JP4297393B2 - Chitosan-calcium phosphate complex and method for producing the same - Google Patents
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【０００１】
【産業上の利用分野】
本発明はキトサン−りん酸カルシウム複合体及びその製造方法に関し、特に人工骨材料として有用な複合体及びその製造方法に関する。
【０００２】
【従来の技術】
現在、人工骨材料としては一般にステンレスやチタンなどの金属材料、アルミナやジルコニアなどのセラミック材料が用いられている。しかしながら、金属材料は生体骨より強度が高すぎるため、そこに荷重がかかった場合、再生生体骨が生体に吸収され生体骨摩耗現象が生ずる。また、場合によっては手術により金属材料を摘出する必要がある。一方、セラミックについても、生体骨と弾性率が異なるため材料の破損が起こることが懸念される。また、これらの材料は材料の表面でしか生体骨と結合しないため、剥離などを引き起こすことがある。これらの問題を解決すべく、金属表面をヒドロキシアパタイト(以下ＨＡｐと略記する)でコーティングしたり、セラミックを多孔化するなど様々な改良が行われているが、セラミックだけでは限界がある。
【０００３】
そこで、有機高分子材料とセラミックあるいは無機材料を複合化させることにより、柔軟性などセラミックあるいは無機材料だけでは望めなかった特性を付加した材料を作製する試みがなされている。
例えば．ＨＡｐ燒結紛体とキトサンゲルの混練物を成形、乾燥することにより人工骨を作製する方法である。この方法によるときは、ＨＡｐの粒子をキトサンが取り巻く状態にあり、微細領域での構造は骨と異なる。また、ＨＡｐとキトサンの相互作用も粒子表面に限られ、構造上混合物に近く、均一性を欠く。更にこの人工骨はキトサンの物性を強く示すため、炎症反応などを引き起こす可能性がある。
【０００４】
上記人工骨よりも更に生体骨に近い性質を有するＨＡｐとコラ−ゲンを混合成形した人工骨も研究されている。しかしながら、この人工骨はコラ−ゲンを使用するため非常に硬く、また、成形性も悪い。特に膜などに成形することは極めて困難である。また、コラーゲン自体の抗原性を抑えるためアテロ処理などの処理を施す必要があり、柔軟性が得られないばかりか、これらの原料を用いて作製した人工骨は高価となる。更にまた、特許第２７７５３８６号には、人工骨として有用なアパタイト・有機物複合体が開示され、有機物としては多糖類、硬蛋白質が例示されている。一般的に多糖類とは広義には加水分解によって１分子から２分子以上の単糖類を生ずる炭水化合物を言い、セルロ−ス、デンプン、グリコ−ゲン、デキストラン、グアラン、マンナン、カロニン、ゴム質など自然界、生物体内を問わず無数の多糖類が知られ、また、多くの多糖類が合成されている。
【０００５】
【発明が解決しようとする課題】
本発明はかかる従来技術の現状に鑑み創案されたものであり、その目的は生体適合性、強度及び柔軟性に優れた複合体及びその製造方法を提供することにある。
【０００６】
【課題を解決するための手段】
本発明者らはかかる目的を達成するために鋭意検討した結果、上述の多糖類のうちキトサンがりん酸イオン、カルシウムイオンと特異的に反応し、生成するりん酸カルシウム結晶がキトサン上に結着配向し、高い強度と柔軟性を有する複合体が得られることを発見し、かかる知見に基づき本発明を完成した。
即ち、本発明は、キトサン上にりん酸カルシウム結晶が結着してなるキトサン−りん酸カルシウム複合体に関する。
また、本発明はキトサン液にりん酸又は水溶性りん酸塩を加え、これを水溶性カルシウム塩又は水酸化カルシウム懸濁液に添加して沈殿を生成させる工程を含むキトサン−りん酸カルシウム複合体の製造方法に関する。
【０００７】
【発明の実施の態様】
本発明の複合体は例えば次のようにして製造することができる。
キトサンを酢酸、クエン酸、リンゴ酸、シュウ酸、塩酸等の酸に溶解してキトサン溶液を製造する。キトサン濃度としては０．０１〜３０重量％がよい。０．０１重量％を下廻ると反応溶液量が多くなり経済的でない。また、３０重量％を上廻ると粘度が高くなるため、作業操作性が悪くなり、キトサン溶解性も悪くなる。またカルシウム溶液と混合時の拡散性も悪くなる。本発明で使用するキトサンの分子量についていえば、重量平均分子量約１〜１００万、更に望ましくは３〜３０万である。即ち１万未満の場合、成形体強度が弱くなり、１００万を超えると酸への溶解が困難となる。また脱アセチル度について言えば、特に限定されないが５０〜１００％のものが良い。
