rapid prototyping tecnique in rigenerative medicine

Vincenzo Guarino, PhD Researcher at Institute of Composite and Biomedical Materials (IMCB) National Research Council of Italy

Mail: [email protected] or [email protected]

Address: Viale Kennedy, 54 - Mostra d'Oltremare Pad. 20 - 80125 Napoli NA Campania

Fax.: (0039) 081 2425932

Rapid prototyping technique in rigenerative

medicine

Vincenzo Guarino, PhD Researcher at Institute of Composite and Biomedical Materials (IMCB) National

Research Council of Italy

INTRODUCTION



DEFINITION

Rapid Prototype is a common name for a group of techniques that can generate a physical model directly from computer-aided design

data.

It is an additive process in which each part is constructed in a layer-by-layer manner.

Wai-Yee Yeong, Chee-Kai Chua, Kah-Fai Leong, Margam Chandrasekaran, Rapid prototyping in tissue engineering: challenges and potential, Trends in Biotechnology, Volume 22, Issue 12,

December 2004, Pages 643-652



Basic Principles of Rapid Prototyping

• 3d model generated

• Sliced

• Each slice manufactured and layers are fused together

• A voxel (volumetric pixel or, more correctly, Volumetric Picture Element) is a volume

element, representing a value on a regular grid in three dimensional space. This is

analogous to a pixel, which represents 2D image data in a bitmap (which is sometimes

referred to as a pixmap).



D. T. Pham, S. S. Dimov, Rapid manufacturing, Springer-Verlag, 2001, ISBN:1-85233-360-X, page 6

Rapid Prototyping by Industry Sectors

Tissue Regeneration



IUPAC definition

Use of a combination of cells, engineering and materials methods, and suitable biochemical and

physico-chemical factors to improve or replace biological functions.

The textbook of pharmaceutical medicine Griffin, J P (John Parry). 6th ed.



Why study the rapid prototype in tissue regeneration ?



Result

Why study the rapid prototype in tissue regeneration ? ……



Analysis of the technique



HISTORY

Rapid prototyping is quite a recent invention. The first machine of rapid prototyping hit the markets in the late 1980s, with the enormous growth in Computer

Aided Design and Manufacturing (CAD/CAM) technologies when almost unambiguous solid models with knitted information of edges and surfaces could

define a product and also manufacture it by CNC machining.

Pandey, Pulak M. "RAPID PROTOTYPING TECHNOLOGIES, APPLICATIONS AND PART DEPOSITION PLANNING."

HISTORY……



Pandey, Pulak M. "RAPID PROTOTYPING TECHNOLOGIES, APPLICATIONS AND PART DEPOSITION PLANNING."

Milestones ….

HISTORY……



Different rapid prototyping (RP) technologies applied in tissue engineering

Different rapid prototyping (RP) technologies applied in tissue engineering …



In a typical melt–dissolution deposition system, each layer is created by extrusion of a strand of material through an orifice while it moves across the plane of the layer crosssection. The material cools, solidifying itself and fixing to the previous layer.

Successive layer formation, one atop another, forms a complex 3D solid object. Porosity in the horizontal XY plane is created by controlling the spacing between adjacent filaments The vertical Z gap is formed by depositing the subsequent layer of filaments at an angle

with respect to the previous layer. Repetitive pattern drawing will produce a porous structure ready to be used as a scaffold. A representative system using melt–dissolution deposition is FDM. This method spins off several new systems that operate under similar

principles.

Melt – dissolution deposition technique





Build Volume: 8" x 8" x 10" Materials: ABS, Casting Wax Build Step Size: 0.007", 0.010", 0.013" Up to 4x faster than the FDM 2000

Fused Deposition Modeling

Melt – dissolution deposition technique …



In particle-bonding techniques, particles are selectively bonded in a thin layer of powder material. The thin 2D layers are bonded one upon another to form a complex 3D solid object. During fabrication, the object is supported by and

embedded in unprocessed powder. Therefore, this technique enables the fabrication of through channels and overhanging features. After completion of all layers, the object is removed from the bed of unbonded powder. The powder utilized can be a pure powder or surface-coated powder, depending on the application of the scaffold. It is

possible to use a single one-component powder or a mixture of different powders, blended together. These techniques are capable of producing a porous structure with controllable macroporosity as well as microporosity. The microporosity arises from the space between the individual granules of powder. These techniques offer control over pore architecture by manipulating the region of bonding. However, the pore size is limited by the powder size of the stock material. Larger pores can be generated by mixing porogen into the powder bed before the bonding process. The powder-based materials provide a rough surface to the scaffold. It has been suggested that topographical cues

might have a significant effect upon cellular behavior. As a cell attaches to the scaffold, stretch receptors are activated. Receptors on the scaffold surface might be subjected to varying degrees of deformation, leading to

activation of cell signal transduction pathways. Therefore, scaffolds fabricated via a particle-bonding technique might be more advantageous in the context of cell attachment.

