Designing a scaffold for bone growth
The purpose of this report will help to overcome the selection of material and design of scaffold for artificial bone replacement. This report is based on creating scaffolds on rapid prototyping technique (RP) Fused Deposition Method (FDM) the report concludes by the results obtained from the research and the discussion on future works that can be done to make this report more successful. Selection of material (bio-degradable) for producing scaffolds is a raising problem and the design of scaffolds which directs the organ recovery with the providing structural support as natural bone.
Table of Contents
Table of Contents 5
Chapter 1 6
Chapter 2 7
Literature review 7
Chapter 3 12
Rapid prototyping (RP) 13
Chapter 4 18
Chapter 5 23
Conclusion and future works: 24
Tissue Engineering is a emerging technology and basic researches are been done by many companies, Educational intuitions strengthening the knowledge by sharing them between different researches and capability of producing artificial organs, for production of artificial organs materials should be selected innovation in biomaterials, natural bio materials and their production and designing according to the required aspects. Manufacturing process, new therapies are induced to produce the tissues at reasonable cost. Transplantation technology is also a major aspect in tissue engineering this includes new and assured procedures to performance of organ or tissue transplantation and makes the tissue stable under various conditions. Tissue engineering can repair the old organs such as hearts, bones and livers, bone repairs with tissue engineering may be one of the first applications to succeed . Scaffold is a three dimensional structure which accommodates cell in their matrix and help the growth of new cells in three dimensions. To rise above immunological barriers and any risk of pathogen relocate transplant. Existing replacement tissues/organs produced from cells isolated from individual patient are transplanted back into the same human being (i.e. autogeneous tissue transplantation) . The three dimensional matrix is the key for the tissue engineering development and success the artificial matrix should provide environment for the cell to breed and reinstate the tissue and perform its ecological function.
1.2 Problems and sub problems:
Identify the different materials to be used in building scaffold for bone.
Designing the complicated shape as required exactly.
Designing the artificial scaffold various shapes as suitable as required (which directs the growth of organ) in CAD software (PRO-ENGINEERING).
Manufacture scaffold using rapid prototyping method (FDM) with similar physical properties of real bone.
1.3 The hypotheses:
Different parameters can affect the production of scaffolds using fused deposition methods.
Appropriate polymer is chosen and manufactured by electro spinning process which will increase the mechanical properties.
We can improve the properties by changing the parameters like diameter of the nozzle in the FDM machine.
These are the set of assumptions are taken in to consideration during the project and conclusions is related to these set of assumptions.
1.4 The delimitation:
Various structural properties may effect the production like Mechanical strength of scaffold, pore size and pore inter connectively good, overall shape and design of the scaffold, Bio-compatibilities of the material used in construction, working temperature, Poly (propylene fumarate) synthesis, layer thickness while production. In this report first four parameters are taken in to consideration other parameters don't have greatly effect on production. For high bearing applications, clinically no scaffolds with 70% porosity are available.
1.5 Key words:
Tissue Engineering, Scaffold, Rapid prototyping (RP), CAD (Computer Aided Design) software, Fused Deposition Method (FDM), (STL), (SML), poly-glycolic acid (PGA),Poly L-lactic acid (PLLA).
The literature review provides some of the problems and major drawbacks in the research of construction, designing and selection of material for artificial scaffold. It also provides important information regarding the progress made in the development of artificial scaffolds and information regarding the future direction of tissue engineering.
