Monitoring of hardening and hygroscopic induced strains in a calcium phosphate bone cement using FBG sensor.

This study initially deals with the investigation of the induced strains during hardening stage of a self-setting calcium phosphate bone cement using fiber-Bragg grating (FBG) optical sensors. A complementary Scanning Electron Microscopy (SEM) investigation was also conducted at different time intervals of the hardening period and its findings were related to the FBG recordings. From the obtained results, it is demonstrated that the FBG response is affected by the microstructural changes taking place when the bone cement is immersed into the hardening liquid media. Subsequently, the FBG sensor was used to monitor the absorption process and hygroscopic response of the hardened and dried biocement when exposed to a liquid/humid environment. From the FBG-based calculated hygric strains as a function of moisture concentration, the coefficient of moisture expansion (CME) of the examined bone cement was obtained, exhibiting two distinct linear regions.

Pore geometry regulates early stage human bone marrow cell tissue formation and organisation.

Porous architecture has a dramatic effect on tissue formation in porous biomaterials used in regenerative medicine. However, the wide variety of 3D structures used indicates there is a clear need for the optimal design of pore architecture to maximize tissue formation and ingrowth. Thus, the aim of this study was to characterize initial tissue growth solely as a function of pore geometry. We used an in vitro system with well-defined open pore slots of varying width, providing a 3D environment for neo-tissue formation while minimizing nutrient limitations. Results demonstrated that initial tissue formation was strongly influenced by pore geometry. Both velocity of tissue invasion and area of tissue formed increased as pores became narrower. This is associated with distinct patterns of actin organisation and alignment depending on pore width, indicating the role of active cell generated forces. A mathematical model based on curvature driven growth successfully predicted both shape of invasion front and constant rate of growth, which increased for narrower pores as seen in experiments. Our results provide further evidence for a front based, curvature driven growth mechanism depending on pore geometry and tissue organisation, which could provide important clues for 3D scaffold design.

Thermosensitive hydrogels for nasal drug delivery: the formulation and characterisation of systems based on N-trimethyl chitosan chloride.

Towards the development of a thermosensitive drug-delivery vehicle for nasal delivery, a systematic series of N-trimethyl chitosan chloride polymers, synthesised from chitosans of three different average molecular weights, have been co-formulated into a hydrogel with poly(ethylene glycol) and glycerophosphate. Rheological evaluations have shown that hydrogels derived from N-trimethyl chitosan with a low degree of quaternisation and high or medium average molecular weight exhibit relatively short sol-gel transition times at physiologically relevant temperatures. Also, the same hydrogels display good water-holding capacity and strong mucoadhesive potential, and their mixtures with mucus exhibit rheological synergy. An aqueous hydrogel formulation, derived from N-trimethyl chitosan of medium average molecular weight and low degree of quaternisation, appears particularly promising in that it exhibits most favourable rheological and mucoadhesive behaviour and a sol-gel transition that occurs at 32.5°C within 7 min.

Physisorbed o-carborane onto lyso-phosphatidylcholine-functionalized, single-walled carbon nanotubes: a potential carrier system for the therapeutic delivery of boron.

A combination of data from ICP-MS, Raman spectroscopy, UV-vis spectrometry, atomic force microscopy, zeta-potential measurements and gel electorphoresis studies has shown that o-carborane may be immobilized on stable aqueous dispersions of lyso-phosphatidylcholine-functionalized single-walled carbon nanotubes, which in turn indicates the potential of such structures for deployment as carrier vehicles in boron neutron capture therapy.

Chitosan derivatives alter release profiles of model compounds from calcium phosphate implants.

