1,720,984 research outputs found
The impact of fabrication parameters and substrate stiffness in direct writing of living constructs.
No full textBiomolecules and living cells can be printed in high-resolution patterns to fabricate living constructs for tissue engineering. To evaluate the impact of processing cells with rapid prototyping (RP) methods we modelled the printing phase of two RP systems that employ biomaterial inks containing living cells: a high-resolution inkjet system (BioJet) and a lower resolution nozzle based contact printing system (PAM(2) ). In the first fabrication method, we reasoned that cell damage occurs principally during drop collision on the printing surface, in the second we hypothesise that shear stresses act on cells during extrusion (within the printing nozzle). The two cases were modelled changing the printing conditions: biomaterial substrate stiffness and volumetric flow rate, respectively in BioJet and PAM(2) . Results show that during inkjet printing impact energies of about 10(-8) J are transmitted to cells, while extrusion energies of the order of 10(-11) J are exerted in direct printing. Viability tests of printed cells can be related to those numerical simulations, suggesting a threshold energy of 10(-9) J to avoid permanent cell damage. To obtain well-defined living constructs, a combination of these methods is proposed for the fabrication of scaffolds with controlled 3D architecture and spatial distribution of biomolecules and cell
Riboflavin and collagen: New crosslinking methods to tailor the stiffness of hydrogels
No full textFabricating materials with tailored mechanical properties is a challenge and crucial for their successful application in a variety of fields such as tissue engineering. Here collagen and riboflavin were used to create hydrogels with controlled mechanical properties mimicking those of soft tissues (e.g. liver). Collagen-based hydrogels were obtained using a two-step gelation method. Firstly a physical gelation step (i.e. modulation of temperature and pH) was used to fix a specific shape; then photo-initiated cross-links were formed to increase the stiffness. Specifically the chemical cross-linking step was initiated with UV (ultra-violet) radiation to obtain riboflavin derivatised radical polymerization of collagen chains. Cylindrical shaped samples with controlled dimensions were fabricated, and then tested using compressive loading. We show that the compressive elastic modulus of collagen-based hydrogels can be tuned between 0.9 and 3.6 kPa by changing collagen concentration, irradiation with UV in the presence of riboflavin and freeze-drying
Rapid Prototyping Composite and Complex Scaffolds with PAM(2).
No full textTo create composite synthetic scaffolds with the same degree of complexity and multilevel organization as biological tissue, we need to integrate multilevel biomaterial processing in rapid prototyping systems. The scaffolds then encompass the entire range of properties, which characterize biological tissue. A multilevel microfabrication system, PAM(2), has been developed to address this gap in material processing. It is equipped with different modules, each covering a range of material properties and spatial resolutions. Together, the modules in PAM(2) can be used to realize complex and composite scaffolds for tissue engineering, bringing us a step closer to real clinical applications. This chapter describes the PAM(2) system and discusses some of the practical issues associated with scaffold microfabrication and biomaterial processing
PAM2 System: a Modular Approach for the Realisation of Complex Shaped Scaffold Able to Reproduce the Main Features of a Specific Micro-environment,
No full textA phase diagram for microfabrication of geometrically controlled hydrogel scaffolds.