2.2 Tissue engineering:
Tissue engineering (TE) was introduced since 1980s; it's a combination of medical science, biology and material science. Tissue engineering is brought a radical change in field of medical ways to enrich the health and quality of people around the globe by helping to restore their worn out parts, organ function and maintain them thus help to maintain quality life. With the help of tissue engineering tissues of organs can be restored by growing them inside or outside the body, they can be transplanted to replace the damaged tissues. Tissue is made in vitro and used in diagnostic application like treating with drug and the results of it. The aim of the regenerative medicine is to test the ability to explore the different ways for diagnosis by exposing them to different drugs this helps in understand the toxicity and pathogen city. Tissue engineering (TE) is a process of replacing or repair the damaged tissue in organs or bone's with artificial materials which are suitable like bio materials. As a part of our daily life we use our body and bones as we need, by the stage of old age the bones and joints and organs will ware out and cause medical issues and quality of life would be reduced and the medical expenses would rise. The concept of tissue engineering is to explore different ways to exploit cells like biomaterials like designing and replacing the tissue in a damaged organ and helps in heel the wound and make the organ recover and make it function again this helps in improving human living standards and medical standards by both physical and chemical ways. Different properties of native tissues are considered and designing the tissue as required is required for generating tissue have the same mechanical signals and effiency, capacity and safety for the tissues of organ to perform the tasks and health. A study of characterization of cells in tissue engineering helps in selection of different cells for different organs. The cells should be carefully characterized, like stem cells, autologus cells, allogeneic cells and generally engineered cells, this helps in selection for choosing cells according to the tissue to be made. Biomolecules are included with different factors like growth factor of bone according to age and the strength of bone and proteins. Analysis is a helpful process in determining the efficiency and protein expression and interaction analysis, quantitative cellular image analysis, automated quality assurance systems done on the artificial tissues. The engineering design is also a main aspect in tissue engineering including 3 dimension tissue growth and 2 dimension growth, vascularization and tissue and cell storage.
Advances in biochemistry, biomedical engineering, material science, genetics and cell biology helped in advancement in tissue engineering. Currently United States of America have an industry cost of tissue engineering around 68 million dollars and this is an economical benefit. Different fields of study and technology come together in tissue engineering to replace living cells like bone, cartilage, muscle and skin to replace the damaged organs in body and make life better.
Scaffolds are the supportive structure which helps to grow the cells or tissues to replace the damaged ones will act as a temporary support to the structure helps the cells grow and the scaffold is gradually absorbed. Biomaterials are being tested for making scaffolds polymers and ceramics are currently under research to initiate the adhesion and rejection responses.
Every year thousands of patients are treated and the medical cost is also reduced by the advancement in tissue engineering, before organ transplantation is a major problem due to significant donor not available. Around 10,000 people have died while waiting for a donor and organ transplant in past 5 years. The drugs are very costly to balance their health conditions, common man cannot afford it, so this is also a limitation for patients to get treated. Artificial replaced organs will be a new technique and its fewer hazards, problems with donor and cost of it is relatively low.
In United States of America 4,160 liver transplants were performed in 1987 to 1989 and after five years 1,887 patients were died due to unbalanced issues and the people who survived and the medical cost of all of them is $960 million. The estimated artificial liver transplantation will be around $50000 and yearly medical will be estimated $2000 and by this we can save up to $710 million by this better quality of life with increase in survival rate of patients. Artificial tissue engineered liver is under development and replaced for time being use unless the permanent donor is available, it can become a permanent duplicate device for the original organ due to some technical problems yet to be solved, To overcome technical problems research are being conducted. Not only the liver other applications like skin replacement or replacement of burnt skin, ulcers, replacement of cells and other important living cells in body, damaged blood vessels or blocked blood vessels, broken or worn out damaged bones can be replaced or repaired, connective tissues between organs, intervertebral discs and replacing of aged corneas or muscles. The main benefit in advancing tissue engineering is the cost of medical treatments will be available at low prices, less expensive for treatments and quality of life is increased due to replacement of organs is possible and for example Diabetes is effecting around 14 million people in America alone it's a serious disease and by this several illness can be caused like retinal, renal lead to blindness, kidney problems and heart problems estimated cost for the diabetes patients is about $120 billion or 10% of the total national health care cost.
An artificial pancreas can reduce many secondary diseases linked to glucose level in blood are associated with current therapies. The artificial pancreas increase the glucose levels in blood dramatically the secondary cause for illness will be reduced and improves the health conditions of the patients who are suffering from diabetes, cost for replacing the pancreas will be costing $20000, and the annual health maintenance of the diabetic patient will be reduced around 10 to 20%. Over all tissue engineering solutions can reduce half of the annual health care cost of the nation by curing or replacing the organs with tissue engineered organs.
Technology and industrial commitment support tissue engineering basic research are done on promising applications are been conducted in various health care centers and educational intuitions. These early research have promising results but some technical challenges are raised and these questions must be addressed and several technologies must be developed to have benefits for nation. Technique to produce long term cell and tissue storage to make artificial organs and available in different conditions. Producing cells and culturing them with change or contaminating in the genetics of the outcome. For efficient manufacturing of the organs correct materials (biocompatible) for chemical synthesis they should be choose and implement different experiments on them and check weather stable for required conditions. Tissue engineered products should be kept under observation and check their reactions with the host.
