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T Clive Lee

Publications and source records attributed to T Clive Lee.

16 recordsLinked to original sources
PubMed2006

Highly selective 4-amino-1,8-naphthalimide based fluorescent photoinduced electron transfer (PET) chemosensors for Zn(II) under physiological pH conditions.

The design and synthesis of two novel fluorescent sensors based on the photoinduced electron transfer (PET) concept, and , for the detection of zinc under competitive media is described. These sensors are based on the 4-amino-1,8-naphthalimide fluorophore, which has an absorption band centred at 450 nm and emits in the green with lambda(max) approximately 550 nm. By functionalizing the chromophore with a simple benzyl or ethyl-aryl based iminodiacetate receptor at the 4-position, both high selectivity and sensitivity were achieved for the sensing of Zn(II) over other competitive transition and Group I and II metal ions. These sensors were also shown to be pH independent, with a pKa of 2.3 being determined for , which allows these to be used in highly competitive pH media. Upon sensing of Zn(II) the fluorescence emission spectrum is 'switched on' demonstrating the suppression of PET from the receptor to the fluorophore. For , the sensing of Zn(II) was achieved with Kd = 4 nM when measured in pH 7.4 buffered solution, in the presence of 1.1 mM of EGTA.

1-Naphthylamine↗
PubMed2006

The role of osteocytes and bone microstructure in preventing osteoporotic fractures.

The skeleton alters its geometry following trauma, the introduction of artificial defects and of fatigue-induced microcracks. The precise mechanism by which the skeleton adapts remains unclear. Microcracks might directly affect the cell by damaging the osteocyte cell network or causing apoptosis. Bone microstructure may play an important role in these processes by diverting and arresting propagating microcracks and so prevent fracture failure. This paper discusses the effects of microstructure on propagating cracks, how microdamage may act as a stimulus for bone adaptation and its potential effects on bone biochemistry.

Bone Remodeling↗
PubMed2006

Synthesis and evaluation of potential CT (computer tomography) contrast agents for bone structure and microdamage analysis.

The design and synthesis of several novel X-ray contrast agents 1-3, developed for targeting bone structures, and in particularly microcracks in bones, using CT (Computer Tomography) detection is described. These contrast agents are based on the use of the well known triiodobenzene platform, which was conjugated into one or more phenyliminodiacetate moieties, which can be used to 'lock' onto bone matrices. Compounds 1-3 were all tested for their ability to visualise cracks in bone structures (bovine bones) using micro-CT imaging.

Animals↗
PubMed2006

The cellular transducer in bone: What is it?

Bone is able to detect its strain environment and respond accordingly. In particular it is able to adapt to over-use and under-use by bone deposition or resorption. How can bone sense strain? Various physical mechanisms have been proposed for the so-called cellular transducer, but there is no conclusive proof for any one of them. This paper examines the theories and evidence, with particular reference to a new theory proposed by the authors, involving damage to cellular processes by microcracks. Experiments on bone samples ex-vivo showed that cracks cannot fracture osteocytes, but that cellular processes which span the crack can be broken. A theoretical model was developed for predicting the number of broken processes as a function of crack size and applied stress. This showed that signals emitted by fractured processes could be used to detect cracks which needed repairing and to provide information on the overall level of damage which could be used to initiate repair and adaptation responses.

Adaptation, Physiological↗
PubMed2006

Dynamic short crack growth in cortical bone.

It is well known for almost half a century that bones contain microcracks. Very little is known about the crack growth behaviour of very small cracks, e.g. the stage before they become macroscopically long. The aim of this work was to investigate the dynamic crack growth behaviour of sub-millimetre microcracks in cortical bone. It was found that slow stable crack growth occurs in specimens subjected to static loading conditions. Crack growth direction was dominated by the local fibre orientation of the bones. Crack angles varied between 10 and 36 degrees of the long axis of the bone. Short cracks were found to show periods of rapid growth followed by intervals of temporary crack arrest. Histological analysis showed that crack arrest occurred due to vascular canals in the bone. During these periods of crack arrest, crack opening displacements increased until the local strain was sufficient to overcome these features. These observations indicate a mechanism for growth of small cracks in bone at constant stress, involving microstructural barriers, time-dependent deformation of material near the crack tip and strain-controlled propagation.

