scispace - formally typeset
Search or ask a question

Showing papers by "Radboud University Nijmegen published in 1995"


Journal ArticleDOI
TL;DR: The Modified DAS that included 28-joint counts were able to discriminate between high and low disease activity (as indicated by clinical decisions of rheumatologists) and are as valid as disease activity scores that include more comprehensive joint counts.
Abstract: Objective. The development and validation of Modified Disease Activity Scores (DAS) that include different 28-joint counts. Methods. These scores were developed by canonical discriminant analyses and validated for criterion, correlational, and construct validity. The influence of disease duration on the composition of the DAS was also investigated. Results. No influence of disease duration was found. The Modified DAS that included 28-joint counts were able to discriminate between high and low disease activity (as indicated by clinical decisions of rheumatologists). Conclusion. The Modified DAS are as valid as disease activity scores that include more comprehensive joint counts.

5,718 citations


Journal ArticleDOI
TL;DR: This work has identified a common mutation in MTHFR which alters a highly-conserved amino acid; the substitution occurs at a frequency of approximately 38% of unselected chromosomes and may represent an important genetic risk factor in vascular disease.
Abstract: Hyperhomocysteinaemia has been identified as a risk factor for cerebrovascular, peripheral vascular and coronary heart disease. Elevated levels of plasma homocysteine can result from genetic or nutrient-related disturbances in the trans-sulphuration or re-methylation pathways for homocysteine metabolism. 5, 10-Methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the predominant circulatory form of folate and carbon donor for the re-methylation of homocysteine to methionine. Reduced MTHFR activity with a thermolabile enzyme has been reported in patients with coronary and peripheral artery disease. We have identified a common mutation in MTHFR which alters a highly-conserved amino acid; the substitution occurs at a frequency of approximately 38% of unselected chromosomes. The mutation in the heterozygous or homozygous state correlates with reduced enzyme activity and increased thermolability in lymphocyte extracts; in vitro expression of a mutagenized cDNA containing the mutation confirms its effect on thermolability of MTHFR. Finally, individuals homozygous for the mutation have significantly elevated plasma homocysteine levels. This mutation in MTHFR may represent an important genetic risk factor in vascular disease.

5,606 citations


Journal ArticleDOI
02 Mar 1995-Nature
TL;DR: Evidence is presented that a gene encoding myosin VIIA is responsible for USH1B and that USH IB appears as a primary cytoskeletal protein defect, which implicate the genes encoding other unconventional myosins and their interacting proteins as candidates for other genetic forms of Usher syndrome.
Abstract: USHER syndrome represents the association of a hearing impairment with retinitis pigmentosa1 and is the most frequent cause of deaf–blindness in humans. It is inherited as an autosomal recessive trait which is clinically and genetically heterogeneous2,3. Some patients show abnormal organization of microtubules in the axoneme of their photoreceptors cells (connecting cilium)4–6, nasal ciliar cells7 and sperm cells5, as well as widespread degeneration of the organ of Corti8. Usher syndrome type 1 (USH1) is characterized by a profound congenital sensorineural hearing loss, constant vestibular dysfunction and prepubertal onset of retinitis pigmentosa. Of three different genes responsible for USH19–11,USH1B maps to 11q13.5 (ref. 10) and accounts for about 75% of USH1 patients2,3. The mouse deafness shaker-1 (shl) mutation has been localized to the homologous murine region12,13. Taking into account the cytoskeletal abnormalities in USH patients, the identification of a gene encoding an unconventional myosin as a candidate for shaker-1(ref. 14) led us to consider the human homo-logue as a good candidate for the gene that is defective in USH1B. Here we present evidence that a gene encoding myosin VIIA is responsible for USH1B. Two different premature stop codons, a six-base-pair deletion and two different missense mutations were detected in five unrelated families. In one of these families, the mutations were identified in both alleles. These mutations, which are located at the amino-terminal end of the motor domain of the protein, are likely to result in the absence of a functional protein. Thus USH IB appears as a primary cytoskeletal protein defect. These results implicate the genes encoding other unconventional myosins and their interacting proteins as candidates for other genetic forms of Usher syndrome.

1,063 citations


Journal ArticleDOI
TL;DR: It was concluded that the method developed offers new perspectives for the study of trabecular bone, which uses three-dimensional serial reconstruction techniques to construct a large-scale FE model, by directly converting voxels to elements.