Tissue engineering is a emerging technology and basic researches are been done by many companies, Educational intuitions strengthening the knowledge by sharing them between different researches and capability of producing artificial organs, fro production of artificial materials should be selected innovation in biomaterials, natural bio materials and their production and designing according to the required aspects. Manufacturing process, new therapies are induced to produce the tissues at reasonable cost. Transplantation technology is also a major aspect in tissue engineering this includes new and assured procedures to performance organ or tissue transplantation and makes the tissue stable under various conditions.
2.3 Importance of the study:
Every year thousands of patients around the world are dieing while waiting for organ donor and organ transplant in past 5 years. The drugs are very costly to balance their health conditions, common man cannot afford it, so this is also a limitation for patients to get treated. As new techniques are emerging to replace organs with artificial organs with Tissue Engineering (TE) roughly every year 6 million spinal and grafting procurers are performed in that 10% artificial bones are preferred due to lack of donors and its fewer hazards, problems with donor and cost of it is relatively low. Selection of material for production of Scaffolds is a major aspect according to the tissue and its functionality to be replaced, material science and other areas are conducting many researchers and investigating the outcome. In order to make a scaffold which is non toxic (bio-degradable) and have the same physical and mechanical properties like bulking effect, blood reactions with the material, for bone tissue engineering, major issues of tissue engineering scaffolds incorporate the use of suitable matrix for scaffolds, control of porosity and pore quality of scaffolds, mechanical strength of scaffold, scaffold degradation properties and bioactivity of scaffold (i.e. osteoconductivity) . Fabrication of scaffolds done by solvent casting, particulate leaching, gas foaming, fiber meshing and fiber bonding and freeze drying. But they have some limitations in processing and control over the porosity required, pore shape, pore interconnectivity, researches are being conducted and trying to overcome these limitations and new emerging techniques are being adopted for fabrication of scaffolds. To overcome technical problems research are being conducted. Not only the liver other applications like skin replacement or replacement of burnt skin, ulcers, replacement of cells and other important living cells in body, damaged blood vessels or blocked blood vessels, broken or worn out damaged bones can be replaced or repaired, connective tissues between organs, intervertebral discs and replacing of aged corneas or muscles. The matrix for producing scaffolds serves a reservoir of the required habitat (Mechanical sustain, Cell connection, Osteogenesis and Osteoinduction) for recover the damaged part.
The main benefit in advancing tissue engineering is the cost of medical treatments will be available at low prices, less expensive for treatments and quality of life is increased due to replacement of organs is possible and for example Diabetes is effecting around 14 million people in America alone it's a serious disease and by this several illness can be caused like retinal, renal lead to blindness, kidney problems and heart problems estimated cost for the diabetes patients is about $120 billion or 10% of the total national health care cost .
Fig: different fields of tissue engineering 
Rapid prototyping (RP)
Rapid prototype (RP) fabrication method: RP techniques can produce the model directly from the CAD (computer aided design) file, in this the model is constructed layer by layer by converting the CAD file to STL file and can be used to fabricate scaffold directly. RP have different types of fabrication methods 1) 3D printing, 2) Selective laser sintering (SLS) 3) Fused Deposition Method (FDM) etc
3.2.1 Fused deposition modelling:
This is an addictive manufacturing technology, which is developed by S. SCOTT CRUMP in the mid 80's came into effective from 1990. This technology is mainly used for modeling, prototyping and production applications. FDM works on a principle of laying the material layer by layer. The procedure in this process is, a plastic or a filament wire is wounded around the mould. An extrusion nozzle is connected which can be moved in both horizontal and vertical positions by a numerical controlled mechanism. Material is supplied through this extrusion nozzle; this controls the flow of the material into the surface. Nozzle is heated to melt the material which is coming through it. The model or a part is formed by taking small beads of the thermoplastic materials to form layers, as this material will get hardened as soon as it passes through the extrusion nozzle.
