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3D cell culture engineering
- 1. 3D CELL CULTURE ENGINEERING: Microenvironment directed manipulation and mathematical models By: Naghmeh Poorinmohammad
- 2. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can it help us—microbial biotechnologists? • Summary
- 3. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can it help us—microbial biotechnologists? • Summary
- 4. Why three-dimensional cell cultures? • Growing cells on flat surfaces is artificial and unnatural. • Naturally ECM plays an important role in regulating cellular behaviors by influencing cells with: biochemical signals and topographical cues. • In 3-D cultures, we can control scaffold morphology, architecture and components (haman). • Therefore cells behave and respond more like they would in vivo to stimuli. Blagovic, Katarina, et al. "Engineering cell–cell signaling." Current opinion in biotechnology 24.5 (2013): 940-947.
- 5. Why three-dimensional cell cultures? Lee, Jungwoo, Meghan J. Cuddihy, and Nicholas A. Kotov. "Three-dimensional cell culture matrices: state of the art." Tissue Engineering Part B: Reviews 14.1 (2008): 61-86.
- 6. Why three-dimensional cell cultures? • 2D culture substrates not only fall short of reproducing the complex and dynamic environments of the body, but also are likely to misrepresent findings to some degree by forcing cells to adjust to an artificial flat, rigid surface 1. • These matrices, or scaffolds, are porous substrates that can support cell growth, organization, and differentiation on or within their structure. Architectural and material diversity is much greater on 3D matrices than on 2D substrates 1. • Other than physical properties, chemical/ biochemical modification with specific biological motives to facilitate cell adhesion, cell-mediated proteolytic degradation and growth factor binding and release 2 . [1] Lee, Jungwoo, Meghan J. Cuddihy, and Nicholas A. Kotov. "Three-dimensional cell culture matrices: state of the art." Tissue Engineering Part B: Reviews 14.1 (2008): 61-86. [2] Lienemann, Philipp S., et al. "A Versatile Approach to Engineering Biomolecule‐Presenting Cellular Microenvironments." Advanced healthcare materials 2.2 (2013): 292-296.
- 7. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can it help us—microbial biotechnologists? • Summary
- 8. What is the technology used for? Clinical application in vitro studies Regenerative medicine Drug Discovery process Analysis of cell biology at the molecular level Lee, Jungwoo, Meghan J. Cuddihy, and Nicholas A. Kotov. "Three-dimensional cell culture matrices: state of the art." Tissue Engineering Part B: Reviews 14.1 (2008): 61-86.
- 9. 3D culture engineering to regenerate tissues Adopted from: Tandon, Nina, et al. "Bioreactor engineering of stem cell environments."Biotechnology advances 31.7 (2013): 1020-1031.
- 10. 3D culture engineering to regenerate tissues • In order to induce cell growth in the third dimension and to support tissue development, it is critical to provide mass transport to and from all cells using dynamic culture systems such as bioreactors. • In bioreactors, stirring, perfusion, and dynamic loading have been applied to provide convective transport and allow tissue development on a millimeter to centimeter scale Tandon, Nina, et al. "Bioreactor engineering of stem cell environments."Biotechnology advances 31.7 (2013): 1020-1031. Figure adopted from: http://www.tissuegrowth.com/prod_systems.cfm
- 11. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can it help us—microbial biotechnologists? • Summary
- 12. 1. Matrix elasticity/stiffness CASE STUDY A: • Cells experience a wide range of matrix mechanics, from soft (e.g. brain 0.1 kPa) to stiffer (e.g. precalcified bone 80 kPa) tissues, which direct many aspects of cellular function. az guvendiren • Hydrogel mechanics can be easily controlled by increasing crosslinking density. Engler, Adam J., et al. "Matrix elasticity directs stem cell lineage specification." Cell 126.4 (2006): 677-689.
