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Biomedical subjects

Peter Kroll

Publications and source records attributed to Peter Kroll.

At least 19 recordsLinked to original sources
PubMed2006

High-pressure chemistry of nitride-based materials.

Besides temperature at one atmosphere, the applied pressure is another important parameter for influencing and controlling reaction pathways and final reaction products. This is relevant not only for the genesis of natural minerals, but also for synthetic chemical products and technological materials. The present critical review (316 references) highlights recent developments that utilise high pressures and high-temperatures for the synthesis of new materials with unique properties, such as high hardness, or interesting magnetic or optoelectronic features. Novel metal nitrides, oxonitrides as well as the new class of nitride-diazenide compounds, all formed under high-pressure conditions, are highlighted. Pure oxides and carbides are not considered here. Moreover, syntheses under high-pressure conditions require special equipment and preparation techniques, completely different from those used for conventional synthetic approaches at ambient pressure. Therefore, we also summarize the high-pressure techniques used for the synthesis of new materials on a laboratory scale. In particular, our attention is focused on reactive gas pressure devices with pressures between 1.2 and 600 MPa, multi-anvil apparatus at P < 25 GPa and the diamond anvil cell, which allows work at pressures of 100 GPa and higher. For example, some of these techniques have been successfully upgraded to an industrial scale for the synthesis of diamond and cubic boron nitride.

Journal Article↗
PubMed2006

Autologous serum for the treatment of corneal epithelial abrasions in diabetic patients undergoing vitrectomy.

PURPOSE: To compare the effect of autologous serum versus hyaluronic acid for the treatment of epithelial corneal lesions in patients such as diabetics with reduced wound healing. DESIGN: Prospective, randomized, masked clinical trial. METHODS: Diabetic patients undergoing pars plana vitrectomy mostly combined with cataract extraction and intraocular lens (IOL) implantation who received corneal abrasion for better intraoperative visualization were included in this study. A standardized 8-mm diameter corneal abrasion was performed. Patients were randomized into one group treated with hourly application of autologous serum and another treated with hyaluronic acid drops (Vislube). Besides the time necessary for closure of the corneal epithelium other parameters such as patients' age, gender, duration of surgery, history of diabetes, and current HbA1C were evaluated. RESULTS: A total of 23 patients were enrolled (15 men, eight women); the autologous serum group consisted of 13 patients, the hyaluronic acid (Vislube) group consisted of 10 patients. Patients' mean age was 64.8 years; mean duration of diabetes was 19.4 years. On average, the operation lasted 145 minutes. Mean epithelialization time was 7.1 days in the hyaluronic acid group. In the autologous serum group, epithelium healed after a mean of 4.3 days. Mann-Whitney U test for statistical analysis showed a significant difference of epithelial closure time between both groups (P < .05); therefore, the study was stopped after treatment of 23 patients. CONCLUSIONS: It appears that autologous serum leads to a much faster closure of corneal epithelial wounds after abrasion compared with artificial tears.

Cataract Extraction↗
PubMed2006

Visual recovery after scleral buckling surgery in macula-off rhegmatogenous retinal detachment.

PURPOSE: The primary goal of this study was to investigate the functional results after scleral buckling (SB) surgery in macula-off rhegmatogenous retinal detachment (RRD), with more or less than 7 days' duration of macular detachment (DMD). The secondary outcome measure was to determine the long-term functional results in these two groups 5 years after SB surgery. METHODS: The retrospective studies included 96 eyes of 96 patients with primary, uncomplicated, macula-off RRD. Two studies, one with a short-term follow-up and one with a long-term follow-up, were performed, and in both studies the eyes were divided into two groups according to the DMD. In study I, 96 patients were divided into DMD or=4 days and 7 days (n = 11). Additional preoperative predictive factors including DMD, preoperative visual acuity (VA) and patients' age at the time of the RRD were correlated with the postoperative VA. RESULTS: In study I, the mean final VA was significantly better (0.45) after a DMD of less than or equal to 7 days, compared to patients with a DMD of more than 7 days (0.22; Student's t test, p = 0.02). VA >or=0.4 was achieved in 68% with a subacute DMD compared to 52% in patients with prolonged DMD (chi(2) test, p < 0.001). However, the postoperative VA (0.48 +/- 0.09) in eyes with DMD of 1-3 days was similar (0.42 +/- 0.07) to eyes with DMD of 4-7 days (Student's t test, p = 0.455). We divided the 96 patients into 2 groups according to a preoperative VA. Eyes with a preoperative VA 0.1 (n = 34; Student's t test, p < 0.001). Patients 75 years of age or younger were more likely to achieve a VA of 0.4 or better after SB surgery than older patients (more than 75 years; chi(2) test, p = 0.008). In study II, VA improved (by a mean of 1.60 +/- 0.02 lines) during the follow-up period from 0.32 +/- 0.08 at the 3-month follow-up to 0.46 +/- 0.10 at the 5-year follow-up. Eyes with a subacute DMD had a significantly better VA than eyes with a prolonged DMD (Student's t test, p = 0.004). Patients aged 75 years or less were more likely to achieve a VA of 0.4 or better than patients older than 75 (chi(2) test, p = 0.003). CONCLUSION: The time point of SB surgery has no statistical impact on the final visual recovery in patients with an acute primary macular-off RRD of less than or equal to 7 days. A delay of SB surgery within this time frame does not contribute to an impaired final visual outcome. There was no evidence, that primary macula-off RRDs are emergencies, which cannot wait for a systemic evaluation of the RRD and surgical treatment at the next available scheduled day. A preoperative VA of more than 0.1 and patients' age under 60 years at presentation had an additional prognostic value on the final outcome. Surgeons should be aware that visual function after reattachment may continue to improve over a long period. This study provides useful guidelines for the clinical management of macula-off RRD and the assessment of potential visual recovery in patients after successful SB surgery.