There are several materials available with different strengths and temperature properties. A water soluble material is also available which is very much used for temporary supports while the manufacturing process is going on. This material is quickly dissolved using the mechanical equipment which consists of a partiatially heated sodium hydroxide solution.
Selective laser sintering (SLS):
Technology was introduced and developed by Dr. Clark Deckard at the University of Texas, Austin in the mid 80's. This technology is used all around the world due to its flexibility and due to easily make complex geometrics directly from digital CAD. This technology also uses the art which made it more popular. This technique is used to convert small particles like plastic, ceramic, glass powders into solid, which will be having a desired 3 dimensional shape using high power laser. This laser converts the powdered materials into a solid structure by scanning the cross section of the 3- D digital description of the part, which was generated. The cross-sectional scanning will take place on the surface of a powder bed. This powder will be scanned again and again, after each and every cross section is scanned. The thickness of the power bed layer will be lowered by one layer and the new layer of material will be applied on the top of the power bed, this process will be repeated until the part is completed.SLS additive manufacturing can produce parts from the powder materials, which are vastly available in the market. This type of manufacturing is affordable when compared to other additive manufacturing.These powdered materials include polymers, alloy mixtures, metals, and green sand. Some of the materials can achieve 100% density depending on the materials and also the physical process can be partial melting, full melting or liquid phase sintering.
There are also some other addictive manufacturing processes such as stereolithography (SLA) and Fused Deposition Modeling (FDM) out of these three manufacturing processes Selective Laser Sintering(SLS) is the best process because SLS constructed path is surrounded by the unsintered powder at all the times that is the reason it does not support structures as in SLA and FDM.
Stereolithography can also be called as 3D printing, Optical Fabrication, photo solidification, solid imaging. This is an addictive processing which uses a liquid called UV curable photopolymer resin and also UV laser to build the pars of the layer. For each and every layer, the layer beam traces the cross section pattern area of the liquid resin which is used for processing. Then the liquid layer is exposed to the UV laser which will harden the pattern which was traced on the resin and then it will get sticked to the below layer. This pattern gets repeated after each and every pattern has been detected. After a pattern has been detected, The SLA elevator will reduce the thickness of the layer by 0.05 mm to 0.15 mm. after the thickness has been reduced a resin filled blade will sweep the part of the cross section, then a new layer will be coated. For this new layer, a matched layer will be traced out and get adhered to the previous layer. This process continues until a 3-D part is completed. After building a 3-D part, all the parts are cleaned by dipping into the chemical bath to take of the excess resin and then cured in a UV oven.
The most important part of the SLS is that, the functional part can be created within one day, which would be very much useful in the time based environment. Some time it takes much time in producing a part it depends on complexity of the project and size where it can take few hours or more than a day. The main disadvantage of SLA is it is very expensive. The photo curable resin costs up to 300$ to 800$ per gallon, where as SLA machine costs about $100,000 to $ 500,000.
Laminated object manufacturing:
This process is developed by Helysis inc. this is the process where the layers of the paper, plastic or metal which are adhesively coated. These layers will be successively stick together and then cut into shape with knife or laser cutter. The process is performed as follows first the sheets of paper, plastic or metal will get adhered to the respective layer using the heated roller. Laser traces the desired dimensions which are meant to be removed. Then the laser will cut the layer as per the prototype. Then the completed layer will be moved down the way, new layer will come into that position this process continues. Advantages of the laminated object manufacturing is it is less expensive because of the readily available materials, large parts can be made by this process because there will be no chemical reaction takes place. The main disadvantage of this process is that the dimension accuracy will be slightly less when compared with Stereolithography and Selective Laser Sintering.
Electron beam melting (EBM):
This is one of the addictive manufacturing parts. This process produces fully dense metal parts directly from the metal powder as per the characteristics of target material. The EBM machine will read the design from the 3D CAD model and then it will successively create the layers from the powdered material. These layers are melted using the computer controlled electron beam. This whole process takes place under vaccum makes it suitable for some parts which have high affinity with oxygen. The melted material in this process is a pure alloy material which comes in the powder form in the final material to be fabricated. That's the reason electron beam does not require additional thermal treatment to obtain the full mechanical properties of the parts. The EBM operates at very high temperature around 700 to 1000 degrees centigrade.
