The effects of experimental conditions on the amount of wear of the metal surface during fretting... more The effects of experimental conditions on the amount of wear of the metal surface during fretting of steel on polycarbonate in laboratory air have been studied within the following limits: amplitude 2–20 μm, frequency 10–120 Hz and normal load 130–830 g. The influence of water vapour on the wear has also been investigated. The polycarbonate induces fretting damage of the steel, with α-Fe2O3 particles being transferred from the steel to the polymer surface. After an incubation period during which wear does not take place a running in period occurs during which the rate of wear decreases with the number of cycles, followed by a steady state period, during which the rate of wear remains fairly constant. The length of the incubation period generally increases with decreasing amplitude of slip and with increasing frequency of vibration, while the amount of subsequent wear generally increases with increasing amplitude of slip, with decreasing frequency of vibration and with decreasing applied load within the range studied. It is found that water vapour content has the most significant effect on the amount of wear. In moist oxygen, moist argon and moist nitrogen (relative humidity about 85%) the amount of wear is greater than in laboratory air (relative humidity about 50%), while in dry gases virtually no wear of the metal is observed.
Abstract The effects of the nature of the polymer on the amount of metal wear during fretting of ... more Abstract The effects of the nature of the polymer on the amount of metal wear during fretting of steel on polymers in laboratory air have been studied under a range of loads (130–330 g), amplitudes (3–10 μm) and frequencies (30–60 Hz). A number of polymers can cause damage to the metal, which takes the form of adhesive transfer of α-Fe 2 O 3 particles to the polymer surface. The amount of metal wear depends on the polymer counterface and, under a given set of experimental conditions, increases in the order polytetrafluoroethylene (PTFE) and polyethylene, polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polysulphone, Polyvinylchloride (PVC), polymethylmethacrylate (PMMA), polycarbonate, nylon 66. No metal wear occurs when the counterface is PTFE and only occurs with polyethylene when the amplitude is greater than 7 μm. These differences are explained in terms of the adhesive properties of the polymers, as determined by their surface energetics. Wear of the polymer during fretting takes the form of fibre formation for polysulphone, PVC, polycarbonate, nylon 66 and, to a small extent, polyethylene, while it takes the form of a transfer of a polymer film to the metal for PTFE and PVDF. No polymer wear occurs for PCTFE or PMMA.
A method for applying HA coatings to metallic surfaces, without the use of high temperature plasm... more A method for applying HA coatings to metallic surfaces, without the use of high temperature plasma spraying, has been developed. The HA coating is precipitated in an aqueous solution under conditions similar to those occurring in the body during bone formation. This surface mineralization process results in a coating which is highly crystalline and 100% HA. Processing and characterization experimentation and results are included in the paper. The coating method has the ability to penetrate macroporous (>100 micron pores) metal structures and coat the undersides and interior surfaces of the areas designed for bone ingrowth on orthopedic devices used for joint replacements. This ability to coat all around a surface is the basis for the name Peri-Apatite HA. Electron microscopy is presented illustrating the coverage and morphology of the coating. The Peri-Apatite HA coating is currently used on both knee joint replacement and hip joint replacement implants.
Abstract Fretting between steel components may be reduced by inserting a polymer layer between th... more Abstract Fretting between steel components may be reduced by inserting a polymer layer between the components, or by using a polymer as a replacement for one metal component. This paper describes the wear behaviour, in a fretting situation, of several polymers and relates the damage inflicted on the carbon steel counterface to properties of the polymer which depend on its surface energetics
ABSTRACTIon Implantation is emerging as a specialized surface treatment method by which orthopaed... more ABSTRACTIon Implantation is emerging as a specialized surface treatment method by which orthopaedic alloys can be doped in order to modify for corrision, fatigue and wear properties.In this paper alterations in the corrosion and fatigue resistance of 316LVM stainless steel and Ti 6A1-4V ELI titanium alloy are considered. The effect of various variables was investigated; ion species, flux, accelerating voltage.Changes in corrosion resistance were monitored by performing anodic polarization studies in deaerated 0.1M NaCi solution at 22°C. The most effective species were found to be tantalum and boron for improvements to stainless steel.Fatigue properties were investigated using a Wohler type rotating bend test. Preliminary results show that nitrogen ion implantation improved the fatigue life for the steel but not the titanium alloy. Indications were found to suggest that time since implantation affect the fatigue properties.