The aim of the current study was to evaluate the impact of chitosan derivatives, namely N-octyl-chitosan and N-octyl-O-sulfate chitosan, incorporated in calcium phosphate implants to the release profiles of model drugs. The rate and extent of calcein (on M.W. 650 Da) ED, and FITC-dextran (M.W. 40 kDa) on in vitro release were monitored by fluorescence spectroscopy. Results show that calcein release is affected by the type of chitosan derivative used. A higher percentage of model drug was released when the hydrophilic polymer N-octyl-sulfated chitosan was present in the tablets compared with the tablets containing the hydrophobic polymer N-octyl-chitosan. The release profiles of calcein or FD from tablets containing N-octyl-O-sulfate revealed a complete release for FD after 120 h compared with calcein where 20% of the drug was released over the same time period. These results suggest that the difference in the release profiles observed from the implants is dependent on the molecular weight of the model drugs. These data indicate the potential of chitosan derivatives in controlling the release profile of active compounds from calcium phosphate implants.

Vickers hardness studies of calcium oxalate monohydrate and brushite urinary stones.

PURPOSE: To measure the hardness of two types of urinary stones: calcium oxalate monohydrate (COM; CaC2O4 . H2O) and dicalcium phosphate dihydrate (brushite; CaHPO4 . 2H2O). MATERIALS AND METHODS: The composition of 28 calcium oxalate monohydrate and 22 brushite stones was characterized by infrared spectroscopy (FT-IR). Stone specimens were embedded in crystallographic resin, polished, and subjected to indentation tests using a Vickers tester. The hardness was calculated from measuring the diagonal lengths of the residual indentation on the specimen using the appropriate equation. RESULTS: The COM stones showed hardness values ranging from 15.3 to 64.2 HV with a mean of 35.8 +/- 13.3, while brushite stones ranged from 10.1 to 46.1 HV with a mean of 26.5 +/- 15.1. The results of ANOVA showed that there were significant differences (P < 0.05) between the two stone types. CONCLUSIONS: Calcium oxalate monohydrate stones exhibited greater hardness than brushite stones when assessed with Vickers studies.

Aging assessment by dynamic mechanical analysis of in vivo encrusted polymeric urinary stents.

PURPOSE: To investigate the viscoelastic properties of plastic pigtail stents after removal from patients using the method of dynamic mechanical analysis (DMA). MATERIALS AND METHODS: Dynamic mechanical analysis was performed in 12 polymeric pigtail stents left indwelling for various periods of time (0-120 days). The encrustations were characterized by infrared spectroscopy, and their morphology was observed using scanning electron microscopy. RESULTS: Softening and stiffening behavior was observed. Stiffening was found specifically in the stents with heavy mineral deposits. CONCLUSIONS: Material degradation becomes obvious after certain periods of time. The effect of stent degradation appeared in two forms: softening of the stent polymer, possibly through interaction with urine, and stiffening of the stent secondary to the formation of various insoluble mineral deposits covered by layers of organic matrix.

Assessment of encrustations on polyurethane ureteral stents.

PURPOSE: To determine the composition and the extent of crystalline (and other) encrustation on ureteral catheters inserted under sterile conditions in stone formers, in comparison with catheters of the same type inserted in nonstone formers for the same time but for different clinical reasons. MATERIALS AND METHODS: Forty consecutive self-retained polyurethane pigtail ureteral catheters removed by cystoscopy between November 2000 and February 2002 were studied, 30 from stone formers and 10 from patients without stone histories. The mean dwelling time was 55 days for the stone formers and 79 days for the other patients. The encrustations were collected and analyzed with Fourier-transform infrared spectroscopy, powder X-ray diffraction, or both. The stones from nine of the patients were also subjected to the same spectroscopic analysis. Representative sections of the catheters were investigated by scanning electron microscopy and energy-dispersive X-ray analysis. RESULTS: The most common encrustation in stone formers was calcium oxalate monohydrate. In patients without stones, deposits of organic compounds were found consistently. The mean mass of encrustation of stone formers was larger (71.05 mg) than that of patients without stones (1 mg). CONCLUSIONS: Calcium oxalate is the predominant type of encrustation on ureteral catheters in stone formers. Prevention of heavy encrustation should be directed to therapeutic measures concerning calcium oxalate lithiasis and development of new materials by the medical industry that are less prone to encrustation.

