Indeed, uniaxially constrained collagen gel without cells also become anisotropic. This surprising result could be explained by the force generated by collagen polymerisation [ 38 ]. They also developed a mathematical model to predict anisotropy in fibroblast-populated collagen gels [ 39 ]. They found that mechanical anisotropy could not be explained solely by collagen fibers alignment, but also take into account the redistribution of collagen fibers upon remodeling, nonaffine fiber kinematics [ 40 , 41 ] and fiber lengths.
They constrained fibroblast-containing collagen gels with different shapes square, triangle and circle and liberated one or more of the edges to create anisotropy into the gel. Contrasting with a previous report of Klebe et al. Nevertheless, on the basis of the results obtained in their study, Costa et al. An interesting result was obtained with the round shape constrain.
As expected, no alignment were present when gel was uniformly constrained, but when they cut a central hole in the construct, the gel contracted away from the central hole and cells aligned in the circumferential orientation. This result is consistent with previous results obtained in blood vessel reconstruction in which a collagen gel is contracting around a central mandrel causing circumferential cell alignment [ 34 ]. Grinnell and Lamke [ 44 ] cultured fibroblasts on hydrated collagen lattices. They found that cells reorganized the network and aligned the collagen fibrils in the plane of cell spreading, becoming more densely packed.
They noted that the lattice has thinned to one-tenth of its original thickness. Weinberg and bell [ 45 ] used collagen gel seeded with bovine cells to produce the first tissue-engineered blood vessel. This weak construct was supported by a Dacron mesh in order to sustain physiological pressure. This method was improved later by other groups to enhance mechanical properties of the collagen gel to get rid of the synthetic material, but those constructs were still too weak to be implanted.
The anisotropic strain generated by the mandrel constraining gel compaction, combined to a manual detachment of the gel adhesion to the mandrel, caused a progressive circumferential alignment of the SMC. The same process was repeated to produce the adventitia, using human dermal fibroblast embedded in collagen gel and casted around the media layer. Contrasting with the result obtained with the SMC media layer, fibroblasts of the adventitial layer did not get self-oriented. This type of construct was still too weak to be implanted. This paper also showed that gel compaction speed is influenced by initial cell seeding concentration in the construct.
Collagen gel has also been used to engineered intervertebral disc. The highly organized annulus fibrosus which present a cell and matrix alignment, is contrasting with the nucleus pulposus showing random organization. Interestingly, cells kept their capacities to become organized or not when cultured in vitro and seeded into collagen gel constructs. Robert Tranquillo published several papers using collagen gel, mostly on engineered vascular constructs.
Some of his work was done using magnetic alignment of fibers, it will be discussed in the following section. In , they [ 46 ] described mathematical theories to understand the complex coupling of cell and matrix deformation in collagen gel populated with cells. Thus, alignment of cells in collagen gel was one of the first cell alignment method applied to tissue engineering. It is easy to perform, relatively inexpensive and gives interesting results for specific applications.
Summary Alignment Is Not Just for Wheels - Science And Art of It-business Alignment - Study Smart
On the other hand, collagen gel do not show mechanical properties sufficient for load bearing application such as bone, cartilage, ligament and blood vessels, at least if it is used alone. We are always in contact with EMF, either coming from the earth, high voltage lines or mobile phones [ 47 , 48 ]. It is still unclear whether EMF are linked or not to health problems such as cancer, but this hypothesis seems unlikely in most cases [ 49 ]. Even if mobile phone usage is probably not linked with brain cancer, the capability of EMF to influence cells and extracellular matrix are clearly demonstrated [ 50 - 55 ].
It is therefore crucial to investigate this relation to first prevent potential deleterious exposure that might lead to health problem and second, to understand mechanisms and eventually develop novel medical therapies [ 56 - 58 ] as well as tissue engineering applications [ 59 - 63 ]. When exposed to a strong EMF, collagen, as well as other biomolecules such as fibrin, will align perpendicularly to the field. This phenomenon is caused by the negative diamagnetic anisotropy of the collagen molecules [ 64 ].
This property causes the polymerisation process to take place in a particular orientation. Tissue engineers have used this property to produce alignment of ECM scaffolds and cells in different reconstructed tissues. EMF was also shown to induce orientation of cells, including epithelial cells [ 65 - 67 ], fibroblasts [ 65 , 68 ], erythrocytes [ 69 ] and osteoblasts [ 61 , 70 ].