- 13. Cigognini, Daniela, et al. "Engineering in vitro microenvironments for cell based therapies and drug discovery." Drug discovery today 18.21 (2013): 1099-1108. 1. Matrix elasticity/stiffness
- 14. 2. Mechanical properties Cigognini, Daniela, et al. "Engineering in vitro microenvironments for cell based therapies and drug discovery." Drug discovery today 18.21 (2013): 1099-1108.
- 15. 3. Matrix topology Lee, Jungwoo, Meghan J. Cuddihy, and Nicholas A. Kotov. "Three-dimensional cell culture matrices: state of the art." Tissue Engineering Part B: Reviews 14.1 (2008): 61-86.
- 16. CASE STUDY B: • Neural stem cells (NSCs) are capable of self-renewal and differentiation into three principle central nervous system cell types under specific local microenvironments. 3. Matrix topology Chi-F Chi-MC Chi-PS Wang, Gan, et al. "The effect of topology of chitosan biomaterials on the differentiation and proliferation of neural stem cells." Acta biomaterialia 6.9 (2010): 3630-3639.
- 17. Wang, Gan, et al. "The effect of topology of chitosan biomaterials on the differentiation and proliferation of neural stem cells." Acta biomaterialia 6.9 (2010): 3630-3639.
- 18. 3. Matrix topology Cigognini, Daniela, et al. "Engineering in vitro microenvironments for cell based therapies and drug discovery." Drug discovery today 18.21 (2013): 1099-1108.
- 19. 4. soluble signaling molecules • Natural ECM hosts soluble signaling molecules, including growth factors (GFs). • They play significant roles in tissue development by triggering a wide range of cellular responses. • Therefore, it is important to introduce well-controlled GF presentation into hydrogels to instruct encapsulated stem cell behavior. • Direct encapsulation is the traditional method of GF presentation in hydrogels. • Limitations in this approach (e.g. lack of control over delivery profiles) led to the development of micro/ nano delivery vehicles within hydrogels for GF delivery. Guvendiren, Murat, and Jason A. Burdick. "Engineering synthetic hydrogel microenvironments to instruct stem cells." Current opinion in biotechnology24.5 (2013): 841-846.
- 20. CASE STUDY C: • Amsden and colleagues reported rapid induction and enhancement of chondrogenesis of encapsulated adipose-derived stem cells (ASCs) in chitosan-based hydrogels with coencapsulation of microspheres containing either BMP-6 or TGF-b3 . 4. soluble signaling molecules Guvendiren, Murat, and Jason A. Burdick. "Engineering synthetic hydrogel microenvironments to instruct stem cells." Current opinion in biotechnology24.5 (2013): 841-846.
- 21. 4. soluble signaling molecules Cigognini, Daniela, et al. "Engineering in vitro microenvironments for cell based therapies and drug discovery." Drug discovery today 18.21 (2013): 1099-1108.
- 22. Analytical/Mathematical modeling of 3D cultures bioreactor Supporting 3D scaffold cells The choice of cells concerns mainly their capability to proliferate and the preservation of biological activity The scaffold is not only a physical support for the cells, but it also affects cell metabolism, differentiation, and morphogenesis its function is to provide suitable nutrients and oxygen flow to the cells in the scaffold to ensure their growth and to remove catabolic products
- 23. Analytical/Mathematical modeling of 3D cultures • Mathematical models are very useful in order to better understand the complex chemical, mechanical, and biological factors involved in engineered tissue cultures. • Since many studies have highlighted, especially for osteoblasts, the sensitivity of cell growth to mechanical stress, several studies have been made of fluid dynamics inside the bioreactor. • Botchwey calculated the shear stress inside the construct, describing the velocity with Darcy’s law for porous media. • Critical for fluid dynamic studies is the identification of scaffold geometry. For this purpose, optical methods have been used. Raimondi captured a light microscopy image of a cross section of the construct’s histological sample to generate a computation fluid dynamics (CFD) model and, then, computed the shear stress inside a perfused scaffold. Coletti, Francesco, Sandro Macchietto, and Nicola Elvassore. "Mathematical modeling of three-dimensional cell cultures in perfusion bioreactors." Industrial & engineering chemistry research 45.24 (2006): 8158-8169.
