TY - GEN
T1 - Stereolithographic rendering of low molecular weight polymer scaffolds for bone tissue engineering
AU - Dean, D.
AU - Wallace, J.
AU - Kim, K.
AU - Mikos, A. G.
AU - Fisher, J. P.
PY - 2010
Y1 - 2010
N2 - The choice of materials for bone tissue engineering scaffolds depends greatly on whether the resulting implants will be directly implanted (i.e., neobone grown in vivo) or whether they will be used as scaffolds for bioreactor (i.e., in vitro) pre-culturing. With the former situation, it may be necessary to rely on the implant material, at least initially, to provide material properties similar to native bone, especially when the implant will be heavily loaded (e.g., in the hip, knee, or spine) during ambulation. However, it is our goal that the scaffold material be completely resorbed by the process of neobone formation and maturation prior to implantation; thereby, effectively, creating an artificial bone graft. In our application, cranial implants, complete implant-host integration and final material properties will determine whether the implant will protect the patient's brain from trauma and infection. The use of low molecular weight resorbable polymers might facilitate the development of neobone and maximize the replacement of scaffold materials with bone prior to implantation. Our prior published work with stereolithographically rendered poly(propylene fumarate) (PPF) scaffolds has primarily involved PPF with a molecular weight over 1200 Daltons (Da). In order to maximize resorption in a bioreactor we have recently been working with 800 Da PPF. We expect that, with the proper surface properties and pore geometry, we will be able to optimize cell attachment, proliferation, and maturation. We also expect that the PPF in these scaffolds will significantly, if not fully, resorb prior to implantation. In order to promote the implant's fullest integration, it is especially important that the final pores (i.e., the spaces left behind after bone has replaced the initial PPF scaffold) facilitate ingrowth of host tissue that includes a blood supply. Building obliquely oriented pores is challenging for most rapid prototyping technologies. However, it is critical that a bioreactor pre-cultured, tissue engineering implant's pores present an open face towards the blood vessels and advancing bone front in adjacent host bone. In our experiments with 800 Da PPF we have also encountered challenges in handling newly rendered low molecular weight PPF implants prior to post-curing (i.e., exposure to a UV light bath after rendering). These implants are soft enough to make handling challenging. Because the 800 Da PPF resin is somewhat viscous, the challenge is to drain unpolymerized resin from the 400-800 μm diameter implant channels prior to post-curing. If this were not done the pores might lose their patency filled during post-curing. We are using an implant support apparatus to insure that the implants remain undeformed during the draining and post-curing procedures. Following post-curing the implants are strong enough to be handled directly. We have done this work in a "clean machine", a 3D Systems (Rock Hill, SC) ViperTM HA, that has not been exposed to standard industrial stereolithographic resins (i.e., resins that may contain toxic compounds). This pilot project presents the optimization of all of these components (i.e., low molecular weight PPF, geometry, and handling during manufacture) to stereolithographically render bone tissue engineering implants for bioreactor pre-culturing.
AB - The choice of materials for bone tissue engineering scaffolds depends greatly on whether the resulting implants will be directly implanted (i.e., neobone grown in vivo) or whether they will be used as scaffolds for bioreactor (i.e., in vitro) pre-culturing. With the former situation, it may be necessary to rely on the implant material, at least initially, to provide material properties similar to native bone, especially when the implant will be heavily loaded (e.g., in the hip, knee, or spine) during ambulation. However, it is our goal that the scaffold material be completely resorbed by the process of neobone formation and maturation prior to implantation; thereby, effectively, creating an artificial bone graft. In our application, cranial implants, complete implant-host integration and final material properties will determine whether the implant will protect the patient's brain from trauma and infection. The use of low molecular weight resorbable polymers might facilitate the development of neobone and maximize the replacement of scaffold materials with bone prior to implantation. Our prior published work with stereolithographically rendered poly(propylene fumarate) (PPF) scaffolds has primarily involved PPF with a molecular weight over 1200 Daltons (Da). In order to maximize resorption in a bioreactor we have recently been working with 800 Da PPF. We expect that, with the proper surface properties and pore geometry, we will be able to optimize cell attachment, proliferation, and maturation. We also expect that the PPF in these scaffolds will significantly, if not fully, resorb prior to implantation. In order to promote the implant's fullest integration, it is especially important that the final pores (i.e., the spaces left behind after bone has replaced the initial PPF scaffold) facilitate ingrowth of host tissue that includes a blood supply. Building obliquely oriented pores is challenging for most rapid prototyping technologies. However, it is critical that a bioreactor pre-cultured, tissue engineering implant's pores present an open face towards the blood vessels and advancing bone front in adjacent host bone. In our experiments with 800 Da PPF we have also encountered challenges in handling newly rendered low molecular weight PPF implants prior to post-curing (i.e., exposure to a UV light bath after rendering). These implants are soft enough to make handling challenging. Because the 800 Da PPF resin is somewhat viscous, the challenge is to drain unpolymerized resin from the 400-800 μm diameter implant channels prior to post-curing. If this were not done the pores might lose their patency filled during post-curing. We are using an implant support apparatus to insure that the implants remain undeformed during the draining and post-curing procedures. Following post-curing the implants are strong enough to be handled directly. We have done this work in a "clean machine", a 3D Systems (Rock Hill, SC) ViperTM HA, that has not been exposed to standard industrial stereolithographic resins (i.e., resins that may contain toxic compounds). This pilot project presents the optimization of all of these components (i.e., low molecular weight PPF, geometry, and handling during manufacture) to stereolithographically render bone tissue engineering implants for bioreactor pre-culturing.
UR - http://www.scopus.com/inward/record.url?scp=77957320480&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:77957320480
SN - 9780415873079
T3 - Innovative Developments in Design and Manufacturing - Advanced Research in Virtual and Rapid Prototyping
SP - 37
EP - 43
BT - Innovative Developments in Design and Manufacturing - Advanced Research in Virtual and Rapid Prototyping
T2 - 4th International Conference on Advanced Research in Virtual and Physical Prototyping, VRAP 2009
Y2 - 6 October 2009 through 10 October 2009
ER -