An in vivo investigation into the safety of a novel hydrogel implant designed to replace the dise... more An in vivo investigation into the safety of a novel hydrogel implant designed to replace the diseased nucleus pulposus. To determine the local and systemic safety of this new implant in a nonhuman primate model. A poly (vinyl alcohol) (PVA) hydrogel has been developed as a prosthetic replacement for the diseased nucleus pulposus. PVA implants were inserted into discectomy defects created in the L3-L4 or L4-L5 intervertebral disc in 20 male baboons. Empty discectomy defects served as a surgical control in 8 additional animals. Routine follow-up evaluations included radiography, magnetic resonance imaging, gross pathology, and histopathology of both local and remote tissues. Insertion of the PVA hydrogel from an anterior direction produced extrusions in 5 animals from the first series of 15 surgeries (33%). A modified surgical technique, involving an anterolateral rather than anterior approach, was used in 5 animals, but the extrusion rate remained high (20%). Despite these surgical complications, the PVA implants were well tolerated over 24 months in vivo, with no evidence of device-related pathology in the adjacent disc tissue, spinal cord, or remote tissues. Implantation of the PVA implant for periods of up to 24 months produced no evidence of local or systemic toxicity. Additional studies are now needed to determine the efficacy of the device in its intended application.
Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decr... more Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decreased the current during anodic polarization by as much as two orders of magnitude. A potential scan reversal at +700 mV forall specimens resulted in a hysteresis for passivated specimens (both smooth and porous) but not for nonpassivated specimens. The protection potential was +296 ′ 68 and +345 ′ 69 mV versus the saturated calomel electrode (SCE) for porous and smooth passivated specimens, respectively. There were two objectives of this work. The first was to see if a simple anodic polarization test could detect any basic difference in corrosion behavior between porous and smooth Vitallium. The second was to see if a standard passivation treatment affected these two geometries differently, again as detected by anodic polarization. The authors found that this porous configuration responds to polarization in a manner similar to the smooth surface in either the passivated or nonpassivated condition. There is an increase in current associated with the increased surface area. However, the increase in current appeared to be less than one would predict, assuming a linear proportionality between the current and surface area. All tests were performed on Vitallium in the form of modified patella buttons. The specimens were manufactured by Howmedica, Inc. The porous surface was identical to the P.C.A. configuration. All specimens, both smooth and porous-coated, underwent the same production heat cycle.
Although fretting damage is normally associated with contacting metal surfaces subjected to relat... more Although fretting damage is normally associated with contacting metal surfaces subjected to relative oscillatory slip of a few microns amplitude, it can also occur when polymers are in contact with metals. The fretting damage between polycarbonate-steel surfaces is made up of iron oxide debris from the steel surface and the formation of cracks on, and fibres from, the polymer surface.
We compared the mechanical and morphological characteristics of cement-bone structures created wi... more We compared the mechanical and morphological characteristics of cement-bone structures created with either standard- or low-viscosity cement using a human cadaver model that simulated intramedullary bleeding. The goal is to determine if the viscosity of the cement would affect the strength of the cement-bone interface and the degree of apposition between the cement and bone. The tensile strength of cement-bone constructs with standard-viscosity cement (2.42 +/- 1.55 MPa) was 21% stronger than with low-viscosity cement (2.00 +/- 1.51 MPa, P = .034). Cement-bone apposition was positively correlated (r2 = 0.29, P <. 0001) with the strength of the interface. There was 15% greater apposition between cement and bone (P = .036) for standard-viscosity cement. Low-viscosity cement may be less effective in displacing bone marrow and in preventing hemodynamic backflow, resulting in less apposition and a weaker interface.
