WO2012054010A1

WO2012054010A1 - Bone cement formula and bioresorbable hardened bone cement composites prepared with the same

Info

Publication number: WO2012054010A1
Application number: PCT/US2010/002777
Authority: WO
Inventors: Jiin-Huey Chern Lin; Chien-Ping Ju
Original assignee: Jiin-Huey Chern Lin; Chien-Ping Ju
Priority date: 2010-10-19
Filing date: 2010-10-19
Publication date: 2012-04-26

Abstract

The present invention provides a bone cement formula having a powder component and a setting liquid component, wherein the powder component includes a calcium sulfate source and a calcium phosphate source with a weight ratio of the calcium sulfate source less than 65%, based on the total weight of the calcium sulfate source and the calcium phosphate source, and the setting liquid component comprises ammonium ion (NH4+) in a concentration of about 0.5 M to 4 M, wherein the calcium phosphate source includes tetracalcium phosphate (TTCP) and dicalcium phosphate in a molar ratio of TTCP to dicalcium phosphate of about 0.5 to about 2.5, and the calcium sulfate source is calcium sulfate hemihydrate (CSH), calcium sulfate dehydrate (CSD), or anhydrous calcium sulfate.

Description

Bone cement formula and bioresorbable hardened bone cement composites prepared with the same

Field

The exemplary embodiment(s) of the present invention relates to bone repairing substance for medicaments. More specifically, the exemplary embodiment(s) of the present invention relates to a bone cement formula.

Background

Bone cement compositions are widely used in bonding, filling, and/or repairing damaged natural bone. Bone cement is typically used in orthopedic, dental procedures, and/or other medicinal applications.

Despite many advantages such as excellent biocompatibility, superior osteoconductivity, and enhanced mechanical or physical strength, the majority of calcium phosphates exhibit clinically low bioresorption rates. On the other hand, the compound of calcium sulfates also illustrate higher dissolution rates, which, for many applications, is typically too high of dissolution rate for allowing new bone cells to quickly grow in a bone cavity. The composite including calcium sulfates generally has lower mechanical and/or physical strengths than calcium phosphates.

Another problem associated with conventional bone cement paste is prolong setting time whereby it hampers applicability to various applications. For example, calcium phosphate (CPC) paste, which is described in US patent No. : 4,612,053, typically requires prolong setting time.

Summary

Embodiment(s) of the present invention discloses a method of providing a calcium phosphate-calcium sulfate composite that exhibits enhanced strength, excellent biocompatibility, superior osteoconductivity, appropriate and adjustable bioresorption rate.

The objectives of embodiments are to provide a bone cement formula, a bone cement paste, a hardened bone cement composite from paste, a hardened bone cement composite with enhanced strength by pressurizing the paste while leaking solution from the paste, and porous hardened bone cement composite from the paste.

The embodiments of the present invention provides methods for providing a bone cement formula, bone cement paste, hardened bone cement composite, hardened bone cement composite with enhanced strength, and porous hardened bone cement composite.

An embodiment of the present invention provides a method for filling a hole or cavity in a bone with an exemplary embodiment of bone cement paste which will cure or harden in a hole or cavity in need of treatment. Another embodiment of the present invention provides a method for implanting hardened bone cement composite during a treatment.

One embodiment of the present invention provides a bone cement formula which includes a powder component and a setting liquid component with a liquid to powder ratio of 0.20 cc/g to 0.50 cc/g (cc is cubic centimeter, g is gram), preferably 0.25 cc/g to 0.35 cc/g. The powder component, in one aspect, includes a calcium sulfate source and a calcium phosphate source with a weight ratio of the calcium sulfate source less than 65%, based on the total weight of the calcium sulfate source and the calcium phosphate source. The setting liquid component, in one aspect, includes ammonium ion (NH₄ ⁺) in a concentration of about 0.5 M to 4 M. The calcium phosphate source, in one aspect, includes tetracalcium phosphate (TTCP) and dicalcium phosphate in a molar ratio of TTCP to dicalcium phosphate of about 0.5 to about 2.5, preferably about 1 .0, and the calcium sulfate source is calcium sulfate hemihydrate (CSH), calcium sulfate dehydrate (CSD), or anhydrous calcium sulfate, and preferably, CSH.

