Biomedical subjects

K E Tanner

Publications and source records attributed to K E Tanner.

At least 19 recordsLinked to original sources

PubMed2007

In vitro osteoblastic response to 30 vol% hydroxyapatite-polyethylene composite.

Hydroxyapatite-reinforced high-density polyethylene (HA-HDPE) composite, as a bone replacement material, has successfully been used clinically as middle ear prostheses and orbital floor implants. The aim of this study was to examine its in vitro biocompatibility in order to develop a further application, that is, as skull reconstruction implants. Human osteoblast cells isolated from femoral heads and crania were used to determine the biological response of the composites. HA-HDPE composites (30 vol %) with two grades of HA filler that had different surface morphologies were selected for this in vitro assessment. The results showed that HA-HDPE composite was bioactive and supported osteoblast attachment, proliferation, and differentiation. The composite with rough-surfaced HA filler demonstrated slightly better cellular response than the composite with smooth-surfaced HA filler. Although osteoblastic cells derived from skull showed an overall slower response compared with those from femoral heads, these in vitro results show that HA-HDPE composite potentially could be used as a skull implant.

Bone Substitutes↗

PubMed2006

2-Dimensional MEMS dielectrophoresis device for osteoblast cell stimulation.

A fixed microelectrode device for cell stimulation has been designed and fabricated using micro-electro-mechanical systems (MEMS) technology. Dielectrophoretic forces obtained from non-uniform electric fields were used for manipulating and positioning osteoblasts. The experiments show that the osteoblasts experience positive dielectrophoresis (p-DEP) when suspended in iso-osmotic culture medium and exposed to AC fields at 5 MHz frequency. Negative dielectrophoresis (n-DEP) is obtained at 0.1 MHz. The viability of osteoblasts under dielectrophoresis has been investigated. The viability values for cells exposed to DEP are nearly three times higher than the control values, indicating that dielectrophoresis may have an anabolic effect on osteoblasts.

Cell Culture Techniques↗

PubMed2006

Biodegradable and semi-biodegradable composite hydrogels as bone substitutes: morphology and mechanical characterization.

Biodegradable and semi-biodegradable composite hydrogels are proposed as bone substitutes. They consist of an hydrophilic biodegradable polymer (HYAFF 11) as matrix and two ceramic powders (alpha-TCP and HA) as reinforcement. Both components of these composites have been of great interest in biomedical applications due to their excellent biocompatibility and tissue interactions, however they have never been investigated as bone substitute composites. Morphological and mechanical analysis have shown that the two fillers behave in a very different way. In the HYAFF 11/alpha-TCP composite, alpha-TCP is able to hydrolyze in contact with water while in the HYAFF 11 matrix. As a result, the composite sets and hardens, and entangled CDHA crystals are formed in the hydrogel phase and increases in the mechanical properties are obtained. In the HYAFF11/HA composite the ceramic reinforcement acts as inert phase leading to lower mechanical properties. Both mechanical properties and microstructure analysis have demonstrated the possibility to design hydrophilic biodegradable composite structures for bone tissue substitution applications.

Biocompatible Materials↗

PubMed2006

Relationship between locking-bolt torque and load pre-tension in the Ilizarov frame.

The wire-bolt interface in an Ilizarov frame has been mechanically tested. The optimal torque to be applied to the frame locking-bolts during physiological loading has been defined. The set-up configuration was as is used clinically except a copper tube was used to simulate bone. The force-displacement curves of the Ilizarov wires are not altered by locking-bolt torque. The force in the bone model at which pre-tension is lost increases as the locking-bolts are tightened to 14 Nm torque, but decreases if torque exceeds 14 Nm. Thus, 14 Nm is the optimal locking-bolt torque in frame. The relationship between pre-tension versus load for different locking-bolt torques arises because at low and high clamping torques poor wire holding and plastic deformation respectively occur. Wire damage was seen under light and electron microscopy. Clinically, over or under-tightening locking-bolts will cause loss of pre-tension, reduction in frame stiffness and excessive movement at the fracture site, which may be associated with delayed union.