【０００８】
次いで、このキトサン溶液に濃度０．１〜６５重量％（Ｐ２Ｏ５換算）のりん酸溶液をキトサンに対し０．１〜４２０重量％（Ｐ２Ｏ５換算）添加し、良く攪拌する。りん酸溶液の濃度が下限を下廻るとキトサン上に生成するりん酸カルシウムの量が不十分であり、上限を上廻るとキトサンの分子鎖が切断され、劣化が起こりやすい。本発明に使用するりん酸溶液としては、りん酸の他、第１、第２りん酸水素ナトリウム、りん酸水素カリウムを好例として挙げられるが、要はりん酸の水溶性塩であれば良く、これらに限定されるものではない。次いで、このキトサン−りん酸溶液を濃度約０．０５〜３０重量％（ＣａＯ）のカルシウム溶液または水酸化カルシウム懸濁液に添加混合する。０．０５重量％未満の場合、溶液濃度が薄く反応溶液量が多くなり経済的でない。一方、３０重量％を超えると生成物によって粘度が高くなり、攪拌による均一化が困難になる。
【０００９】
両者の混合割合はりん酸（Ｐ２Ｏ５）に対してカルシウム（ＣａＯ）として８０〜１４０重量％の範囲である。この範囲を逸脱すると、過剰のりん酸あるいはカルシウムが存在することとなり人工骨として使用する場合望ましくない。
また、キトサンとりん酸カルシウム（ＣａＯ＋Ｐ２Ｏ５）の割合について言えば、９９／１〜１／９９（重量）、更に好ましくは、１５／８５〜８５／１５（重量）である。即ちこの範囲にあるときは大略キトサンがりん酸カルシウムで被覆され、優れた生体適合性を有するものとなる。一般にキトサン上に生成結着するりん酸カルシウム結晶に対しキトサン量が多い程成形体は柔軟であり、一方キトサン量が少ない程成形体は硬くなる。従って用途により配合割合を調整することが望ましい。
【００１０】
次いで混合熟成時間について言えば、一般に１〜７２時間である。熟成時間が長くなる程りん酸カルシウム結晶の生成反応が進行し結晶性は高くなる。熟成後は、即ち結晶を発達させた後は遠心分離機、フイルタ−プレス、ベルトプレス等任意の濾過機により脱水する。望ましい方法は予め脱水機を所望する任意の形状にしておくことである。この場合脱水圧力が強い程、複合体の強度は大きくなる。またこのスラリ−を所望する形状の容器に流し込み、自然乾燥、通風乾燥、強熱乾燥、凍結乾燥等任意の乾燥方法により乾燥することによっても複合体を製造することができる。このようにして製造したキトサン−りん酸カルシウム複合体はキトサン上にりん酸カルシウム結晶が結着し、キトサンをりん酸カルシウム結晶が良く被覆しており、優れた生体適合性を有する。
【００１１】
また、りん酸カルシウム結晶のＣ軸は配向、即ち同一方向に向いている。本発明のりん酸カルシウム結晶のＣ軸が同一方向に向いている理由については定かではないが、キトサン分子のＯＨ基あるいはＮＨ２基とりん酸イオンあるいはカルシウムイオンが順次反応し、りん酸カルシウム結晶のＣ軸が配向性を有するものと推定される。ここで、りん酸カルシウムがＣ軸方向に配向しているとは、透過型電子顕微鏡で確認されるりん酸カルシウム結晶の集合体の電子線回折において、りん酸カルシウム結晶がＣ軸方向に配向していることを言う。本発明における望ましい配向度は５０゜以内に配向していることである。ここで配向度５０゜以内とは先の電子線回折においてデバイ−シェラー環が中心角５０゜以内の弧になっていることを言う。特に５０゜以内の場合りん酸カルシウムの結晶が良く発達しており、成形体にした場合高強度の成形体が得られる。
【００１２】
また本発明のりん酸カルシウムとは、ＨＡｐ、りん酸三カルシウム、りん酸八カルシウム等りん酸カルシウム化合物を言う。本発明に於いて最も望ましいりん酸カルシウム結晶はＨＡｐである。更に言えば、りん酸カルシウム結晶としてＨＡｐが７０重量％以上含まれていることが望ましい。本発明のりん酸カルシウム結晶の集合体の大きさは製造方法により異なるが、概ね長径１００〜４００ｎｍである。
【００１３】
