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Fabrication of 3D chitosan-hydroxyapatite scaffolds using a robotic dispensing system

Materials Science and engineering C 2002年第1-2期20卷 35-42页

作者： Ang, T.H. Sultana, F.S.A. Hutmacher, D.W. Wong, Y.S. Fuh, J.Y.H. Mo, X.M. Loh, H.T. Burdet, E. Teoh, S.H. Tissue Engineering Group National University of Singapore 10 Kent Ridge Crescent Singapore 119260 Singapore Division of Bioengineering Department of Mechanical Engineering National University of Singapore 10 Kent Ridge Crescent Singapore 119260 Singapore Laboratory for Concurrent Engineering and Logistics Department of Mechanical Engineering National University of Singapore 10 Kent Ridge Crescent Singapore 119260 Singapore Control and Mechatronics Laboratory Department of Mechanical Engineering National University of Singapore 10 Kent Ridge Crescent Singapore 119260 Singapore

A new robotic desktop rapid prototyping (RP) system was designed to fabricate scaffolds for tissue engineering applications. The experimental setup consists of a computer-guided desktop robot and a one-component pneumatic dispenser. The dispensing material (chitosan and chitosan-hydroxyapatite (HA) dissolved in acetic acid) was stored in a 30-ml barrel and forced out through a small Teflonlined nozzle into a dispensing medium (sodium hydroxide-ethanol in ratio of 7:3). Layer-by-layer, the chitosan was fabricated with a preprogramed lay-down pattern. Neutralization of the chitosan forms a gel-like precipitate, and the hydrostatic pressure in the sodium hydroxide (NaOH) solution keeps the cuboid scaffold in shape. Comparison of the freeze-dried scaffold to the wet one showed linear and volumetric shrinkage of about 31% and 62%, respectively. A good attachment between layers allowed the chitosan matrix to form a fully interconnected channel architecture. Results of in vitro cell culture studies revealed the scaffold biocompatibility. The results of this preliminary study using the rapid prototyping robotic dispensing (RPBOD) system demonstrated its potential in fabricating three-dimensional (3D) scaffolds with regular and reproducible macropore architecture. © 2002 Elsevier Science B.V. All rights reserved.

关键词： Hydroxyapatite

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Asymptotic Stabilization of Single-Input Linear Systems Having Unknown but Bounded Parameters

Asymptotic Stabilization of Single-Input Linear Systems Havi...

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American control Conference (ACC)

作者： Kehui Wei Concurrent Control Engineering Group Institute for Flight Systems Dynamics German Aerospace Research Establishment (DLR) Oberpfaffenhofen Germany

This paper investigates the stabilization problem of single-input linear uncertain systems via constant state feedback control. The systems under consideration contain time-invariant uncertain parameters whose values are unknown but bounded in given compact sets and are thus called interval systems. The criterion for the asymptotic stability of the closed-loop system (obtained when a state feedback control is applied) is that all the eigenvalues of the resulting system matrix are in the strict left half of the complex plane. First, we show that to insure an interval system stabilizable, some entries of the system matrices must be sign invariant. More precisely, the number of the least-required sign-invariant entries in system matrices is equal to the system order. Then, we study the stabilizability of a set of interval systems called standard systems which contain sufficient numbers of sign-invariant entries in proper locations. After dividing all standard systems into some subsets by the uncertainty locations, we then derive necessary and sufficient conditions under which every system in a subset is stabilizable, regardless of its parameter varying bounds. The conditions show that all uncertain entries in system matrices should form a particular geometrical pattern called a "generalized antisymmnetric stepwise configuration". The result is further generalized for unstandard systems via linear transformation.

关键词： Linear systems Uncertain systems Robustness Uncertainty control system synthesis Robust stability control systems State feedback Sufficient conditions Stability criteria

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Solvability of a transcendental problem in system theory

Solvability of a transcendental problem in system theory

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IEEE Conference on Decision and control

作者： K. Wei Concurrent Control Engineering Group Institute of Flight Systems Dynamics German Aerospace Research Establishment (DLR) Oberpfaffenhofen Germany

The author gives a complete solution for a special transcendental problem in system theory: given three polynomials F/sub 1/(s), F/sub 2/(s), and F/sub 3/(s), when do there exist two Hurwitz polynomials H/sub 1/(s), H/sub 2/(s) and one polynomial H'/sub 3/(s) having no real roots in the closed right half of the complex plane such that F/sub 1/(s) H/sub 1/(s)+F/sub 2/(s) H/sub 2/(s)+F/sub 3/(s) H'/sub 3/(s)=0? It is found that the solvability of the transcendental problem depends solely on the real unstable roots of the three given polynomials. More precisely, those roots must have a special interlacing property called the strong interlacing property, which is introduced. For a triplet of polynomials having the strong interlacing property, a computation procedure for solving the problem is provided and illustrated via an example.< >