857 citations


Journal ArticleDOI
TL;DR: MR imaging was the most accurate of the three preoperative imaging modalities in assessing the size and number of malignant lesions in the breast.
Abstract: PURPOSE: To evaluate the comparative accuracy of magnetic resonance (MR) imaging relative to mammography and ultrasonography (US) for assessing the extent of breast tumors. MATERIALS AND METHODS: Histologic results and preoperative imaging findings (mammography, US, MR imaging) were analyzed regarding tumor size and multifocality of 61 tumors in 60 women undergoing mastectomy for carcinoma. RESULTS: In 10% of cases, the index tumor was not seen at mammography. With US, 15% of the index tumors were not recognized, while MR imaging missed 2% of the index tumors. On mammographic and US images, tumor size was underestimated significantly (P < .005), by 14% and 18%, respectively, while MR imaging showed no significant difference in size compared with that found in a pathologic evaluation. Mammography showed 31% of the additional invasive lesions, while US showed 38% and MR imaging showed 100%. CONCLUSION: MR imaging was the most accurate of the three preoperative imaging modalities in assessing the size and nu...

515 citations


Journal Article
TL;DR: In 28% of the hyperhomocysteinemic patients with premature vascular disease, abnormal homocysteine metabolism could be attributed to thermolabile MTHFR.
Abstract: Summary Thermolability of 5,10-methylenetetrahydrofolate reduc­ tase (MTHFR) was examined as a possible cause of mild hyperhomocysteinemia in patients with premature vascu­ lar disease. Control subjects and vascular patients with mild hyperhomocysteinemia and with normohomocysteinemia were studied. The mean (±SD) specific MTHFR activity in lymphocytes of 22 control subjects was 15.6 (±4.7) nmol CH20 /m g protein/h (range: 9.1-26,6), and the residual activity (±SD) after heat inactivation for 5 min at 46°C was 55.3 (±12.0)% (range: 35.9-78.3). By measurement of MTHFR activity, two distinct subgroups of hyperhomocysteinemic patients became evident. One group (n - 11) had thermolabile MTHFR with a mean (±SD) specific activity of 8.7 (±2.1) nmol CH20 /m g pro­ tein/h (range: 5.5 -12.7) and a residual activity, after heat inactivation, ranging from 0% to 33%. The other group (n = 28) had normal specific activity (±SD) of 21.5 (±7.2) nmol CH20 /m g protein/h (range: 10.0-39.0) and a nor­ mal residual activity (±SD) of 53.8 (±9.2)% (range: 33.171.5) after heat inactivation, The mean (±SD) specific ac­ tivity of 29 normohomocysteinemic patients was 20.7 (±6.5) nmol CH20 /m g protein/h (range: 9.4-33.8), and the mean (±SD) residual activity after heat inactivation was 58.2 (±10.2)% (range: 43.0-82.0). Thus, in 28% of the hyperhomocysteinemic patients with premature vascular disease, abnormal homocysteine metabolism could be at­ tributed to thermolabile MTHFR.

431 citations


Journal ArticleDOI
TL;DR: The suppression of PG synthesis in both ZIA and AIA in mice is due to the combined local action of IL-1 (alpha + beta), and neither IL-6 nor TNF is involved.
Abstract: OBJECTIVE: To determine the involvement of interleukin-1 (IL-1), tumor necrosis factor (TNF), and IL-6 in the cartilage pathology of murine antigen-induced arthritis (AIA) and zymosan-induced arthritis (ZIA). METHODS: Arthritis was induced by intraarticular injection of zymosan in naive mice or by subcutaneous injection of methylated bovine serum albumin in sensitized animals. Mini-osmotic pumps releasing human recombinant IL-1 receptor antagonist (IL-1ra) protein were implanted intraperitoneally 2 days before arthritis induction, and neutralizing antibodies directed against murine IL-1 alpha, IL-1 beta, TNF alpha, or IL-6 were administered 1 day before. Proteoglycan (PG) synthesis and degradation were assessed in patellar cartilage. RESULTS: Murine IL-1 alpha and IL-1 beta injected intraarticularly at doses of 0.1-100 ng suppressed chondrocyte PG synthesis. The highest dose of TNF tested (100 ng) decreased PG synthesis marginally. In contrast, the maximum dose of IL-6 (1 microgram) stimulated PG synthesis 2 days after injection. Treatment of AIA with neutralizing monoclonal antibodies against either TNF alpha or IL-6 did not reduce either the PG degradation or the suppression of its synthesis. However, treatment with anti-IL-1 (alpha + beta) polyclonal antibodies totally prevented PG suppression, although the initial breakdown of PG was unaffected. This effect was confirmed when IL-1ra was administered in high doses. Moreover, treatment of ZIA with anti-IL-1 (alpha + beta), but not with anti-TNF, resulted in normal PG synthesis, confirming the key role played by IL-1 in the inhibition of PG synthesis. Treatment of AIA with anti-IL-1 did not affect inflammation during the acute phase, but a significant reduction of ongoing inflammation was noted at day 7, and there was a marked reduction in the loss of cartilage PG. CONCLUSION: The suppression of PG synthesis in both ZIA and AIA in mice is due to the combined local action of IL-1 (alpha + beta), and neither IL-6 nor TNF is involved. Moreover, the normalization of PG synthesis brought about by blocking of IL-1 ameliorates the cartilage damage associated with AIA.

