PubMed Health⌕ Search

Biomedical subjects

Y Sakka

Publications and source records attributed to Y Sakka.

13 recordsLinked to original sources
PubMed2001

A high-strain-rate superplastic ceramic.

High-strain-rate superplasticity describes the ability of a material to sustain large plastic deformation in tension at high strain rates of the order of 10-2 to 10-1 s-1 and is of great technological interest for the shape-forming of engineering materials. High-strain-rate superplasticity has been observed in aluminium-based and magnesium-based alloys. But for ceramic materials, superplastic deformation has been restricted to low strain rates of the order of 10-5 to 10-4 s-1 for most oxides and nitrides with the presence of intergranular cavities leading to premature failure. Here we show that a composite ceramic material consisting of tetragonal zirconium oxide, magnesium aluminate spinel and alpha-alumina phases exhibits superplasticity at strain rates up to 1 s-1. The composite also exhibits a large tensile elongation, exceeding 1,050 per cent for a strain rate of 0.4 s-1. The tensile flow behaviour and deformed microstructure of the material indicate that superplasticity is due to a combination of limited grain growth in the constitutive phases and the intervention of dislocation-induced plasticity in the zirconium oxide phase. We suggest that the present results hold promise for the application of shape-forming technologies to ceramic materials.

Journal Article↗
PubMed2001

Prevalence of A-to-G mutation at nucleotide 3243 of the mitochondrial tRNA(Leu(UUR)) gene in Japanese patients with diabetes mellitus and end stage renal disease.

The A-to-G mutation at nucleotide 3243 of the mitochondrial tRNA(Leu(UUR)) gene (mt.3243A>G) is associated with both diabetes mellitus and myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Recently, this mutation was found in three diabetic subjects with progressive kidney disease, suggesting that it may be a contributing factor in the development of kidney disease in patients with diabetes. The aim of this study was to evaluate the contribution of this mutation to the development of end stage renal disease (ESRD) in patients with diabetes. The study group consisted of 135 patients with diabetes and ESRD. The control group consisted of 92 non-diabetic subjects with ESRD who were receiving hemodialysis. The mt.3243A>G mutation was detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). We found the mt.3243A>G mutation in eight patients (8/135; 5.9%), all of whom were initially diagnosed with type II diabetes. Five of the eight patients were subsequently also diagnosed with MELAS. We did not find the mutation in any of the 92 nondiabetic subjects with ESRD. The prevalence of this mutation was 6.5-fold higher in patients with diabetes and ESRD than in those with diabetes alone (8/135 vs 5/550, respectively; chi2 = 13.704; P = 0.0002). The mt.3243A>G mutation may be a contributing genetic factor in the development of ESRD in Japanese patients with diabetes.

Adult↗
PubMed2000

Electric double-sleeved vacuuming microtrephine for lens refilling.

An automated electric double-sleeved vacuuming microtrephine has been developed that consistently creates a 0.8 to 1.0 mm tear-free hole in the anterior lens capsule. This hole is required for lens refilling to retain accommodation after cataract removal. The trephine is double-sleeved. The stainless-steel outer sleeve vacuums the internal anterior capsule; the stainless steel rotating inner sleeve, which has a blade on the head, then slides forward and cuts the taut anterior capsule. All manipulations are controlled automatically by depressing a foot pedal. Using this instrument, a 0. 8 to 1.0 mm tear-free microhole in the anterior capsule was created successfully in 80% of excised pig (n = 30) and eye-bank (n = 10) eyes. This trephine will be useful for lens refilling in the future.

Animals↗
PubMed1996

Accommodation in primate eyes after implantation of refilled endocapsular balloon.

PURPOSE: To restore accommodation after crystalline lens removal. METHODS: The crystalline lens of one eye of each of four primates was removed by phacoemulsification. Each operated-on eye underwent endocapsular silicone balloon implantation followed by filling with an organosilicone mixture. Seven months postoperatively, the anterior chamber depth and refractive power changes were measured before and after topical application of 4% pilocarpine. RESULTS: In the refilled eyes, the average anterior chamber depth reduction was 0.50 mm and the average maximal myopic change was 6.74 diopters. CONCLUSION: After lens removal, measurable accommodation was restored in the eyes with the endocapsular balloon filled with an organosilicone mixture.

Accommodation, Ocular↗
PubMed1995

[A case of multifocal choroiditis associated with progressive subretinal fibrosis].

Multifocal choroiditis associated with progressive subretinal fibrosis, which was reported by Cantrill and Folk in 1986, is characterized by acute multifocal choroiditis resulting in progressive subretinal fibrosis. All cases were young, healthy females. Our case was a 17-year-old female who complained of visual disturbance in her left eye. Ophalmoscopy showed multiple, small, yellowish-white hypopigmented, choroidial lesions in the posterior fundus of her left eye. These lesions showed hyperfluorescence in fluorescein angiography and hypofluorescence in indocyanine green (ICG) angiography. One month later the yellowish-white hypopigmented, choroidal lesions increased in number and subretinal fibrosis appeared in the macular area. Two months later subretinal fibrosis was also found in the area except for the macula. In her right eye, ophthalmoscopy and fluorescein angiography showed no abnormal findings, but ICG angiography revealed choroidal hypofluorescence areas. Two years later the subretinal fibrosis was increased and the yellowish-white lesions showed pigmentation.

