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PubMed2004

CONDORR--CONstrained Dynamics of Rigid Residues: a molecular dynamics program for constrained molecules.

A computer program CONDORR (CONstrained Dynamics of Rigid Residues) was developed for molecular dynamics simulations of large and/or constrained molecular systems, particularly carbohydrates. CONDORR efficiently calculates molecular trajectories on the basis of 2D or 3D potential energy maps, and can generate such maps based on a simple force field. The simulations involve three translational and three rotational degrees of freedom for each rigid, asymmetrical residue in the model. Total energy and angular momentum are conserved when no stochastic or external forces are applied to the model, if the time step is kept sufficiently short. Application of Langevin dynamics allows longer time steps, providing efficient exploration of conformational space. The utility of CONDORR was demonstrated by application to a constrained polysaccharide model and to the calculation of residual dipolar couplings for a disaccharide. [Figure: see text]. Molecular models (bottom) are created by cloning rigid residue archetypes (top) and joining them together. As defined here, the archetypes AX, HM and BG respectively correspond to an alpha-D-Xyl p residue, a hydroxymethyl group, and a beta-D-Glc p residue lacking O6, H6a and H6b. Each archetype contains atoms (indicated by boxes) that can be shared with other archetypes to form a linked structure. For example, the glycosidic link between the two D-Glc p residues is established by specifying that O1 of the nonreducing beta-D-Glc p (BG) residue (2) is identical to O4 of the reducing Glc p (BG) residue (1). The coordinates of the two residues are adjusted so as to superimpose these two (nominally distinct) atoms. Flexible hydroxymethyl (HM) groups (3 and 4) are treated as separate residues, and the torsional angles (normally indicated by the symbol omega) that define their geometric relationships to the pyranosyl rings of the BG residues are specified as psi3 and psi4, respectively. The torsional angles phi3 and phi4, defined solely to maintain the orientation of the geminal H-atoms of the hydroxymethyl group, are not shown. (See text.). The illustrated trisaccharide is thus specified as a collection of 5 residues which are represented by 3 archetypes. Models of the disaccharide cellobiose (beta-D-Glc p-(1-->4)-D-Glc p) must include residues 1 and 2, but the hydroxymethyl groups (residues 3 and 4) can also be explicitly included in this model

Carbohydrates↗
PubMed2006

Modeling of aqueous transport in rigid porous matrices near the percolation threshold.

PURPOSE: To demonstrate control of passive diffusion of small molecules through rigid ceramic matrices via manipulation of matrix porosity near the percolation threshold, and to model such control using percolation scaling relationships on both infinite and finite lattices. MATERIALS AND METHODS: Rigid alumina disks of controlled porosity were prepared using standard ceramic casting and sintering techniques. Structural void space distributions in sintered disks were measured by dimensional and volume displacement (pycnometry) methods. The impact of void space on transport was determined by tracking the diffusion of ionized benzoic acid across sintered disks mounted in Stokes diffusion cells. Critical percolation thresholds were estimated by fitting structural and transport-dependent results to percolation scaling relationships. Finite-size scaling studies were performed by adding polymer microspheres of known diameter to the disks to generate artificially large pores. RESULTS: Nonlinear least squares techniques were used to fit both structural and transport-dependent properties of rigid alumina disks to total disk porosity using percolation scaling relationships. The critical percolation threshold determined from structural properties (0.129) was lower than that determined from benzoic acid transport (0.169). The transport-derived percolation threshold exactly matched that expected for a tetrakaidecahedral (14 sided) lattice. Finite-size scaling was demonstrated through a nonzero effective volume fraction for transport at the percolation threshold. CONCLUSIONS: Manipulation of total disk porosity near the percolation threshold was shown to be a suitable means of controlling the transport rate of a model small molecule, while deliberate enlargement of individual pores was demonstrated to decrease this threshold without increasing total porosity. The lower-than-expected percolation threshold obtained from the structural model was ascribed to limitations of the measurement technique. The threshold determined from the aqueous transport model was concluded to represent the true threshold for this system.

Algorithms↗
PubMed1982

Penetration in trochanteric fractures of the femur treated with rigid nail plates.