It should be noted that, for different medical indications, the required resorption rates can be different. As such, more desirable cement should be able to provide a range of bone resorption rates without substantially changing its primary formula, performance and working/setting times. For example, a resorption rate of implanted hardened cement composite can be adjustable due to co-existence of a calcium sulfate source and a calcium phosphate source. Our animal study demonstrates that the resorption rate of our hardened sulfate-phosphate cement composite can be adjusted by adjusting the sulfate/phosphate ratio. In one embodiment, calcium sulfate source of the powder component is greater than 5%, and preferably in a range of 10% to 55%, based on the total weight of the calcium sulfate source and the calcium phosphate source powder. Calcium phosphate source, in one aspect, includes tetracalcium phosphate (TTCP) and dicalcium phosphate, preferably DCPA, in a molar ratio of TTCP to dicalcium phosphate of approximately 0.5 to 2.5, preferably about 1.0, and the calcium sulfate source is calcium sulfate hemihydrate (CSH), calcium sulfate dehydrate (CSD), or anhydrous calcium sulfate, and preferably, CSH.

As illustrated or demonstrated in Control Examples 1-4, detailed discussion in the section of Experiential Procedures below, the combination of TTCP, DCPA and CSH is essential. As TTCP, DCPA, and CSH can be combined or mixed in a certain weight-ratio range, various unique and non-replaceable results are obtained. On the other hand, various experiments of mixtures of two compounds, such as TTCP/CSH and

DCPA/CSH, result unsatisfactory results.

Although ammonium is generally considered as a rather toxic

component, the experiment, shown below, illustrates that ammonium provides not only a cytotoxically acceptable cement formula, but also a cement formula with unprecedented performance. When concentration of ammonium ions is too low, the cement paste can be either dispersed right upon contact with liquid, such as water or body fluid (i.e., blood), or has an initial mechanical strength that is too low to maintain cement paste integrity which can cause premature fracture of cement paste. On the other hand, when ammonium ion concentration is too high, the cement paste becomes too toxic to be used as an implant.

In one embodiment, the setting liquid component comprises ammonium ion (NH₄ ⁺) in a concentration of about 1.0 M to 2.0 M, and more preferably about 1.2 M.

The setting liquid component, in one example, is a solution of

NH4H2PO4, (NH₄)₂HP0₄, (NH₄)₃P04-3H₂0 or a mixture of them. Preferably, the setting liquid component is an aqueous solution. Selectively, the setting liquid component further comprises citric acid or tartaric acid dissolved therein. The setting liquid component preferably has a pH of about 7.0 to about 9.0.

In one embodiment, the powder component comprises a pore-forming agent which is to be dissolved in a solution when hardened bone cement composite is immersed in the solution. Preferably, the pore-forming agent is selected from the group consisting of LiCI, KCI, NaCI, MgCI₂, CaCI₂, NalC>3, Kl, Na₃P0₄, K₃P0₄, Na₂C0₃, amino acid-sodium salt, amino acid-potassium salt, glucose, polysaccharide, fatty acid-sodium salt, fatty acid-potassium salt, potassium bitartrate (KHC₄H₄C>6), potassium carbonate, potassium gluconate (KC₆Hn0₇), potassium-sodium tartrate (KNaC₄H 0₆-4H₂0), potassium sulfate (K₂S0 ), sodium sulfate, sodium lactate and mannitol. The amount of the pore-forming agent used is proportional to the porosity of the hardened bone cement composite to be achieved.

In one embodiment, the calcium phosphate source is a mixture of TTCP and DCPA. The bone cement formula, in one aspect, allows bone cement paste having a desirable working time and a setting time, so that the operator has a sufficient period of time to fill the hole or cavity with the paste before the paste becomes hardened. It should be noted that filled paste will develop minimum strength required by the treatment within an acceptable short period of time.

The hardened bone cement composite, in one embodiment, possesses a low toxicity whereby it is safe to be applied to a patient, for example. Note that hardened bone cement has a characteristic of high initial strength with an improved bioresorbable rate.

Additional features and benefits of the present invention will become apparent from the detailed description, figures and claims set forth below.

Detailed Description

Embodiments of the present invention are described herein in the context of method, formula, system, and/or process for preparing a hardened bone cement composite having an enhanced bioresorbable rate for medicaments. Those of ordinary skills in the art will realize that the following detailed description of the embodiment(s) is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure.