The tendency of biomolecules to align in an EMF has been demonstrated more than 30 years ago, but tissue engineering applications have arisen more recently. Strong EMF were proposed as a method to align fibrin polymer by Torbet et al. They reported that polymerisation of fibrin gels under a strong EMF resulted in oriented fibrin polymerisation. They also speculate right when proposing that this technique could be extended to other polymers and to living cells as it was done afterward. Twenty-six years later, the same researcher [ 72 , 73 ] used EMF to align collagen fibers, in order to replicate the physiologic structure of the corneal stroma.
This structure possesses a particular arrangement of aligned collagen fibers that cross each other orthogonally. When corneal fibroblasts, or keratocytes, are seeded in the construct, they align themselves by contact guidance in the local orientation of the scaffold. This technique was used to produce a hemi-cornea, composed of the stroma and the epithelial layer and showed promising results when grafted on an animal model [ 62 ]. Even if this represents a significant advance in corneal tissue engineering, the resulting corneal stroma substitute presents a slightly different geometry than native cornea.
In a non-pathological cornea, the arrangement of orthogonal lamellas within the stroma consist of a mesh of orthogonal collagen lamellas that are woven together in multilayer. This arrangement provides the cornea with a strong mechanical resistance while remaining a transparent structure [ 74 - 77 ]. Reproducing this geometry over the normal thickness of the stroma seems quite difficult using this layer-by-layer technique.
Kotani et al [ 70 ] studied the effect of EMF on bone formation and orientation. They have shown that, when exposed to a strong EMF of 8 T, osteoblasts oriented parallel to the field. In contrast, when osteoblasts and collagen are mix together, the alignment of both constituents is perpendicular to the field, as for collagen alone. This supposed that contact guidance is a stronger inducer of cell alignment than EMF.
Two years later, [ 61 ] they showed that exposure of mouse osteoblasts to a strong EMF improved differentiation and matrix synthesis in vitro. They also demonstrated that ectopic bone formation in vivo is stimulated by EMF. When pellets of collagen 1. Robert Tranquillo used EMF as a method to align cells and ECM in tissue-engineered constructs [ 59 , 63 , 78 , 79 ], with a particular focus on media substitutes. In , Guido et al. This method used time-lapse image analysis and live automated birefringence measurements to quantify this phenomenon. Compaction of the gel around a central mandrel by SMCs induced a circumferential alignment of cells and collagen fibers, as demonstrated previously [ 34 ].
Magnetic circumferential alignment was performed prior gel compaction to produce prealigned gels. When those gels were allowed to contract freely, the circumferential alignment was lost, but when a mandrel was present, the alignment was better than with EMF alone. This method can also be used to guide neurite outgrowth of neural cells. When fibers were aligned, neurite outgrowths were stimulated and could therefore grow longer than random aligned controls. Retrospectively, this method is effective for biological scaffold such as collagen and fibrin, but to our knowledge, alignment of synthetic materials such as poly glycolic acid PGA or poly D,L-lactide-co-glycolide PLGA has not been performed yet.
Alignment is not just for wheels - Science and Art of IT-Business Alignment
This technique requires a special apparatus capable of generating a strong EMF. Cell viability does not seem to be affected by EMF, allowing for a uniform cell distribution in the construct. Electrospinning of nanofibers is an interesting approach to produce scaffold for tissue engineering [ 83 - 89 ]. This technique can be used to produce aligned scaffold that will dictate cell elongation by contact guidance [ 90 ].
The process of producing polymer microfiber using electrostatic forces was patented in by Formhals [ 91 ] but tissue engineering applications such as musculoskeletal [ 92 ] and vascular [ 93 ] has been developed recently. Electrospinning can be performed with simple setup consisting of a syringe pump, a high voltage source, and a rotating collector [ 85 ]. Precise description of the different possible setups and techniques have been reviewed in details previously [ 94 ]. Briefly, a polymer solution is hanging at the tip of a syringe needle by surface tension. When an electric current is applied, EMF results in charge repulsion within the polymer solution, causing the initiation of a jet.
Solvent evaporate while jet is traveling, resulting in polymerisation into fibers, which are captured by a collector [ 94 ]. It is also possible to create composite scaffolds by spinning different polymer solution either together or consecutively on the same target.
Due to the great plasticity of the technique, it is simple to engineer different patterns to guide cell fate in the desired direction. In order to do so, a rotating mandrel can be used to collect the fiber, resulting in aligned nanofibers [ ]. Schematization of an electrospinning setup. The polymer solution is positively charged while the rotating mandrel is negative.
The solution is pushed through the nozzle at constant speed. The solvent evaporates while the jet is travelling, resulting in fibers formation. Fiber alignment capability was not influenced by nano-HA concentration. Influences were also seen in degradation rate and storage modulus. In order to show cell compatibility, a collagen component was added to the PLGA They used a nanofibrous mesh of PCL collected at zero, 3, and 6, rpm for bone tissue engineering.
