Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-11-12
2002-09-17
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023560, C623S023750, C623S023760, C427S002270
Reexamination Certificate
active
06451059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to resorbable ceramic fibers and scaffolds for use in biological application, and their method of production. Specifically, this invention relates to novel fibers and scaffolds, formed via a wet spinning technique, and useful as biological replacements for hard tissue.
BACKGROUND OF THE INVENTION
Bone grafts formed of porous calcium phosphates (CaP) show potential as a scaffolding for the growth of new bone in applications such as spinal fusion, long bone fractures, non-union fractures, bone defects, and hip revisions. In present devices, the porosity is either randomly distributed, or the manufacturing techniques have limited ability to control pore size. Control of pore distribution and size may be advantageous in optimizing bone growth into the graft.
The present invention relates to novel bone implants and their use in bone repair and reconstruction. More particularly, it relates to resorbable ceramic fibers and scaffolds, formed via a wet spinning technique, and useful as biological replacements for hard tissue. Bone grafts are used in the repair of significant fractures, the treatment of skeletal tumors, spinal fusion, and the reconstruction of failed total arthroplasties. Autogenous bone, or autograft, is bone harvested from another location in the patient, and used as the graft. Autograft performs very well in the applications cited above. The disadvantages of autograft include the limited supply of excess bone in the patient, as well as the inherent risks of morbidity and recovery pain taken by performing a second surgery. Allograft, bone taken from another human, has the advantage of being in larger supply than autograft bone. However, the greater immunogenic response of allograft, and risk of viral contamination or risk of transmission of live virus to the recipient, have led to the decline in use of allograft bone as a bone graft material. Xenograft, or bone grafts taken from another species, often elicits acute antigenic response. In the vast majority of cases, xenograft fails in its role as a graft material.
Synthetic bone graft materials have been described in Bone Graft and Bone Graft Substitutes: A Review of Current Technology and Applications; Damien and Parsons;
J. Applied Biomaterals
, Vol. 2, 1991, pages 187-208, which is incorporated herein by reference. The ideal graft should be able to support a load equivalent to the bone that is being replaced, so that the newly formed bone can remodel to the same quality and dimensions of the original bone that is being replaced. Ideal graft is also osteoactive, enhancing the formation of new bone. This is achieved both by the chemical nature of the material, as well as the structure, or architecture of the graft. Structurally, the graft needs to be porous to allow for ingrowth of the new bone. Though no optimal pore size has been established, the size of the pores required for good bone growth is between 100 and 500 microns. The ability to tailor the pore size and distribution is also viewed as a method of enhancing bone growth. Load support can be achieved by having the supporting phase of the graft three-dimensionally connected.
The materials in bone graft substitutes include, but are not limited to, plaster of Paris (calcium sulfate, CaSO
4
. 1/2H
2
O) tricalcium phosphate (Ca
3
(PO
4
)
2
), hydroxyapatite (Ca
10
(PO
4
)
6
(OH)
2
), calcium phosphate cements, calcium aluminates, the family of Bioglass® (composed of SiO
2
, Na
2
O, CaO, and P
2
O
5
), apatite-wollastinite glass-ceramics (AWGC), polymers such as polymethylmethacrylate (PMMA) or polyhydroxyethylmethacrylate (PHEMA), and blends of the above. They may be in the form of loose particles, particles bound in polymer or other carrier material (a paste), ceramic precursors that react when blended together (calcium phosphate cements), porous solids, or loose fiber constructs (such as felts), or textile processed fibers (weaves, braids, or knits).
The disadvantages of using loose particles as a bone graft include the difficulty of handling them, the tendency of the particles to settle (or pack tightly) into the defect, the inability of loose particles to support load, and particle migration away from the defect site in bodily fluids. Particle settling results in two problems. First, when the particles pack together, the pore size is reduced in the graft to less than 100 &mgr;m. This pore size does not allow the migration and ingrowth of cells into the graft. Particle settling also results in an inability to control the pore size and distribution in these systems. The size and distribution of pores in these types of grafts are determined by the size of the particles and how they pack together. Since settling is not controllable, there is no ability to use graft architecture to control new bone growth into the graft. Particle migration from the site results in possible tissue irritation and undesired tissue response in regions were the particles eventually settle.
Particle settling and migration problems have been mitigated to some extent by the use of synthetic or natural matrix materials, including polymers such as PMMA, polysulfone (PS), or polyethylene (PE), which are not resorbable, and ceramics, such as plaster of Paris or calcium phosphate cements. Particles have also been enclosed in tubes of resorbable polymers, such as collagen or polyglycolide. The size and distribution of pores in these types of grafts are also not controllable. The distribution is determined by the size of the particles, how they pack together, and the relative proportions of the matrix and particle phases. As with loose particles, there is limited ability to use graft architecture to control new bone growth into the graft.
For bone grafts in the form of cements, there is also a limited ability to control the pore size and distribution. Pore creating agents may be put into the cement prior to its formation. However, the size and distribution of pores are determined by the size, form, and concentration of the agent, resulting in the inability to use graft architecture to control new bone growth into the graft. This inability to control pore size and distribution also results in limits in load support capability. A random distribution of pores results in a random distribution of defects in the structure. So, although the load-supporting phase of the graft is three-dimensionally connected, these types of grafts have shown low load support capability. Control of the pore size and distribution in porous solid bone grafts is also limited. Porous solid bone grafts have been formed using the replamine process on naturally occurring coral. Here, the pore size and distribution is limited to that of the species of coral used. Defect location is also uncontrollable, lowering the load support capability of the graft in a fashion similar to that discussed above for cements. Pore creating agents may also be put into a ceramic prior to its formation. But, as is the case with cements, the size and distribution of pores are determined by the size, form, and concentration of the agent.
Bone grafts in the form of textile architectures, such as weaves, braids, or knits, have advantages over the other forms of bone grafts. Textile technology may by used to precisely place the fibers in a desired location in space, allowing for a large degree of control in the size and distribution of pores in the bone graft structure. However, since there is no interconnection of fiber in three dimensions, load support capabilities of grafts of this type are limited.
There are a number of woven structured formed with fibers composed of the materials found in bone graft substitutes cited in the prior art. Tagai et al., in U.S. Pat. Nos. 4,820,573, 4,735,857, and 4,613,577, disclose a glass fiber provided for the filling of a defect or hollow portion of a bone. In this case, the calcium phosphate glass fiber may be in the form of short fibers, continuous fiber, or woven continuous fibers. In this prior work, the load support capability of the graft is limited since th
Janas Victor F.
TenHuisen Kevor S.
Ethicon Inc.
Stewart Alvin
Willse David H.
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