On the mechanical characteristics of a self-setting calcium phosphate cement.

OBJECTIVE: To perform a mechanical characterization of a self-setting calcium phosphate cement in function of the immersion time in Ringer solution. MATERIALS AND METHODS: Specimens of self-setting calcium phosphate cement were prepared from pure α-TCP powder. The residual strains developed during hardening stage were monitored using an embedded fiber Bragg grating sensor. Additionally, the evolution of the elastic modulus was obtained for the same time period by conducting low-load indentation tests. Micro-computed tomography as well as microscope-assisted inspections were employed to evaluate the porosity in the specimens. Moreover, diametral compression tests were conducted in wet and dried specimens to characterize the material strength. RESULTS: The volume of the estimated porosity and absorbed fluid mass, during the first few minutes of the material's exposure in a wet environment, coincide. The immersion in Ringer solution lead to a noticeable increase in the moduli values. The critical value of stresses obtained from the diametral compression tests were combined with the data from uniaxial compression tests, to suggest a Mohr-Coulomb failure criterion. CONCLUSIONS: This study presents different techniques to characterize a self-setting calcium phosphate cement and provides experimental data on porosity, mechanical properties and failure. The investigated material possessed an open porosity at its dried state with negligible residual strains and its Young's modulus, obtained from micro-indentation tests, increased with hardening time. The failure loci may be described by a Mohr-Coulomb criterion, characteristic of soil and rock materials.

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.

Cyclocryotherpay and noncontact Nd:YAG laser cyclophotocoagulation in cats.

PURPOSE: To investigate physiological and histologic alterations of the cat eye in response to cyclocryotherapy (CCT) and noncontact transscleral Nd:YAG laser cyclophotocoagulation (TSNYC). METHODS: One eye of 29 cats was treated with 12 applications (1 minute, -80 degrees C) of CCT or 80 applications of noncontact TSNYC (7 to 9 J, retrofocus 3.6 mm). Blood-aqueous barrier function was studied measuring aqueous protein and fluorescein concentration after intravenous dye injection. Ocular blood flow was determined using 85Sr microspheres. RESULTS: Intraocular pressure after CCT was 29% lower in the treated than in the control eye after 3 and 12 weeks. After TSNYC, pressure was reduced by 34% at 3 weeks and by 27% after 12 weeks. Aqueous protein concentration was elevated in all treated eyes. Neither technique altered tonographic outflow facility or episcleral venous pressure. Calculated aqueous flow was lower in the treated eye than in the control eye 3 and 12 weeks after each cyclodestructive procedure. After CCT, anterior chamber fluorescein concentration was 2.5 times greater in 3-week and 3 times greater in 12-week eyes. After TSNYC, fluorescein concentration was 3 and 3.5 times greater at 3 and 12 weeks, respectively. Ciliary body blood flow in control eyes was similar to CCT and TSNYC eyes. Histopathology 12 weeks after CCT and TSNYC showed pigment dispersion, disorganized architecture, and cystic elevation of the nonpigmented ciliary epithelium. Areas of absent pigmented and nonpigmented epithelium at the ciliary process base were more discrete in TSNYC eyes. Electron microscopy demonstrated normal junctional complexes. CONCLUSIONS: CCT and TSNYC lower pressure by reducing aqueous formation. Ciliary body blood flow is not altered after either technique. Both techniques result in similar histologic disruption of the ciliary epithelium, resulting in breakdown of the blood-aqueous barrier.

Prolonged intraocular pressure reduction following intravitreal barium injection in rabbits.