391 citations


Journal ArticleDOI
TL;DR: It is concluded that the trabecular adaptation to mechanical load, as described by Wolff, can be explained by a relatively simple regulatory model and is useful for investigating the effects of physiological parameters on the development, maintenance, and adaptation of bone.

386 citations


Journal ArticleDOI
10 Feb 1995-Cell
TL;DR: The results suggest that mutations in collagen XI genes are associated with a spectrum of abnormalities in human skeletal development and support the conclusion of others, based on studies of murine chondrodysplasia, that collagen XI is essential for skeletal morphogenesis.

363 citations


Journal ArticleDOI
TL;DR: The ever-increasing number of proteins identified as belonging to the family of small heat-shock proteins (shsps) and α-crystallins enables us to reassess the phylogeny of this ubiquitous protein family.
Abstract: The ever-increasing number of proteins identified as belonging to the family of small heat-shock proteins (shsps) and α-crystallins enables us to reassess the phylogeny of this ubiquitous protein family. While the prokaryotic and fungal representatives are not properly resolved, most of the plant and animal shsps and related proteins are clearly grouped in distinct clades, reflecting a history of repeated gene duplications. The members of the shsp family are characterized by the presence of a conserved homologous “α-crystallin domain,” which sometimes is present in duplicate. Predictions are made of secondary structure and solvent accessibility of this domain, which together with hydropathy profiles and intron positions support the presence of two similar hydrophobic β-sheet-rich motifs, connected by a hydrophilic α-helical region. Together with an overview of the newly characterized members of the shsp family, these data help to define this family as being involved as stable structural proteins and as molecular chaperones during normal development and induced under pathological and stressful conditions.

354 citations


Journal ArticleDOI
TL;DR: Finite element analyses of the pelvic bone are used to investigate its basic load transfer and stress distributions under physiological loading conditions and show that the major part of the load is transferred through the cortical shell.

Journal ArticleDOI
TL;DR: It is proposed that, in addition to an aspecific warning signal, the reduction of saccadic latency is due to interactions that take place at a multimodal stage of sAccade programming, where theceived positions of visual and auditory stimuli are represented in a common frame of reference.
Abstract: In this paper, we show that human saccadic eye movements toward a visual target are generated with a reduced latency when this target is spatially and temporally aligned with an irrelevant auditory nontarget. This effect gradually disappears if the temporal and/or spatial alignment of the visual and auditory stimuli are changed. When subjects are able to accurately localize the auditory stimulus in two dimensions, the spatial dependence of the reduction in latency depends on the actual radial distance between the auditory and the visual stimulus. If, however, only the azimuth of the sound source can be determined by the subjects, the horizontal target separation determines the strength of the interaction. Neither saccade accuracy nor saccade kinematics were affected in these paradigms. We propose that, in addition to an aspecific warning signal, the reduction of saccadic latency is due to interactions that take place at a multimodal stage of saccade programming, where theperceived positions of visual and auditory stimuli are represented in a common frame of reference. This hypothesis is in agreement with our finding that the saccades often are initially directed to the average position of the visual and the auditory target, provided that their spatial separation is not too large. Striking similarities with electrophysiological findings on multisensory interactions in the deep layers of the midbrain superior colliculus are discussed.