3D Printing is more reliable, easier to use than other additive manufacturing processes, low cost. 3D printing generates a print of the physical parts and assembles are made with different parts whose physical and mechanical process are in a single build process. 3D printing process consists of inkjet printing. The 3D CAD file is inserted into the software. The software will slice the file into thin cross sectional pattern, which will be fed into the 3D printer. This printer creates the layer, one layer at a time by spreading the layer of powder until every layer is printed. This method is recognized as the fastest method of all the processes. This is the only technology that allows printing of full colour prototype.
Advantages of 3D Printing:-
It has an online service which can be used anywhere from the world. Where it creates a 3D printing with many range of materials to be 3D printed and delivered to the customers worldwide with no investment cost.
On - the - Fly modeling creates a proto type of the object which will have the same mechanical properties of the target design.
Time and cost can be saved as there is no need of design, print or glue together (where separate model parts are designed with different model parts in order to complete the final model)
Digital light Protection:
In this process a liquid polymer is processed through a DLP projector, where it is exposed to the light of the projector. Then the polymer will get harden as it was passed through the DLP projector light. Then that polymer is moved down in small increments and again it will be exposed to the DLP projector light. This process will be repeated until the desired layer is built. Then the liquid polymer is drained out after the layer has been built.
For all the above addictive manufacturing techniques, there are advantages and disadvantages.
Most of the companies consider the aspect of powder or polymer as the material for which the object is developed. And the other considerations which the companies consider are cost of the printed prototype are made, material considerations, cost of 3D printer, and speed of the process.
3.3 Prototyping techniques and materials used in this techniques:-
Selective Laser Sintering (SLS): Material used in this technique is Metals, Thermoplastics, sand, Glass
Fused Deposition Modelling (FDM): materials used in this technique are thermoplastics
Stereolithography (SL): Materials used in this technique are Photopolymer.
Laminated Systems: Materials used in this technique are Paper and Plastic.
Electron Beam Melting (EBM): Materials used in this technique are Titanium Alloys.
3D Printing (3DP): Various Materials used in this technique, Including resins
Digital Light Protection (DLP): Materials used in this technique are Photopolymer.
This methodology chapter provides information about problems and problem solving techniques used in fabrication of scaffold. The method of producing scaffold, different steps involved in production in FDM process and designing it in CAD software (PRO-E).
4.2 Specific treatment of the data for each sub problem:
4.2.1 Sub problem1:
Identify the different materials to be used in building scaffold for bone
Data needed to address the sub problem:
There are various parameters to produce scaffolds and obtaining the properties of scaffolds : (1) it should be Bio-degradable with degradation and resorption rate according to time as the tissue growth. (2) Should be processed to produce in complicated shapes as required. (3) Highly porous and should have good inter connectivity and flow transport of nutrients waste. (4) Suitable surface for cell attachment. (5) Mechanical strength should be enough to support new tissue.
B) Treatment of the data:
Scaffold should provide larger pore size to provide space for cell attachment, nutrient and metabolism. Actual bone pore size defers from 60 to 97% and the channel size is about 145 to 520Âµm and the poisons ratio is 0.46 and young's modulus is 17gpa many polymer materials have porosity of 10 to 450 Âµm synthetic polymers like poly-glycolic acid (PGA) and poly L-lactic acid(PLLA) and their co-polymers are widely used in tissue engineering and these materials are approved by the food and drug administration because they have good bio compatibility properties and they are widely used in human clinical surgical. For engineering purposes other type of protein tissue as collagens are used because of the toxic effects are found when acid try to dissolves the scaffold through time. Mechanical strength for supporting scaffold is the main aspect, synthetic calcium phosphate have considerable porosity, grain construction and composition of micro porosity gives high rigidity, tensile strength and greater resist to fracture.
4.2.2Sub problem 2:
Designing the complicated shape as required exactly as the damaged part.
Treatment of the data
To obtain the exact image or shape of the defective part shape CT scanner can be used and process the image to the computer and after we can directly slice the scaffold and manufacture, this will help in designing scaffold ,as this process can be used to know what's exactly the shape of the defected. The steps involved in any process in tissue engineering 1) Imaging 2) modelling 3) manufacturing. There are many challenges to overcome in order to make a system from obtaining the satisfactory knowledge of wound healing to create better scaffolds.