When the collector rotation speed is increased, more aligned fibers were produced. This resulted in a modification of the morphology and mechanical properties of individual fibers and of the resulting scaffold. Ultimate tensile strength of the scaffold in the axis of alignment rises from 2. This result could be explained by increasing fiber alignment and packing as well as a decrease in inter-fiber pore size when rotation speed is increased. They used electrospun aligned nanofibrous scaffold to control anisotropy into tissue-engineered musculoskeletal constructs.
Their scaffolds were also made of a biodegradable PCL polymer, casted on a rotating target to align fibers. Increasing the rotation speed of the shaft from 0 to 9. Alignment of the ECM leads to an increase in the isotropic tensile modulus ranging from 2. Human MSCs and meniscus fibrochondrocytes, seeded on these aligned scaffolds, attached and elongated in the fibers direction. It is also possible with this technique to produce successive layers at different angles by changing the rotation vector. Silk is an interesting material for tissue engineering, but the hyper-allergenic sericin component must be removed.
It has an interesting degradation rate and show remarkable mechanical properties. Silk was previously used to culture fibroblasts and keratinocytes [ ]. The new design proposed by Teh et al. This construct was seeded with MSCs before rolling it into a cylindrical ligament analog. They found that MSCs differentiation into ligament fibroblast was enhanced by the alignment of the fibers.
This resulted in an improvement of tensile properties from to N after 14 days and in an increase of ligament-related protein levels such as collagen I and III as well as Tenascin-c. They demonstrated that human coronary SMCs elongated and migrated in the direction of the fibers and express a spindle-like contractile phenotype with better adherence and proliferation than on control polymer. They have shown that cell elongation and neurite outgrowth is parallel to fiber's direction. They found that the differentiation of neural precursor cells was higher on nanofibers than on microfibers but independent of cell alignment.
Collagen scaffold produced by electrospinning was done by Matthews et al. In this paper, they set the basis for electrospinning of collagen fibers for tissue engineering application by varying different parameters collagen source and concentration, solvent, input voltage. With optimal conditions found in this study, they obtained a matrix containing collagen fibers of nm of diameter that exhibited a 67 nm banding pattern, characteristic of native collagen fibers.
They cultured aortic SMCs into this collagen scaffold and obtained uniform distribution of cells into the construct. After seeding the construct with rabbit conjunctiva fibroblasts, they measured cell adhesion, proliferation, morphology and interaction with the scaffold. In addition to cell alignment, they noted a lower cell adhesion but higher cell proliferation on aligned constructs.
Given that electrospinning is a versatile technique to produce aligned ECM for tissue engineering, by modifying the casting parameters rotation speed, input voltage, distance from target, dimension of the tip or the composition of the solution type of polymer, solvent, concentration it is possible to produce different structures in terms of fiber diameters and composition. It is also possible to cast successive layers with different orientations to obtain a complex scaffold. This technique will certainly be perfected in the future using computerized and robotized set-up to produce reproducible and complex scaffolds for various tissue engineering applications.
As explained above, topographic guidance is the process by which cells respond to the particular arrangement of their environment by modifying their shape and migration vectors [ ]. In vivo, cell environment is composed mostly of native collagen molecules and proteoglycans, in vitro, researchers tried to mimic the cues given by proteins to influence cell fate.
Those cues can come from different structures resembling or not collagen molecules and have been discuss in previous pages. In the following section, it is the very structure of the culture plate that dictates the organization of cells. To do so, gratings of various dimensions and shapes are created by various methods into a cell-compatible plastic and cells are seeded over it.
Among the different methods to create and control the type and the shape of the guiding structures, there are very interesting and versatile approaches using microfabrication processes analog to the ones developed by the microelectronic industry [ , ]. Structures with features ranging from nano- to tens of microns scale matching both the ECM proteins or cells dimension can now be created. These techniques can be adapted to different polymers for various applications and use either polymer casting, micromachining or thermoforming.
This section will focus on the most common process that uses photolithography and hot embossing as an example. Briefly, a pattern is printed in chromium on a quartz plate to form the mask for photolithography. A photoresist is poured over a silicon plate and exposed to UV light under the mask. The resist is then developed in organic solvent to reveal the pattern and obtain the first wafer master. This master wafer is then replicated in a polydimethylsiloxan PDMS mold that is cured into the silicon wafer.
