Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
2001-09-20
2004-05-04
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S211140, C264S234000
Reexamination Certificate
active
06730252
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to medical apparatus and methods in general, and more particularly to apparatus and methods for tissue engineering.
BACKGROUND OF THE INVENTION
Tissue engineering is a truly multidisciplinary field, which applies the principles of engineering, life science, and basic science to the development of viable substitutes that restore, maintain, or improve the function of human tissues. Large-scale culturing of human or animal cells (including but not limited to skin, muscle, cartilage, bone, marrow, endothelial and stem cells) may provide substitutes to replace damaged components in humans. Naturally derived or synthetic materials are fashioned into “scaffolds” that, when implanted in the body as temporary structures, provide a template that allows the body's own cells to grow and form new tissues while the scaffold is gradually absorbed. Conventional two-dimensional scaffolds are satisfactory for multiplying cells, but are less satisfactory when it comes to generating functional tissues. For that reason, a three-dimensional (3D) bioresorbable scaffold system is preferred for the generation and maintenance of highly differentiated, tissues. Ideally, the scaffold should have the following characteristics: (i) be highly porous with an interconnected pore network for cell growth and flow transport of nutrients and metabolic waste; (ii) be biocompatible and bioresorbable, with controllable degradation and resorption rates so as to substantially match tissue replacement; (iii) have suitable surface chemistry for cell attachment, proliferation and differentiation; and (iv) have mechanical properties to match those of the tissues at the site of implantation. In vivo, the scaffold structure should protect the inside of the pore network proliferating cells and their extracellular matrix from being mechanically overloaded for a sufficient period of time. This is particularly important for load-bearing tissues such as bone and cartilage.
Bone Tissue Engineering
It is estimated that the number of bone repair procedures performed in the United States alone is over 800,000 per year. Today, skeletal reconstruction has become an increasingly common and important procedure for the orthopedic surgeon. The traditional biological methods of bone-defect management include autografting and allografting cancellous bone, applying vascularized grafts of the fibula and iliac crest, and using other bone transport techniques. Today, bone grafting is increasing and the failure rate is unacceptably high. In patients who receive various bone grafts, a failure rate ranging from 16% to 50% is reported. The failure rate of autografts is at the lower end of this range, but the need for a second (i.e., donor) site of surgery, limited supply, inadequate size and shape, and the morbidity associated with the donor site are all major concerns. Furthermore, the new bone volume maintenance can be problematic due to unpredictable bone resorption. In large defects, the body can resorb the grafts before osteogenesis is complete. Furthermore, not only is the operating time required for harvesting autografts expensive, but often the donor tissue is scarce, and there can be significant donor site morbidity associated with infection, pain, and hematoma. Allografting introduces the risk of disease and/or infection; it may cause a lessening or complete loss of the bone inductive factors. Vascularized grafts require a major microsurgical operative procedure requiring a sophisticated infrastructure. Distraction osteogenesis techniques are often laborious and lengthy processes that are reserved for the most motivated patients.
Engineering osseous tissue by using cells in combination with a synthetic extracellular matrix is a new approach compared to the transplantation of harvested tissues. Numerous tissue-engineering concepts have been proposed to address the need for new bone graft substitutes. One potentially successful repair solution seeks to mimic the success of autografts by removing cells from the patient by biopsy and then growing sufficient quantities of mineralized tissue in vitro on implantable, 3D scaffolds for use as functionally equivalent autogenous bone tissue. In this way, reproducing the intrinsic properties of autogenous bone material creates an ideal bony regeneration environment, which includes the following characteristics: (i) a highly porous, 3D architecture allowing osteoblast, osteoprogenitor cell migration and graft revascularization; (ii) the ability to be incorporated into the surrounding host bone and to continue the normal bone remodeling processes; and (iii) the delivery of bone-forming cells and osteogenic growth factors to accelerate healing and differentiation of local osteoprogenitor cells.
Cartilage Tissue Engineering
Research on cartilage goes back more than 250 years when Hunter stated in 1743, “From Hippocrates to the present age, it is universally known that ulcerated cartilage is a troublesome thing and that once destroyed, is not repaired”. Since then, a substantial amount of research has been conducted on hyaline cartilage, fibrocartilage and elastic cartilage, with significant advances in our understanding of the development biology and biological cartilage repair process being made over the past four decades. However, the cartilage repair and regeneration response is limited in terms of form and function. While many surgical techniques and drug treatments have been proposed over the past 10 years, none have successfully regenerated long-lasting cartilage tissue to replace damaged or diseased cartilage from a clinical point of view. In fact, most of the surgical interventions to repair damaged cartilage have been directed toward the treatment of clinical symptoms rather than the regeneration of hyaline cartilage, such as pain relief and functional restoration of joint structures and articulating surfaces.
Since cartilage is limited in its ability to repair, significant efforts have also been dedicated to growing cartilage ex vivo or to supplement implants with cells to improve healing. Modern tissue engineering approaches, such as the transplantation of isolated and seeded chondrocytes in combination with bioresorbable polymeric scaffolds of synthetic and natural origin, have recently demonstrated significant clinical potential for the regeneration of different cartilaginous tissues. The success of chondrocyte transplantation and/or the quality of neocartilage formation strongly depends on the specific cellcarrier material.
Current research has largely focused on chondrocyte interaction with biodegradable polymers and devices that are FDA approved, namely, foams and textiles made of poly (glycolic acid) (PGA), poly (L-lactic acid). (PLLA) and their copolymer, poly (DL-lactic-co- glycolic acid) (PLGA). The physical and mechanical scaffold properties can have a profound effect on the healing response of the cartilage. Furthermore, the proper mechanical environment of chondrocytes and their matrix is essential to obtain a structurally and biochemically functional tissue. PGA and PLA and their copolymers have frequently been chosen for tissue engineering applications because their degradation can be tailored. In a highly porous configuration, however, their mechanical properties may be limited.
Bone Grafting in Craniofacial Surgery
The clinical goals for craniofacial skeletal reconstruction are multifaceted. Aesthetic and functional considerations often dictate the use of malleable implant materials. However, in most cases these three-dimensional shaped implants must also provide immediate structural integrity. The host-graft interface should not produce an immunological or inflammatory response to minimize peri-implant morbidity.
Successful craniofacial surgical experience with the patient's own bone has made it the graft material against which all others are measured. Unfortunately, autografted bone is limited in amount and desired morphology. In addition, the use of the patient's own bone is associated with donor-site morbidity an
Hutmacher Dietmar Werner
Tam Kock Fye
Tan Kim Cheng
Teoh Swee Hin
Zein Iwan
Pandiscio & Pandiscio P.C.
Tentoni Leo B.
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