- 24. Analytical/Mathematical modeling of 3D cultures • Cell growth and mass transport are the two major phenomena that affect bioreactor performance. • For this reason, efforts have been made to describe cell growth and the supply of metabolites to the growing cells. • Nehring proposed a reaction/diffusion model in a spherical chondrocytes pellet. • Malda developed a mathematical model for oxygen gradient calculations in a three dimensional polymeric scaffold and compared simulated with experimental data given by a glass microelectrode. • Using the method of volume averaging, Pathi developed a dynamical mathematical model for the growth of haematopoietic cells in a perfusion bioreactor in which the scaffold is placed between two perfusion chambers where the medium flows. • Coletti, Francesco, Sandro Macchietto, and Nicola Elvassore. "Mathematical modeling of three-dimensional cell cultures in perfusion bioreactors." Industrial & engineering chemistry research 45.24 (2006): 8158-8169.
- 25. Analytical/Mathematical modeling of 3D cultures • Various types of bioreactors have been used to culture cells for tissue regeneration or repair. • Recent studies show the importance of perfusion (the forcing of medium flow through the scaffold) in growing a uniform and high-density tissue. • Intlet Outlet Scaffold Coletti, Francesco, Sandro Macchietto, and Nicola Elvassore. "Mathematical modeling of three-dimensional cell cultures in perfusion bioreactors." Industrial & engineering chemistry research 45.24 (2006): 8158-8169.
- 26. Analytical/Mathematical modeling of 3D cultures • Coletti, Francesco, Sandro Macchietto, and Nicola Elvassore. "Mathematical modeling of three-dimensional cell cultures in perfusion bioreactors." Industrial & engineering chemistry research 45.24 (2006): 8158-8169.
- 27. Analytical/Mathematical modeling of 3D cultures Coletti, Francesco, Sandro Macchietto, and Nicola Elvassore. "Mathematical modeling of three-dimensional cell cultures in perfusion bioreactors." Industrial & engineering chemistry research 45.24 (2006): 8158-8169.
- 28. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can we—microbial biotechnologists— involve? • Summary
- 29. How can we involve? • Problem: scaffolds can be colonized by bacteria, and the ensuing infection can have catastrophic consequences. • Solution case study: “Development of bioactive glass based scaffolds for controlled antibiotic release in bone tissue engineering via biodegradable polymer layered coating”. • Our involvement: Antibiotics can affect ell adhesions and differentiation....*. Antimicrobial scaffolds for tissue engineering [*] Xing, Zhi-Cai, et al. "In vitro assessment of antibacterial activity and cytocompatibility of quercetin-containing PLGA nanofibrous scaffolds for tissue engineering." Journal of Nanomaterials 2012 (2012): 1.
- 30. How can we involve? • Appropriate topology for neuroblastoma differentiation generated by using a nanocellulose extracellularly excreted by Gluconacetobacter xylinus. • Case study: “3D Culturing and differentiation of SH-SY5Y neuroblastoma cells on bacterial nanocellulose scaffolds”. • Our involvement: Other potential bacterial products to be used in 3D matrice with optimized geometry for a specific application.... Bacterial nanofibers
- 31. How can we involve? • Problem: Immobilization of microbial cells in membranes and bioreactors provides enhanced catalytic activity and stability, protecting microorganisms from mechanical degradation and deactivation and allowing for an overall intensification of biochemical reactions **. • Pattern and rate of proliferation and function can be depended on the matrix properties which should be studied. Scaffolds with Immobilized Bacteria for 3D Cultures! [**] Gutiérrez, María C., et al. "Hydrogel scaffolds with immobilized bacteria for 3D cultures." Chemistry of materials 19.8 (2007): 1968-1973.