References to "one embodiment," "an embodiment," "example embodiment," "various embodiments," "exemplary embodiment," "one aspect," "an aspect," "exemplary aspect," "various aspects," etc. , indicate that the embodiment(s) of the invention so described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic.

Further, repeated use of the phrase "in one embodiment" does not necessarily refer to the same embodiment, although it may.

In the interest of clarity, not all of the routine features of the

implementations and/or processes described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions will be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skills in the art having the benefit of this disclosure.

Embodiment(s) of the present invention is bioresorbable bone cement applicable to various medical fields, such as orthopedic, spinal, and root canal surgeries. Characteristics or properties of the bioresorbable bone cement or formula have convenient working environment(s) and setting times to form a hardened block with high strength, excellent biocompatibility and superior osteoconductivity, and adjustable (or flexible) bioresorption rate.

To prepare or make the bioresorbable bone cement having properties of flexible (or convenient) work environment (or time) and setting times to form hardened bone cement composites with desirable strength and biological compatibility, one embodiment of the present invention discloses a bone cement formula which is be described more details below. In one aspect, a method or process for preparing hardened bone cement composite involves producing bone cement paste and placing the paste in an environment where the paste can set.

A process for preparing bone cement paste, in one embodiment, comprises mixing powder component with setting liquid component by a mixing mechanism such as agitation. The powder component, for example, may include mixture of calcium sulfate source and calcium phosphate source. Alternatively, calcium sulfate source and calcium phosphate source can be separate powders. In this case, calcium sulfate source and calcium phosphate source are combined first to form a power mixture prior to mixing with setting liquid component.

The calcium sulfate source and calcium phosphate source discussed earlier can be tetracalcium phosphate (TTCP) and/or dicalcium phosphate anhydrous (DCPA) powders. It should be noted that other types of sources can be used as long as they have similar chemical properties or

characteristics as TTCP and/or DCPA.

The bone cement paste, in one embodiment, becomes hard or cured within a period of setting time under an atmosphere environment or an environment surrounded by body fluid such as blood. During an operation, an operator or doctor places bone cement paste into a hole or cavity at a damaged bone via a suitable tool through an incision. For example, for an orthopedic, spinal or root canal treatment, when bone cement paste becomes or cures into hardened bone cement composite in-situ, the hardened bone cement will be resorbed by the subject body over time in accordance with a predefined bioresorption rate. Depending on

applications, bone cement paste, in one embodiment, can be shaped into a rigid or semi-rigid block of bone cement composite before it is implanted in the subject body to repair damaged parts such as bones or teeth.

The bone cement paste, in one embodiment, can be injected into a bone hole or cavity with an orthopedic paste delivering tool such as a

conventional medical instrument described in US 7,325,702 B2 or shaped through a mold, in which the paste will form a block of hardened bone cement composite. It should be noted that an orthopedic delivering tool is able to continually deliver the paste into a bone cavity until the cavity is filled. Depending on applications, a dense block of cement can be formed if the powder component does not contain the appropriate pore-forming agents. The dense block, for example, can be formed by pressurizing the bone cement paste in a mold before the paste sets in order to drain or remove a portion of liquid from the paste whereby a liquid/powder ratio of the paste decreases. In one aspect, the pressure applied to the paste at the mold has a range from approximately 1 megapascal ("MPa") to 500 MPa, preferably from 100 MPa to 500 MPa. It is noted that the dense block has a superior compressive strength which can be used as a medical implant. It should be further noted that a rigid or solid dense block of calcium phosphate cement is impregnated with an impregnating liquid for a predefined period of time, so that overall compressive strength of the resulting impregnated block is increased compared to a block which has not undergone such impregnating treatment. The impregnating liquid, in one embodiment, is phosphate-containing solution. Exemplary aqueous solution may include, but not limited to, (NH₄)₃P0₄, (NH₄)₂H P0₄, NH₄H₂P0₄, K₃P0₄, K₂HP0₄, KH₂P0₄, Na₃P0₄, Na₂HP0₄, NaH₂P0₄, or H₃P0₄. The phosphate-containing solution, in one example, has a phosphate

concentration of about 0.1 M to about 6 M, preferably from about 1 M to about 3 M.

