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

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

1 Micromoulding: consideration of processing effects on medical materials Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates, 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, 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

2 Outline 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

3 Medical implant features Compatible materials Complex 3-dimensional structures Tailored surface properties Compatible materials Complex 3-dimensional structures Tailored surface properties

4 Medical 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

5 Conventional 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

6 Conventional injection moulding - material waste

7 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

8 Battenfeld Microsystem 50 Metering Piston Hopper Shut off valve Extrusion screw Heated Regions Injection piston

9 Battenfeld Microsystem 50

10 Dynisco PCI 4011 Piezo load transducer Dynisco PCI 4006 piezo load transducer The Data Acquisition Setup Temposonics R series displacement transducer J-type thermocouples

11 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 ~ Hz

12 Experimental Mould temperature influence High shear rate investigations Surface feature replication Mould temperature influence High shear rate investigations Surface feature replication

13 Mould temperature investigation

14 Hypothesis 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

15 Step 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

16 Cavity Pressure – Hapex, step plaque 80C 50C 20C

17 Product Mass – Hapex, step plaque 0.12% variation

18 Mould 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

19 High shear rate experiments

20 Calculated wall shear rates 0.1 x 0.1mm 0.2 x 0.2mm 0.5 x 0.5mm 1.0 x 1.0mm

21 In-process rheometry Measurements performed on a 30 tonne Cincinnatti Milacron servo-electric injection moulding machine with a custom rheometric nozzle Dynisco Pressure Transducer M Dynisco Pressure Transducer M Capillary die inserts Capillary die inserts 0.5 x 8.0 mm 0.5 x 0.25 mm 1.0 x 16 mm 1.0 x 0.25 mm Thermocouple

22 High-shear capillary rheometry test results

23 Shear heating effects Source: Anthony Bur, Steven Roth, NIST

24 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

25 Molecular 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

26 Molecular weight distributions Source: RAPRA UK

27 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?

28 Surface feature replication

29 Plaque cavity 25 x 2.5 x 0.25 mm Fabricated using micro-milling technique Kern machine 0.2mm cutter at 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 rpm. Left in an unpolished state.

30 Surface 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

31 Surface feature replication - gate AFM scan size 75 µm x 75 µm Cavity Product

32 Surface 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

33 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

34 A single compounding/moulding process

35 The Rondol Micro-Injection Compounder

36

37 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

38 The Rondol Micro-Injection Compounder

39 Initial 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

40 Concluding 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

41 The authors gratefully acknowledge the support of the UK Micromoulding Interest Group (www.ukmig.com), particularly Ultratools Ltd for their assistance with cavity manufacture. Thanks also to Queen Mary University for supply of Hapex material. The authors gratefully acknowledge the support of the UK Micromoulding Interest Group (www.ukmig.com), particularly Ultratools Ltd for their assistance with cavity manufacture. Thanks also to Queen Mary University for supply of Hapex material. Acknowledgements

42 Thank you


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