Induction of apatite by the cooperative effect of amelogenin and the 32-kDa enamelin.

Extracellular matrix proteins are considered to play essential roles in controlling the nucleation, growth, and organization of hydroxyapatite crystals during enamel formation. The effects of amelogenin and the 32-kDa enamelin proteins on apatite nucleation were investigated by a steady-state gel diffusion device containing 10% gelatin gels loaded with 0, 0.75%, and 1.5% (w/w) native porcine amelogenins. It was found that the induction time for hydroxyapatite precipitation was strongly increased by the presence of amelogenins, suggesting an inhibitory effect of apatite nucleation. Addition of 18 micro g/mL of 32-kDa enamelin to 10% gelatin also caused inhibition of nucleation. Remarkably, addition of 18 and 80 micro g/mL of 32-kDa enamelin in gels containing 1.5% amelogenin accelerated the nucleation process in a dose-dependent manner. Our observations strongly suggest that the 32-kDa enamelin and amelogenins cooperate to promote nucleation of apatite crystals and propose a possible novel mechanism of mineral nucleation during enamel biomineralization.

Assembly of amelogenin proteolytic products and control of octacalcium phosphate crystal morphology.

The formation of enamel apatite crystals involves extracellular molecular events among which matrix assembly, interactions with growing crystals, and protein processing and removal are the subject of numerous investigations. Following the description of amelogenin nanospheres and the evidence for their presence in vivo as the principal structural component of developing dental enamel, we have focused our studies on investigating at the molecular level the process of nanosphere assembly and evaluating the effects of amelogenin on crystal growth and morphology. This paper is a short review of our recent studies with a focus on the assembly of amelogenin proteolytic products and their modulating effect on octacalcium phosphate (OCP) crystal morphology. In addition, we report that incorporation of amelogenins into 10% gelatin gel does not affect diffusion of calcium. This remarkable finding indicates that the observed modulation effect by amelogenin on OCP crystal morphology is not due to alteration of calcium diffusion into the gels but is the result of direct amelogenin-mineral interactions.

Analysis of hydroxyapatite surface coverage by amelogenin nanospheres following the Langmuir model for protein adsorption.

The assembly of amelogenin protein into nanospheres is postulated to be a key factor in the stability of enamel extracellular matrix framework, which provides the scaffolding for the initial enamel apatite crystals to nucleate and grow. Adsorption isotherms were evaluated in order to investigate the nature of interactions of amelogenin nanospheres with hydroxyapaite crystals in solution, where their assembly status and particle size distribution are defined. We report that the adsorption isotherm of a recombinant mouse amelogenin (rM179) on synthetic hydroxyapatite crystals can be described using a Langmuir model indicating that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. The adsorption affinity and the maximum adsorption sites were 19.7 x 10(5) L/mol and 6.09 x 10(-7) mol/m2, respectively, with an r2 value of 0.99. Knowing the composition and particle size distribution of amelogenin nanospheres under the condition of adsorption experiments, we have calculated the number of nanospheres and the crystal surface area covered by each population of nanospheres at their maximum adsorption. It was found that total maximum binding covers 64% of the area unit. This observation supports the speculation that amelogenin binding onto apatite surface is selective and occurs only at certain sites.

Calcium oxalate crystals in tomato and tobacco plants: morphology and in vitro interactions of crystal-associated macromolecules.