Animals↗
PubMed2005

Microdamage in bone: surface analysis and radiological detection.

Microdamage accumulation leads to reduced bone strength and fracture. Intact, damaged and Rose Bengal stained cortical bone specimens were studied using SEM and EDXA imaging. SEM coupled with EDXA studies showed selective labelling of surface damage due to binding of dye at free lattice sites. A series of novel iodinated X-ray contrast agent were synthesised. These agents demonstrated excellent stability, water solubility and lack of atropisomerism. Preliminary imaging studies, using cone-beam mu-CT, demonstrated their ability to provide visible contrast in the solid state on bone surfaces.

Absorptiometry, Photon↗
PubMed2005

Microcracks in cortical bone: how do they affect bone biology?

Microcrack accumulation in cortical bone has been implicated in skeletal fragility and stress fractures. These cracks have also been shown to affect the mechanical and material properties of cortical bone. Their growth has been linked to osteocyte apoptosis and the initiation of the remodeling process, which also has a role in their repair. Clinically, osteoporosis is diagnosed using dual energy x-ray absorptiometry. However, evidence now indicates that bone mass alone is insufficient to satisfactorily explain the skeletal fragility of osteoporosis and consideration needs to be given to bone quality in the diagnosis and treatment of the disease. Bone quality includes parameters such as trabecular and cortical microarchitecture, morphology, bone turnover, degree of mineralization of the bone matrix, and significantly, the amount of microdamage present in the bone. Current clinical treatments concentrate on the inhibition of osteoclast activity to maintain bone mass in osteoporotic patients. However, these cells have a major role in removing existing microcracks from the bone matrix, and hence the use of bone resorption- inhibiting drugs may lead to insufficient bone repair and therefore an increase in microdamage accumulation and loss of bone quality.

Animals↗
PubMed2005

The effect of bone microstructure on the initiation and growth of microcracks.

Osteonal bone is often compared to a composite material and to metals as discontinuities within the material may provide sites of stress concentration for crack initiation and serve as barriers to crack growth. However, little experimental data exist to back up these hypotheses. Fluorescent chelating agents were applied at specific intervals to bone specimens fatigue tested in cyclic compression at a stress range of 80 MPa. The failed specimens were sectioned and labelled microcracks identified using UV epifluorescence microscopy. Microcrack lengths were measured and their relationship to cement lines surrounding secondary osteons recorded. Microcrack length at the time of encountering a cement line was also measured. Microcracks of less than 100mum stopped growing when they encountered a cement line. Microcracks of greater than 100mum in length continued to grow after encountering a cement line surrounding an osteon. Only microcracks greater than 300mum in length were capable of penetrating osteons and these microcracks were the only ones which were observed to cause failure in the specimen. These experimental data support the hypothesis that secondary osteons act as barriers to crack propagation in compact bone. However, it shows that this microstructural barrier effect is dependent on the crack length at the time of encountering an osteon. For the vast majority of cracks, osteons act as barriers to growth but for the minority of cracks that are long enough and do break through the cement line, an osteon may actually act as a weakness in the bone and facilitate crack propagation.

Animals↗
PubMed2004

Microcracks in the alveolar bone following orthodontic tooth movement: a morphological and morphometric study.