本発明の複合体の更に望ましい製造方法は上記のようにして製造した複合体を水熱処理することである。水熱温度としては５０〜２００℃が良い。熱処理温度に関して言えば、５０℃未満では長時間の熱処理時間を要する上にその効果も小さい。２００℃を越えるとキトサン鎖の切断や分解が起こり望ましくない。また、水熱処理時間に関して言えば、１〜１２０分が良い。１分未満では本発明の効果を期待することができず、１２０分を超えてもそれ以上の効果は得られない。即ち、水熱処理を行うことにより、最大点応力、最大点変位は著しく大きくなる。更にまた、水熱処理を行うことの利点は、１２０℃以上、２０分以上の熱処理条件の場合、殺菌剤等の薬剤を使用することなく複合体の殺菌を行うことができることである。
【００１４】
本発明のキトサン−りん酸カルシウム複合体は上記の方法により製造することができるがこれらに限定されるものではない。また、本発明の複合体の用途については主に人工骨について述べたが、本発明の複合体はキトサンとりん酸カルシウムの割合を調整することにより、その硬度、柔軟性を自由に調整することができ、人工靱帯、人工腱、人工腱や人工軟骨のアンカ−充填材、人工軟骨、骨欠損部充填材、人工血管、人工食道、人工皮膚等にも使用することができる。また本発明の複合体は、用途に応じて糸状、メッシュ状、スクリュ−状、円筒状等任意の形状にすることができる。
【００１５】
【実施例】
以下に本発明の実施例を掲げて更に説明するが、本発明はこれらに限定されるものではない。尚、％は特に断らない限り全て重量％を示す。
【００１６】
［参考例１］
炭酸カルシウム１１６ｇを電気炉中で１２００℃で３時間焼成し、酸化カルシウムを得た。得られた酸化カルシウム６５ｇを振とうさせながら蒸留水６３ｇを徐々に加え発熱がおさまるまで待った。これに更に８７２ｇの蒸留水を加え、１時間攪拌することにより水酸化カルシウム懸濁液を得た。
一方、キトサン１００ｇ（重量平均分子量約１０万、脱アセチル度約８０％）を１％酢酸水溶液１９００ｇに溶解し、キトサン水溶液を得た。上記キトサン水溶液と４．３％（Ｐ２Ｏ５換算）りん酸水溶液１０００ｇを混合し、キトサン−りん酸混合水溶液を得た。
こうして得られたキトサン−りん酸混合水溶液を２５℃で攪拌中の水酸化カルシウム懸濁液中に１０ｍｌ／ｍｉｎの速度で滴下した。滴下終了後、微量の水酸化カルシウムもしくはりん酸を添加してｐＨを８〜９に調整し、１昼夜攪拌下で保持した。これを吸引ろ過し、蒸留水５０００ｇで攪拌洗浄した後、再度吸引ろ過を行った。次いで更に、２００ＭＰａで圧縮脱水することによりキトサン−りん酸複合体を得た（Ａ）。
【００１７】
この複合体（３×５×２０ｍｍ、以下同じ）の曲げ強度は下部支点間距離１５ｍｍ、試験速度０．５mm／minの測定条件（以下同じ）において２．４ＭＰａ、最大点変位は０．３６ｍｍ、弾性率は１０８ＭＰａであつた。
また、熱分解による重量減少からこの複合体のキトサン／りん酸カルシウム結晶比を調査したところ、略々１／１（重量比）であった。
また、吸引ろ過を行う前のキトサン−りん酸カルシウム複合体懸濁液を、透過型電子顕微鏡で観察することにより、りん酸カルシウム結晶の集合体が観察された。この電子線回折像から、これらの結晶がＨＡｐのＣ軸方向に２０℃以内の角度範囲で配向していることが確認された。
【００１８】
［参考例２］
参考例１と同様の方法により表１記載の原料割合でりん酸カルシウム複合体を製造した。その結果を表１に示す。
【００１９】
【表１】
注）表１のキトサン−りん酸カルシウム複合体を透過型電子顕微鏡（日本電子(株)製）により３万〜１０万倍で観察した結果、いずれもりん酸カルシウム結晶の集合体が確認され、集合体の大きさは長径１００〜４００ｎｍ、短径３０〜６０ｎｍであった。また、その電子線回折像からＨＡｐがＣ軸方向に３０°以内で配向していることが確認された。表１の結果から明らかなように、キトサン−りん酸カルシウム複合体はキトサン含有量の減少にともない硬くなり、柔軟性及び弾力性がなくなることがわかる。
【００２１】
［実施例１］
参考例１で製造したキトサン−りん酸カルシウム複合体試料（Ａ）を表２に示す条件で水熱処理した。その結果を合わせ表２に示す。
【００２２】
【表２】
表２から明らかな通り、水熱処理することにより柔軟性(最大点変位)が向上することが分かる。また、その効果は水熱処理温度が高い程高い。水熱処理温度が高くなると一般的傾向として柔軟性は低下する。また水熱処理時間が長い程効果は大きくなることが分かる。従って用途により水熱処理条件を選択することが必要である。