Journal ArticleDOI
TL;DR: It is concluded that a homozygous LH receptor gene mutation underlies the syndrome of autosomal recessive congenital Leydig cell hypoplasia in this family, and results have implications for the understanding of the development of the male genitalia.
Abstract: Leydig cell hypoplasia is a rare autosomal recessive condition that interferes with normal development of male external genitalia in 46,XY individuals. We have studied two Leydig cell hypoplasia patients (siblings born to consanguineous parents), and found them to be homozygous for a missense mutation (Ala593Pro) in the sixth transmembrane domain of the luteinizing hormone (LH) receptor gene. In vitro expression studies showed that this mutated receptor binds human choriogonadotropin with a normal KD, but the ligand binding does not result in increased production of cAMP. We conclude that a homozygous LH receptor gene mutation underlies the syndrome of autosomal recessive congenital Leydig cell hypoplasia in this family. These results have implications for the understanding of the development of the male genitalia.

Journal ArticleDOI
TL;DR: The data confirm the hypothetical localization of a maternally imprinted gene (or more than one such gene) on chromosome 7 and suggest to search for UPD 7 in families with an offspring with sporadic Silver-Russell syndrome or primordial growth retardation.
Abstract: Maternal uniparental disomy for the entire chromosome 7 has so far been reported in three patients with intrauterine and postnatal growth retardation. Two were detected because they were homozygous for a cystic fibrosis mutation for which only the mother was heterozygous, and one because he was homozygous for a rare COL1A2 mutation. We investigated 35 patients with either the Silver-Russell syndrome or primordial growth retardation and their parents with PCR markers to search for uniparental disomy 7. Four of 35 patients were found to have maternal disomy, including three with isodisomy and one with heterodisomy. The data confirm the hypothetical localization of a maternally imprinted gene (or more than one such gene) on chromosome 7. It is suggested to search for UPD 7 in families with an offspring with sporadic Silver-Russell syndrome or primordial growth retardation.

Journal ArticleDOI
TL;DR: Experimental data are presented on particle correlations and fluctuations in various high-energy multiparticle collisions, with special emphasis on evidence for scaling-law evolution in small phase-space domains as discussed by the authors.
Abstract: Experimental data are presented on particle correlations and fluctuations in various high-energy multiparticle collisions, with special emphasis on evidence for scaling-law evolution in small phase-space domains. The notions of intermittency and fractality as related to the above findings are described. Phenomenological and theoretical work on the subject is reviewed.

01 Jan 1995
TL;DR: In this paper, the authors examine the divergence of practice and impression of gender distinctions: gender inequality is still persistent in organizational practices while a dominant perception of equality occurs at the same time.
Abstract: This paper describes the results of an empirical study of the gender subtext in organizations. We examine the divergence of practice and impression of gender distinctions: gender inequality is still persistent in organizational practices while a dominant perception of equality occurs at the same time. Our analysis focuses on the processes (re)producing this divergence. We argue that both the persistency of gender inequality and the perception of equality emerge from a so-called gender subtext: the set of often concealed, power-based gendering processes, i.e. organizational and individual arrangements (objectives, measures, habits), systematically (re)producing gender distinctions. These gendering processes are examined in five departments in the Dutch banking sector. We explore the gender subtext in three organizational settings: show pieces (the token position of the few women in top functions), the mommy track (the side track many women with young children are shunted to) and the importance of being ask...

Journal ArticleDOI
TL;DR: A more realistic FE model of the pelvic bone is developed, which implies that the model has to be three-dimensional, but also that the thickness of the cortical shell and the density distribution of the trabecular bone throughout the pelvicBone have to be incorporated in the model in a realistic way.
Abstract: Due to both its shape and its structural architecture, the mechanics of the pelvic bone are complex. In Finite Element (FE) models, these aspects have often been (over)simplified, sometimes leading to conclusions which did not bear out in reality. The purpose of this study was to develop a more realistic FE model of the pelvic bone. This not only implies that the model has to be three-dimensional, but also that the thickness of the cortical shell and the density distribution of the trabecular bone throughout the pelvic bone have to be incorporated in the model in a realistic way. For this purpose, quantitative measurements were performed on computer tomography scans of several pelvic bones, after which the measured quantities were allocated to each element of the mesh individually. To validate this FE model, two fresh pelvic bones were fitted with strain gages and loaded in a testing machine. Stresses calculated from the strain data of this experiment were compared to the results of a simulation with the developed pelvic FE model.

Journal ArticleDOI
TL;DR: In this paper, a multivariate analysis based on Cox's proportional hazards regression model was performed on the most important prognostic factors and their association with invasion and death, an index was computed reflecting the risk of both invasion and malignant disease, respectively.

Journal ArticleDOI
TL;DR: A model of a topologically organized neural network of a Hopfield type with nonlinear analog neurons is shown to be very effective for path planning and obstacle avoidance.