Clinical Orthopaedics and Related Research, Aug 1, 1993
Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieve... more Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieved postmortem, 13-56 months after implantation, and were sectioned and evaluated histologically and histomorphometrically for bone ingrowth. The prosthesis-bone interface was divided into the following four zones: (1) the tissue prosthetic surface interface; (2) the beaded area; (3) the immediate beadless area; and (4) the marrow space. Although fibroosseous ingrowth was present in all cases, it varied quantitatively with each case and component. Average component bone ingrowth for the prosthesis interface (Zones 1 and 2) of patellae was 29%; tibias, 6%; and femora, 8%. In Zone 3, the percentage of bone apposed to the prosthesis for the patellae was 53%; tibias 36%; and femora, 32%. Zone 4, the marrow space, was not quantitated. The fibrous tissue filling nonbone-ingrown porous space in Zone 2 appeared "ligamentoid," connecting bone to beads within Zone 2 and between Zones 2 and 3. Zone 3 exhibited a bony plate formation parallel to the prostheses. No significant inflammation was noted. Overall there was more bone ingrowth into Zone 3 than Zones 1 and 2 with greater bone ingrowth found in the patellar components. The implant interface in clinically successful noncemented porous-coated prostheses of this design is characterized histologically by a noninflammatory fibroosseous ingrowth of varying degrees, and the fibrous component of this composite structure exhibits a highly organized pattern.
... steel plate 30 mm x 30 mm x 3 mm in size used both with a 6 Itm diamond finish and a 6 pin ce... more ... steel plate 30 mm x 30 mm x 3 mm in size used both with a 6 Itm diamond finish and a 6 pin centre-line average ground finish surface. 1t was clamped to a water-cooled electrode with a source-tosubstrate distance of 25 cm. Bias voltages in the range of -3.0 to -4.5 kV and argon ...
In this investigation, the static tensile strength of bone cement was quantified after mixing it ... more In this investigation, the static tensile strength of bone cement was quantified after mixing it in an open bowl or in a commercially available vacuum mixer and molding it under pressures consistent with values obtained by finger/digital application, as it is used in surgery. Pressure, held for a brief time span on cement in its lower viscosity state, has been demonstrated to increase penetration of the cement into bone. Clinically, bone cement is pressurized by digital pressure, specialized instruments, or by implant design. Specimens were cured under constant pressures of up to 100 kPa, which is in the range reported for thumb pressurization of plugged proximal femurs and instrumented pressurization of acetabular sockets. The results showed that application of constant pressure during the polymerization of open bowl mixed bone cement significantly improved its mechanical properties. Application of 100 kPa constant pressure to the open bowl mixed bone cement while it cured increased its ultimate strength to a value similar to vacuum mixed cement. Curing under pressure showed no significant effect on the tensile properties of vacuum mixed cement. Curing under pressure did not significantly reduce the size of the largest pores in the tensile specimens.
Examination has been made of the wear of the metal surface during fretting of contacting steel-po... more Examination has been made of the wear of the metal surface during fretting of contacting steel-polymer surfaces in air. The worn surfaces have been examined by optical and scanning electron microscopy and the wear debris by transmission electron microscopy and electron diffraction. Polycarbonate, polyvinyl chloride, polysulphone, polyethylene, polymethylmethacrylate and nylon 66 cause fretting damage to the steel surface, with the damage involving a transfer of ct-Fe20,, together with small amounts of either FesO4 or a-FeOOH, to the polymer surface. This transferred debris consists of very small, plate-like particles, the average size of which is independent of fretting conditions (load, amplitude, frequency and number of cycles) but does depend on the adhesive nature of the polymer. Average particle sizes range from 8nm for polyethylene to 70nm for nylon 66. The extent of damage to the metal is very small in dry environments but is quite considerable in moist environments. The wear is accounted for in terms of a mechanico-chemical process, with oxidation of the steel surface being followed by adhesion between the oxide and the polymer, and transfer of the oxide to the polymer.
