Micromoulding: consideration of processing effects on medical materials Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, IRC in Polymer Engineering,

Micromoulding: consideration of processing effects on medical

materials

Micromoulding: consideration of processing effects on medical

materials

Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates,

IRC in Polymer Engineering, University of Bradford, Bradford UK.IRC in Polymer Engineering, University of Bradford, Bradford UK.

P S Allan, G. Greenway and P Hornsby,

Wolfson Centre for Materials Processing, Brunel University, Uxbridge, UK

Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates,

IRC in Polymer Engineering, University of Bradford, Bradford UK.IRC in Polymer Engineering, University of Bradford, Bradford UK.

P S Allan, G. Greenway and P Hornsby,

Wolfson Centre for Materials Processing, Brunel University, Uxbridge, UK

OutlineOutline

• Introduction• Micromoulding technology• Experimental

• Mould temperature investigation• High shear rate experiments• Product surface measurements

• Moulding/compounding technology

• Introduction• Micromoulding technology• Experimental

• Mould temperature investigation• High shear rate experiments• Product surface measurements

• Moulding/compounding technology

Medical implant featuresMedical implant features

• Compatible materials• Complex 3-dimensional structures• Tailored surface properties

• Compatible materials• Complex 3-dimensional structures• Tailored surface properties

Medical material issuesMedical material issues

• Tight controls

• Process should not influence the integrity and structure of the material

•Temperature sensitive

• Exposure of materials to high temperatures to be minimised

• Tight controls

• Process should not influence the integrity and structure of the material

•Temperature sensitive

• Exposure of materials to high temperatures to be minimised

Conventional IM disadvantagesConventional IM disadvantages

• Positional control of screw/ram not sufficient

• Barrel size causes high residence times of material at melt temperature

• A high proportion of material is wasted in the sprue/runner system

• Positional control of screw/ram not sufficient

• Barrel size causes high residence times of material at melt temperature

• A high proportion of material is wasted in the sprue/runner system

Conventional injection moulding -material waste

Conventional injection moulding -material waste

Micromoulding benefits for medical applications

Micromoulding benefits for medical applications

• Allows production of complex 3-dimensional products with dimensional tolerances <10um

• Highly repeatable process with little material wastage

• Incorporation of clean room conditions and sealing/ packaging systems

• Allows production of complex 3-dimensional products with dimensional tolerances <10um

• Highly repeatable process with little material wastage

• Incorporation of clean room conditions and sealing/ packaging systems

Battenfeld Microsystem 50Battenfeld Microsystem 50

Metering PistonMetering Piston

HopperHopper

Shut off valveShut off valve

Extrusion screwExtrusion screw

Heated RegionsHeated Regions Injection pistonInjection piston

Battenfeld Microsystem 50Battenfeld Microsystem 50

Dynisco PCI 4011 Piezo load transducer

Dynisco PCI 4011 Piezo load transducer

Dynisco PCI 4006 piezo load transducer

Dynisco PCI 4006 piezo load transducer

The Data Acquisition SetupThe Data Acquisition Setup

Temposonics R series displacement transducer

Temposonics R series displacement transducer

J-type thermocouplesJ-type thermocouples

1 Process Measurement – Data Capture

1 Process Measurement – Data Capture

Injection Pressure

Cavity Pressure

Ram Displacement

Ram Velocity

3 Temperature Channels

Injection Pressure

Cavity Pressure

Ram Displacement

Ram Velocity

3 Temperature Channels

Max sampling rate ~ 30 000HzMax sampling rate ~ 30 000Hz

ExperimentalExperimental

• Mould temperature influence• High shear rate investigations• Surface feature replication

• Mould temperature influence• High shear rate investigations• Surface feature replication

Mould temperature investigationMould temperature investigation

HypothesisHypothesis

• The high surface area to volume ratio of micro-moulded products allows rapid removal of heat from the product through the cavity wall

• Mould temperatures should be higher than those used in conventional IM to prevent premature solidification and part-filled products

• The high surface area to volume ratio of micro-moulded products allows rapid removal of heat from the product through the cavity wall

• Mould temperatures should be higher than those used in conventional IM to prevent premature solidification and part-filled products

Step plaque mouldingStep plaque moulding

Material: HAPEX (40% sintered hydroxyapatite HDPE matrix)

Produced by IRC in Biomaterial Science

Queen Mary and Westfield College, London

Material: HAPEX (40% sintered hydroxyapatite HDPE matrix)

Produced by IRC in Biomaterial Science

Queen Mary and Westfield College, London

Cavity Pressure – Hapex, step plaque

Cavity Pressure – Hapex, step plaque

80C

50C

20C

Product Mass – Hapex, step plaqueProduct Mass – Hapex, step plaque

0.12% variation0.12% variation

Mould temperature - conclusionsMould temperature - conclusions

• For products ~25mg recommended mould temperatures for standard injection moulding can be used with confidence for the Hapex material

• Further investigations to be performed at smaller length scales

• For products ~25mg recommended mould temperatures for standard injection moulding can be used with confidence for the Hapex material

• Further investigations to be performed at smaller length scales

High shear rate experimentsHigh shear rate experiments

Calculated wall shear ratesCalculated wall shear rates

0.1 x 0.1mm

0.2 x 0.2mm

0.5 x 0.5mm

1.0 x 1.0mm

In-process rheometryIn-process rheometry

• Measurements performed on a 30 tonne Cincinnatti Milacron servo-electric injection moulding machine with a custom rheometric nozzle

• Measurements performed on a 30 tonne Cincinnatti Milacron servo-electric injection moulding machine with a custom rheometric nozzle