Biomechanical Phenomena↗

PubMed2006

Selective laser sintering of hydroxyapatite reinforced polyethylene composites for bioactive implants and tissue scaffold development.

Selective laser sintering (SLS) has been investigated for the production of bioactive implants and tissue scaffolds using composites of high-density polyethylene (HDPE) reinforced with hydroxyapatite (HA) with the aim of achieving the rapid manufacturing of customized implants. Single-layer and multilayer block specimens made of HA-HDPE composites with 30 and 40 vol % HA were sintered successfully using a CO2 laser sintering system. Laser power and scanning speed had a significant effect on the sintering behaviour. The degree of particle fusion and porosity were influenced by the laser processing parameters, hence control can be attained by varying these parameters. Moreover, the SLS processing allowed exposure of HA particles on the surface of the composites and thereby should provide bioactive products. Pores existed in the SLS-fabricated composite parts and at certain processing parameters a significant fraction of the pores were within the optimal sizes for tissue regeneration. The results indicate that the SLS technique has the potential not only to fabricate HA-HDPE composite products but also to produce appropriate features for their application as bioactive implants and tissue scaffolds.

Biocompatible Materials↗

PubMed2005

In vitro and in vivo biological responses to a novel radiopacifying agent for bone cement.

Iodixanol (IDX) and iohexol (IHX) have been investigated as possible radiopacification agents for polymethylmethacrylate (PMMA) bone cement, to replace the currently used barium sulphate and zirconia. IDX and IHX are both water-soluble iodine-based contrast media and for the last 20 years have been used extensively in clinical diagnostic procedures such as contrast media enhanced computed tomography, angiography and urography. One of the major reasons to remove the current radiopacifying agents is their well-documented cytotoxicity and their potential to increase bone resorption. Using in vitro bone resorption assays, the effect of PMMA particles plus IDX or IHX to induce osteoclast formation and lacunar resorption on dentine slices has been investigated. These responses have been compared with the in vitro response to PMMA particles containing the conventional radiopacifying agents, that is, barium sulphate and zirconia. In parallel, the in vivo reaction, in terms of new bone formation, to particles of these materials has been tested using a bone harvest chamber in rabbit tibiae. In vitro cell culture showed that PMMA containing IHX resulted in significantly less bone resorption than PMMA containing the conventional opacifiers. In vivo testing, however, showed no significant differences between the amounts of new bone formed around cement samples containing the two iodine-based opacifying agents in particulate form, although both led to fewer inflammatory cells than particles of PMMA containing zirconia. Our results suggest that a non-ionic radiopacifier could be considered as an alternative to the conventional radiopacifying agents used in biomaterials in orthopaedic surgery.

Animals↗

PubMed2005

Hydroxyapatite promotes superior keratocyte adhesion and proliferation in comparison with current keratoprosthesis skirt materials.

AIM: Published clinical series suggest the osteoodontokeratoprosthesis (OOKP) may have a lower extrusion rate than current synthetic keratoprostheses. The OOKP is anchored in the eye wall by autologous tooth. The authors' aim was to compare adhesion, proliferation, and morphology for telomerase transformed keratocytes seeded on calcium hydroxyapatite (the principal mineral constituent of tooth) and materials used in the anchoring elements of commercially available synthetic keratoprostheses. METHODS: Test materials were hydroxyapatite, polytetrafluoroethylene (PTFE), polyhydroxyethyl methacrylate (HEMA), and glass (control). Cell adhesion and viability were quantified at 4 hours, 24 hours, and 1 week using a calcein-AM/EthD-1 viability/cytotoxicity assay. Focal contact expression and cytoskeletal organisation were studied at 24 hours by confocal microscopy with immunoflourescent labelling. Further studies of cell morphology were performed using light and scanning electron microscopy. RESULTS: Live cell counts were significantly greater on hydroxyapatite surfaces at each time point (p<0.04). Dead cell counts were significantly higher for PTFE at 7 days (p<0.002). ss(1) integrin expression was highest on hydroxyapatite. Adhesion structures were well expressed in flat, spread out keratocytes on both HA and glass. Keratocytes tended to be thinner and spindle shaped on PTFE. The relatively few keratocytes visible on HEMA test surfaces were rounded and poorly adherent. CONCLUSIONS: Keratocyte adhesion, spreading, and viability on hydroxyapatite test surfaces is superior to that seen on PTFE and HEMA. Improving the initial cell adhesion environment in the skirt element of keratoprostheses may enhance tissue integration and reduce device failure rates.