- 32. We are going to talk about... • Why three-dimensional cell cultures? • What is the technology used for? • Factors affecting SC differentiation in 3D cultures • How can we—microbial biotechnologists— involve? • Summary
- 33. Summary • 2D cell cultures differ greatly from natural state of cells in vitro studies are not much reliable. • 3D culture preparation for any application must be comprehensively optimized it is complex • No general mathematical analysis exists. • Researches are still being conducted in tuning the cultures.
- 34. Thank you
Notes de l'éditeur
- PICTURE SOURCES FROM LEFT TO RIGHT: http://www.microtissues.com/three_dimensional_3d_cell_culture_versus_two_dimensional_2d_cell_culture.htm http://www.medgadget.com/2011/05/new_scaffold_for_controlled_threedimensional_cell_culture.html http://nextbigfuture.com/2011/03/nanomembrane-tubes-support-controlled.html http://www.kit.edu/kit/english/pi_2010_790.php
- The ECM is variable in different tissues ECM is tissue-specific. since it does not bear a resemblance to the in vivo architectures where cells flourish at their best. 3-dimensional (3-D) cell culture scaffolds are a better representation of the natural environment experienced by cells in the living organism. Reflecting natural conditions allows for intercellular interactions with more realistic biochemical and physiological responses. The ECM is variable in different tissues ECM is tissue-specific. In the body, nearly all tissue cells reside in an extracellular matrix (ECM) consisting of a complex 3D fibrous meshwork with a wide distribution of fibers and gaps that provide complex biochemical and physical signals.1 az lee2008 internal and external : such as changes in temperature, pH, nutrient absorption, transport, and differentiation. 2-dimensional (2D) surfaces such as micro-well plates, tissue culture flasks, and Petri dishes because of the ease, convenience, and high cell viability of 2D culture. az lee 2008 Significant attention has been given to engineering the soluble microenvironment and adhesive scaffolds that emulate the extracellular matrix (ECM). az blagovic2013
- from lee 2008 Comparison of natural cell and tissue morphology cultured on 2D and 3D substrates. Natural tissues and cells have distinct 3D organized morphological features: histological images of (A) bone and (D) liver,2 and (G) scanning electron microscope image of the thymus.21 When tissue cells are cultured on 2D substrate, they show a similar morphological pattern (stretched). Optical microscope images of (B) osteoblasts, (E) hepatocytes, and (H) co-culture of lymphocytes and stromal cells.21 Cellular morphology becomes closer to that of natural tissue when cultured on 3D matrices; different appearance of (C) osteoblasts,22 (F) hepatocytes,23 and (I) mononuclear cells in a 3D matrix. For example, osteoblasts are located on the surface of bone in a sheet-like arrangement of cuboidal cells, hepatocytes are closely packed together in the liver in hexagonal-shaped lobules, and lymphocytes are individually suspended in circulating blood or lymphatic vessels (Fig. 1).
- Applications of 3D matrices can be divided into clinical and in vitro 3D modeling approaches. Clinical applications mainly consist of tissue engineering or regenerative medicine, which target the creation of a functional implants using artificial 3D matrices.16,17 Scaffolds are designed to be implanted in a patient as a temporary template to restore or maintain original tissue function. Accordingly, scaffolds should not only have proper architecture for supporting cell growth, but should also match the shape of the defect site. Materials should be biodegradable and metabolized in the body without causing serious systemic or immunogenic. lee 2008 use as an in vitro 3D model system. Here, the aim is to facilitate systematic analysis of cell biology at the molecular level that will significantly improve the understanding of tissue physiology and pathophysiology.19,20 For experiments within this application, the 3D matrix should be designed to mimic the 3D organization and the differentiated function of tissues in the body. Three-dimensional matrix accessibility through optical or other imaging tools and processability to precisely control matrix properties are important in this experimental context.