【００２４】
［参考例３］
参考例１と同一の方法で製造したキトサン−りん酸混合水溶液と水酸化カルシウム懸濁液を、蒸留水５０００ｇの入った反応容器に同時に滴下した。このとき、滴下速度を調整しながら滴下中の反応容器内の溶液ｐＨを８．５〜９．５に保った。滴下終了後、微量の水酸化カルシウムもしくはりん酸を添加してｐＨを８〜９に調整し、一昼夜攪拌下で保持した。これを吸引濾過し、蒸留水５０００ｇで攪拌洗浄した後、再度吸引濾過を行った。次いで更に、２００ＭＰａで圧縮脱水することによりキトサン−りん酸カルシウム複合体を得た。この複合体の物性を測定した結果、曲げ強度２．３ＭＰａ、最大点変位０．３８ｍｍ、弾性率１０８ＭＰａであった。これを透過型電子顕微鏡で観察することにより、りん酸カルシウム結晶の集合体が観察された。この電子線回折像から、これらの結晶がＨＡｐのＣ軸方向に３０℃以内の角度範囲で配向していることが確認された。
【００２５】
［参考例４］
キトサンを溶解させる水溶液を１．５％乳酸水溶液にする以外、参考例１と同一の方法で、キトサン−りん酸カルシウム複合体を得た。この複合体の曲げ強度は２．８ＭＰａ、最大点変位は０．４３ｍｍ、弾性率は１２８ＭＰａであった。
また、熱分解による重量減少からこの複合体のキトサン／りん酸カルシウム比（重量）を調査したところ、ほぼ１／１であった。
また、吸引ろ過を行う前のキトサン−りん酸複合体懸濁液を、透過型電子顕微鏡で観察することにより、りん酸カルシウム結晶の集合体が観察された。この電子線回折像から、これらの結晶がＨＡｐのＣ軸方向に３０°以内の角度範囲で配向していることが確認された。
【００２６】
［参考例５］
塩化カルシウム１１１ｇに蒸留水８８９ｇを加え、塩化カルシウム水溶液を得た。一方、キトサン１００ｇを１％酢酸水溶液１９００ｇに溶解し、キトサン水溶液を得た。
上記キトサン水溶液と４．３％（Ｐ２Ｏ５換算）りん酸ナトリウム水溶液１０００ｇを混合し、キトサン−りん酸ナトリウム混合水溶液を得た。
こうして得られたキトサン−りん酸ナトリウム混合水溶液を２５℃で攪拌中の塩化カルシウム水溶液中に１０ｍｌ／ｍｉｎの速度で滴下し、ｐＨが８〜９になるように調整した。ｐＨの調整には微量の水酸化カルシウム、もしくはりん酸を使用した。添加終了後、１昼夜攪拌下で保持した。これを吸引ろ過し、蒸留水５０００ｇで攪拌洗浄した後、再度吸引ろ過を行った。次いで更に、２００ＭＰａで圧縮脱水することによりキトサン−りん酸カルシウム複合体を得た。この複合体の曲げ強度は２．６ＭＰａ、最大点変位は０．５４ｍｍ、弾性率は１１９ＭＰａであった。
また、熱分解による重量減少からこの複合体のキトサン／りん酸カルシウム比（重量）を調査したところ、ほぼ１／１であった。
また、吸引ろ過を行う前のキトサン−りん酸複合体懸濁液を、透過型電子顕微鏡で観察することにより、りん酸カルシウム結晶の集合体が観察された。この電子線回折像から、これらの結晶がＨＡｐのＣ軸方向に４０°以内の角度範囲で配向していることが確認された。
【００２７】
【発明の効果】
本発明のキトサン−りん酸カルシウム複合体はりん酸カルシウム結晶がキトサンに結着し、またキトサンを良く被覆しているため優れた生体適合性を有する。そしてりん酸カルシウム結晶がヒドロキシアパタイトであるときは更に優れた生体適合性を有する。更に本発明複合体は有機−無機の複合体であるため、その量比を任意に設定することにより、強度の大きいもの、柔軟性のあるものを所望用途により容易に製造することができる。また複合体を水熱処理することにより、その効果は更に大きくなる。以上のような特性を有することから、本発明の複合体は人工骨材料として特に有用である。[0001]
[Industrial application fields]
The present invention relates to a chitosan-calcium phosphate complex and a method for producing the same, and more particularly to a complex useful as an artificial bone material and a method for producing the same.
