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PubMed2001

Fabrication of porous polymeric matrix drug delivery devices using the selective laser sintering technique.

New techniques in solid freeform fabrication (SFF) have prompted research into methods of manufacturing and controlling porosity. The strategy of this research is to integrate computer aided design (CAD) and the SFF technique of selective laser sintering (SLS) to fabricate porous polymeric matrix drug delivery devices (DDDs). This study focuses on the control of the porosity of a matrix by manipulating the SLS process parameters of laser beam power and scan speed. Methylene blue dye is used as a drug model to infiltrate the matrices via a degassing method; visual inspection of dye penetration into the matrices is carried out. Most notably, the laser power matrices show a two-stage penetration process. The matrices are sectioned along the XZ planes and viewed under scanning electron microscope (SEM). The morphologies of the samples reveal a general increase in channel widths as laser power decreases and scan speed increases. The fractional release profiles of the matrices are determined by allowing the dye to diffuse out in vitro within a controlled environment. The results show that laser power and scan speed matrices deliver the dye for 8-9 days and have an evenly distributed profile. Mercury porosimetry is used to analyse the porosity of the matrices. Laser power matrices show a linear relationship between porosity and variation in parameter values. However, the same relationship for scan speed matrices turns out to be rather inconsistent. Relationships between the SLS parameters and the experimental results are developed using the fractional release rate equation for the infinite slab porous matrix DDD as a basis for correlation.

Computer-Aided Design↗
PubMed1999

Prolongation of heart xenograft survival in a hamster-to-rat model after therapy with a rationally designed immunosuppressive peptide.

BACKGROUND: Modification of the aminoacid sequence of peptides derived from the HLA class I heavy chain in combination with computer rational design resulted in the development of a peptide, RDP1258, with enhanced immunosuppressive activity. METHODS: We evaluated the activity of this peptide, analyzing infiltrate by immunohistology and cytokine transcripts by reverse transcriptase-polymerase chain reaction method, in a hamster-to-rat xenograft model where recipients were treated with cobra venom factor (CVF) and peptide. RESULTS: Although CVF or peptide alone had no effect, a combination of CVF/peptide RDP1258 resulted in a significant prolongation of graft survival (7.9+/-1 vs. 4.5+/-0 and 3.5+/-0 days, P<0.001). This effect was associated with an increased expression of heme oxygenase 1 (HO-1) in spleen, a significant reduced graft infiltrate, and a decrease of tumor necrosis factor-alpha mRNA transcripts (P<0.05) compared with CVF-treated recipients (1.6+/-0.07 vs. 3.3+/-0.3%, P=0.001) on day 3 after transplantation. CONCLUSION: These observations are consistent with the observation that up-regulation of HO-1 results in inhibition of immune effector functions and suggest that the peptide acts, at least partially, through HO-1 regulation.

Animals↗
PubMed2004

CAD/CAM-machining effects on Y-TZP zirconia.

OBJECTIVES: Computer-Aided-Design/Computer-Aided-Manufacturing (CAD/CAM) techniques are gaining importance in fabricating crowns and fixed partial dentures (FPDs) made of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The specific aims of this study were (1) to test the hypothesis that surface flaws and microcracks are induced by the grinding of crowns (2) to analyze the material removal and the grinding-induced surface layer as well as to estimate the crack size caused by machining Y- TZP under conditions simulating the grinding of crowns. METHODS: Y-TZP disks and sectioned cylinders with polished separation planes were used for the analysis of the grinding procedure. While simulating the inner surface grinding of crowns, feed and cutting depth were varied (vw = 100, 75, 50 mm/min; ap = 0.1, 0.06, 0.02 mm). SEM was used for the quantitative assessment of the machined surface. RESULTS: While the crack length is not significantly influenced by the grinding parameters, the type of material removed varied with the cutting depth as well as with the feed. Grinding induced surface flaws and microcracks were detected at the internal top surface of the crowns. Half-cylinders machined under conditions simulating the inner surface grinding of crowns showed crack lengths between 2 and 15 microm. SIGNIFICANCE: Sectioned specimens with polished section planes are suitable for the analysis of the grinding process using the face and peripheral grinding procedure. The inner surface grinding of fixed restorations is the most challenging step of CAM of crowns and FPDs. Most important appeared to be the diamond tool, especially the number and shape of the active diamond grains.

Computer-Aided Design↗
PubMed2004

A new topological descriptors based model for predicting intestinal epithelial transport of drugs in Caco-2 cell culture.