- tandon 2013 In the 1990s, it was proposed that 3D human tissue substitutes could be engineered in vitro by the cultivation of cells on scaffolding materials, which act as temporary biodegradable templates for tissue development, in bioreactor systems providing environmental control and biochemical and biophysical signaling
- tandon 2013 In static cultures, mass transport is based on diffusion, and generally limits tissue development to thicknesses less than 0.2 mm due to drops in oxygen tension and increased concentrations of toxic metabolites In the 1990s, it was proposed that 3D human tissue substitutes could be engineered in vitro by the cultivation of cells on scaffolding materials, which act as temporary biodegradable templates for tissue development, in bioreactor systems providing environmental control and biochemical and biophysical signaling ax : http://www.tissuegrowth.com/prod_systems.cfm site ro bara anave bioreac ha bekhun
- az stiff betartib az chap neurogenic/myogenic/osteogenic
- Mesenchymal stem cells (MSCs) become adipocyte-like, neuron-like, myocyte-like and osteoblast-like when cultured on substrates having elasticity typical of fat, brain, muscle and cross-linked collagen of osteoid, respectively. az cigognini2013 In the field of drug discovery there is increasing evidence that changes in matrix stiffness influence cancer cell behaviour and sensitivity to therapeutic drugs. Cancer progression in soft tissues is typically associated with an increase in ECM rigidity [86,87]. haman
- Examples of how mechanical forces have been applied in cell culture studies and tissue engineering strategies to affect stem cell fate, extracellular matrix (ECM) synthesis, and cell phenotype and proliferation. Abbreviations: MSCs, mesenchymal stem cells. ac cigognini
- Overview of polymer processing techniques for obtaining porous scaffolds. Macro-scale structure of (A) an electrospun fibrous mesh sheet and (B) a poly(lactic-co-glycolic acid) scaffold.160 Micro-scale fibrous structures: (C),161 (D),162 (E),152 and micro-scale sponge-like structures: (F),163 (G),163 (H).147 Nano-scale (I) alginate-based nanofibers164 and (J) surface topology after sodium hydroxide treatment.165 Modification of polymer processing techniques: (K) compartmented scaffold structures,155 (L) nano-fibrous scaffolds,48 and (M) inverted colloidal crystal scaffolds. az lee2008
- wang2010 Chitosan films (Chi-F), chitosan porous scaffolds (Chi-PS) and chitosan multimicrotubule conduits (Chi-MC) were used to investigate their effects on the differentiation and proliferation of NSCs isolated from the cortices of fetal rats. Fig. 1. SEM characterization of three different topological chitosan biomaterials. (a) Chi-F; (b) Chi-PS; (c) cross-section of Chi-MC; (d) longitudinal section of Chi-MC. Scale bar: 100 lm. These observations indicate that chitosan topology can play an important role in regulating differentiation and proliferation of NSCs and raise the possibility of the utilization of chitosan in various structural biomaterials in neural tissue engineering.
- Immunofluorescence analysis of NSCs cultured on three different topological chitosan biomaterials in the presence of 10% FBS for 5 days. (a and b) Cells cultured on Chi-F; (c) cells on Chi-PS; (d) cells on Chi-MC. The differentiated cells were verified using anti-b-tubulin III antibody (red) and anti-GFAP antibody (green), with the nuclei counterstained with DAPI. Scale bars: (a) 100 lm; (b–d) 20 lm.
- The ratio of b-tubulin III-positive cells. Error bars represent means ± SD (n = 3). **P < 0.01.
- SEM images of NSCs cultured on three different topological chitosan biomaterials in the presence of 10% FBS for 5 days. (a and b) Cells cultured on Chi-F; (c and d) cells on Chi-PS; (e and f) cells on Chi-MC. Scale bars: (a, b and d–f) 10 lm; (c) 100 lm. Arrows indicate the cells.
- NSCs cultured on Chi-F in the presence of 10% FBS preferentially differentiated into astrocytes and showed the highest proliferation in serum-free medium in the presence of 20 ng ml1 bFGF. Chi-MC significantly promoted neuronal differentiation and acceptable proliferation. However, Chi-PS did not perform well in either regulation of NSC differentiation The differentiation and proliferation properties of NSCs cultured on Chi-MC might be exploited in the treatment of spinal cord injuries. The utilization of different topological chitosan biomaterials to control NSCs behavior could result in the design of more efficient biomaterials for neural tissue engineering.