The effects of experimental conditions on the amount of wear of the metal surface during fretting... more The effects of experimental conditions on the amount of wear of the metal surface during fretting of steel on polycarbonate in laboratory air have been studied within the following limits: amplitude 2–20 μm, frequency 10–120 Hz and normal load 130–830 g. The influence of water vapour on the wear has also been investigated. The polycarbonate induces fretting damage of the steel, with α-Fe2O3 particles being transferred from the steel to the polymer surface. After an incubation period during which wear does not take place a running in period occurs during which the rate of wear decreases with the number of cycles, followed by a steady state period, during which the rate of wear remains fairly constant. The length of the incubation period generally increases with decreasing amplitude of slip and with increasing frequency of vibration, while the amount of subsequent wear generally increases with increasing amplitude of slip, with decreasing frequency of vibration and with decreasing applied load within the range studied. It is found that water vapour content has the most significant effect on the amount of wear. In moist oxygen, moist argon and moist nitrogen (relative humidity about 85%) the amount of wear is greater than in laboratory air (relative humidity about 50%), while in dry gases virtually no wear of the metal is observed.
Abstract The effects of the nature of the polymer on the amount of metal wear during fretting of ... more Abstract The effects of the nature of the polymer on the amount of metal wear during fretting of steel on polymers in laboratory air have been studied under a range of loads (130–330 g), amplitudes (3–10 μm) and frequencies (30–60 Hz). A number of polymers can cause damage to the metal, which takes the form of adhesive transfer of α-Fe 2 O 3 particles to the polymer surface. The amount of metal wear depends on the polymer counterface and, under a given set of experimental conditions, increases in the order polytetrafluoroethylene (PTFE) and polyethylene, polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polysulphone, Polyvinylchloride (PVC), polymethylmethacrylate (PMMA), polycarbonate, nylon 66. No metal wear occurs when the counterface is PTFE and only occurs with polyethylene when the amplitude is greater than 7 μm. These differences are explained in terms of the adhesive properties of the polymers, as determined by their surface energetics. Wear of the polymer during fretting takes the form of fibre formation for polysulphone, PVC, polycarbonate, nylon 66 and, to a small extent, polyethylene, while it takes the form of a transfer of a polymer film to the metal for PTFE and PVDF. No polymer wear occurs for PCTFE or PMMA.
A method for applying HA coatings to metallic surfaces, without the use of high temperature plasm... more A method for applying HA coatings to metallic surfaces, without the use of high temperature plasma spraying, has been developed. The HA coating is precipitated in an aqueous solution under conditions similar to those occurring in the body during bone formation. This surface mineralization process results in a coating which is highly crystalline and 100% HA. Processing and characterization experimentation and results are included in the paper. The coating method has the ability to penetrate macroporous (>100 micron pores) metal structures and coat the undersides and interior surfaces of the areas designed for bone ingrowth on orthopedic devices used for joint replacements. This ability to coat all around a surface is the basis for the name Peri-Apatite HA. Electron microscopy is presented illustrating the coverage and morphology of the coating. The Peri-Apatite HA coating is currently used on both knee joint replacement and hip joint replacement implants.
Abstract Fretting between steel components may be reduced by inserting a polymer layer between th... more Abstract Fretting between steel components may be reduced by inserting a polymer layer between the components, or by using a polymer as a replacement for one metal component. This paper describes the wear behaviour, in a fretting situation, of several polymers and relates the damage inflicted on the carbon steel counterface to properties of the polymer which depend on its surface energetics
ABSTRACTIon Implantation is emerging as a specialized surface treatment method by which orthopaed... more ABSTRACTIon Implantation is emerging as a specialized surface treatment method by which orthopaedic alloys can be doped in order to modify for corrision, fatigue and wear properties.In this paper alterations in the corrosion and fatigue resistance of 316LVM stainless steel and Ti 6A1-4V ELI titanium alloy are considered. The effect of various variables was investigated; ion species, flux, accelerating voltage.Changes in corrosion resistance were monitored by performing anodic polarization studies in deaerated 0.1M NaCi solution at 22°C. The most effective species were found to be tantalum and boron for improvements to stainless steel.Fatigue properties were investigated using a Wohler type rotating bend test. Preliminary results show that nitrogen ion implantation improved the fatigue life for the steel but not the titanium alloy. Indications were found to suggest that time since implantation affect the fatigue properties.
