Rapid Prototyping Technology of Tissue Engineering Scaffold

管金鹏

GUAN Jin-peng

（南安普顿大学，英国 南安普顿SO17 1BJ）

（The University of Southampton，Southampton SO17 1BJ,U.K.）

0 Backgrounds

Nowadays，because the demands of organs and tissues for transplant increase fast which lead to a big gap between supply and demand of transplant.In the year 2000，there are about 72，000 people need an organ transplant，but only 23，000 transplants were supplied.[1]Recently，a new method called cell transplantation has been used.It is believed that the isolated cells from donor can be cultured in vitro to form suitable tissue，but these isolated cells cannot form new tissues by themselves.Meanwhile，maybe only a small quantity of these cells could be appropriate for implants.Hence，the suitable substrates and environment condition play a critical role for cell growth.For example，the tissue engineering scaffolds could provide three -dimensional structure and frame with specific chemical and physical characters.

1 Tissue engineering

Tissue engineering involves many fields，such as biology，materials engineering and especially in clinical research which aims to create new tissues and organs for implantation.Once upon a time，tissue engineering was considered as embranchment of bioengineering，but nowadays，it has become a significant independent subject and field.Through the combination and cooperation of cells and suitable biochemical methods，it could improve or replace human biological functions.In practice，the tissue engineering has a broad of applications which can repair or replace parts or the whole of tissues，such as bone，vessels，bladder，skin etc.[2]Furthermore，the regenerative technology which has been used widely in clinical field has synonymously and similar theory with tissue engineering.

2 Organ and tissue transplantation

The principle of organ and tissue transplantation is that in order to replace the damaged organ，the organ from donor body is moved to the patient body.There are two kinds of transplantation named autografts and allografts.The allograft moves the same organ and tissue from donor to patient which is different with autografts which the transplantation organ is from patient own body.The general transplant organ and tissue is kidneys and bone.Nowadays，there is large number of problems in tissue and organ transplantation.The first is organ trafficking.Some organ and tissue has limited activity for long time trafficking.Meanwhile，some organs could not be replaced，such as brain.The second problem is rejection of transplantation.Due to the different source of organ and tissue，some immune response will happen after transplantation，such as rejection which could be controlled by some immunosuppressant drugs.[3]

3 Scaffold

Scaffold is a type of artificial structure and frame that cells could be seeded into and form three-dimensional tissue.In scaffolds，due to the full of nutrients environment and condition，cells can migrate，increase and meanwhile maintain their biochemical character.In some cases，the behavior of the cell phase can be adjusted by some mechanical and biological effect.In order to achieve the tissue reconstruction，scaffolds must satisfy some specific requirements.For example，good inject ability，a high porosity and a suitable pore size.Moreover，biodegradability is often a fundamental factor which could help scaffolds integrate to surrounding tissues effectively without artificial help.According to recent research，a better 3D growing environment of cells can offer better results in tissue.[4]

4 Traditional fabrication of tissue engineering scaffold

There are plenty of conventional techniques to build scaffolds，such as solvent casting，particulate leaching，gas foaming，fiber meshes and fiber bonding，phase separation，melt molding，emulsion freeze drying，solution casting and freeze drying.However，these methods are difficult to control pore size and pore geometry，meanwhile the space distribution of pores and internal channels is no uniform in the scaffold.Therefore，many researchers try to improve the conventional techniques.Although they have achieved great progress，the conventional techniques still could not get ideal result.

5 Adva nced scaffold -fabrication methods -rapid prototyping

Rapid prototyping (RP) technologies can be separated into the addition of material and the removal of material.According to the state of materials before part formation，the RP technologies may be divided into the liquid-based，solid sheet and discrete particle technologies.Actually，metal，polymer and ceramic can all be used as material to create 3D models by rapid prototyping (RP) technologies.Because nowadays most RP systems are too expensive that cannot be supported by everyone except the large companies，the cost is the essential factor which confines the use of RP system.In order to increase competitive forces，the goal of rapid prototyping focuses on how to reduce product costs and times of manufacturing.Moreover，the RP technology should be also continuously to improve the speed，accuracy and reliability of systems and broaden the application range which may help RP technology to popularize quickly that is also the long-range aim of my project.

6 Conclusion

With the improvement of manufacture technique，the rapid prototyping technology is more important than before.Moreover，the extensive applications of this technology also promote it forward.Especially in medical domain，artificial organs and tissues，this technique has been used widely that has overcome a mass of challenges of traditional fabrication methods.However，because the complex requirements of tissue engineering scaffold in practice，this technology still face various difficulties and limitations.

［1］Port F (2002) OPTN/SRTS annual report.Scientific Registry of Transplant Recipients and Organ Procurement Transplantation Network[R].Washington，D.C.

［2］Vacanti J.P，Langer R (1999)，Tissue engineering:the design and fabrication of living replacement devices for surgical reconstruction and transplantation[J].Lancet 354:SI32－SI34.

［3］Frohn C，Fricke L，Puchta JC，Kirchner H (February 2001).the effect of HLAC matching on acute renal transplant rejection [J].Nephrol.Dial.Transplant.16 (2):355－60.

［4］Ma P.X，Elisseeff J，Scaffolding in Tissue Engineering [M].Publisher:Crc Press(Aug 2005).

［5］Yeong W.Y，Chua C.K，Leong K.F and Chandrasekaran M，TRENDS in Biotechnology:Rapid prototyping in tissue engineering:challenges and potential[J].Vol.22，No.12 December 2004.