One hundred and twelve trochanteric fractures have been analysed. A Jewett nail-plate was used in 81 patients and a Thorton nail-McLaughlin plate in 31. Penetration of the nail into or through the hip joint was the only complication studied in detail. It occurred in 41 cases: 31 (38 per cent) with the Jewett nails and 10 (33 per cent) in the other group. Both groups are comparable in that the nail-plate acts as a single rigid unit and the nail/plate angle varied, but the overall incidence of migration of the nail was similar. All the 112 cases were reviewed as one group. Penetration was more common in comminuted unstable types of fracture, in those poorly fixed, and in the older patients. Sixteen (14 per cent) well-fixed fractures showed penetration. It appears that one important additional reason for penetration in this series was the rigidity of the device and the poor quality of the bone. The incidence of nail penetration in comminuted unstable fractures of the femur might be reduced by using methods of fixation other than rigid nail-plates.

Aged↗
PubMed1983

The influence of timing and rigidity of internal fixation on bony union of fractures of the forearm.

Sixty-one patients with fractures of the shafts of both bones of the forearm treated by internal fixation were studied retrospectively. The importance of the rigidity of the fixation and the time that elapsed before operation was investigated. Eight cases of non-union and one of delayed union were noted after fractures which had been operated on during the first week by non-rigid internal fixation. On the other hand, in the group of rigidly fixed fractures, the time of operation was not found to have a statistically significant effect on the healing process.

Adolescent↗
PubMed1995

A procedure for determining rigid body transformation parameters.

For many biomechanical applications it is necessary to determine the parameters which describe the transformation of a rigid body from one reference frame to another. These parameters are a scaling factor, an attitude matrix, and a translation vector. The paper presents a new procedure for the determination of these parameters incorporating the work of Arun et al. [IEEE Trans. Pattern Anal. Machine Intell, 9, 698-700 (1987)] but expanding their analysis to allow for the determination of a scale factor, the scalar weighting of the least-squares problem, and the problem of obtaining the incorrect determinant when determining the attitude matrix. The procedure, which requires the coordinates of three or more non-collinear points, is based around the singular value decomposition, and provides a least-squares estimate of the rigid body transformation parameters. Examples are presented of the use of this procedure for determining the attitude of a rigid body, and for osteometric scaling. When used for osteometric scaling mirror transformations are possible, therefore a right-hand specimen can be scaled to the left-hand side of another specimen.

Algorithms↗
PubMed1994

Reduction of rigidity in human activated natural killer cells by thioglycollate treatment.

Successful delivery of effector cells to tumor vasculature and the expression of cellular activities, such as extravasation and tumor infiltration are important aspects of the immune intervention of neoplastic disease. The structural rigidity of the effector cell, an indication of its cytoskeletal characteristics, plays an important role in influencing cellular functions and hemodynamic behavior as well as systemic distribution. The present study was designed to identify an agent which can modify the viscoelastic properties of human natural killer cells. A reducing compound, thioglycollate (TGA), was found to be an effective agent. Changes in cellular rigidity with respect to dose and duration of treatment with TGA were quantified. Micropipet aspiration was used to measure the resistance of NK cells to an imposed external deformation. Cultures of adherent human NK cells were expanded in interleukin 2 (IL-2) for 14 days, removed from culture and resuspended in medium with IL-2 and selected concentrations of TGA ranging from 0.032 mg/ml to 0.250 mg/ml. At 24 h intervals, the cell samples were removed and tested for their viscoelastic properties. Following 24 h of incubation, only TGA at 0.032 mg/ml produced a significant increase in cellular deformability. At 48 h of incubation, NK cell deformability was twice that obtained at 24 h. Higher concentrations of TGA also produced increased deformability after 48 h of incubation. Following 72 h of incubation, all concentrations of TGA tested produced increased deformability; however, the 0.032 mg/ml concentration produced the highest level of deformability combined with high viability (> 95%) as well as activated cell morphology. This treatment did not significantly alter the cytotoxic activity of these cells against a sensitive tumor target cell. These findings indicate that short term culture with TGA may be used to significantly reduce NK cell rigidity without decreasing cell viability or function. Thus, TGA may be a useful compound for altering the rheological properties of activated lymphocytes prior to adoptive transfer.

Cell Adhesion↗
PubMed1986

Management of mandibular trauma with rigid internal fixation.

The use of rigid internal fixation has become an acceptable method for the treatment of fractures and continuity defects of the mandible. This technique has a wide variety of applications, including stabilization of mandibular segments for the application of bone grafts. The primary advantage of rigid fixation is that it obviates the need for maxillomandibular fixation associated with the treatment of mandibular trauma by traditional methods. This article reviews twenty cases in which rigid internal fixation was used for the treatment of fractures and continuity defects of the mandible. In only one case was early removal of the implant necessary as a result of infection.