PURPOSE: Quantitative Structure-Permeability Relationships (QSPerR) of the intestinal permeability across the (Caco-2) cells monolayer could be obtained by the application of new molecular descriptors. METHOD: A novel topologic-molecular approach to computer molecular design ( TOMOCOMD-CARDD ) has been used to estimate the intestinal-epithelial transport of drug in Caco-2 cell culture. RESULTS: The Permeability Coefficients in Caco-2 cells (P) for 33 structurally diverse drugs were well described using quadratic indices of the molecular pseudograph's atom adjacency matrix as molecular descriptors. A quantitative model that discriminates the high-absorption compounds from those with moderate-poor absorption was obtained for the training data set, showing a global classification of 87.87%. In addition, two QSPerR models, through a multiple linear regression, were obtained to predict the P [apical to basolateral (AP-->BL) and basolateral to apical (BL-->AP)]. A leave- n -out and leave- one -out cross-validation procedure revealed that the discriminant and regression models respectively, had a good predictability. Furthermore, others 18 drugs were selected as a test set in order to assess the predictive power of the models and the accuracy of the final prediction was similar to achieve for the data set. Besides, the use of both regression models, in a combinative way, is possible to predict the Permeability Directional Ratio (PDR, BL-->AP/AP-->BL) value. The found models were used in virtual screening of drug intestinal permeability and a relationship between calculated P and percentage of human intestinal absorption for several compounds was established. Furthermore, this approximation permits us to obtain a good explanation of the experiment based on the molecular structural features. CONCLUSIONS: These results suggest that the proposed method is able to predict the P values and it proved to be a good tool for studying the oral absorption of drug candidates during the drug development process.

Biological Transport↗
PubMed1998

Optimization of the granulation process for designing tablets.

A computer optimization technique based on surface response methodology was applied to optimize the wet granulation process for designing tablets. Physical properties (mean granule size, granule size distribution, compressibility, granule strength) of a model granule formulation containing ethenzamide were accurately described by a second polynomial equation based on two independent variables (amounts of binder and binder solution). This regression equation also gave a good correlation for three physical properties of tablets (distintegration time, compactibility, compression force variance), but the correlation for tablet hardness and weight variation was poor. These results imply that not only the above physical properties of granules but also the rheological behavior and porous structure of granules are closely related to tablet properties. Using an optimization of five tablet properties using the generalized distance function, the predicted values of the physical properties of both granules and tablets agreed well with experimental values. This agreement indicates that the computer optimization technique is useful for optimizing the granulation process for designing tablets.

Computers↗
PubMed2002

The theoretical design of neutral planar tetracoordinate carbon molecules with C(C)(4) substructures.

Using a new charge-compensation strategy, we designed neutral molecules with perfectly planar C(C)(4)-type tetracoordinate carbon arrangements (ptC) employing DFT computations. These designs, based on the planar preference of methane dications, replace two remote carbons in spiroalkaplanes by borons or two remote hydrogens by BH(3) groups; the two formally anionic boron units which result compensate the formal double positive charge on the central ptC's. The LUMOs correspond to the "wasted" lone pair HOMOs of the alkaplanes. As compared to the latter, pi occupancies on the central carbon are much smaller (less than 0.7e), and the IPs are much larger. The newly predicted compounds utilize all of the electrons more effectively. There are no lone pairs, and the ptC-C bond lengths are ca. 1.50 A. The Wiberg bond index sums of the ptC's are near 3.2, and the boron sums are close to 4.

Journal Article↗
PubMed2002

Dynamic torque and apical forces of ProFile.04 rotary instruments during preparation of curved canals.

AIM: To analyse torque and force generated whilst shaping curved canals using rotary instruments. METHODOLOGY: A specially designed computer-controlled testing platform was used to record events during the shaping of straight and curved canals in plastic blocks and in extracted human teeth using ProFile.04 instruments. Size 40 apical stops were prepared using crown-down, apical preparation and step-back procedures. Maximum torque, apically directed force and the numbers of revolutions were recorded at a resolution of 100 samples s-1. Load causing separation as required by the ISO 3630-1 test and cyclic fatigue was also recorded. Mean maximum scores were calculated and statistically tested using one- and two-way analyses of variance. RESULTS: Highest and lowest torque scores were recorded, respectively, in straight canals in plastic blocks at 25 Nmm and in natural canals at 14 Nmm. Significant differences were recorded for canal type and preparation phase (P < 0.0001). Loads causing separation varied from 3.7 to 32.3 Nmm. Apically directed forces ranged from 1 to 7.5 N. Again, there were significant differences depending on canal type and preparation phase (P < 0.0001). The number of revolutions during preparation ranged from 18 to 41. Size 15, 30 and 45 ProFile.04 instruments separated after 581, 430 and 402 revolutions, respectively, in a standard cyclic fatigue test. CONCLUSIONS: The new torque-testing platform details physical parameters during preparation of curved canals. To improve predictability, instrumentation sequences must be tested for excessively high torsional moments or forces. This study indicated that up to 10 curved canals could be safely prepared with a sequence of ProFile. 04 rotary instruments without separation due to cyclic fatigue. Efforts should continue to correlate root canal anatomy with torque and force generated during rotary root canal preparation.