- Examples of how topographical cues influence cell behaviour in vitro. Abbreviation: MSCs, mesenchymal stem cells. from cigognini2013
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- az guvendiren In contrast to physical encapsulation techniques, covalent tethering of GFs to the hydrogel provides long-term control over GF availability; however, this approach may affect the activity of GFs due to possible changes in protein conformations or hindrance of active binding sites An alternative approach is to harness endogenous GF activity by mimicking noncovalent interactions of proteoglycans (PGs) and glycosaminoglycans (GAGs) with GFs [53], such as with the covalent or noncovalent incorporation of chondrotin sulfate or heparin sulfates into hydrogels to sequester GFs [54,55]. For instance, the stimulation and sequestering of BMP2 within heparin-functionalized PEG hydrogels promoted hMSC osteogenesis [56]. In some occasions, heparin binding GFs can exhibit direct reversible binding to the hydrogels, such as in alginate hydrogels, enabling sustained and localized release [15,57]. These approaches represent another step toward controlling stem cell signaling with synthetic hydrogels. The effect of the localized release of BMP-6 and TGF-β3 from P(TMC-CL)2-PEG microspheres on the chondrogenic differentiation of the encapsulated ASCs in the RGD-grafted gels was assessed over 28 days. Based on gene and protein expression data, the ASCs were directed towards the chondrogenic lineage more rapidly when induced with BMP-6 and TGF-β3 delivered from the embedded microspheres, as compared to growth factor supplementation in the culture medium. Overall, injectable, in situ gelling N-methacrylate glycol chitosan grafted with a cell adhesive peptide shows great potential for the minimally invasive delivery of ASCs. Further, the localized, controlled co-delivery of BMP-6 and TGF-β3 using microspheres may be a promising alternative to enhance the chondrogenic differentiation of human ASCs. In addition, the biological half-life of most growth factors is short (in the range of minutes), emphasizing the importance of controlled, continuous release within a protective delivery vehicle az suarto2012 disscusiion ash ham bekhun
- az cigognini Routinely, cells are cultured under hyperoxic conditions (21% O2), although physiological conditions in several adult and developing tissues are hypoxic. Considerable effort is ongoing to adjust oxygen levels of cultured cells with the desired tissue engineering application. Examples of how hypoxia influences stem cell fate and matrix production are shown. Abbreviations: ECM, extracellular matrix; MSCs, mesenchymal stem cells; NSCs, neural stem cells; ESCs, embryonic stem cells. Indeed, in vitro and in vivo data convincingly demonstrate that molecular oxygen levels regulate cell behaviour and play a significant part in developmental pro-cesses, such as angiogenesis, haematopoiesis and morphogenesis [91]. Therefore, a considerable research effort has been directed towards optimisation of oxygen supplementation for in vitro engi-neering (Fig. 3) of various tissues [92], including cartilage [93,94], tendon [95], bone [96,97], intervertebral disc [98], nucleus pulpo-sus [99] and heart [100,101]. Recent studies also demonstrate that oxygen tension is of paramount importance in maintaining stem cell niche and stem cell commitment towards a specific lineage [109]. In MSC cultures it has been shown that low oxygen tension (5% O2) retains their undifferentiated and multipotent status [110,111]. Moreover, dif-ferent oxygen concentrations have been employed to stabilise a chondrogenic phenotype or to promote hypertrophy of cartilagi-nous grafts, suggesting a possible application for cartilage repair therapies or endochondral bone repair strategies, respectively [112]. Human ESCs maintain pluripotency at oxygen tensions between 3% and 5%, whereas they spontaneously differentiate when cultured at 21% O2 [113]. This is not surprising considering the relatively oxygen-poor environment in which the mammalian embryo develops.