Adult↗
PubMed1989

Integrated cystoscope: first rigid multipurpose operating cystoscope for local anesthetic endoscopy.

The Miller Integrated Cystoscope is the first small-diameter (17 Ch), rigid, multipurpose, operating cystoscope (biopsy, urethrotomy, ureteric catheterization, cutting, retrieval of stones and foreign bodies, and injection) designed with patient comfort in mind. Despite a small outside diameter, the 8.7-Ch instrument channel conducts a 7.5-Ch accessory including the unique rigid Endoknife, which converts it into an optical urethrotome and rigid Endoneedle which can deliver local anesthetic and other pharmacologic agents into the bladder, prostate, and urethra of both male and female patients. The simplicity of design has dispensed with the need for more costly and conventional instrumentation (e.g., optical urethrotome, Albarron lever) at a fraction of the cost. The urologist can not only inspect the lower urinary tract (Cf fiberscopes) but also perform endoscopic procedures short of a full transurethral prostatectomy with maximum patient comfort.

Ambulatory Surgical Procedures↗
PubMed1994

Histological observations of coated and prestressed dental implants under flexible or rigid loading conditions.

Hydroxyapatite-coated and hydroxyapatite-prestressed titanium implants were implanted under load-free, flexible-loaded and rigid-loaded conditions in dog mandibula in vivo. The bone response, bone contact and the quality of the coating were evaluated histologically and histometrically. Hydroxyapatite coating on titanium implants enhanced the bone apposition. The bone contact can still be present while the coating is resorbed. Gingiva contact with the coating led to a faster degradation of the coating. There was no significant difference in bone contact between hydroxyapatite-coated and -prestressed implants with regard to the loading systems: rigid, flexible and load-free. All three implants showed the highest amount of bone contact apically. Only at the mesial side of the implant did the flexible element show rather high amounts of bone contact compared to the rigid and load-free implants. The hydroxyapatite coating more or less degraded during the implantation period. The degree of degradation varied in the implant itself, between the implants and between the animals.

Analysis of Variance↗
PubMed1988

Mobility of the mandible following advancement and maxillomandibular or rigid internal fixation: an experimental investigation in Macaca mulatta.

This study examined the postsurgical range of mandibular motion following sagittal advancement osteotomy in Macaca mulatta when either maxillomandibular or rigid osseous fixation were used. Seventeen adult female Macaca mulatta underwent sagittal advancement osteotomy of approximately 4 to 6 mm. Six had 6 weeks of maxillomandibular fixation and eleven had rigid osseous fixation with no maxillomandibular fixation. Mandibular range of motion was measured by the change in the angle of the posterior aspect of the mandibular ramus from a closed-mouth and an open-mouth cephalogram. Parametric tests were used to statistically analyze the results. The results of this investigation showed that the animals who did not undergo maxillomandibular fixation maintained a greater range of motion in the early postsurgical period and obtained preoperative mobility by 12 weeks postsurgery. The animals who underwent six weeks of maxillomandibular fixation showed statistically significant decreases in range of motion when compared to the rigid fixation group at each period of time postsurgery, with significant reductions from preoperative values at 12 weeks postsurgery.

Animals↗
PubMed1991

Mandibular anatomy as it relates to rigid fixation of the sagittal ramus split osteotomy.

Rigid fixation of osteotomy segments is frequently used to reduce relapse and allow for early mobilization of the mandible following the sagittal ramus split osteotomy. This study evaluated cortical bone thickness in the retromolar area of 49 human mandibles to determine if there is an advantage (in terms of cortical thickness) to placement of screws for rigid fixation at the external oblique ridge versus placement at the inferior border. The mandibles were sectioned vertically at three sites in the retromolar area, corresponding to the bone available for rigid fixation of the sagittal osteotomy. Cortical bone thickness was measured at the external oblique ridge and 5 mm above the inferior border. The buccal and lingual cortices were found to be significantly (P less than .001) thicker at the external oblique ridge than at the inferior border. This suggests that there may be an advantage in terms of stability to placement of internal fixation screws at the superior border.

Bone Screws↗
PubMed1985

Elastic properties of bacterial flagellar filaments. II. Determination of the modulus of rigidity.