A porous block can be utilized as a tissue-engineered scaffold when the powder component of the bone cement formula contains pore-forming agent. The pore-forming agent can be removed from a molded block by immersing the molded block in immersing liquid so that the pore-forming agent is dissolved in the immersing liquid. The pore-forming agent may be added during the mixing of the powder component and the setting liquid component, or may be added to the resultant paste before it is placed in a mold. The immersing liquid, for example, can be an acidic aqueous solution, a basic aqueous solution, a physiological solution, an organic solvent or

substantially pure water. In one embodiment, the immersing liquid is the same as the above-mentioned impregnating liquid. In one embodiment, the immersing liquid is waster. In one aspect, the porous block has a porosity of 50-90 vol%. The dense block or porous block prepared in accordance with the bone cement formula, in one embodiment, can be deposited within living cells, a growth factor and/or a drug by impregnating the block in a suspension of living cells or a solution of the growth factor and/or drug. The dense block and the porous block prepared in the present invention may be further broken up into pellets for other medical applications.

The following examples via experimental procedures are illustrative and are intended to demonstrate embodiments of the present invention, which, however, should not be taken to limit the embodiments of the invention to the specific embodiments, but are for explanation and understanding only, since numerous modifications and variations will be apparent to those skilled persons in this art.

Experimental proced ures

Abbreviation

TTCP: tetracalcium phosphate

DCPA: dicalcium phosphate anhydrous

CSH: calcium sulfate hemihydrate

WT: Working time

ST: Setting time

UP ratio: Liquid/powder ratio

CS: Compressive strength

Symbols used in tables

#: Paste cannot be formed by mixing powder and liquid for 2 minutes.

*: After being removed from the mold (30 minutes from mixing powder and liquid), the hardened cement blocks collapses and disintegrates into powder form when it is immersed in Hanks' solution for 1 day.

·½ Hardened cement blocks are broken (fractured/cracked but not dispersed into powder form) after being immersed in Hanks' solution for 1 day.

Preparation of TTCP powder

The TTCP powder was fabricated in-house from the reaction of dicalcium pyrophosphate (Ca_{2 2}0₇) (Sigma Chem. Co. , St. Louis, MO, USA) and calcium carbonate (CaC0₃) (Katayama Chem. Co. , Tokyo, Japan) using the method suggested by Brown and Epstein [Journal of Research of the National Bureau of Standards- A Physics and Chemistry 6 ( 1965) 69A 1 2].

TTCP powder was prepared by mixing Ca₂P₂0₇ powder with CaCC>3 powder uniformly for 12 hours. The mixing ratio of Ca₂P20₇ powder to CaC0₃ powder was 1 : 1 .27 (weight ratio) and the powder mixture was heated to 1400°C to allow two powders to react to form TTCP.

Preparation of a TTCP/DCPA/CSH com posite paste

Appropriate amounts of TTCP and DCPA powders were uniformly mixed in a ball miller, followed by uniformly mixing with appropriate amount of CSH powder. The resultant TTCP/DCPA/CSH mixed powders were mixed uniformly with a desirable setting solution (e. g . , 0.6M (N H₄)₂H P0₄) at a desirable UP ratio (e.g. , 0.28 cc/g) to form a TTCP/DCPA/CSH paste. Chemicals used for the study

Com pressive strength testing of composite cement To measure the CS of a hardened cement, after mixing for 1 min, the cement paste was packed in a 6 mm diameter, 12 mm deep cylindrical stainless steel mold under a pressure of 1 .4 MPa for 30 min. After being removed from the mold, the hardened cement samples were immersed in Hanks' physiological solution which was maintained at 37°C and agitated daily to help maintain uniform ion concentrations. After immersion, samples were removed from the solution for CS testing while samples are still wet ("test under wet condition"). The CS testing was conducted using a desk-top mechanical tester (Shimadzu AG-10kNX, Tokyo, Japan) at a crosshead speed of 1 .0 mm/min. The test method is according to ASTM 451 -99a method.

Working time/setting time measurement

The working time of cement paste was determined by the time after that the cement paste was no longer workable. The setting time of cement paste was measured according to the standard method set forth in ISO 1566 for dental zinc phosphate cements. The cement is considered set when a 400 gm weight loaded onto a Vicat needle with a 1 mm diameter tip fails to make a perceptible circular indentation on the surface of the cement. pH measurement

The early stage (during setting process) variation in pH was determined using a pH meter (Suntex Instruments SP2000, Taipei, Taiwan) that was buried in the cement paste immediately after the powder and setting liquid were mixed. The first reading was taken at 1 minute after mixing. The measurement was continued until the paste nearly becomes set. Readings were taken every 30 seconds until 30 minutes after mixing. After then they were taken every 60 seconds.