Microcracks and microdamage have been associated with bone remodelling. The aim of this study was to investigate the role of microcracks as a trigger for alveolar bone remodelling after the application of an orthodontic load. In 25 3-month-old male Danish land-race pigs, the lower right first molar was moved buccally with a force of 130 cN. The contralateral molar was not treated and was used as an internal control. After 1, 2, 4, 7 and 15 days of treatment, the regions containing the right and left molars were excised and en bloc stained in basic fuchsin. The presence of microcracks on the buccal and lingual sides of both treated and untreated teeth was detected and expressed as crack density (number/mm2). The buccal treated side showed significantly more cracks than the buccal untreated side at day 1. This difference was significantly larger than that observed at days 2, 7 and 15. The same side showed significantly more microcracks than the lingual treated side at day 1, and this difference was larger compared with that observed at days 4 and 15. The presence of more microcracks on the treated side than on the untreated side suggests a role for microcracks in the initiation of bone remodelling after orthodontic loading. The increased presence of microcracks on the side towards which the tooth was moved, and where bone resorption is usually observed, suggests that microcracks could represent the first damage induced by orthodontic force that has to be repaired by bone remodelling. Finally, the strain levels in the alveolar bone during the orthodontic load transfer in the experiment were examined by finite element (FE) analysis. Although this showed that the strains were very low (10-100 microstrain), it should be noted that occlusal loading was not taken into account. In addition, high-resolution microtomography of the alveolar bone/periodontal ligament (PDL) interface revealed that the actual surface of the alveolar bone was very rough, predisposing it to high local stress/strain peaks.

Alveolar Process↗
PubMed2003

Cd(II) sensing in water using novel aromatic iminodiacetate based fluorescent chemosensors.

[structure: see text]. Compounds 1 and 2 were designed as fluorescent chemosensors for Cd(II). For both, a selective determination of Cd(II) over Zn(II) was achieved. The fluorescence emission of both was pH-independent and switched off between pH 3-11 in 100% water. Whereas the recognition of Cd(II) at pH 7.4 gave rise to the formation of charge-transfer complexes (exciplexes) for both (lambdamax ca. 500 and 506 nm, respectively), the recognition of Zn(II) only switched on the (monomeric) anthracene emission of 2, while for 1 it was red-shifted (lambdamax = 468 nm).

Journal Article↗
PubMed2003

Microcrack accumulation at different intervals during fatigue testing of compact bone.

Fatigue damage in bone occurs in the form of microcracks. This microdamage contributes to the formation of stress fractures and acts as a stimulus for bone remodelling. A technique has been developed, which allows microcrack growth to be monitored during the course of a fatigue test by the application of a series of fluorescent chelating agents. Specimens were taken from bovine tibiae and fatigue tested in cyclic compression at a stress range of 80MPa. The specimens were stained before testing with alizarin and up to three other chelating agents were applied during testing to label microcracks formed at different times. Microcracks initiated in interstitial bone in the early part of a specimen's life. Further accumulation of microcracks is then suppressed until the period late in the specimen's life. Microcracks were found to be longer in the longitudinal than in the transverse direction. Only a small proportion of cracks are actively propagating; these are longer than non-propagating cracks. These results support the concept of a microstructural barrier effect existing in bone, whereby cracks initiate easily but slow down or stop at barriers such as cement lines.

Adaptation, Physiological↗
PubMed2002

An improved labelling technique for monitoring microcrack growth in compact bone.

Fatigue-induced damage plays an important role in bone remodelling and in the formation of stress and fragility fractures. Recently, a technique has been developed (Lee, T.C. et al., Sequential labelling of microdamage in bone using chelating agents. Journal of Orthopedic Research, 18 (2000) 322-325) which allows microcrack growth in trabecular bone to be monitored by the application of a series of chelating fluorochromes, however, some limitations were identified with the process. The aims of this study were to refine the method of detection using these agents in order to determine the optimal sequence of application and the optimal concentrations which allowed all the agents to fluoresce equally brightly using UV epifluorescence. A chemical analysis process, ion chromatography, followed by validation tests on bone samples showed that the optimal sequence of application and concentration of each agent was alizarin complexone (0.0005 M) followed by xylenol orange (0.0005 M), calcein (0.0005 M) and calcein blue (0.0001 M). A fifth agent, oxytetracycline was excluded from the study after recurring problems were found with its ability to chelate exposed calcium when applied in sequence with the other agents. This work has developed a sequential labelling technique, which allows for microcrack propagation during fatigue testing of bone specimens to be monitored without the problem of chelating agent substitution occurring.

Animals↗
PubMedDate not supplied

Microdamage in porcine alveolar bone due to functional and orthodontic loading.