[0002]
[Prior art]
Currently, metal materials such as stainless steel and titanium, and ceramic materials such as alumina and zirconia are generally used as artificial bone materials. However, since a metal material has a strength higher than that of a living bone, when a load is applied thereto, the regenerated living bone is absorbed by the living body, and a living bone wear phenomenon occurs. In some cases, it is necessary to remove the metal material by surgery. On the other hand, there is a concern that ceramics may be damaged because the elastic modulus is different from that of living bone. Moreover, since these materials are bonded to living bones only on the surface of the material, they may cause peeling. In order to solve these problems, various improvements have been made such as coating the metal surface with hydroxyapatite (hereinafter abbreviated as HAp) and making the ceramic porous, but there are limits to the ceramic alone.
[0003]
Therefore, an attempt has been made to fabricate a material to which characteristics such as flexibility, which cannot be expected only with ceramic or inorganic material, are added by combining an organic polymer material and ceramic or inorganic material.
For example: This is a method for producing an artificial bone by molding and drying a kneaded product of a HAp sintered compact and chitosan gel. When this method is used, the HAp particles are surrounded by chitosan, and the structure in the fine region is different from that of bone. In addition, the interaction between HAp and chitosan is also limited to the particle surface, is structurally close to a mixture, and lacks uniformity. Furthermore, since this artificial bone strongly shows the physical properties of chitosan, it may cause an inflammatory reaction.
[0004]
An artificial bone obtained by mixing and molding HAp and collagen having properties closer to living bones than the artificial bone has been studied. However, since this artificial bone uses collagen, it is very hard and has poor moldability. In particular, it is extremely difficult to form a film or the like. Moreover, in order to suppress the antigenicity of collagen itself, it is necessary to perform treatments such as atelo-treatment, so that not only flexibility cannot be obtained, but artificial bones produced using these raw materials are expensive. Furthermore, Japanese Patent No. 2775386 discloses an apatite / organic composite useful as an artificial bone, and examples of the organic include polysaccharides and hard proteins. In general, a polysaccharide is a charcoal compound that produces one to two or more monosaccharides by hydrolysis. Cellulose, starch, glycogen, dextran, guaran, mannan, caronin, gum Numerous polysaccharides are known regardless of the natural world or living organisms, and many polysaccharides have been synthesized.
[0005]
[Problems to be solved by the invention]
The present invention has been developed in view of the current state of the prior art, and an object thereof is to provide a composite excellent in biocompatibility, strength and flexibility, and a method for producing the same.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors of the present invention have confirmed that chitosan specifically reacts with phosphate ions and calcium ions among the above-mentioned polysaccharides, and the resulting calcium phosphate crystals bind to chitosan. It was discovered that a composite having an orientation and high strength and flexibility was obtained, and the present invention was completed based on such knowledge.
That is, the present invention relates to a chitosan-calcium phosphate complex formed by binding calcium phosphate crystals on chitosan.
The present invention also includes a chitosan-calcium phosphate complex comprising a step of adding phosphoric acid or a water-soluble phosphate to a chitosan solution and adding this to a water-soluble calcium salt or calcium hydroxide suspension to form a precipitate. It relates to the manufacturing method.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The composite of the present invention can be produced, for example, as follows.
A chitosan solution is prepared by dissolving chitosan in an acid such as acetic acid, citric acid, malic acid, oxalic acid or hydrochloric acid. The chitosan concentration is preferably 0.01 to 30% by weight. If it is less than 0.01% by weight, the amount of the reaction solution increases, which is not economical. Moreover, since the viscosity will become high when it exceeds 30 weight%, work operativity will worsen and chitosan solubility will also worsen. Moreover, the diffusibility at the time of mixing with a calcium solution also worsens. Regarding the molecular weight of chitosan used in the present invention, the weight average molecular weight is about 1 to 1,000,000, more preferably 3 to 300,000. That is, when it is less than 10,000, the strength of the molded product becomes weak, and when it exceeds 1,000,000, it becomes difficult to dissolve in an acid. Further, the degree of deacetylation is not particularly limited, but 50 to 100% is preferable.