Analysis of Variance↗
PubMed2003

In vivo fluoroscopic analysis of the normal human knee.

The objective of the current study was to use fluoroscopy and computed tomography to accurately determine the three-dimensional, in vivo, weightbearing kinematics of five normal knees. Three-dimensional computer-aided design models of each subject's femur and tibia were recreated from the three-dimensional computed tomography bone density data. Three-dimensional motions for each subject then were determined for five weightbearing activities. During gait, the lateral condyle experienced -4.3 mm (range, -1.9--10.3 mm) of average motion, whereas the medial condyle moved only -0.9 mm (range, 3.4--5.8 mm). One subject experienced 5.8 mm of medial condyle motion. On average, during deep flexion activities, subjects experienced -12.7 mm (range, 1.4--29.8 mm) of lateral condyle motion, whereas the medial condyle motion only was -2.9 mm (range, 3.0--9.0 mm). One subject experienced 5.8 and 9.0 mm of medial condyle motion during gait and a deep knee bend, respectively leading to the occurrence of a lateral pivot motion. During the deep flexion activities, the subjects experienced significantly more axial rotation (> 13 degrees) than gait (< 5 degrees). During all five activities, the lateral condyle experienced significantly more anteroposterior translation, leading to axial rotation of the tibia relative to the femur.

Biomechanical Phenomena↗
PubMedDate not supplied

An assessment of computer use, knowledge, and attitudes of diabetes educators.

A questionnaire to survey attitudes, use, and knowledge of computers was sent to 816 randomly selected members of AADE to determine the degree to which currently available computer resources are used in diabetes education and to investigate the need for future computing resources designed to support diabetes education. Analysis of the data showed that even diabetes educators who use computers infrequently have a generally favorable attitude toward them. Highest use of computers is in noneducational applications, mostly for word processing and record keeping. Most respondents believe that computers have yet to make a major contribution to the teaching and learning process in diabetes education, and few felt adequately prepared for creative use or development of computer applications. Increasing the role of computers in support of patient education will require encouragement and demonstrations of computer efficacy from health care institutions and professional organizations.

Adult↗
PubMedDate not supplied

[PROCID: a project of the European Community for the study and prevention of muscular disorders in computer terminal operators].

This paper presents an EC funded concerted action aimed at studying the prevention of muscle disorders in the operation of computer input devices. About 40% the today's working population use computers in their daily work. This percentage is expected to increase dramatically in the coming years. At the same time health statistics indicate an increased incidence of work related musculoskeletal disorders among computer users. A deeper knowledge in this field may improve the health risk assessment approach, the design of computer input devices and the revision process of existing standards, norms and guidelines concerning computer work. Specific research objectives include: the development of intramuscular techniques suitable for mapping motor unit recruitment under operation of computer input devices; the evaluation of muscle fatigue and motor unit recruitment in dynamic tasks in normal subjects and in patients with pain syndromes; the experimental evaluation of stress induced muscular tension at the motor unit level, in operation of computer input devices; the formulation of recommendations for work with computer input devices.

Computer Terminals↗
PubMedDate not supplied

Computer assistance in keratoconus lens design.

In the past, keratoconus patients have been custom fit with multi-curve spherical contact lenses. Recently it has become possible to commercially manufacture aspherical contact lenses of high-Dk material. A computer assisted fitting technique may be used with these new lenses. We report 90 consecutive keratoconus eyes that were fit with aspherical high-Dk contact lenses using a computer-aided fitting system. Mild and severe grades of keratoconus cases were included, with a 6 to 12 month follow-up time. The combination of new lens geometry and lens material produced a reduction in corneal complications. The asphericity of the lens geometry had a slight negative influence on the visual acuity in mild keratoconus cases, but the visual acuity in the severe keratoconus cases was good. The contact lens material proved acceptably durable, despite the high oxygen transmissibility. We found the computer assisted fitting technique very accurate in determining the initial fitting lens and much faster than the former trial-and-error procedure.

Contact Lenses↗
PubMed2003

[Commentary about the 16th National Symposium of Medicinal Chemistry Italian Chemical Society--Sorrento, September 18-22, 2002].

The Congress was been structured on four main sections: 1) receptors chemistry; 2) developments in pharmaceutical analysis; 3) computational molecular design; 4) antineoplastic, antiviral, antibacteric and cytostatic agents. In the present review we summarize the more important communications, and we emphasize that all the communications were of a high standard.

Chemistry, Pharmaceutical↗
PubMed2005

A residue-pairwise generalized born scheme suitable for protein design calculations.