Biocompatible Materials↗

PubMed2005

A circumferentially flanged tibial tray minimizes bone-tray shear micromotion.

Aseptic loosening of the tibial component is the major complication of total knee arthroplasty. There is an association between early excessive shear micromotion between the bone and the tray of the tibial component and late aseptic loosening. Using non-linear finite element analysis, whether a tibial tray with a circumferentially flanged rim and a mating cut in the proximal tibia could minimize bone-tray shear micromotion was considered. Fifteen competing tray designs with various degrees of flange curvature were assessed with the aim of minimizing bone-tray shear micromotion. A trade-off was found between reducing micromotion and increasing peripheral cancellous bone stresses. It was found that, within the limitations of the study, there was a theoretical design that could virtually eliminate micromotion due to axial loads, with minimal bone removal and without the use of screws or pegs.

Computer Simulation↗

PubMed2004

Bone cement X-ray contrast media: a clinically relevant method of measuring their efficacy.

It is important to compare different contrast media used in bone cement according to their ability to attenuate X-rays and thereby produce image contrast between bone cement and its surroundings in clinical applications. The radiopacity of bone cement is often evaluated by making radiographs of cement in air at an X-ray tube voltage of 40 kV. We have developed a method for ranking contrast media in bone cement simulating the clinical situation, by (1) choosing the same X-ray tube voltage as used in clinical work, and (2) using a water phantom to imitate the effects of the patients' soft tissue on the X-ray photons. In clinical work it is desirable to have low radiation dose, but high image contrast. The voltage chosen is a compromise, because both dose and image contrast decrease with higher voltage. Three contrast media (ZrO(2), BaSO(4), and Iodixanol) have been compared for degree of "image contrast." Comparing 10 wt % contrast media samples at an X-ray tube voltage of 40 kV, ZrO(2) produced higher image contrast than the other media. However, at 80 kV, using a water phantom, the results were reversed, ZrO(2) produced lower image contrast than both BaSO(4) and Iodixanol. We conclude that evaluations of contrast media should be made with voltages and phantoms imitating the clinical application.

Barium Sulfate↗

PubMed2004

Effect of particle morphology and polyethylene molecular weight on the fracture toughness of hydroxyapatite reinforced polyethylene composite.

Fracture toughness testing has been performed on hydroxyapatite-polyethylene composites. Sintered and unsintered grades of hydroxyapatite and two grades of high-density polyethylene were used to make 40 vol % hydroxyapatite composites. Compact tension testing was performed at both room temperature and at 37 degrees C and at three strain rates. The effect of increasing the loading rate from 2 to 200 microm s(-1) was to increase the fracture toughness. Increasing the testing temperature or decreasing the surface area of the reinforcing particles also increased the fracture toughness. However, using a lower molecular weight, injection moulding, grade of polyethylene reduced the fracture toughness. Thus for higher fracture toughness, a low surface area sintered hydroxyapatite in a high-molecular weight polyethylene is required.

Biocompatible Materials↗

PubMed2004

Biodegradation and biocompatability of a calcium sulphate-hydroxyapatite bone substitute.