[0008]
Next, 0.1 to 420% by weight (converted to P 2 O 5 ) of a phosphoric acid solution having a concentration of 0.1 to 65% by weight (converted to P 2 O 5 ) is added to the chitosan solution and stirred well. If the concentration of the phosphoric acid solution is below the lower limit, the amount of calcium phosphate produced on the chitosan is insufficient, and if it exceeds the upper limit, the molecular chain of the chitosan is cleaved and deterioration is likely to occur. Examples of the phosphoric acid solution used in the present invention include, in addition to phosphoric acid, primary and secondary sodium hydrogen phosphates and potassium hydrogen phosphates as good examples. It is not limited to these. Next, this chitosan-phosphate solution is added to and mixed with a calcium solution or calcium hydroxide suspension having a concentration of about 0.05 to 30% by weight (CaO). If it is less than 0.05% by weight, the solution concentration is low and the amount of the reaction solution is increased, which is not economical. On the other hand, if it exceeds 30% by weight, the product will increase the viscosity, making it difficult to achieve homogenization by stirring.
[0009]
The mixing ratio of both is in the range of 80 to 140% by weight as calcium (CaO) with respect to phosphoric acid (P 2 O 5 ). If it deviates from this range, excess phosphoric acid or calcium is present, which is not desirable when used as an artificial bone.
The ratio of chitosan and calcium phosphate (CaO + P 2 O 5 ) is 99/1 to 1/99 (weight), more preferably 15/85 to 85/15 (weight). That is, when it is in this range, chitosan is generally coated with calcium phosphate and has excellent biocompatibility. In general, the greater the amount of chitosan relative to the calcium phosphate crystals produced and bound on chitosan, the more flexible the molded body, while the smaller the amount of chitosan, the harder the molded body. Therefore, it is desirable to adjust the blending ratio depending on the application.
[0010]
Next, the mixing and aging time is generally 1 to 72 hours. The longer the aging time, the more the calcium phosphate crystal formation reaction proceeds and the crystallinity increases. After ripening, that is, after the crystal is developed, it is dehydrated by an optional filter such as a centrifuge, a filter press, a belt press or the like. The preferred method is to have the dehydrator in any desired shape in advance. In this case, the stronger the dehydration pressure, the greater the strength of the composite. The composite can also be produced by pouring this slurry into a container having a desired shape and drying it by any drying method such as natural drying, ventilation drying, ignition drying, freeze drying and the like. The chitosan-calcium phosphate complex thus produced has excellent biocompatibility because calcium phosphate crystals are bound on chitosan and chitosan is well coated with calcium phosphate crystals.
[0011]
The C-axis of the calcium phosphate crystal is oriented, that is, in the same direction. Although the reason why the C-axis of the calcium phosphate crystal of the present invention is oriented in the same direction is not clear, the OH group or NH 2 group of the chitosan molecule and phosphate ion or calcium ion react in sequence to produce the calcium phosphate crystal. It is presumed that the C-axis of these has orientation. Here, the calcium phosphate is oriented in the C-axis direction in the electron diffraction of the aggregate of calcium phosphate crystals confirmed by a transmission electron microscope. Say that. A desirable degree of orientation in the present invention is that it is oriented within 50 °. Here, the orientation degree within 50 ° means that the Debye-Scherrer ring is an arc having a central angle within 50 ° in the previous electron beam diffraction. In particular, when it is within 50 °, calcium phosphate crystals are well developed, and when formed into a molded body, a molded body with high strength can be obtained.
[0012]
The calcium phosphate of the present invention refers to calcium phosphate compounds such as HAp, tricalcium phosphate and octacalcium phosphate. The most desirable calcium phosphate crystal in the present invention is HAp. Furthermore, it is desirable that HAp is contained in an amount of 70% by weight or more as calcium phosphate crystals. The size of the aggregate of calcium phosphate crystals of the present invention varies depending on the production method, but is generally 100 to 400 nm in major axis.