No full textHydrogels are considered as excellent candidates for tissue substitutes by virtue of their high water content and biphasic nature. However, the fact that they are soft, wet and floppy renders them difficult to process and use as custom-designed scaffolds. To address this problem alginate hydrogels were modeled and characterized by measuring stress-strain and creep behavior as well as viscosity as a function of sodium alginate concentration, cross-linking time and calcium ion concentration. The gels were then microfabricated into scaffolds using the pressure-assisted microsyringe. The mechanical and viscous characteristics were used to generate a processing window in the form of a phase diagram which describes the fidelity of the scaffolds as a function of the material and machine parameters. The approach can be applied to a variety of microfabrication methods and biomaterials in order to design well-controlled custom scaffolds
A microfluidic gradient maker for toxicity testing of bupivacaine and lidocaine
No full textA great deal of effort is being dedicated to the development of new devices able to conduct effective in vitro toxicology analyses, This paper describes the use of a microfluidic gradient maker for the toxicological analysis of two conventional local anesthetics, bupivacaine and lidocaine on cell cultures The. microfluidic device was designed and simulated using COMSOL Multiphysics (R) and the concentration gradient in the microfluidic network was analysed through a fluidodynamic and diffusive Study
PAM2 (Piston Assisted Microsyringe): A New Rapid Prototyping Technique for Biofabrication of Cell Incorporated Scaffolds
No full textRapid prototyping techniques are widely used to fabricate well-defined three-dimensional structures of tissue homologs. The piston-assisted microsyringe (PAM2) is a rapid prototyping technology specifically developed for low-shear stress extrusion of viscous hydrogel solutions containing cells. In this article the working parameters of the system were established to guarantee the realization of spatially controlled hydrogel scaffolds. Moreover the shear stresses acting on the cell membrane during extrusion was investigated through a computational fluid-dynamic analysis. The computational models show that the shear stress on the cells is of the order of 100 Pa during the extrusion process. HepG2 cells encapsulated in alginate were then extruded into spatially organized hepatic lobule-like architectures and their viability and function were evaluated. The results show that the metabolic fingerprint of the cells is preserved with respect to controls and the cells are uniformly distributed through the gel scaffold
Functionally Graded Materials (FGMs) with Predictable and Controlled Gradient Profiles: Computational Modelling and Realisation
No full textBiological function is intricately linked with structure. Many bio- logical structures are characterised by functional spatially distributed gradients in which each layer has one or more specific functions to perform. Reproducing such structures is challenging, and usually an experimental trial-and-error approach is used. In this paper we investigate how the gravitational sedimentation of discrete solid particles (secondary phase) within a primary fluid phase with a time-varying dynamic viscosity can be used for the realisation of stable and reproducible con- tinuous functionally graded materials (FGMs). Computational models were used to simulate the distribution of a particle phase in a fluid domain. Firstly a model of particle sedimentation was implemented in order to predict the particle gradient profiles. Then the fluid domain was modelled as phase with time dependent viscos- ity. Experiments were then used to validate the computational results. The models show that selected composition gradients can be tailored by controlling fluid and particle properties. Using this method the gradient of a custom two-phase system can be designed and tailored in a simple fashion. Moreover this approach can also be employed for the fabrication of porous structures, using a porogen as settling particle. The method is particularly useful in tissue engineering applications, to first predict and then control biomaterial gradients without the use of complicated rapid prototyping or computer aided manufacturing systems
Sphyga: a multiparameter open source tool for fabricating smart and tunable hydrogel microbeads.
No full textHydrogel microbeads are used in many biological applications, particularly for cell, protein or drug encapsulation. Although there are several methods for fabricating microbeads with controlled shapes and dimensions, many are limited to a small range of materials or sizes. We describe a compact open source tool-the spherical hydrogel generator (Sphyga)-for the fabrication of highly reproducible hydrogel based microbeads with predictable shapes and diameters ranging from 100 to 2000 µm. The unique feature of the system is the ability to modulate multiple parameters independently, so as to create a wide range of working conditions for fabricating tailored microbeads. Hence, by combining the different fabrication parameters, hydrogel beads with chosen shapes, sizes and materials can be generated with Sphyga. A multiparameter working-window was obtained by fixing the concentration of the base material, alginate, and varying the viscosity of the solution along with Sphyga's fabrication parameters (needle size, external air pressure, and material outflow). To validate the multiparameter working window, components such as proteins, cells, dyes and nanoparticles were also used to fabricate composite microbeads. The results show that the architecture of hydrogel microbeads can be engineered by considering the viscosity of the initial solution, which depends principally on the pH and composition of alginate solution. Coupled with Sphyga's multiple working parameters, material viscosity can then be used to tune hydrogel domains and thereby generate complex biologically relevant microenvironments for many biomedical applications
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