Elongation of a helical bacterial flagellar filament subjected to fluid flow was calculated on the assumption that one end of the filament is firmly attached to a substratum. It was found that the quantity [E(d/2 pi r)2 + 2 mu] could be determined by measuring the elongation at various flow rates, where E is Young's modulus, mu the modulus of rigidity, r the radius of the helix, and d the helical pitch. Experiments were carried out to determine the above quantity for Salmonella flagellar filaments assuming a close-coil form. Because the above quantity is almost equal to 2 mu for a helical form with a large radius/pitch ratio, we were able to determine the modulus of rigidity for this kind of flagellar filament from plots of elongation vs. flow rates. The modulus of rigidity was determined to be about 1 X 10(11) dyn/cm2, i.e., 2 orders of magnitude larger than the previously estimated value.

Bacteria↗
PubMed1982

Role of GABAergic mechanisms in the substantia nigra pars reticulata in modulating morphine-induced muscular rigidity in rats.

Systemic administration of morphine (15 mg/kg i.p.) induced a muscular rigidity in rats, which was recorded from the gastrocnemius-soleus muscle as tonic activity in the electromyogram (EMG). Administration of muscimol (12.5 or 25 ng) into the substantia nigra pars reticulata (SNR) antagonized the rigidity in a dose-dependent manner, whereas bicuculline enhanced it. It was concluded that GABAergic mechanisms in the SNR play an important role in mediating or modulating the expression of the morphine-induced rigidity, which is known to be due to an alteration of striatal function via opioid receptors located in this brain area.

Animals↗
PubMed1993

A template for rigid stereotaxic afterloading brachytherapy of the brain.

PURPOSE: This paper describes a system for the implantation of rigid stainless steel afterloading tubes into the brain using a stereotaxic head frame for both localization and treatment. METHODS AND MATERIALS: The stereotaxic frame is attached to the skull throughout the treatment, and the afterloading tubes are both rigid and fixed to the frame. The source positions are therefore fixed relative to the skull throughout the irradiation. Design and construction of templates, afterloading tubes and clamps are discussed in detail. RESULTS: The rigidity of the resulting implant provides accurate and immobile positioning of the planned isodose distribution relative to the defined treatment volume and makes it possible to carefully and rapidly plan a source loading which will best cover the volume of interest. The source template is not in contact with the patient at any time. The afterloading tubes are held strictly parallel during treatment, allowing for rapid and versatile preplanning prior to surgical placement. Placement options are enhanced by using a set of rotating templates. CONCLUSION: This system has been used for over 60 procedures without any mechanical or safety problems and has provided a significant improvement in both the speed and confidence of localization and treatment planning. There are significant advantages of such a system for High Dose Rate Afterloading Brachytherapy.

Brachytherapy↗
PubMed1992

Rigid internal fixation and the effects on the temporomandibular joint and masticatory system: a prospective study.

A prospective study of 22 patients who underwent a bilateral sagittal osteotomy to advance the mandible and subsequent rigid internal fixation, were examined for signs and symptoms of temporomandibular joint (TMJ) pain and masticatory dysfunction. A modified Helkimo index was used to analyze the anamnestic, clinical, and occlusal data. In addition, 12 of the cases chosen at random were mounted on a semiadjustable (SAM2) articulator and analyzed with the mandibular position indicator (MPI) to determine the amount and the direction of condylar displacement postoperatively. Anamnestic dysfunction decreased because of a reported decrease in muscular pain, joint noise, headache frequency, and parafunctional habits postoperatively. Clinical dysfunction remained unchanged, with a decrease in muscular soreness but with an increased incidence of joint clicking of 7%. The increased incidence of temporomandibular joint pain postoperatively was 4%. Increase in clinical dysfunction was most often seen in women and older patients. Occlusal dysfunction decreased, with the majority of interferences remaining after surgery as a result of insufficient lingual crown torque of the maxillary buccal segments. Occlusion is thought to have played only a minor role in temporomandibular joint and masticatory dysfunction. Reduction in range of motion was 10%, indicating the added benefit of early mobilization with rigid internal fixation procedures. The MPI study found the condyles inferiorly or inferoposteriorly displaced less than 1 mm from their preoperative position. These findings suggest that rigid internal fixation had no adverse effects on the temporomandibular and masticatory system. The variable responses and results can be attributed, at least in part, to the heterogenous population of patients studied and the variations in surgical techniques employed.

Adolescent↗
PubMed1995

Lipid peroxidation contributes to age-related membrane rigidity.