An in vivo investigation into the safety of a novel hydrogel implant designed to replace the dise... more An in vivo investigation into the safety of a novel hydrogel implant designed to replace the diseased nucleus pulposus. To determine the local and systemic safety of this new implant in a nonhuman primate model. A poly (vinyl alcohol) (PVA) hydrogel has been developed as a prosthetic replacement for the diseased nucleus pulposus. PVA implants were inserted into discectomy defects created in the L3-L4 or L4-L5 intervertebral disc in 20 male baboons. Empty discectomy defects served as a surgical control in 8 additional animals. Routine follow-up evaluations included radiography, magnetic resonance imaging, gross pathology, and histopathology of both local and remote tissues. Insertion of the PVA hydrogel from an anterior direction produced extrusions in 5 animals from the first series of 15 surgeries (33%). A modified surgical technique, involving an anterolateral rather than anterior approach, was used in 5 animals, but the extrusion rate remained high (20%). Despite these surgical complications, the PVA implants were well tolerated over 24 months in vivo, with no evidence of device-related pathology in the adjacent disc tissue, spinal cord, or remote tissues. Implantation of the PVA implant for periods of up to 24 months produced no evidence of local or systemic toxicity. Additional studies are now needed to determine the efficacy of the device in its intended application.
Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decr... more Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decreased the current during anodic polarization by as much as two orders of magnitude. A potential scan reversal at +700 mV forall specimens resulted in a hysteresis for passivated specimens (both smooth and porous) but not for nonpassivated specimens. The protection potential was +296 ′ 68 and +345 ′ 69 mV versus the saturated calomel electrode (SCE) for porous and smooth passivated specimens, respectively. There were two objectives of this work. The first was to see if a simple anodic polarization test could detect any basic difference in corrosion behavior between porous and smooth Vitallium. The second was to see if a standard passivation treatment affected these two geometries differently, again as detected by anodic polarization. The authors found that this porous configuration responds to polarization in a manner similar to the smooth surface in either the passivated or nonpassivated condition. There is an increase in current associated with the increased surface area. However, the increase in current appeared to be less than one would predict, assuming a linear proportionality between the current and surface area. All tests were performed on Vitallium in the form of modified patella buttons. The specimens were manufactured by Howmedica, Inc. The porous surface was identical to the P.C.A. configuration. All specimens, both smooth and porous-coated, underwent the same production heat cycle.
Although fretting damage is normally associated with contacting metal surfaces subjected to relat... more Although fretting damage is normally associated with contacting metal surfaces subjected to relative oscillatory slip of a few microns amplitude, it can also occur when polymers are in contact with metals. The fretting damage between polycarbonate-steel surfaces is made up of iron oxide debris from the steel surface and the formation of cracks on, and fibres from, the polymer surface.
We compared the mechanical and morphological characteristics of cement-bone structures created wi... more We compared the mechanical and morphological characteristics of cement-bone structures created with either standard- or low-viscosity cement using a human cadaver model that simulated intramedullary bleeding. The goal is to determine if the viscosity of the cement would affect the strength of the cement-bone interface and the degree of apposition between the cement and bone. The tensile strength of cement-bone constructs with standard-viscosity cement (2.42 +/- 1.55 MPa) was 21% stronger than with low-viscosity cement (2.00 +/- 1.51 MPa, P = .034). Cement-bone apposition was positively correlated (r2 = 0.29, P <. 0001) with the strength of the interface. There was 15% greater apposition between cement and bone (P = .036) for standard-viscosity cement. Low-viscosity cement may be less effective in displacing bone marrow and in preventing hemodynamic backflow, resulting in less apposition and a weaker interface.