An injectable material consisting of calcium sulphate mixed with hydroxyapatite was investigated as a possible alternative to autograft in the restoration of bone defects. The material was studied both in vitro in simulated body fluid (SBF) and in vivo when implanted in rat muscles and into the proximal tibiae of rabbits. Variation in the strength and weight of the material during ageing in SBF was measured. Tissue response, material resorption and bone ingrowth were studied in the animal models. A good tissue response was observed in both the rat muscles and rabbit tibiae without inflammatory reactions or the presence of fibrous tissue. Ageing in SBF showed that during the first week carbonated hydroxyapatite precipitated on the surfaces of the material and this may enhance bone ingrowth.

Animals↗

PubMed2003

Experimental validation of a microcracking-based toughening mechanism for cortical bone.

It has been proposed that cortical bone derives its toughness by forming microcracks during the process of crack propagation (J. Biomech. 30 (1997) 763; J. Biomech. 33 (2000) 1169). The purpose of this study was to experimentally validate the previously proposed microcrack-based toughening mechanism in cortical bone. Crack initiation and propagation tests were conducted on cortical bone compact tension specimens obtained from the antlers of red deer. For these tests, the main fracture crack was either propagated to a predetermined crack length or was stopped immediately after initiating from the notch. The microcracks produced in both groups of specimens were counted in the same surface area of interest around and below the notch, and crack growth resistance and crack propagation velocity were analyzed. There were more microcracks in the surface area of interest in the propagation than in initiation specimens showing that the formation of microcracks continued after the initiation of a fracture crack. Crack growth resistance increased with crack extension, and crack propagation velocity vs. crack extension curves demonstrated the characteristic jump increase and decrease pattern associated with the formation of microcracks. The scanning electron micrographs of crack initiation and propagation displayed the formation of a frontal process zone and a wake, respectively. These results support the microcrack-based toughening mechanism in cortical bone. Bone toughness is, therefore, determined by its ability to form microcracks during fracture.

Animals↗

PubMed2003

Impact behavior of hydroxyapatite reinforced polyethylene composites.

Hydroxyapatite particulate reinforced high density polyethylene composite (HA-HDPE) has been developed as a bone replacement material. The impact behavior of the composites at 37 degrees C has been investigated using an instrumented falling weight impact testing machine. The fracture surfaces were examined using SEM and the fracture mechanisms are discussed. It was found that the fracture toughness of HA-HDPE composites increased with HDPE molecular weight, but decreased with increasing HA volume fraction. Examination of fracture surfaces revealed weak filler/matrix interfaces which can debond easily to enable crack initiation and propagation. Increasing HA volume fraction increases the interface area, and more cracks can form and develop, thus decreasing the impact resistance of the composites. Another important factor for the impact behavior of the composites is the matrix. At higher molecular weight, HDPE is able to sustain more plastic deformation and dissipates more impact energy, hence improving the impact property.

Journal Article↗

PubMed2003

Factors influencing the compressive strength of an injectable calcium sulfate-hydroxyapatite cement.

A biphasic injectable bone substitute, suitable for filling bone defects, that sets in the body, based on calcium sulfate and hydroxyapatite (HA), is presented. For applications in bone defects the compressive strength is important to assure support of the defect site during loading when the patient is weight bearing. To control the strength, the influence of four different factors; the liquid-to-powder (L/P) ratio, the HA particle morphology, the HA content and the amount of accelerator, were investigated. alpha-Calcium sulfate hemihydrate (CSH) and four different HA powders (three sintered and one spray-dried) were used. All differed in size and morphology. CSH and each HA powder were mixed together with distilled water to form the bone substitute. An accelerator, in form of calcium sulfate dihydrate, was added to the powder phase to obtain an adequate setting time. Cylindrical specimens were compression tested. A lower L/P-ratio gave stronger cement, but was more difficult to inject. The shape and the morphology of the HA particles influenced the strength, and reducing the amount of HA increased the strength. The amount of accelerator (calcium sulfate dihydrate) had no influence.

Journal Article↗

PubMed2002

A biomechanical study on fixation stability with twin hook or lag screw in artificial cancellous bone.