Journal ArticleDOI
TL;DR: The 'inside-out' and 'outside-in' signaling properties of LFA-1, as a prototype leukocyte integrin, in normal and malignant T cells are discussed, and a model that highlights the role of the cytoskeleton in the regulation of L FA-1 is integrated.

Journal ArticleDOI
TL;DR: In Xenopus oocytes the inability of Gly64-Arg, Arg187Cys or Ser216Pro substituted AQP-2 proteins to facilitate water transport is caused by an impaired routing to the plasma membrane.
Abstract: Congenital nephrogenic diabetes insipidus is a recessive hereditary disorder characterized by the inability of the kidney to concentrate urine in response to vasopressin. Recently, we reported mutations in the gene encoding the water channel of the collecting duct, aquaporin-2 (AQP-2) causing an autosomal recessive form of nephrogenic diabetes insipidus (NDI). Expression of these mutant AQP-2 proteins (Gly64Arg, Arg187Cys, Ser216Pro) in Xenopus oocytes revealed nonfunctional water channels. Here we report further studies into the inability of these missense AQP-2 proteins to facilitate water transport in Xenopus oocytes. cRNAs encoding the missense AQPs were translated with equal efficiency as cRNAs encoding wild-type AQP-2 and were equally stable. Arg187Cys AQP2 was more stable and Gly6-4Arg and Ser216Pro AQP2 were less stable when compared to wild-type AQP2 protein. On immunoblots, oocytes expressing missense AQP-2 showed, besides the wild-type 29 kDa band, an endoplasmic reticulum-retarded form of AQP-2 of approximately 32 kD. Immunoblots and immunocytochemistry demonstrated only intense labeling of the plasma membranes of oocytes expressing wild-type AQP-2. Therefore, we conclude that in Xenopus oocytes the inability of Gly64-Arg, Arg187Cys or Ser216Pro substituted AQP-2 proteins to facilitate water transport is caused by an impaired routing to the plasma membrane.

Journal ArticleDOI
TL;DR: In this paper, fast magic angle sample spinning (MAS) is combined with APHH-CP to preserve the heteronuclear dipolar order, established in the course of the transfer, which can indeed be created and preserved.

Journal ArticleDOI
TL;DR: Oocytes expressing MIP failed to exhibit ion channel activity and consistently exhibited water transport by a facilitated pathway that was qualitatively similar to the Aquaporins but of lesser magnitude, concluding that MIP functions as an Aquaporin in lens, but the protein may also have other essential functions.

Journal ArticleDOI
TL;DR: Physicochemical parameters such as wettability and surface free energy influence cell growth but play no measurable role in the shape and orientation of cells on microtextured surfaces.
Abstract: To evaluate the effect of surface treatment and surface microtexture on cellular behavior, smooth and microtextured silicone substrata were produced. The microtextured substrata possessed parallel surface grooves with a width and spacing of 2.0 (SilD02), 5.0 (SilD05), and 10 microns (SilD10). The groove depth was approximately 0.5 microns. Subsequently, these substrata were either left untreated (NT) or treated by ultraviolet irradiation (UV), radiofrequency glow discharge treatment (RFGD), or both (UVRFGD). After characterization of the substrata, rat dermal fibroblasts (RDF) were cultured on the UV, RFGD, and UVRFGD treated surfaces for 1, 3, 5, and 7 days. Comparison between the NT and UV substrata revealed that UV treatment did not influence the contact angles and surface energies of surfaces with a similar surface topography. However, the contact angles of the RFGD and UVRFGD substrata were significantly smaller than those of the UV and NT substrata. The dimension of the surface microevents did not influence the wettability characteristics. Cell culture experiments revealed that RDF cell growth on UV-treated surfaces was lower than on the RFGD and UVRFGD substrata. SEM examination demonstrated that the parallel surface grooves on the SilD02 and SilD05 substrata were able to induce stronger cell orientation and alignment than the events on SilD10 surfaces. By combining all of our findings, the most important conclusion was that physicochemical parameters such as wettability and surface free energy influence cell growth but play no measurable role in the shape and orientation of cells on microtextured surfaces.