Particle-bonding techniques





3-dimensional printinge

Particle-bonding techniques…



Indirect RP fabrication methods

RP systems can also be utilized to produce a sacrificial mould to fabricate tissue engineering scaffolds. These multistep methods usually involve casting of material in a

mould and then removing or sacrificing the mould to obtain the final scaffold. Such techniques enable the user to control both the external and the internal morphology of the final construct. In addition, indirect methods also require less raw scaffold material while increasing the range of materials that can be used and making it possible to use composite blends that might require conflicting processing parameters. The original

properties of the biomaterial are well conserved because no heating process is imposed on the scaffold material.





Droplet deposition

Indirect RP fabrication methods…



Rapid Prototyping Systems

All RP techniques employ the basic five-step process

1. Create a CAD model of the design

2. Convert the CAD model to STL format (stereolithography)

3. Slice the STL file into thin cross-sectional layers

4. Construct the model one layer atop another

5. Clean and finish the model



• First, the object to be built is modeled using a Computer-Aided Design (CAD) software package.

• Solid modelers, such as Pro/ENGINEER, tend to represent 3-D objects more accurately than wire-frame modelers such as AutoCAD, and will therefore yield better results.

• This process is identical for all of the RP build techniques.

Create a CAD model of the design

Rapid Prototyping Systems …



• To establish consistency, the STL (stereolithography, the first RP technique) format has been adopted as the standard of the rapid prototyping industry.

• The second step, therefore, is to convert the CAD file into STL format. This format represents a three-dimensional surface as an assembly of planar triangles

• STL files use planar elements, they cannot represent curved surfaces exactly. Increasing the number of triangles improves the approximation

Convert the CAD model to STL format (stereolithography)




• In the third step, a pre-processing program prepares the STL file to be built.

• The pre-processing software slices the STL model into a number of layers from 0.01 mm to 0.7 mm thick, depending on the build technique.

• The program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features such as overhangs, internal cavities, and thin-walled sections.

Slice the STL file into thin cross-sectional layers




• The fourth step is the actual construction of the part.

• RP machines build one layer at a time from polymers, paper, or powdered metal.

• Most machines are fairly autonomous, needing little human intervention.

Layer by Layer Construction




• The final step is post-processing. This involves removing the prototype from the machine and detaching any supports.

• Some photosensitive materials need to be fully cured before use

• Prototypes may also require minor cleaning and surface treatment.

• Sanding, sealing, and/or painting the model will improve its appearance and durability.

Clean and Finish




Pandey, Pulak M. "RAPID PROTOTYPING TECHNOLOGIES, APPLICATIONS AND PART

DEPOSITION PLANNING."




Materials For Rapid Prototyping

Materials covered:

• Thermoplastics (FDM, SLS)• Thermosets (SLA)• Powder based composites (3D printing)• Metals (EBM, SLS) • Sealant tapes (LOM



Machine Cost Response

Time Material Application

Fused Deposition Modeler 1600

(FDM) $10/hr 2 weeks ABS or Casting

Wax Strong Parts

Casting Patterns Laminated Object

Manufacturing (LOM)

$18/hr 1 week Paper (wood-like)

Larger Parts Concept Models

Sanders Model Maker 2 (Jet) $3.30/hr 5 weeks Wax Casting Pattern

Selective Laser Sintering 2000

(SLS) $44/hr 1 week

Polycarbonate TrueForm SandForm

light: 100%; margin: 0">Casting Patterns

Concept Models

Stereolithography 250 (SLA) $33/hr 2 weeks Epoxy Resin

(Translucent) Thin walls

Durable Models Z402 3-D Modeller

(Jet) $27.50/hr 1 week Starch/Wax Concept Models

Cost



Biomimetic approach to tissue engineering



Biomimetic approach to tissue engineeringIn living organisms, tissue development is orchestrated by numerous regulatory factors, dynamically interacting at multiple levels, in space and time. Recent developments in the field of tissue engineering are aimed at designing a new generation of tissue-engineering systems with an in vivo like, but fully controllable cell environment. Such a ‘biomimetic’ environment, as a result of biology and engineering interacting at multiple levels, should be suitable to direct the cells to differentiate at the right time, in the right place and into the right phenotype and eventually to assemble functional tissues by using biologically derived design requirements.