The isolated ciliary epithelium contains barium-inhibitable potassium channels. The present study was aimed at testing the in vivo effects of barium on aqueous humor dynamics in rabbits. BaCl2 was administered to one eye by topical delivery or intravitreal injection. Dynamic measurements included intraocular pressure, outflow facility, episcleral venous pressure and aqueous flow (fluorophotometry). Barium dynamics were studied using 133Ba. Intraocular pressure was not altered after topical administration of BaCl2. 133Ba was not detected in the aqueous after delivery of eyedrops containing the radiochemical. Intraocular pressure decreased following intravitreal injection of BaCl2 (0.15 microgram). The onset of this pressure reduction was 12 to 16 hr, the maximum decrease (-11.3 mmHg) occurred at 2 days, and the effect persisted (-4.2 mmHg) for approximately 12 days after the injection. Outflow facility and episcleral venous pressure were not altered. However, aqueous humor flow 5 to 6 days after the injection was decreased by 42% to 63% as determined by fluorophotometry or calculated tonographic data. The injection was not associated with findings of intraocular inflammation. Radioactivity was detected in the vitreous within the first 3 days after the injection; however, activity was present in the ciliary body, equally distributed between the cell membrane and soluble fractions, seven days after the injection. Intravitreally injected BaCl2 results in a prolonged intraocular pressure decrease relating to reduced aqueous formation. While the mechanism(s) for the BaCl2-induced decrease in pressure are not clear, possibilities include a Ba2+ interaction with ciliary epithelial K+ or N-type Ca2+ channels.

Apraclonidine and anterior segment laser surgery. Comparison of 0.5% versus 1.0% apraclonidine for prevention of postoperative intraocular pressure rise.

PURPOSE: To compare the efficacy of 0.5% and 1.0% apraclonidine in preventing laser-induced intraocular pressure (IOP) elevation after trabeculoplasty, neodymium: YAG (Nd: YAG) iridotomy, and capsulotomy. METHODS: This is a prospective, masked, and randomized study of 83 patients undergoing trabeculoplasty, 62 patients undergoing iridotomy, and 57 patients undergoing capsulotomy. Surgical eyes received one drop of 0.5% or 1.0% apraclonidine immediately after surgery. RESULTS: Intraocular pressure reduced 2 hours after trabeculoplasty in the 0.5% (P = 0.028) and 1.0% (P = 0.004) groups. Intraocular pressure was higher than baseline in a greater number of eyes treated with 0.5% (12 of 39 eyes, 31%) compared with 1.0% apraclonidine (5 of 44 eyes, 11%) (P = 0.032). Intraocular pressure in eyes with a narrow chamber angle was reduced in 16 (85%) of 19 eyes treated with 0.5% and in 10 (84%) of 12 eyes treated with 1.0% apraclonidine after iridotomy. Of patients with chronic angle-closure glaucoma, IOP was similar to prelaser values in 11 (69%) of 16 eyes treated with 0.5% (P > 0.7) and 12 (80%) of 15 eyes treated with 1.0% apraclonidine (P > 0.3). In patients undergoing capsulotomy, pressure was significantly lowered in the 0.5% group (P = 0.04) but not in the 1.0% apraclonidine group. After capsulotomy, both treatment groups had similar (P > 0.3) numbers of eyes with an IOP less than baseline (83% for 0.5% apraclonidine and 81% for 1.0% apraclonidine). CONCLUSION: The single postoperative administration of 0.5% apraclonidine is as effective as the 1.0% concentration in preventing IOP elevation immediately after trabeculoplasty, iridotomy, or capsulotomy.

The effect of acute changes in blood glucose on lenses in diabetic and non-diabetic subjects using quasi-elastic light scattering spectroscopy.

Quasi-elastic light scattering spectroscopy was used to non-invasively monitor affects of transient blood glucose changes on lenses of non-diabetic subjects undergoing glucose tolerance testing and diabetic subjects undergoing glucose clamping protocols. Non-diabetic subjects exhibited a characteristic biphasic change in lens protein diffusion coefficient in response to glucose loading. There was an initial rapid decrease in diffusion coefficient followed by an increase to a maximum attained approximately 30 minutes after peak blood glucose levels had been reached. The diffusion coefficients then returned to baseline values approximately 60 minutes later. These changes in diffusion coefficient in the non-diabetic lens may be related to changes in lens hydration in response to glucose loading. Diabetic subjects, in contrast, did not exhibit a marked change in diffusion coefficient in response to acute blood glucose level changes. This may be attributed to an osmotic buffering in the diabetic lens which could offset the transient changes in aqueous glucose levels.