[0013]
A more desirable method for producing the composite of the present invention is hydrothermal treatment of the composite produced as described above. The hydrothermal temperature is preferably 50 to 200 ° C. Regarding the heat treatment temperature, if it is less than 50 ° C., a long heat treatment time is required and the effect is small. If it exceeds 200 ° C., the chitosan chain is broken or decomposed, which is not desirable. In terms of hydrothermal treatment time, 1 to 120 minutes is preferable. If it is less than 1 minute, the effect of the present invention cannot be expected, and if it exceeds 120 minutes, no further effect can be obtained. That is, the maximum point stress and the maximum point displacement are remarkably increased by performing the hydrothermal treatment. Furthermore, the advantage of performing the hydrothermal treatment is that the composite can be sterilized without using a chemical such as a sterilizing agent under the heat treatment conditions of 120 ° C. or higher and 20 minutes or longer.
[0014]
The chitosan-calcium phosphate complex of the present invention can be produced by the above method, but is not limited thereto. The use of the composite of the present invention has been described mainly for artificial bones, but the composite of the present invention can be adjusted freely in its hardness and flexibility by adjusting the ratio of chitosan and calcium phosphate. It can also be used for artificial ligaments, artificial tendons, anchors for artificial tendons and artificial cartilage, artificial cartilage, bone defect filling materials, artificial blood vessels, artificial esophagus, artificial skin and the like. The composite of the present invention can be formed into an arbitrary shape such as a thread shape, a mesh shape, a screw shape, or a cylindrical shape depending on the application.
[0015]
【Example】
Examples of the present invention will be further described below, but the present invention is not limited thereto. All percentages are by weight unless otherwise specified.
[0016]
[Reference Example 1]
116 g of calcium carbonate was calcined at 1200 ° C. for 3 hours in an electric furnace to obtain calcium oxide. While shaking 65 g of the obtained calcium oxide, 63 g of distilled water was gradually added and waited until the exotherm subsided. To this was further added 872 g of distilled water and stirred for 1 hour to obtain a calcium hydroxide suspension.
On the other hand, 100 g of chitosan (weight average molecular weight of about 100,000, deacetylation degree of about 80%) was dissolved in 1900 g of 1% acetic acid aqueous solution to obtain a chitosan aqueous solution. The chitosan aqueous solution was mixed with 1000 g of 4.3% (P 2 O 5 equivalent) phosphoric acid aqueous solution to obtain a chitosan-phosphoric acid mixed aqueous solution.
The chitosan-phosphate mixed aqueous solution thus obtained was added dropwise at a rate of 10 ml / min to the calcium hydroxide suspension being stirred at 25 ° C. After completion of the dropwise addition, a small amount of calcium hydroxide or phosphoric acid was added to adjust the pH to 8-9, and the mixture was kept under stirring for a whole day and night. This was subjected to suction filtration, stirred and washed with 5000 g of distilled water, and then subjected to suction filtration again. Subsequently, the chitosan-phosphate complex was further obtained by compression dehydration at 200 MPa (A).
[0017]
The bending strength of this composite (3 × 5 × 20 mm, the same shall apply hereinafter) is 2.4 MPa, the maximum point displacement is 0.36 mm under the measurement conditions of the distance between the lower fulcrums of 15 mm and the test speed of 0.5 mm / min (hereinafter the same) The elastic modulus was 108 MPa.
Further, when the chitosan / calcium phosphate crystal ratio of this composite was investigated from the weight loss due to thermal decomposition, it was about 1/1 (weight ratio).
Moreover, aggregates of calcium phosphate crystals were observed by observing the chitosan-calcium phosphate complex suspension before suction filtration with a transmission electron microscope. From this electron beam diffraction image, it was confirmed that these crystals were oriented in the angle range within 20 ° C. in the C-axis direction of HAp.
[0018]
[Reference Example 2]
In the same manner as in Reference Example 1, calcium phosphate composites were produced at the raw material ratios shown in Table 1. The results are shown in Table 1.
[0019]
[Table 1]
Note) As a result of observing the chitosan-calcium phosphate complex shown in Table 1 at a magnification of 30,000 to 100,000 times with a transmission electron microscope (manufactured by JEOL Ltd.), all aggregates of calcium phosphate crystals were confirmed. The size of the aggregate was 100 to 400 nm in the major axis and 30 to 60 nm in the minor axis. Further, it was confirmed from the electron diffraction image that HAp was oriented within 30 ° in the C-axis direction. As is apparent from the results in Table 1, it can be seen that the chitosan-calcium phosphate complex becomes harder as the chitosan content decreases, and loses flexibility and elasticity.
[0021]
[Example 1]
The chitosan-calcium phosphate complex sample (A) produced in Reference Example 1 was hydrothermally treated under the conditions shown in Table 2. The results are shown in Table 2.