The aim of this work was to assess the relative contributions of lipid peroxidation and cholesterol content to the increase in membrane rigidity observed during senescence. Membrane fluidity was manipulated through exposure to peroxidized or cholesterol-loaded liposomes. Small unilamella liposomes were prepared and either peroxidized by Fe(++)-ADP-ascorbic acid or loaded with cholesterol. After incorporation of the liposomes into rat liver microsomal membranes, membrane fluidity was quantitated by measuring changes in polarization. Membranes exhibited a greater sensitivity to peroxidation than cholesterol in that incorporation of peroxidized liposomes induced microsomal membrane rigidity substantially more than did cholesterol-loaded liposomes. Thus it is proposed, based on data from the present and earlier studies, that membrane fluidity can be modulated readily by lipid peroxidation of membrane phospholipids, irrespective of the influences of cholesterol. These results support the proposal that alterations of lipid structure are more potent and effective than compositional changes in cholesterol in inducing age-related increases in membrane rigidity.

Aging↗
PubMed2006

Results of chest wall resection and reconstruction with and without rigid prosthesis.

BACKGROUND: Chest wall resections are associated with significant morbidity, with respiratory failure in as many as 27% of patients. We hypothesized that our selective use of a rigid prosthesis for reconstruction reduces respiratory complications. METHODS: The records of all patients undergoing chest wall resection and reconstruction were reviewed. Patient demographics, use of preoperative therapy, the location and size of the chest wall defect, performance of lung resection if any, the type of prosthesis, and postoperative complications were recorded. Predictor of complications were identified by chi2 and logistic regression analyses. RESULTS: From January 1, 1995, to July 1, 2003, 262 patients (median age, 60 years) underwent chest wall resection for tumor in 251 (96%), radiation necrosis in 7 (2.7%); and infection in 4 patients (1.3%). The median defect size was 80 cm2 (range, 2.7 to 1,200 cm2) and the median number of ribs resected was 3 (range, 1 to 8). Major lung resection was performed in 85 patients (34%). Prosthetic reconstruction was rigid (polypropylene mesh/methylmethacrylate composite) in 112 (42.7%), nonrigid (polytetrafluoroethylene or polypropylene mesh) in 97 (37%), and none in 53 patients. Postoperatively, 10 patients died (3.8%), 4 of whom had pneumonectomy plus chest wall resection. Respiratory failure occurred in 8 patients (3.1%). By multivariate analysis, the size of the chest wall defect was the most significant predictor of complications. CONCLUSIONS: Our incidence of respiratory failure is lower than previously reported and may relate to our use of rigid repair for defects likely to cause a flail segment. Pneumonectomy plus chest wall resection should be performed only in highly selected patients.

Adult↗
PubMed2005

Systemic regulation of angiogenesis and matrix degradation in bone regeneration--distraction osteogenesis compared to rigid fracture healing.

Aim of this study was the investigation of systemic biochemical regulation mechanisms of bone regeneration by angiogenic and matrix-degrading enzymes during distraction osteogenesis compared to rigid osteotomy bone healing. Serum samples of 10 otherwise healthy patients with callus distraction for lower limb-lengthening and 10 osteotomy patients undergoing elective axis correction have been collected prospectively in a standardized time schedule before and up to 6 months after the procedure. At the end of the individual investigation period, concentrations of metalloproteinases (MMP-9, -13), tissue inhibitors of metalloproteinases (TIMP-1, TIMP-2) and the angiogenic factors angiogenin and VEGF have been detected by use of commercially available enzyme immunoassays. Results have been compared to our preliminary study on proMMP-1-3. In distraction osteogenesis, significantly elevated serum concentrations compared to baseline could be detected postoperatively for proMMP-1, MMP-9, TIMP-1, angiogenin and VEGF but not for proMMP-2, proMMP-3 or TIMP-2. In patients with rigid osteotomy healing, MMP-9, TIMP-1, TIMP-2, angiogenin and VEGF were significantly increased respectively. Comparison of both patient collectives revealed significantly higher increases of serum proMMP-1, VEGF and TIMP-1 in distraction patients during the lengthening period and significantly higher serum concentrations of TIMP-2 in late fracture healing period in osteotomy patients. Serum levels of MMP-13 were below the lowest standards, and therefore quantitative analysis was not possible. Bone regeneration in distraction osteogenesis and rigid osteotomy healing is accompanied by systemic increase of matrix-degrading and angiogenic factors in a certain time course and quantity. This might reflect biochemical regulation of local bone healing in the circulation. ProMMP-1, VEGF and TIMP-1 seem to be key regulatory factors during distraction osteogenesis.

Adult↗