Acute Disease↗
PubMed1994

Complications associated with endocapsular balloon implantation in rabbit eyes.

After phacoemulsifying the lens in six rabbit eyes through a 1.3 mm anterior capsule opening, we implanted a silicone balloon in the capsular bag and filled it with liquid silicone. The eyes were enucleated nine to 21 months postoperatively, embedded in paraffin, stained with toluidine blue, and examined by stereoscopic and light microscopy. We looked at the postoperative complications primarily. All balloons were securely fixated within the capsule. Surface wrinkles were observed in two balloons. The injected silicone remained transparent. None of the lens capsules was completely transparent, although all remained relatively clear. Retrocorneal membranes were produced in one eye in which the silicone leaked.

Accommodation, Ocular↗
PubMed1992

Refilling the lens with a inflatable endocapsular balloon: surgical procedure in animal eyes.

In this report we describe the surgical details involved in refilling the lenses of 13 rabbit and 3 primate eyes using an inflatable endocapsular balloon to restore accommodation. The procedure involves endocapsular phacoemulsification through a small "buttonhole" or "dumbbell" anterior capsulotomy or minicircular capsulotomy and the simultaneous preservation of capsular integrity, including the zonules and ciliary muscles. An inflatable balloon made of thin silicone membrane is then inserted into the empty capsular bag. A liquid silicone polymer is injected into the balloon through a delivery tube, and the empty capsular bag is refilled by the inflated balloon. The procedure was found to be reproducible, and an accommodation of 6 D was confirmed in one primate eye. Capsular opacification occurred, but the proliferation and migration of residual lens epithelial cells could be hindered by abundant refilling. This lens-refilling technique may provide restoration of accommodation in future cataract surgery.

Accommodation, Ocular↗
PubMed1991

Intercapsular cataract surgery with lens epithelial cell removal. Part IV: Capsular fibrosis induced by poly(methyl methacrylate).

Characteristic lens epithelial cell behavior in the pseudophakic eye was examined by comparing 30 eyes that had extracapsular cataract surgery by the intercapsular technique and posterior chamber intraocular lens (IOL) implantation with lens epithelial cell removal but without anterior capsule capsulectomy and nine aphakic eyes that had the same procedure but without posterior chamber lens implantation over a mean follow-up period of 30 and 23 months, respectively. Fibrous anterior capsule opacification was observed in 83% of the pseudophakic eyes in the area of contact with the IOL, while the region beyond the margin of the IOL remained transparent. Fibrous anterior capsular opacification was not noted in the aphakic eyes. This suggests that the IOL material, poly(methyl methacrylate), stimulates lens epithelial cells to undergo fibrous metaplasia and to produce collagen fibers. Various cytokines such as IL-1 and TGF-beta synthesized by lens epithelial cells may play a crucial role as mediators in the process. We recommend that this effect be considered as a parameter of biocompatibility in developing and evaluating new biomaterials.

Adult↗
PubMed1990

Anterior capsule-supported intraocular lens. A new lens for small-incision surgery and for sealing the capsular opening.

A new intraocular lens made of PMMA and fixed in the anterior capsular opening is introduced. The lens diameter is 4 mm and the lens has no haptics in the conventional sense but is finely grooved around the circumference edge. The lens is inserted into the anterior capsule via a very small-diameter opening created by mini-circular capsulorhexis. The anterior capsular opening, with a round, smooth-edged margin, avoids stress concentration and, therefore, the capsule does not easily tear. This opening catches the lens and chokes it along the grooved edge. In animal experiments, firm fixation was obtained. This lens may be adequate for small-incision surgery, and in the future it may be used to prevent leakage of filling material during refilling of the lens, since it acts as a part of the anterior capsule and seals the capsular opening completely.

Animals↗
PubMed1990

Histopathologic and immunohistochemical findings in gelatinous drop-like corneal dystrophy.

A cornea with gelatinous drop-like corneal dystrophy was examined by histochemical and immunohistochemical techniques. Pretreatment of the sections with potassium permanganate did not decrease the staining with Congo red dye. Immunohistochemically, amyloid deposits in the cornea with this disease almost did not stain with antibodies to amyloid protein AA and AA-3. However, the corneal epithelium reacted distinctly with antibodies to amyloid protein AA and AA-3. Cross-reactivity with antibodies to protein AA and serum precursor of protein AA has been reported and protein AA-3 is the synthesized peptide corresponding to the amino acid sequence 37-47 of the human amyloid protein AA molecule. The present study suggests at least that corneal epithelial cells with gelatinous drop-like corneal dystrophy may produce a precursor of amyloid related to protein AA-3.

Adult↗
PubMed1989

Further development of experimental techniques for refilling the lens of animal eyes with a balloon.

Various techniques for experimental refilling of the lens of animal eyes are possible. We describe two new methods: Balloon insertion after endocapsular phacoemulsification and after phacoemulsification with circular capsulorhexis. The feasibility of these techniques was tested in both rabbit eyes and pig cadaver eyes. With organo-silicone gel as the balloon filling material, post-operative refractive changes of up to 4 diopters of residual hyperopia were achieved; accommodation changes were up to -1 diopter. The technique of refilling the lens with a balloon to avoid leakage of filling material warrants further study.

Animals↗