[0022]
[Table 2]
As is apparent from Table 2, it can be seen that the flexibility (maximum point displacement) is improved by hydrothermal treatment. The effect is higher as the hydrothermal treatment temperature is higher. As the hydrothermal treatment temperature increases, the flexibility tends to decrease as a general tendency. It can also be seen that the longer the hydrothermal treatment time, the greater the effect. Therefore, it is necessary to select hydrothermal treatment conditions depending on the application.
[0024]
[Reference Example 3]
A chitosan-phosphoric acid mixed aqueous solution and a calcium hydroxide suspension produced by the same method as in Reference Example 1 were simultaneously added dropwise to a reaction vessel containing 5000 g of distilled water. At this time, the solution pH in the reaction vessel during dropping was kept at 8.5 to 9.5 while adjusting the dropping rate. After completion of the dropwise addition, a small amount of calcium hydroxide or phosphoric acid was added to adjust the pH to 8-9, and the mixture was kept under stirring all day and night. This was suction filtered, stirred and washed with 5000 g of distilled water, and then suction filtered again. Subsequently, a chitosan-calcium phosphate complex was obtained by further compressing and dehydrating at 200 MPa. As a result of measuring the physical properties of this composite, the bending strength was 2.3 MPa, the maximum point displacement was 0.38 mm, and the elastic modulus was 108 MPa. By observing this with a transmission electron microscope, an aggregate of calcium phosphate crystals was observed. From this electron beam diffraction image, it was confirmed that these crystals were oriented in an angle range within 30 ° C. in the C-axis direction of HAp.
[0025]
[Reference Example 4]
A chitosan-calcium phosphate complex was obtained in the same manner as in Reference Example 1 except that the aqueous solution for dissolving chitosan was a 1.5% lactic acid aqueous solution. The composite had a bending strength of 2.8 MPa, a maximum point displacement of 0.43 mm, and an elastic modulus of 128 MPa.
Further, when the chitosan / calcium phosphate ratio (weight) of this composite was investigated from the weight reduction due to thermal decomposition, it was almost 1/1.
Moreover, the aggregate of the calcium phosphate crystal | crystallization was observed by observing the chitosan-phosphate complex suspension before performing suction filtration with a transmission electron microscope. From this electron beam diffraction image, it was confirmed that these crystals were oriented in an angle range of 30 ° or less in the C-axis direction of HAp.
[0026]
[Reference Example 5]
Distilled water (889 g) was added to calcium chloride (111 g) to obtain a calcium chloride aqueous solution. On the other hand, 100 g of chitosan was dissolved in 1900 g of a 1% acetic acid aqueous solution to obtain a chitosan aqueous solution.
The chitosan aqueous solution and 1000 g of 4.3% (P 2 O 5 equivalent) sodium phosphate aqueous solution were mixed to obtain a chitosan-sodium phosphate mixed aqueous solution.
The chitosan-sodium phosphate mixed aqueous solution thus obtained was added dropwise at a rate of 10 ml / min to a calcium chloride aqueous solution being stirred at 25 ° C., and the pH was adjusted to 8-9. A small amount of calcium hydroxide or phosphoric acid was used to adjust the pH. After completion of the addition, the mixture was kept under stirring for one day. This was subjected to suction filtration, stirred and washed with 5000 g of distilled water, and then subjected to suction filtration again. Subsequently, a chitosan-calcium phosphate complex was obtained by further compressing and dehydrating at 200 MPa. The composite had a bending strength of 2.6 MPa, a maximum point displacement of 0.54 mm, and an elastic modulus of 119 MPa.
Further, when the chitosan / calcium phosphate ratio (weight) of this composite was investigated from the weight reduction due to thermal decomposition, it was almost 1/1.
Moreover, the aggregate of the calcium phosphate crystal | crystallization was observed by observing the chitosan-phosphate complex suspension before performing suction filtration with a transmission electron microscope. From this electron beam diffraction image, it was confirmed that these crystals were oriented within an angle range of 40 ° or less in the C-axis direction of HAp.
[0027]
【The invention's effect】
The chitosan-calcium phosphate complex of the present invention has excellent biocompatibility because calcium phosphate crystals are bound to chitosan and well coated with chitosan. And when the calcium phosphate crystal is hydroxyapatite, it has further excellent biocompatibility. Furthermore, since the composite of the present invention is an organic-inorganic composite, it is possible to easily produce a high-strength or flexible one depending on the desired application by arbitrarily setting the amount ratio. The effect is further increased by hydrothermally treating the composite. Due to the above properties, the composite of the present invention is particularly useful as an artificial bone material.
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