Bioactivity of RP-fabricated scaffolds

The interaction of cells with the scaffold is governed by the structural and chemical signaling molecules that have a decisive role for cell adhesion and the further behavior of cells after initial contact.

Current strategies to control the proliferation and other behaviors of cells on advanced biospecific materials involve patterning the material surfaces with adhesive molecules or

by incorporating a controlled release of biomolecules, such as natural growth factors, hormones, enzymes or synthetic cell cycle regulators.

Some RP systems that have excluded high-temperature operation, such as MDM and bioplotter, offer the opportunity of incorporating the biomolecule during the building cycle. However, further information, such as the type of biomolecule, the optimal concentration and spatial control of these biomolecules, is needed to produce the most favorable scaffold.



Cell seeding and vascularization

One significant challenge in the scaffold-based approach in tissue engineering is to distribute a high density of cells efficiently and uniformly throughout the scaffold volume.

RP systems present great flexibility in scaffold design and development. RP-fabricated scaffolds can be designed to have interconnected flow channels to fit into the operation of the bioreactor, as displayed by the work of Sakai et al.

The RP fabrication method offers the flexibility and capability to couple the design and development of a bioactive scaffold with the advances of cell-seeding technologies, to enhance the success of scaffold-based tissue engineering.



New development: automation and direct organ fabrication

Automated design, development and characterization:

RP has the potential of automating the design and fabrication of patient-specific scaffolds. In the work of Cheah et al., computer-aided design (CAD) data manipulation techniques

were utilized to develop a program algorithm that can be used to design scaffold internal architectures from a selection of open-celled polyhedral shapes. The automated scaffold

assembly algorithm can be interfaced with various RP technologies, to achieve automated production of scaffolds.



Boland et al. developed a cell printer to implement the technology. The device is capable of printing single cells, cell aggregates and the

supportive thermoreversible gel that serves as ‘printing paper’. These authors demonstrated the feasibility of this technique by

printing a tubular collagen gel with bovine aortal endothelial cells.

Organ printing

New development: automation and direct organ fabrication …



Laser printing of cells

A laser-based printer, termed matrix-assisted pulsed laser evaporation direct write (MAPLE DW), was used to deposit micron-scale patterns of pluripotent embryonic

carcinoma cells onto thin layers of hydrogel. A cell viability of 95% was reported.




Valerie and Sangeeta adapted photolithographic techniques from the silicon chip industry. The process

starts with filling a Teflon base with a thin layer of polymer solution loaded with cells. UV light is shone through a

patterned template atop the thin film, curing the exposed polymer that sets with cells inside. Complex 3D structures, containing regions of different cells, can be built by using

different templates and adding layers atop each other.

Photopatterning of hydrogels




Tan and Desai reported a layer-by-layer microfluidic method to build a 3D heterogeneous multiplayer tissue-like structure inside microchannels. This approach extends the 2D cell

patterning technique into the vertical axis, involving immobilization of a cell–matrix assembly, cell–matrix contraction and pressure-driven microfluidic delivery

processes.

Microfluidics technology




The Future? Self-replication

RepRap achieved self-replication at 14:00 hours UTC on 29 May 2008 at Bath University in the UK. The machine that did it - RepRap Version 1.0 “Darwin” - can be built now - see the Make RepRap Darwin link there or on the

left, and for ways to get the bits and pieces you need, see the Obtaining Parts link.

http://reprap.org/bin/view/Main/RepRap

http://reprap.org/bin/view/Main/RepRapOneDarwin





RP technologies hold great potential in the context of scaffold fabrication. This technology enables the tissue engineer to have full control over the design, fabrication and modeling of the scaffold being constructed, providing a systematic learning channel for investigating

cell–matrix interactions. Additionally, indirect RP methods, coupled with conventional pore-forming techniques, further expand the range of materials that can be used in tissue engineering. Inspired by the additive nature of layered manufacturing, the layer-by-layer

fabrication method underlines the future development of tissue engineering.

The Future? Self-replication …

rapid prototyping tecnique in rigenerative medicine

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