关键词： Polynomials Poles and zeros Sufficient conditions Frequency control engineering Aerodynamics Aerospace control Aerospace engineering MIMO Design methodology

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A_Flextool: A concurrent control engineering Tool for control Analysis and Design of ‘Active Structures’

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IFAC Proceedings Volumes 1991年第4期24卷 141-146页

作者： J. Bals G. Grübel DLR German Aerospace Research Establishment Laboratory for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Concurrent Control Engineering Group Laboratory for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany

A structural dynamics and control engineering integration of data and computational procedures for analysis and design of active flexible structures is discussed. The interactive computational and database software environment, called A FLEXTOOL, serves for structural-model handling, sensor/actuator positioning and control oriented finite-element model-order reduction. Via the open module concept of the engineering database system a close interplay of A_FLEXTOOL and the general control analysis and optimization based design packages A_RASP and A_MOPS is possible This concurrent control engineering software environment is used to investigate ‘control-structure interaction’ for a generic flexible structure.

关键词： concurrent engineering flexible structures computer-integrated control engineering database concept of control analysis design control model-handling

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control engineering Data Structures for concurrent engineering

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IFAC Proceedings Volumes 1991年第4期24卷 107-112页

作者： H.-D. Joos M. Otter G. Grübel DLR German Aerospace Research Establishment Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Concurrent Control Engineering Group Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany

concurrent control engineering aims at multidisciplinary integration of control engineering methods with the data and procedures of complementary engineering disciplines in view of holistic system optimization. This implies an intradisciplinary abstraction of relevant control engineering data structures as well as an interdisciplinary export of control engineering data objects. We show how control engineering datatypes can be specified and realized in this view using the class-concept and especially the inheritance mechanism of object-oriented data models. The control engi-neering datatypes to be considered are: general nonlinear dynamic systems, time-invariant state space linear systems, transfer matrices, real functions such as time functions, and complex functions such as frequency response. Feasible operations on these datatypes are: listing or graphical visualization, connection of objects within a class, transformation within a class, transformation into another class, and generation of partial objects.

关键词： concurrent engineering engineering Data Structures Object-oriented Data Models Object-oriented Database control engineering Datatypes

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How to Tie the Man-Machine Dialog to a Project-Data Structure in concurrent control engineering

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IFAC Proceedings Volumes 1991年第4期24卷 129-133页

作者： N. Gaus G. Grübel DLR German Aerospace Research Establishment Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Concurrent Control Engineering Group Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany

concurrent control engineering aims at optimization of active systems within multidis-ciplinary projects. This poses additional problems of engineering data management with respect to intelligible data structuring, consistent data interpretation and recoverable data recording. In order to tie the engineering data produced by any program user to a standard database structure, a common basic dialog-and data handling logic has to be adopted. To enforce this, the paradigm of a ‘dialog gen-erator’ is explored: If the program developer specifies a suitable database structure, a dialog generator yields executable code for a dialog skeleton with the appropriate dialog logic. This dialog environment can be realized both by a menue question-and-anwer and a user-command interface. In turn, if the user activates this dialog environment, the predefined data base structure evolves automatically which yields a standardized view on the individually produced engineering data.

关键词： concurrent engineering Dialog-Generator Man-Machine Dialog Project Database

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A_Integral - A Graphical Problem Editor for control Systems and Multibody Dynamics Modelling in a concurrent control engineering Environment

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IFAC Proceedings Volumes 1991年第4期24卷 135-139页

作者： G. Grübel H. Stahl Concurrent Control Engineering Group DLR German Aerospace Research Establishment Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Linssen & Beese Moosstrasse 12 D-8031 Starnberg Germany

A_InteGral 2 is an active graphical problem editor with state-of-the-art graphic features for interactive dynamics modelling. It provides a common user interface for developing and handling ‘white-box models’, ‘grey-box models’, and ‘black-box models’, while working on the ANDECS ®3 ‘model bus’, which is a unified modular FORTRAN 77 interface between various modelling environments and standardized (nonlinear-) system analysis modules like dynamic simulation by use of differential (-algebraic) equation solvers for event-driven variable-structure systems, equilibrium point determination, and linearization.