Journal ArticleDOI
TL;DR: In this article, the authors isolated several cDNA clones which showed differential expression between highly and lowly metastatic human melanoma cell lines, and one clone, designated nmb, showed preferential expression in the low-meta-static cell lines and was chosen for further characterization.
Abstract: From a subtractive cDNA library, we isolated several cDNA clones which showed differential expression between highly and lowly metastatic human melanoma cell lines. One clone, designated nmb, showed preferential expression in the low-meta-static cell lines and was chosen for further characterization. Sequence analysis revealed that this clone represents a novel gene, encoding a putative transmembrane glycoprotein which showed the highest homology to the precursor of pMEL17, a melanocyte-specific protein. nmb RNA expression was absent in most tumor-cell lines tested and not restricted to the melanocytic lineage. Transfection of a partial nmb cDNA into a highly metastatic melanoma cell line (BLM) resulted, in 2 of 3 transfectants, in slower subcutaneous tumor growth and, in 1 of 3 transfectants, in reduction of the potential for spontaneous metastasis in nude mice. © 1995 Wiley-Liss, Inc.

Journal Article
TL;DR: It was found that 70% of the patients showed radiographic damage after 3 years and this group could already be selected after 1 year, indicating a flattening of the curve of radiographic progression.
Abstract: Objective. To determine the development rate of erosions and joint space narrowing in a cohort of patients during the first 3 years of rheumatoid arthritis (RA). Methods. All consecutive patients fulfilling the American Rheumatism Association criteria and seen within the 1st year of the disease were followed prospectively with biannual radiographs of hands and feet. One hundred and forty-seven patients were followed for 2 years and 90 patients for 3 years. Erosions and joint space narrowing were scored with a modified version of Sharp's method (van der Heijde modification). Wilcoxon's rank sum test was used to test differences between joints and between erosions and joint space narrowing. Results. On average, at 3 year followup most groups of joints showed about 8% of the maximum possible score. In most groups of joints about 20% of the joints were affected, At the start more foot joints were affected than hand joints. However, the increase in the number of affected joints and in the radiographic damage was similar in hands and feet. Consequently, the predominance of affected foot joints was still present after 3 years. The progression in the 3rd year was statistically significantly less compared to the 1st year. This was more pronounced for the number of affected joints than for radiographic damage. Conclusion. We found that 70% of the patients showed radiographic damage after 3 years and this group could already be selected after 1 year. Overall, +/- 18-20% of the joints were affected after 3 years, with relatively few abnormalities per joint (+/- 8% of the maximum possible score was reached). The rate of progression in the 1st year was significantly more than in the 2nd and 3rd years, indicating a flattening of the curve of radiographic progression.

Journal ArticleDOI
TL;DR: An alternative approach to discourse structure is presented according to which topicality is the general organizing principle in discourse, which accounts for the fact that the segmentation structure of discourse is in correspondence with the hierarchy of topics defined for the discourse units.
Abstract: In this paper we present an alternative approach to discourse structure according to which topicality is the general organizing principle in discourse. This approach accounts for the fact that the segmentation structure of discourse is in correspondence with the hierarchy of topics defined for the discourse units. Fundamental to the proposed analysis is the relation it assumes between the notion of topic and that of explicit and implicit questioning in discourse. This relation implies that (1) the topic associated with a discourse unit is provided by the explicit or implicit question it answers and (2) the relation between discourse units is determined by the relation between these topic-providing questions.

Journal ArticleDOI
TL;DR: The article concludes with a tentative scheme to clarify the position of the dynamical approach relative to other extant approaches in movement science.

Journal ArticleDOI
01 Mar 1995-Nature
TL;DR: In this article, a theoretical approach was proposed to predict needle-like shape of growing urea crystals from aqueous solution, which is consistent with experimental observations. But this approach was only applied to the case of urea crystal grown from urea.
Abstract: PREDICTING the shape of growing crystals is important for industrial crystallization processes. The equilibrium form of a crystal can be determined unambiguously from a consideration of the surface free energies of the various crystallographic faces {hkl}1, but the growth morphology is determined by kinetic factors which are harder to predict. This morphology depends on the relative growth rates R rel hkl of the crystal faces. Several theories have been advanced2,3 to relate R rel hkl to geometric or energetic characteristics of the surfaces {hkl}, but these have met with limited success in predicting the crystal morphologies observed. Here we present a theoretical approach to the problem in which R rel hkl is determined by quantities that are accessible either from kinetic models or from computer simulations of the solid-fluid interface. The important parameters controlling the growth rate are the energy required to create a step at the crystal surface and the free-energy barrier for an adsorbed solute molecule to be incorporated into the crystal. Both can be related to the mole fraction of adsorbed solute molecules in dynamic equilibrium with those in the crystal surface. When this approach is applied to the case of urea crystals grown from aqueous solution, we predict a needle-like shape which is consistent with experimental observations.