage of PCL chains Decrease in molecular weight

Polymers with low melting points are typically:

• low molecular weight

Tm Mw

Differential Scanning Calorimetry

Melting point of PCL = 63.245 oC

Decision Tree

P C L

L ow er M od u lus th an P LA 0 .2 7 G Pa

A d just IM Pa ram e te rs

In je ct P C L a t 2 screw sp e edsa nd 2 p re ssu re s, m odu lu s = 0 .43 G Pa

"San dw ich"

P oo r b o ndin g be tw ee n PC L an d ß-T C PT o o d ifficu lt to fa b ricate w e ll

H o m o gen eou s M ixtu re

1 0% TC P b y vo lu m eM o d u lus: 0 .43 G Pa

H o t P ress In je ctio n M o ld

T o o risky(m ay d am a ge m a chin e)

M a ke C o m p osite M ate ria l

M a trix : P C LR e in fo rce r: ß -T C P

P C L

$ 200 /kg

P LA

$ 500 0-$15 ,0 0 0/kgd epe nd in g o n the sup plier

S e lection o f B io de g ra d ab le M a te ria l

Bioglass Fibers

Ceramic Particles:

- Hydroxyapatite

- -tricalcium phosphate

Fabricate bone plate from a completely bioresorbable COMPOSITE

- Satisfy the mechanical requirements of

bone plates

- Mechanically superior to many

bioresorbable homopolymers

... Further Work and StudyFuture Plans

Possible Reinforcers

-tricalcium phosphate (Ca3(PO4)2, -TCP) is a bioresorbable ceramic

FTIR patterns of PDLLA, TCP, and a PDDLA/TCP composite (50 wt. % TCP)

Poor adhesion between polymer matrix

and ceramic reinforcer Poor

mechanical properties

Possible Problems :

- Melting and Hot Pressing - Twin Screw Extrusion

- Pelletize Composite Mixture

- Injection Molding:

Viscosity () is an important parameter

Methods of fabricating a PCL/-TCP bone plate:

XTCP XPCL Ec, low (GPa)0 1 0.30

0.1 0.9 0.330.2 0.8 0.370.3 0.7 0.430.4 0.6 0.500.5 0.5 0.600.6 0.4 0.750.7 0.3 0.990.8 0.2 1.480.9 0.1 2.93

1 0 115.00

“To fabricate a bone plate with a modulus of 3 GPa, the composite would have to be 90 % TCP by volume!”

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1

TCP Volume Fraction

E (

GP

a)

Ecomposite = XTCPETCP + (1-XTCP)EPCL (upper bound)

Ecomposite = 1 / [(XTCP / ETCP) + (1-XTCP)/ EPCL] (lower bound)

Source: Ashby, M.

Engineering Materials I.

Feasibility of a

PCL/-TCP Composite

TemPlate’s Composite Bone Plate

By hot pressing a composite material of volume fraction 90% PCL / 10% -TCP, the modulus was increased by 60%.

Cortical Bone 3 - 30 GPa

PCL 0.270 GPa

90% PCL / 10% TCP 0.428 GPa

Cost Analysis

Cost Analysis

$ Purchase Mold: (Master Unit Die) = $400

$ Design ($60/hr * 30hr) = $1800

$ Machining ($52/hr * 35hr) = $1820 ----------

Total for Mold $4060

Polymer Injection Molding

Cost Analysis

Processing

Cost Analysis

$ Battenfeld Machine Repair = $250

$ Optimizing Initial ProcessingConditions ($60/hr * 6hr) =$360

$ Injection Molding 1000 plates ($60/hr * 40hr) = $2400

----------

Total for IM $3010

Cost Analysis

$ Polycaprolactone (Polysciences, Inc. ($200/kg*20kg)

= $4000

Cost Analysis

Material

$ Mechanical testing (Instron) ($60/hr*10hr) = $600

Product Analysis

Cost Analysis

$ Overhead ~ $7000$ Mold = $4060$ Injection Molding = $3010 $ Materials = $4000$ Product Analysis = $ 600

Summary

Cost Analysis

= $18,670---------------

Total Cost of 1000 bone plates

Cost Analysis

$20/bone plate

*Biomet.com

competition *

$168/bone plate