关键词： concurrent engineering control Modelling Multibody Systems Simulation Code Generation

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A ‘Parallel Coordinate’ Editor as a Visual Decision aid in a Multi-Objective concurrent control engineering Environment

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IFAC Proceedings Volumes 1991年第4期24卷 119-123页

作者： R. Finsterwalder G. Grübel DLR German Aerospace Research Establishment Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Concurrent Control Engineering Group Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany

A search-based multi-objective analysis and design approach is a base-line prerequisite for concurrent control engineering; e.g. a multi-disciplinary integration of control engineering methods with the data and procedures of complementary engineering disciplines in view of holistic system optimization. Search-based multi-objective analysis and design is iterative by nature and it requires decision inter-action based on trade-off analysis. Trade-off analysis involves detection of multivariate relations in multidimensional data. Multidimensional data, say of 5, 6 or higher dimensions, can be visualized by ‘parallel coordinates’. An interactive editor for parallel coordinates is implemented in a database environment to allow a designer to analyze previous design steps and thereby providing him with a decision support for possible changes in his search direction. The parallel-coordinate editor supports an interactive reduction of the dimensionality of data, selecting subsets of data, scanning data in arbitrary directions, etc. This development is along the lines of the currently evolving research area of ‘Algorithm Animation‘. Since the parallel coordinate editor is not bound to data produced by a special algorithm, it can be used for actively exploring the dynamic behavior of any computational procedure. This makes it well suited for the visual decision support of an iterative and interactive search-based design process.

关键词： Parallel Coordinates Multivariate Data Relations Multidimensional Data Visualization Visual Decision Support Algorithm Animation

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Automatic Evolution of a Decision-Supporting Design Project Database in concurrent control engineering

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IFAC Proceedings Volumes 1991年第4期24卷 113-117页

作者： H.-D. Joos G. Grübel DLR German Aerospace Research Establishment Laboratory for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany Concurrent Control Engineering Group Laboratory for Flight Systems Dynamics D-8031 Oberpfaffenhofen Germany

concurrent control engineering aims at multidisciplinary integration of control engineering methods with the data and procedures of complementary engineering disci-plines in view of holistic system optimization This necessitates an iterative and interactive multi-objective search-based design approach its take care of the variety of analysis and design objectives both of a control specific and a multidisciplinary nature. However, the complexity of a multi-objective design process grows with project time as a function of the variability of design decisions and the quantity of design data to be analysed. This requires a top-down design systematic as a framework for explicit decision support and problem decomposition. Such a framework is developed. It leads to a hierarchical database structure where the decision strata of modelling, criteria formulation, and design parameter specification, correspond to the hierarchical strata of a database. Furthermore, a search-based design must allow backtracking and branching of the decision process. This requires a design database with easily recoverable design informations. Specific database management modules are realized within ANDECS_MOPS 2 ) for a com-puterized evolution of such a database as design proceeds. It allows the comparison of any design outcomes at any time (backtracking) and thereby supports the designer in design assessment over an entire design project The automatic recoverability of all necessary decision-and analysis data to restart a new design direction from an earlier design stage allows systematic design branching as well.

关键词： Computer-aided design concurrent engineering multiobjective optimization data structures database management systems decision support

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Dynamic Simulation in concurrent control engineering

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IFAC Proceedings Volumes 1991年第4期24卷 125-128页

作者： N. Gaus M. Otter G. Grubel DLR German Aerospace Research Establishment. Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen. Germany Concurrent Control Engineering Group Institute for Flight Systems Dynamics D-8031 Oberpfaffenhofen. Germany

concurrent control engineering aims at multidisciplinary integration of control engineering methods with the data and procedures of complementary engineering disciplines in view of holistic system optimization. The basic view must be that of an engineering data-and methodbase with an application dependent configurability of functional analysis and synthesis modules, open to the modelling methodologies of different engineering disciplines. In this view, dynamic (time-) simulation, although a key interdisciplinary analysis tool, is just one functional module among others. If based on the features of a general-purpose engineering database system, however, an “open” simulation module is of wider applicability than a selfcontained “closed” simulation package. We describe the features of our simulation module DSSIM. This simulation module operates on blocks which can also refer to a data structure on an engineering database. A block is defined by a set of FORTRAN subroutines. It describes a subclass of systems described by general nonlinear differentialalgebraic equations, as for instance linear state space control systems or nonlinear multibody mechan-ical systems. Any number of models can be kept in the loaded program module which allows online switching between design alternatives or system representations of different complexity. Also the numerics interface is specifically designed to make best use of the features of modern ODE and DAE solvers.

关键词： concurrent engineering Simulation Modelling engineering Database CAE

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