Clinical Orthopaedics and Related Research, Aug 1, 1993
Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieve... more Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieved postmortem, 13-56 months after implantation, and were sectioned and evaluated histologically and histomorphometrically for bone ingrowth. The prosthesis-bone interface was divided into the following four zones: (1) the tissue prosthetic surface interface; (2) the beaded area; (3) the immediate beadless area; and (4) the marrow space. Although fibroosseous ingrowth was present in all cases, it varied quantitatively with each case and component. Average component bone ingrowth for the prosthesis interface (Zones 1 and 2) of patellae was 29%; tibias, 6%; and femora, 8%. In Zone 3, the percentage of bone apposed to the prosthesis for the patellae was 53%; tibias 36%; and femora, 32%. Zone 4, the marrow space, was not quantitated. The fibrous tissue filling nonbone-ingrown porous space in Zone 2 appeared "ligamentoid," connecting bone to beads within Zone 2 and between Zones 2 and 3. Zone 3 exhibited a bony plate formation parallel to the prostheses. No significant inflammation was noted. Overall there was more bone ingrowth into Zone 3 than Zones 1 and 2 with greater bone ingrowth found in the patellar components. The implant interface in clinically successful noncemented porous-coated prostheses of this design is characterized histologically by a noninflammatory fibroosseous ingrowth of varying degrees, and the fibrous component of this composite structure exhibits a highly organized pattern.
... steel plate 30 mm x 30 mm x 3 mm in size used both with a 6 Itm diamond finish and a 6 pin ce... more ... steel plate 30 mm x 30 mm x 3 mm in size used both with a 6 Itm diamond finish and a 6 pin centre-line average ground finish surface. 1t was clamped to a water-cooled electrode with a source-tosubstrate distance of 25 cm. Bias voltages in the range of -3.0 to -4.5 kV and argon ...
In this investigation, the static tensile strength of bone cement was quantified after mixing it ... more In this investigation, the static tensile strength of bone cement was quantified after mixing it in an open bowl or in a commercially available vacuum mixer and molding it under pressures consistent with values obtained by finger/digital application, as it is used in surgery. Pressure, held for a brief time span on cement in its lower viscosity state, has been demonstrated to increase penetration of the cement into bone. Clinically, bone cement is pressurized by digital pressure, specialized instruments, or by implant design. Specimens were cured under constant pressures of up to 100 kPa, which is in the range reported for thumb pressurization of plugged proximal femurs and instrumented pressurization of acetabular sockets. The results showed that application of constant pressure during the polymerization of open bowl mixed bone cement significantly improved its mechanical properties. Application of 100 kPa constant pressure to the open bowl mixed bone cement while it cured increased its ultimate strength to a value similar to vacuum mixed cement. Curing under pressure showed no significant effect on the tensile properties of vacuum mixed cement. Curing under pressure did not significantly reduce the size of the largest pores in the tensile specimens.
Examination has been made of the wear of the metal surface during fretting of contacting steel-po... more Examination has been made of the wear of the metal surface during fretting of contacting steel-polymer surfaces in air. The worn surfaces have been examined by optical and scanning electron microscopy and the wear debris by transmission electron microscopy and electron diffraction. Polycarbonate, polyvinyl chloride, polysulphone, polyethylene, polymethylmethacrylate and nylon 66 cause fretting damage to the steel surface, with the damage involving a transfer of ct-Fe20,, together with small amounts of either FesO4 or a-FeOOH, to the polymer surface. This transferred debris consists of very small, plate-like particles, the average size of which is independent of fretting conditions (load, amplitude, frequency and number of cycles) but does depend on the adhesive nature of the polymer. Average particle sizes range from 8nm for polyethylene to 70nm for nylon 66. The extent of damage to the metal is very small in dry environments but is quite considerable in moist environments. The wear is accounted for in terms of a mechanico-chemical process, with oxidation of the steel surface being followed by adhesion between the oxide and the polymer, and transfer of the oxide to the polymer.
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Papers by Paul Higham