Dynisco Pressure Transducer 435-30M

Dynisco Pressure Transducer 435-30M

Capillary dieinsertsCapillary dieinserts

0.5 x 8.0 mm0.5 x 0.25 mm

1.0 x 16 mm1.0 x 0.25 mm

ThermocoupleThermocouple

High-shear capillary rheometry test resultsHigh-shear capillary rheometry test results

Shear heating effectsShear heating effects

Source: Anthony Bur, Steven Roth, NISTSource: Anthony Bur, Steven Roth, NIST

‘Top Hat’ Cavity‘Top Hat’ Cavity

• Large diameter = 1.0mm• Small diameter = 0.5mm• Gate dimension 0.1 x 0.2mm• Material BP Rigidex 5050 HDPE

• Large diameter = 1.0mm• Small diameter = 0.5mm• Gate dimension 0.1 x 0.2mm• Material BP Rigidex 5050 HDPE

Molecular weight measurementMolecular weight measurement

• Sample material taken from runner system and cavity

• Gel Permeation Chromatography (GPC) analysis performed by Rapra Technology Ltd on each sample to determine molecular weight distribution

• Sample material taken from runner system and cavity

• Gel Permeation Chromatography (GPC) analysis performed by Rapra Technology Ltd on each sample to determine molecular weight distribution

Molecular weight distributionsMolecular weight distributions

Source: RAPRA UKSource: RAPRA UK

High shear investigation - conclusions

High shear investigation - conclusions

• The process contains shear rates orders of magnitude higher than those encountered in conventional IM

• Viscosity curves behave predictably in this region

• Shear heating will be a factor• Stable materials show no sign of

degradation• Temperature sensitive materials?

• The process contains shear rates orders of magnitude higher than those encountered in conventional IM

• Viscosity curves behave predictably in this region

• Shear heating will be a factor• Stable materials show no sign of

degradation• Temperature sensitive materials?

Surface feature replicationSurface feature replication

Surface feature replicationSurface feature replication

• Plaque cavity 25 x 2.5 x 0.25 mm• Fabricated using micro-milling technique

• Kern machine• 0.2mm cutter at 75 000 rpm.• Left in an unpolished state.

• Plaque cavity 25 x 2.5 x 0.25 mm• Fabricated using micro-milling technique

• Kern machine• 0.2mm cutter at 75 000 rpm.• Left in an unpolished state.

Surface feature replication - gateSurface feature replication - gate

AFM scan size 75 µm x 75 µm

Pitch of scroll marks ~ 6µm

AFM scan size 75 µm x 75 µm

Pitch of scroll marks ~ 6µm

Cavity Product

Surface feature replication - gateSurface feature replication - gate

AFM scan size 75 µm x 75 µm AFM scan size 75 µm x 75 µm

Cavity Product

Surface feature replication -downstreamSurface feature replication -downstream

AFM scan size 75 µm x 75 µm

Pitch of scroll marks ~ 6µm

AFM scan size 75 µm x 75 µm

Pitch of scroll marks ~ 6µm

Cavity Product

Surface feature replication - comments

Surface feature replication - comments

• Mould features of the order of a few µm are accurately replicated on the product assuming pressure is sufficient

• Further work to be performed to investigate the limit to which a feature is adequately moulded on a product

• Mould features of the order of a few µm are accurately replicated on the product assuming pressure is sufficient

• Further work to be performed to investigate the limit to which a feature is adequately moulded on a product

A single compounding/moulding process

A single compounding/moulding process

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

Advantages:

• Minimise residence time of polymer in plasticising screw

• Exposure to single heating/cooling cycle

• Positive displacement allows use of low viscosity materials

Advantages:

• Minimise residence time of polymer in plasticising screw

• Exposure to single heating/cooling cycle

• Positive displacement allows use of low viscosity materials

The Rondol Micro-Injection Compounder

The Rondol Micro-Injection Compounder

Initial testingInitial testing

• Pros• Moulding trials successful• Able to process low molecular weight materials

• Pros• Moulding trials successful• Able to process low molecular weight materials

• Cons•Dosing control can fluctuate• Toggle clamp can result in flashing

• Cons•Dosing control can fluctuate• Toggle clamp can result in flashing

Concluding CommentsConcluding Comments

• Micromoulding offers many benefits which make it well suited for manufacture of medical components

• Process conditions may cause problems when processing temperature sensitive materials but initial studies using HDPE show no signs of degradation

• Mould surface features of length scale ~m are replicated on the product• Surface finish can be engineered to influence biocompatibility

• Twin screw compounding micromoulder offers a route for material blending and component manufacture in a single process

• Micromoulding offers many benefits which make it well suited for manufacture of medical components

• Process conditions may cause problems when processing temperature sensitive materials but initial studies using HDPE show no signs of degradation

• Mould surface features of length scale ~m are replicated on the product• Surface finish can be engineered to influence biocompatibility

• Twin screw compounding micromoulder offers a route for material blending and component manufacture in a single process

The authors gratefully acknowledge the support of the UK The authors gratefully acknowledge the support of the UK Micromoulding Interest Group (Micromoulding Interest Group (www.ukmig.com), particularly ), particularly Ultratools Ltd for their assistance with cavity manufacture.Ultratools Ltd for their assistance with cavity manufacture.

Thanks also to Queen Mary University for supply of Hapex Thanks also to Queen Mary University for supply of Hapex material.material.

The authors gratefully acknowledge the support of the UK The authors gratefully acknowledge the support of the UK Micromoulding Interest Group (Micromoulding Interest Group (www.ukmig.com), particularly ), particularly Ultratools Ltd for their assistance with cavity manufacture.Ultratools Ltd for their assistance with cavity manufacture.

Thanks also to Queen Mary University for supply of Hapex Thanks also to Queen Mary University for supply of Hapex material.material.

AcknowledgementsAcknowledgements

Thank youThank you