We describe an efficient generalized Born (GB) approximation for proteins, in which the interaction energy between two amino acids depends on the whole protein structure, but can be accurately computed from residue-pairwise information. Two results make the scheme pairwise. First, an accurate expression exists for the interaction energy between two residues R and R' that depends on the product B = BRBR' of their residue Born solvation radii. Second, this expression is accurately fitted by a parabolic function of B; the (three) fitting coefficients depend only on the pair RR', not on its environment. In effect, the quantity B captures all the information that is relevant about the pair's dielectric environment. The method is tested with calculations on several hundred structures of the proteins trpcage, BPTI, ubiqutin, and thoredoxin. It yields solvation energies in better agreement with Poisson calculations than a traditional GB formulation. We also compute the effect of the protein/solvent environment on the interactions between pairs of charged residues in the active site of the enzyme aspartyl-tRNA synthetase. Our method captures this effect as accurately as traditional GB. Because it is residue-pairwise, the method can be incorporated into efficient protocols for rotamer placement and computational protein design.

Aspartate-tRNA Ligase↗
PubMed1988

[Computer diagnosis of gastric dysplasia and program design].

Two step processes were taken in computer diagnosis of gastric dysplasia. 1. 5 measurement values of dysplastic glandular tube obtained by using image analysis system were taken as the basis for judging the degree of dysplasia. Three glandular tubes of dysplasia were measured in each case. 2. Computer pathology diagnostic program using BASIC language ran in IBM computer. 5 parameters were input into computer for three stage-diagnosis. The first stage: 5 parameters were counted basing on three models to obtain three values which reflected the objective feature of the same glandular tube from different aspects. The second stage: diagnosis of a dysplastic glandular tube was obtained depending on the three values judged synthetically. Variate 'N' was introduced for controlling the first and second stage diagnosis of the three glandular tubes. The third stage diagnosis started as soon as N = 3. The third stage: diagnostic values of three glandular tubes were balanced and analysed depending on diagnostic criteria to reach the final diagnosis.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Human-computer interface evaluation: not user-friendliness but design for operation.

This paper considers human-computer interface evaluation in the context of design and development. It is argued that it is not helpful to view evaluation as a method for achieving user-friendliness, rather it should be seen as a participating activity within design and development. The centre of concern is the operation of the system when employed in practice. Such evaluation is not necessarily to be conducted by independent observation and experiment, but may be closely integrated with other design activities. In fact the very theory underlying the evaluation finds its embodiment in the artifact of the user interface. Taking this view has technical, as well as human factors, implications.

Decision Making, Computer-Assisted↗
PubMed2002

De novo design of biocatalysts.

The challenging field of de novo enzyme design is beginning to produce exciting results. The application of powerful computational methods to functional protein design has recently succeeded at engineering target activities. In addition, efforts in directed evolution continue to expand the transformations that can be accomplished by existing enzymes. The engineering of completely novel catalytic activity requires traversing inactive sequence space in a fitness landscape, a feat that is better suited to computational design. Optimizing activity, which can include subtle alterations in backbone conformation and protein motion, is better suited to directed evolution, which is highly effective at scaling fitness landscapes towards maxima. Improved rational design efforts coupled with directed evolution should dramatically improve the scope of de novo enzyme design.

Antibodies, Catalytic↗
PubMed2005

Backside wear of polyethylene tibial inserts: mechanism and magnitude of material loss.

BACKGROUND: Wear of the underside of modular tibial inserts (backside wear) in total knee replacements has been reported by several authors. Although, for some implant designs, this phenomenon seems to contribute to osteolysis, the actual volume of material lost through wear of the backside surface has not been quantified. This study describes the results of computerized measurements of tibial inserts of one design known to be associated with a high prevalence of backside wear in situ. METHODS: A series of retrieved total knee components of one design were examined. The duration of implantation of the retrieved components ranged from thirty-six to 146 months. Laser surface profilometry and computer-aided design software were used to develop individual three-dimensional models of each worn, retrieved tibial insert to compare with scanned unused inserts. Volumetric subtraction of both models revealed the material lost because of backside wear. RESULTS: Worn and unworn areas on the backside surface were easily identified by stereomicroscopy and laser profilometry. The computer reconstructions showed that, in all retrievals, all unworn surfaces on the nonarticulating surface lay in one plane. The average volume (and standard deviation) of the material lost because of backside wear was 925 +/- 637 mm(3) (range, 197 to 2720 mm(3)). On the basis of the time in situ for each implant, the average volumetric wear rate was 138 +/- 95 mm(3)/yr. CONCLUSIONS: The predicted volume of material removed because of backside wear is substantial and may be sufficient to induce osteolysis. Our results suggest that peg-like protrusions are not generated by the extrusion of polyethylene into screw-holes within the base-plate but by abrasion of the underside of the bearing insert, leaving the protruding pegs as the only remnants of the original surface.

Aged↗