The twin hook has been developed as an alternative to the conventional lag screw to be combined with a barrelled side-plate in the treatment of trochanteric hip fractures. With two oppositely directed apical hooks introduced into the subchondral bone of the femoral head, the twin hook provides different stabilising properties to the lag screw. The femoral head purchase of the twin hook and the lag screw were compared in a biomechanical study using artificial cancellous bone, and responses to axial and torsional loading was determined. A distinct yield point in load and torque was noted for the lag screw, representing failure of the laminas supporting the threads. For the twin hook, gradual increase of load and torque occurred during impaction of the bone supporting the hooks. The peak loads and torques were higher for the lag screw, but were similar for both devices after 8 mm deformation. The stiffness was higher for the lag screw, but in counter-clockwise rotation the stiffness for the lag screw was negligible. The twin hook appeared to provide fixation stability comparable to that offered by the lag screw, but with conceivable advantages in terms of a deformation response involving bone impaction and gradually increasing stability.

Biomechanical Phenomena↗

PubMed2002

Effect of filler content on mechanical and dynamic mechanical properties of particulate biphasic calcium phosphate--polylactide composites.

A bioabsorbable self-reinforced polylactide/biphasic calcium phosphate (BCP) composite is being developed for fracture fixation plates. One manufacturing route is to produce preimpregnated sheets by pulling polylactide (PLA) fibres through a suspension of BCP filler in a PLA solution and compression moulding the prepreg to the desired shape. To aid understanding of the process, interactions between the matrix and filler were investigated. Composite films containing 0-0.25 volume fraction filler, produced by solvent casting, were analysed using SEM, tensile testing and dynamic mechanical analysis (DMA). Homogeneous films could be made, although some particle agglomeration was seen at higher filler volume fractions. As the filler content increased, the failure strain decreased due to a reduction in the amount of ductile polymer present and the ultimate tensile strength (UTS) decreased because of agglomeration and void formation at higher filler content. The matrix glass transition temperature increased due to polymer chain adsorption and immobilization onto the BCP particles. Complex damping mechanisms, such as particle-particle agglomeration, may exist at the higher BCP volume fractions.

Algorithms↗

PubMed2002

Effect of hydroxyapatite morphology/surface area on the rheology and processability of hydroxyapatite filled polyethylene composites.

The commercial success of hydroxyapatite (HA) filled polyethylene composite has generated growing interest in improving the processability of the composite. A number of synthetic procedures and post synthesis heat treatment of HA has lead to the availability of powders with widely varying morphological features. This paper addresses the effect of morphological features of HA on the rheology and processability of an injection-moulding grade HA-HDPE composite. The results showed that low surface area HA filled composite exhibited better injection processing characteristics through improved rheological responses. The effect of reducing the surface area of the filler is to require less polyethylene to wet the filler and allows more polyethylene to be involved in the flow processes. These changes reduced the temperatures and pressures required for successful processing.

Biocompatible Materials↗

PubMed2002

Arch-shaped versus flat arthrodesis of the ankle joint: strength measurements using synthetic cancellous bone.

The aim of this study was to see if preservation of the arch shape of the ankle at arthrodesis contributes to stability. The ankle joint was simulated by paired blocks of a synthetic material corresponding to rheumatoid cancellous bone with low stiffness and strength. Flat end constructs with and without subchondral bone were compared with arch-shape constructs with and without subchondral bone. The pairs were fixed with two screws simulating an arthrodesis. These constructs were then tested to failure in four-point bending and torque. In four-point bending the subchondral bone increased the strength, regardless of shape. Stiffness was higher in the arch-shaped specimens but was not influenced by the subchondral bone. In torque, both arch-shape and subchondral bone increase the strength. Stiffness was increased by arch-shape but not subchondral bone. The results imply that the arch-shape and subchondral bone should be preserved when performing an ankle arthrodesis, especially in weak rheumatoid bone.

Ankle Joint↗