4.2.3 Sub problem 3
Designing the artificial scaffold various shapes as suitable as required (which directs the growth of organ) in CAD software (PRO-ENGINEERING). And manufacturing it using fused deposition method (FDM).
4.3 Steps involved in manufacturing scaffold:
Modelling of scaffold using CAD software the technique is as followed (1) first production of scaffolds structures as desired in CAD software. Pro/Engineer is used for producing complicated 3D structure designs is used in this research. The model is created using Pro Engineer wire frame 4, The 3D model is converted in to STL (stereo lithography) file format in which the model is sliced in to very thin layers of .1 to .5mm thickness this helps in construction of complex shapes in layer by layer format. First the base layer is created by conventional methods and layer by layer the final product is obtained. Following steps are involved for production of scaffolds.
Designing scaffold in Pro/E
Converting the Part file to STL file
Molten bio-material flow through nozzle
Layer by layer manufacturing path
Layer by layer manufacturing by FDM
Fig 1: Flow chart for steps involved in manufacturing scaffold.
4.4 Designing scaffold in Pro/E (CAD Software)
Fig 1 Top view of designed scaffold
Fig 2 Inner view of scaffold
Fig 3 Wire frame view of scaffold
Fig 4 Sectional view of scaffold
4.5 Description of figures
Fig 1: Designing of the outer structure and making circles for easy flow of blood.
Fig 2: designing the inner pard defective part (shape as required) of bone which has to be re-generated and replaced with new tissue.
Fig 3: Wire frame view of the scaffold showing all geometry features in wire frame.
Fig 4: Sectional view of the scaffold geometry showing the interior complicated parts to manufacture.
4.6 Production of scaffold using fused deposition method (FDM):
FDM is a process used for producing complicated designs using layer by layer construction method in three dimensional aspects it uses the part file converted to STL file and the part is constructed layer by layer and this helps in construction of composite models in X&Y axis.
Nozzle moving x-y direction
Manufacturing of scaffold: Manufacturing is done by importing the sliced model by horizontal layers and then it is converted into .sml (Stratasys Machine Language). Supporting material is used to manufacture of the scaffold in this process all the supporting material is removed by washing it in hot water when the final part is constructed. Different types of FDM machines are available in the market according to the required size.
Conclusion and future works:
The main aim of the research is to design a scaffold and select an appropriate material (Bio-material) which help and provide better environment for the growth of new tissue resisting all the mechanical forces induced in the bone. The main property of a good scaffold is it porosity and its interconnectivity this help in cell formation quicker, good blood circulation and helpful in sending out the excess waste of scaffold. The intension of the paper is to prepare the scaffold by conventional method Rapid prototype (RP) used for manufacturing complicated designs with layer by layer process and get the optimized tissue design and deformation of scaffolds with different pore size are considered and do some experiments on them to guess the mechanical support for growing new tissue and cells.
5.2 The qualifications of the researcher:
The qualification for conducting this study, researcher should have knowledge of Rapid prototyping methods for manufacturing (fused deposition method FDM) and should have knowledge in modeling the scaffolds in CAD software. Minimum qualification for doing this study the researcher should have a Master's degree to understand the terms and depth knowledge of fused deposition method (FDM). Basically the back ground should be from manufacturing field would better for the study and have a technical knowledge for operating FDM machine and commuter for fabricating scaffolds.
5.3 An outline of the proposed study:
To understand the concept the researcher should refer all the related pervious work and understand them and their problems yet to be solved, for this review approximately 18 to 20 days should be allocated.
The next move is to draw a new concept and design a new concept as part file with the pores in scaffold for free circulation of blood and then convert the part file to STL file (Sliced format for production). This section will take 3-4 days.
Material properties should be studied for natural bone and gather all mechanical properties should be obtained and find material properties of bio-materials and their reactions and bio degradation, material process ability time for the material used for producing of scaffolds. Then manufacture different samples with different material with different parameters (i.e.: porosity, pore size, properties.) These will take 20-25 days.
Researcher should do tests to find the mechanical properties of the scaffold by applying different loads and series of tests and interpret the results and plot graph to find which material is preferable and have high mechanical strength to support the scaffold for cultivating new tissues. All these analysis will take 13-14days.
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