Bone remodelling has been associated with microdamage. The aim of this study was to investigate the presence of microdamage in the alveolar bone and its potential role in the initiation of bone remodelling following the application of an orthodontic load. The three-dimensional morphology of the alveolar bone was investigated by means of high resolution micro-CT scanning. In 25, 3-month-old, male Danish land-race pigs, the alveolar bone around the lower right and left first molars was analysed. The right first molar was moved buccally with a force of 130 cN by means of a custom-made cantilever made of a TMA 0.017 x 0.025 inch wire. The left molar was left untreated. After 1, 2, 4, 7 and 15 days of treatment the regions containing the right and left molars were excised and en bloc stained in basic fuchsin and the presence of microdamage detected. Diffuse damage was present in the alveolar bone of both the treated and the untreated teeth on both sides. On the lingual sides, diffuse damage showed the same orientation as the periodontal fibres. Bone microcracks were also detected on both the treated and untreated teeth. On the buccal surfaces they where often observed in close proximity to scalloped resorption surfaces. After 1 day of treatment, the presence of microcracks on the buccal-treated side was particularly marked. To conclude, bone microdamage is present in porcine alveolar bone in form of both microcracks and diffuse damage, suggesting that microdamage-driven remodelling also occurs in the alveolar bone. The presence of bone microcracks in the direction of the orthodontic force at day 1 suggests that they could represent the first damage induced by the orthodontic load that has to be repaired.

Animals↗
PubMedDate not supplied

The behaviour of microcracks in compact bone.

This paper summarises four separate studies carried out by our group over the past number of years in the area of bone microdamage. The first study investigated the manner by which microcracks accumulate and interact with bone microstructure during fatigue testing of compact bone specimens. In a series of fatigue tests carried out at four different stress ranges between 50 and 80 MPA, crack density increased with loading cycles at a rate determined by the applied stress. Variations in the patterns of microdamage accumulation suggest that that at low stress levels, larger amounts of damage can build up without failure occurring. In a second study using a series of four-pont bending tests carried out on ovine bone samples, it was shown that bone microstructure influenced the ability of microcracks to propagate, with secondary osteons acting as barriers to crack growth. In a third study, the manner by which crack growth disrupts the canalicular processes connecting osteocytes was investigated. Analysis of individual cracks showed that disruption of the canalicular processes connecting osteocytes occurred due to shear displacement at the face of propagating microcracks, suggesting that this may play some role in the mechanism that signals bone remodelling. In a fourth in vivo study, it was shown that altering the mechanical load applied to the long bones of growing rats causes microcrack formation. In vivo microdamage was present in rats subjected to hindlimb suspension with a higher microcrack density found in the humeri than the femora. Microdamage was also found in control animals. This is the first study to demonstrate in vivo microcracks in normally loaded bones in a rat model.

Analysis of Variance↗
PubMedDate not supplied

Tracking the changes in unloaded bone: Morphology and gene expression.

Bone formation and growth are controlled by genetic, hormonal and biomechanical factors. In this study, an established rat disuse osteoporosis model, hindlimb-suspension (HLS), was used to relate morphological change and gene expression to altered mechanical load in the underloaded femora and the ostensibly normally loaded humeri of the suspended rats (39 days old at onset; 1, 3, 7 and 14 days suspension). Morphological change was measured by labelling new bone formation with fluorescent agents during the experimental period and subsequent histological analysis of bone sections post-sacrifice. Hindlimb suspension reduced both the total amount of bone present, assessed as cross-sectional area, and the bone formation rate at the mid-diaphysis of the unloaded femora while no significant effect was found in the loaded humeri. In addition, the femora of the suspended animals were found to have a markedly increased circularity as a result of unloading. A sensitive semi-quantitative method of gene expression analysis, involving the creation of SMART cDNA arrays, was successfully implemented. This technique amplified all populations of mRNA to levels where they could be assessed using standard molecular biology protocols. Gene expression patterns of two candidate genes, c-fos and osteocalcin were assessed in periosteal tissue. Altered gene expression patterns were identified and tracked over the suspension period. The altered levels of both candidate genes were found to be consistent with the changes observed in the histological analysis.

Animals↗