Compositions: ceramic – Ceramic compositions – Pore-forming
Reexamination Certificate
2000-04-13
2002-01-22
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Pore-forming
C501S001000, C501S123000, C501S084000, C106S035000, C623S016110, C623S023560, C623S023610
Reexamination Certificate
active
06340648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a calcium phosphate porous sintered body usable as a substitute or repairing material for bone or tooth, carrier material for drug delivery and gradual release system and a culture (vessel) or induction vessel for bone or cartilaginous or other tissues and organs, and a method for producing the same. More specifically, it relates to a calcium phosphate porous sintered body having a porous structure excellent in characteristics such as affinity with a living body, cell and tissue intruding property necessary for bone formation, physical, chemical and biological properties and a method for producing the same.
2. Description of the Prior Art
As the materials used for artificial bone, artificial tooth and compensation of bones (hereinafter referred to as “bone filler”) in dentistry, cerebral surgery and orthopaedic surgery, those nontoxic, sufficient in mechanical strength, highly affinitive with a living body so as to facilitate the direct bonding therewith, and naturally in vivo so as to be naturally replaceable by a newly formed bone are preferred.
From such a viewpoint, a bone filler having a porous structure consisting of a calcium phosphate compound has been used.
As a method for producing such a bone filler having a porous structure, it is known to mix a raw material powder with a thermally decomposable material, molding the mixture into a prescribed form, and performing the removal of the thermally decomposable material and sintering of the raw material powder by heating (Japanese Patent Laid-Open No. 60-21763, Japanese Patent Laid-Open No. 60-16879).
In these known methods, however, the contact of the thermally decomposable material added for formation of pores is not necessarily uniform, and the formed pores are mostly apt to be open cells. Even if the formed adjacent pores are in contact and continued to each other, the sectional area of the communicating part of each pore (hereinafter referred to as “communicating part”) is minimized. In such a pore structure, it is difficult to make cells necessary for bone formation (osteoblasts and related cells) intrude uniformly into each pore.
As a method for increasing the sectional area of the communicating part, thus, it is known to cover the surfaces of combustible spherical particles with a binder, house an aggregate of the particles in a molding die followed by pressurization so that the surface part of each particle is fixed in a contact state with the surface of the other particles adjacently arranged around it, fill the spaces among the particles with a slurry prepared by suspending a calcium phosphate powder, which is then dried and solidified, further heat the formed body to thermally decompose and remove the combustible spherical particles and the binder, and then perform a sintering (Japanese Patent Laid-Open No. 7-291759).
The bone filler of porous structure produced according to this method has a sufficient sectional area of the communicating part.
However, in the contact fixation of the combustible spherical particles by pressurization, no consideration is given to the problem that the skeleton part constituting the porous body is apt to break because of a large contraction caused at the time of changing the filled state of the powder by the removal of moisture from the slurry, although the combustible spherical particles fixed in drying are hardly dimensionally changed, although the breakage of the porous structure by springback is taken into consideration to some degree by limiting the pressurizing force.
Further, the fixed combustible spherical particles cause high thermal expansion in the temperature rising step until the fixed combustible spherical particles are thermally decomposed and removed, while the skeleton part constituting the porous body consisting of the filled body of the raw material powder is not so much thermally expanded. Therefore, the thermal expansion difference is increased, resulting in the easy breakage of the skeleton part constituting the porous body. This problem is nor taken into consideration.
No consideration is given either to the problem that a large quantity of a gas generated in the thermal decomposition of the combustible spherical particles and the binder cannot get away to the outside, and the resulting pressure causes the cracking of the porous body inner part.
Therefore, it is difficult to reveal a sufficient mechanical strength according to such conventional methods.
SUMMARY OF THE INVENTION
This invention has an object to provide a calcium phosphate porous sintered body having a porous structure sufficient in mechanical strength and highly affinitive with a living body and comprising pores mostly uniformly laid in mutually communicating state so that osteoblasts and related calls is easy to intrude into most of the pores, and a method for producing the same.
This invention provides a calcium phosphate porous sintered body and a method for producing the same described in each claim.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred mode of this invention, the calcium phosphate porous sintered body comprises spherical pores communicating with one another substantially throughout the porous sintered body. The porosity is 55% or more and 90% or less (preferably 60-85%). The average diameter of the inter-pore communicating parts is 50 &mgr;m or more (preferably, 100-4000 &mgr;m). The pore diameter is 150 &mgr;m or more (preferably, 200-5000 &mgr;m). The there-point bending strength is 5 MPa or more (preferably, 10 MPa or more).
Measurement of Porosity
The porosity of the calcium phosphate porous sintered body is measured according to the following method. A dense sintered body having the same composition as a calcium phosphate porous sintered body to be measured is preliminarily prepared, and a measurement is performed by use of a true density meter to determine the true density (&rgr;*). The calcium phosphate porous sintered body to be measured is worked into a cube or cylinder, and the dimension is measured to determine the volume by calculation. Further, the weight is measured, and this weight is divided by the volume to determine the density (&rgr;). Using these values, the porosity (P) is calculated according to the following expression.
P=1−&rgr;/&rgr;*
The calcium phosphate porous sintered body is embedded in a resin, and the resulting resin is polished and microscopically observed to determine the area (A
p
) of the pore part and the area (A
m
) of the part where the area of the pore part was measured by image analysis. Using these values, the porosity (P) is calculated according to the following expression.
=A
p
/A
m
Measurement of Pore Diameter
The pore diameter of the calcium phosphate porous sintered body is measured according to the following method. The calcium phosphate porous sintered body is embedded in a resin, and this is polished and microscopically observed to determine the substantially spherical pore area by image analysis. The larger number of pores to be measured is more preferable from the viewpoint of precision, but 300 pores or more are generally sufficient for the measurement. Since the pore area determined herein is the section in a plane passing a part of the substantially spherical pore and not the diameter of the pore, a three-dimensional correction is performed.
As the method for correction, Johnson-Saltkov method is used. In the Johnson-Saltkov method, the diameter distribution of pores can be directly obtained from the observed area of the pores. As the average pore diameter, the pore diameter occupying 50% of the total pore volume in the accumulated distribution of the pore volume is calculated.
Since the calcium phosphate porous sintered body according to this invention has the structural characteristic as described above, it has characteristics of sufficient mechanical strength, high affinity with a living tissue so as to facilitate the coupling therewith, and natural extinction in vivo so as to be naturally replaceable with a newly fo
Hojo Akimichi
Imura Kohichi
Kikuchi Masanori
Kinoshita Masami
Minowa Nobuaki
Foley & Lardner
Koslow C. Melissa
Toshiba Ceramics Co. Ltd.
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