PDMS can be used for cell culture or be replicated on another substrate. In order to replicate it, hot embossing with an intermediate epoxy wafer is used to finally obtain the desired pattern in the chosen polymer. Numerous types of materials could be used for the final cell culture step. Polystyrene is an interesting material due to its great biocompatibility, being used regularly for cell culture flask [ ].
They tested various lengths of grooves and ridges to show that cell alignment is similar from 70 nm to nm ridges but is reduced with nm ridges. Those lengths were chosen to match the approximate dimension of the basement membrane features. In another paper [ ], they showed similar results using corneal stromal fibroblasts keratocytes. This is a logical result considering how fibroblastic cells elongate and migrate more than epithelial cells, they are therefore more prone or easy to align.
A Atomic force microscopy of a sample used for replica molding. The master wafer represents the inverse the negative of the final results in polystyrene. B Smooth muscle cells on a microstructured substrate of grooves 1 um and ridges 4 um after 1 day of culture.
Cells are elongated in the direction of the microstructured pattern. They used a combination of photolithography and hot embossing [ ] to reproduce patterns of ridges and grooves on polystyrene substrate coated with a thermoresponsive polymer, poly N-isopropylacrylamide PIPAAm compatible with cell culture [ ]. They seeded human aortic SMC on these microtextured culture substrates and allow them to form cell sheets.
At room temperature, the cell sheet spontaneously detach from the culture substrate and can be manipulated. In this paper, they have shown that cells elongated and migrated in the direction of the grooves but did not evaluate mechanical or structural anisotropy. In , [ ] they tested those parameters and showed mechanical anisotropy in the resulting media layer that mimic the organization of the native vessel.
Aligned sheets of SMCs, dermal fibroblasts and corneal fibroblasts were produced using the self-assembly or cell sheet engineering approach [ , ]. All three cell types aligned in the direction of the long axis of the ridges and grooves, for the cells in direct contact with the substrate. Copyright Office website, http: To file a notice of infringement with us, you must provide us with the items specified below.
Please note that you will be liable for damages including costs and attorneys' fees if you materially misrepresent that the material is infringing your copyright. Accordingly, if you are not sure whether material infringes your copyright, we suggest that you first contact an attorney. This notice and any attachments we receive will be forwarded to the alleged infringer, who will then have the opportunity to file a counter notification pursuant to Sections g 2 and 3 of the DMCA.
Should a properly filed counter notification be filed, you will be notified and have 10 business days within which to file for a restraining order in Federal Court to prevent the reinstatement of the material. All required fields must be filled out for us to be able to process your form.
We help people distribute information and art spanning a wide range of subject matter while providing a safe, friendly, respectful, and serious site for all content creators. Since our community serves a broad range of ages, we do not encourage content that could make a majority of our users uncomfortable. If you are sure that this product is in violation of acceptable content as defined in the agreement or that it does not meet our guidelines for General Access, please fill out the form below.
It will then be reviewed by Lulu Staff to determine the next course of action. Identify in sufficient detail the copyrighted work that you believe has been infringed upon for example, "The copyrighted work at issue is the image that appears on http: Identify each web page that allegedly contains infringing material.
This requires you to provide the URL for each allegedly infringing result, document or item. I have a good faith belief that use of the copyrighted materials described above as allegedly infringing is not authorized by the copyright owner, its agent, or the law. I swear, under penalty of perjury, that the information in the notification is accurate and that I am the copyright owner or am authorized to act on behalf of the owner of an exclusive right that is allegedly infringed.
Your digital signature is as legally binding as a physical signature. If you use a digital signature, your signature must exactly match the First and Last names that you specified earlier in this form. This form does not constitute legal advice and nothing that you read or are provided on this web site should be used as a substitute for the advice of competent legal counsel. If someone believes in good faith that a Lulu Account Holder has infringed their copyright, they can request that we take down the infringing material by filing a DMCA Notice.
When a clear and valid Notice is received pursuant to the guidelines, we will respond by either taking down the allegedly infringing content or blocking access to it, and we may also contact you for more information. If you are not the copyright holder or its agent and if the content is clearly infringing the copyright of a well-known work, please select "Infringes a well-known work" from the dropdown menu.
Summary Alignment Is Not Just for Wheels - Science And Art of It-business Alignment
Lulu Staff has been notified of a possible violation of the terms of our Membership Agreement. Our agents will determine if the content reported is inappropriate or not based on the guidelines provided and will then take action where needed. Thank you for notifying us. The page you are attempting to access contains content that is not intended for underage readers.
This item has not been rated yet. IT and Business are the wheels of the enterprise and leaders should make sure that IT efforts point in the same direction of the business vision.