Plants form calcium oxalate crystals with unique morphologies under well-controlled conditions. We studied the morphology of single calcium oxalate monohydrate (whewellite) crystals extracted from tomato and tobacco leaves. These crystals have a pseudotetrahedral shape. We identified the (101), (101) or (102), (110), and (hk0) faces as stable faces. The morphology is chiral with unique handedness. We also show that calcium oxalate monohydrate crystals isolated from tomato, tobacco, and bougainvillea leaves contain macromolecules rich in Gly, Glx, and Ser. Crystal-associated macromolecules extracted from tomato and tobacco influence the morphology of calcium oxalate monohydrate crystals grown in vitro, promoting preferential development of the [120] faces. Furthermore, crystal-associated macromolecules from tobacco promote nucleation of calcium oxalate monohydrate crystals, whereas model polypeptides do not have any significant effect on nucleation. These results imply an active role of the crystal-associated macromolecules in the formation of pseudotetrahedral shapes in vitro, and these properties may in part be responsible for the unique chiral morphology of the natural pyramidal-shaped crystals.

Encrustation of a metal alloy urinary stent: a mechanistic investigation.

MATERIALS AND METHODS: A section of a metal stent consisting mainly of tantalum coated partially by strongly adhering calcium oxalate monohydrate (COM) crystals was immersed in supersaturated solutions prepared from calcium chloride and sodium oxalate at 37 degrees C and ionic strength 0.15 M in NaCl. Abstract OBJECTIVES: To investigate the kinetics of encrustation of a metall alloy urinary stent system in vitro by calcium oxalate and characterize the crystals forming from solutions supersaturated with respect to all calcium oxalate hydrates. RESULTS: The COM-coated stent mineralized upon immersion in the supersaturated solutions. The process was monitored with a calcium ion-selective electrode and the rates were measured at conditions of sustained solution supersaturation. COM crystals formed on the stent and the rate of COM crystal growth yielded a second-order dependence on the solution supersaturation. CONCLUSIONS: The deposition of COM crystals on the metal stents coated partially with COM crystals by adhesive forces was found to be most important for the acceleration of the encrustation process. The dependence of the rates on the solution supersaturation suggested absence of secondary nucleation and a surface-controlled process for the encrustation process.

The inhibition of calcium oxalate monohydrate crystal growth by maleic acid copolymers.

The crystallization of calcium oxalate monohydrate (COM) was investigated at conditions of constant supersaturation both in the absence and in the presence of synthetic maleic acid copolymers at 37C, 0.15 M NaCl. The dependence of the rates of COM crystallization in the absence of inhibitors was found to be second order at low and first order at higher supersaturations suggesting a surface diffusion controlled mechanism. The presence of all copolymers tested at concentration levels up to 5 ppm retarded the rates of COM crystal growth up to 90%. The decrease of the COM crystal growth rates by the polymers depended on the nature of the comonomer polymerized with maleic acid and the order of inhibition was found to be vinyl acetate > N-vinylpyrrolidone > styrene. Taking into consideration kinetics data published in the literature concerning the inhibition of COM crystal growth, it is suggested that molecular weight also plays a role, with more inhibition at higher molecular weights. The morphology of the COM crystals grown was unaffected yet the crystals growing at lower rates in the presence of the copolymers were larger and their size more uniform. It is concluded that maleic acid copolymers are strong inhibitors of the crystallization of COM, the inhibitory activity being more pronounced in the case of the linear copolymers.

A model system for the investigation of urinary stone formation.

OBJECTIVE: To develop an in vitro model system for the investigation of calcium oxalate urinary stones under conditions of spontaneous precipitation. MATERIALS AND METHODS: Using a calcium-ion selective electrode and automatic titrator, a test solution was kept supersaturated with calcium oxalate and the rate of crystallization measured. RESULTS: During the spontaneous precipitation at constant supersaturation at 37 degrees C, the induction times required for the precipitation of calcium oxalate monohydrate were inversely proportional to the supersaturation of the solution. No transient phases were identified and the interfacial energy determined from kinetic analysis was 28.4 mJ/m2. The rates of precipitation showed a first-order dependence on the degree of supersaturation and were in good agreement with those reported for the in vivo formation of calcium oxalate monohydrate stones. CONCLUSION: This experimental model system allows precise measurements of the kinetics of calcium oxalate monohydrate. From the dependence of the rates of precipitation on supersaturation, a mechanism controlled by surface diffusion is suggested.