Adolescent↗
PubMed2005

Grouped congenital hypertrophy of the retinal pigment epithelium follows developmental patterns of pigmentary mosaicism.

PURPOSE: To determine whether sectorial-oriented grouped pigmentations of the retina follow developmental patterns of pigmentary mosaicism. DESIGN: Systematic literature review. PARTICIPANTS: Fundus images from patients with grouped congenital hypertrophy of the retinal pigment epithelium (CHRPE). METHODS: An extensive Internet and library search was performed to obtain articles dealing with grouped CHRPE. Each article was carefully screened for fundus images and inclusion criteria. Fundus images of sufficient quality were scanned, digitized, and matched in size using Adobe Photo Shop to compare the pattern location and extension of the pigmented lesion. These obtained patterns of grouped CHRPE were than mapped and superimposed. RESULTS: Forty-five images were retrieved from 32 articles with grouped CHRPE. The lesions extended from the margin of the optic disc and radiated in sectors to the fundus periphery. The stream of growth did not follow the pattern of the retinal nerve fiber layer, because the clusters of pigmented cells crossed the midline raphe not sparing the macular area. Smaller lesion clusters were mainly located near the optic disc, whereas larger lesions were found in the periphery. CONCLUSIONS: The growth pattern of grouped CHRPE is similar to cutaneous sectorial pigmentations. We speculate that pigmentary mosaicisms may be a modified wild-type allele in a somatic cell clone during early embryogenesis following developmental lines analogous to the cutaneous lines of Blaschko. The sectorial pigmentations on the ocular fundus may reflect the stream, outgrowth, and migration of retinal pigment epithelium cells during embryogenesis.

Humans↗
PubMed2004

Spontaneous separation of epiretinal membrane in young subjects: personal observations and review of the literature.

BACKGROUND: Idiopathic epiretinal membranes (ERM) grow on the surface of the internal limiting membrane (ILM) and are a very uncommon condition in young subjects. METHODS: We report six young subjects with ERM and describe the spontaneous separation of the membranes. The functional and anatomical recovery was assessed by Snellen visual acuity, Amsler grid and funduscopy. Selected cases were additionally assessed by optical coherence tomography (OCT). RESULTS: All subjects initially claimed a sudden, unilateral, reduction in visual acuity (VA) with severe distortion at the age of 15-30 years. No ocular trauma or disease was ascertained in any case. Initial fundus examination demonstrated a gray-whitish ERM with translucent stress lines over the macula. Visual recovery occurred in all cases after resolution of the ERM. Sequential OCT demonstrated the successive peeling of an ERM accompanied by normalization of foveal thickness. CONCLUSIONS: Young subjects should be counseled about the favorable prognosis for maintaining good vision and possible spontaneous membrane separation. Conservative observation is advocated if the visual disturbance is located temporally, as functional recovery and spontaneous membrane separation may occur. When the contracting forces of the immature ERM are stronger than its adhesions to the retina, the membrane may separate spontaneously.

Adolescent↗
PubMed2004

Unilateral linear hyperpigmentation of the skin with ipsilateral sectorial hyperpigmentation of the retina.

A 32-year-old Caucasian man had a mosaic hyperpigmentation on his left arm, arranged in a pattern following the lines of Blaschko. In addition, a mosaic hyperpigmentation was noted in his left eye, in the form of grouped congenital hypertrophy of the retinal pigment epithelium (CHRPE). Such "bear tracks" are segmentally oriented, well-demarcated, flat, hyperpigmented lesions originating with small dots at the optic disk and expanding towards the periphery. We hypothesize that these mosaic pigmentary lesions involving the skin and the eye on the same side of the body may have originated from an early postzygotic mutation and thus may be etiologically related.

Adult↗
PubMed2003

Melem (2,5,8-triamino-tri-s-triazine), an important intermediate during condensation of melamine rings to graphitic carbon nitride: synthesis, structure determination by X-ray powder diffractometry, solid-state NMR, and theoretical studies.

Single-phase melem (2,5,8-triamino-tri-s-triazine) C(6)N(7)(NH(2))(3) was obtained as a crystalline powder by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C(3)N(3)(NH(2))(3), dicyandiamide H(4)C(2)N(4), ammonium dicyanamide NH(4)[N(CN)(2)], or cyanamide H(2)CN(2), respectively) at temperatures up to 450 degrees C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu K alpha(1): P2(1)/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, beta = 99.912(2) degrees, and Z = 4). In the solid, melem consists of nearly planar C(6)N(7)(NH(2))(3) molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed (13)C and (15)N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent X-ray powder diffractometry investigations above 560 degrees C, melem transforms into a graphite-like C-N material.

Journal Article↗
PubMed2003

Experimental and quantum-chemical studies on the thermochemical stabilities of mercury carbodiimide and mercury cyanamide.

Calorimetric dissolution measurements of the solid compounds mercury carbodiimide HgNCN(I) and mercury cyanamide HgNCN(II) in aqueous HCl that targeted at their thermochemical stabilities show the cyanamide species HgNCN(II) to be the more stable phase in terms of both enthalpy and Gibbs energy with an enthalpy difference of 2-3 kJ mol-1. While the stability ranking of HgNCN(I) and HgNCN(II) thus perfectly matches Pearson's HSAB concept, quantum-chemical stability predictions using common parametrizations of density functional theory appear to be fundamentally flawed. An analysis of the error is attempted on the basis of correlated wave functions for related molecules.

Journal Article↗