- Both experiments and quantitative mathematical models are needed to better understand the physical, mechanical, and biochemical phenomena and for the rational design of suitable reactor geometries and operating protocols for the production of functional engineered artificial grafts. az ie051144v Multifactorial and interdisciplinary approaches are likely to make an impact in the years to come and lead to clinically relevant in vitro tissue equivalents, providing suitable analysis systems are developed. cigognini az ie051144v The tissue reconstruction is based on three fundamental components:
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- az ie051144v Schematic representation of a typical perfusion bioreactor: the medium flows directly through the pores of the scaffold (shaded area) transporting oxygen and other substrates to the cells seeded on the pores surface and removing catabolic products.
- az ie051144v Reference geometry and system coordinates for a total perfusion bioreactor. H and R are the scaffold height and radius; L1 and L2 are, respectively, the lengths of inlet and outlet sections. The three domains for the model in section 3, ¿1, ¿2, and ¿3, are indicated. 2.1. Geometry. Figure 3 shows the cross section of a cylindrical bioreactor and gives the reference coordinates and dimensions used in the mathematical representation. The medium fluid is fed from the bottom of the bioreactor by a volumetric peristaltic pump, flows through an empty inlet section, then perfuses the scaffold, and exits from the top through another empty exit section. Since the flow regime inside the empty sections of the bioreactor is different from that inside the scaffold porous medium, the reactor is divided into three distinct subdomains, as indicated in Figure 3: ¥ ¿1 is an empty inlet section of height L1. ¥ ¿2 is a scaffold section of height H. ¥ ¿3 is an empty outlet section of height L2. All sections have radius R. The medium flow is assumed to be laminar at the entrance of the inlet section ¿1 (this assumption is justified later in the paper). The scaffold is characterized in terms of the usual properties of a porous medium (porosity, tortuosity, void fraction, and permeability). The scaffold void is saturated by the fluid medium that is assumed to be monophase. In this work, we consider in particular a scaffold made of collagen sponges.
- The mass transport within EBs has been measured experimentally128 and modeled mathematically165 as a function of the EB size (radius), ECM composition, cell packing density and molecular uptake rate. az kinney 2014 az ie051144v Interacting phenomena in a perfusion bioreactor. In this network diagram, each arrow corresponds to a mathematical equation or equation set: line A to eqs 2, 3, 18, and 19; line B to eqs 1 and 14; line C to eq 25; line D to eq 27; line E to eq 29; line F to eq 30; line G to eq 31; line H to eq 32; line I to eq 26; line J to eq 27. Living cells are complex systems, and a complete model should include their metabolism, growth, and death mechanisms in addition to other age-dependent aspects.
- In addition, hydrochloride tetracycline loaded in either alginate or gelatin coatings was released rapidly at the initial stage (∼1 h), while the released rate subsequently decreased and was sustained for 14 days in phosphate buffered saline. Therefore, these layered polymer coated scaffolds exhibit attractivecharacteristics in terms of improved mechanical properties and controlled drug release, simultaneously with the added advantage that the drug release rate is decoupled from the intrinsic scaffold Bioglass degradation mechanism. The layered polymer coated scaffolds are of interest for drug-delivery enhanced bone regeneration applications. case study Two types of bacteria strains, Staphylococcus aureus (SA) and Klebsiella pneumoniae (KP), were used to evaluate the antibacterial properties of the scaff. our involve az In vitro assessment of antibacterial activity and cytocompatibility of quercetin-containing PLGA nanofibrous scaffolds for tissue engineering
- BNC is extracellularly excreted by Gluconacetobacter xylinus (G. xylinus) in the shape of long non-aggregated nanofibrils. The cellulose network created by G. xylinus has good mechanical properties, 99% water content, and the ability to be shaped into 3D structures by culturing in different molds. Read More: http://informahealthcare.com/doi/abs/10.3109/21691401.2013.821410 This 3D model based on BNC scaffolds could possibly be used for developing in vitro disease models, when combined with human induced pluripotent stem (iPS) cells (derived from diseased patients) for detailed investigations of neurodegenerative disease mechanisms and in the search for new therapeutics. Read More: http://informahealthcare.com/doi/abs/10.3109/21691401.2013.821410
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