The variation in pH value of Hanks' solution in which the cement paste sample was immersed was monitored using the same pH meter. 2 g cement paste was taken after mixing the powder and the setting solution for 5 minutes, and it was immersed in 20 ml Hanks' solution with a pH value of 7.05 for the test. The solution was maintained at 37°C throughout testing and continually stirred to help maintain uniform ion concentrations of the solution.

Cytotoxicity test

The cytotoxicity test was performed according to ISO 10993-5. The extraction method was used. NIH/3T3 fibroblasts (seeding density 5000 per well) were pre-cultured for 24h in Dulbecco's modified essential medium (DMEM) supplemented with bovine serum (10%) and PSF (1%). An extract was prepared by immersing a hardened cement paste in the culture medium at a ratio of 0.1 (g/ml) at 37°C for 24h and then collecting the liquid by centrifugation. The extract was added to the 96 well microplate (100 μΙ per well) incubated in a 5% C0₂ humidified atmosphere at 37°C. After 24h, the extract was sucked out and then a mixture of the culture medium (100 μΙ) and WST-1 (10 μΙ) was added to the wells and incubated for 1h at 37°C. Cell viability was measured by using the WST-1 assay. This is a

colorimetric assay of mitochondrial dehydrogenase activity where the absorbance at 450 nm is proportional to the amount of dehydrogenase activity in the cell. After 1h incubation, the mixture of medium and WST-1 was transferred to a 96 well microplate and the absorbance at 450 nm was measured with an ELISA reader. Al₂0₃ powder was also assayed as a control. Four bars were tested for each sample (n=4).

Cell line information

Control 1 : TTCP/CSH cement and (NH₄)₂HP0₄ setting solution

Table 1 . TTCP/CSH mixed with 0.25-0.75M (NH₄)₂HP0₄

In the cases where the pastes were prepared with 0.25 M (NH₄)₂H P0 the molded lumps collapse and disintegrate when they are immersed in Hanks' solution (^*), or their compressive strength cannot be measured after being immersed in Hanks' solution for 1 day as shown. in Table 1 . As to the pastes prepared with higher concentration (NH₄)₂HP0₄ setting solutions, the hardened cement blocks give a very low compressive strength after being immersed in Hanks' solution for 1 day ( 1 d-CS) as shown in Table 1 . Apparently the powder component having only TTCP and CSH phases does not give a satisfactory result.

Control 2: TTCP/CSH cement and NH₄H₂P0₄ setting solution

Table 2. TTCP/CSH mixed with 0.25-0.75M N H₄H₂P0₄

Table 2 shows that N H₄H₂P0₄ setting solution used in Control 2 cannot improve the (NH₄)₂H P0 setting solution used in Control 1 in term of the working/setting times and the 1 d-CS. Apparently the powder component having only TTCP and CSH phases dose not give a satisfactory result.

Control 3: DCPA/CSH cement and (N H₄)₂HP0₄ setting solution

Table 3. DCPA/CSH mixed with 0.25-0.75M (N H₄)₂HP0₄

The molded lumps prepared from DCPA/CSH cement collapse and disintegrate when they are immersed in Hanks' solution (^*), or their compressive strength cannot be measured after being immersed in Hanks' solution for 1 day (¾ ) as shown in Table 3. Apparently the powder component having only DCPA and CSH phases does not give a satisfactory result.

Control 4: DCPA/CSH cement and NH₄H₂P0₄ setting solution

Table 4. DCPA/CSH mixed with 0.25-0.75M NH₄H₂P0₄

The compressive strength of the molded lumps prepared from

DCPA/CSH cement cannot be measured after being immersed in Hanks' solution for 1 day as shown in Table 4. Apparently the powder component having only DCPA and CSH phases does not give a satisfactory result.

For Tables 5-14

Note: TTCP and DCPA have a molar ratio of 1 : 1 under all conditions

Example 1 : (TTCP/DCPA)/CSH cement and various setting solutions

Table 5. 75 wt% phosphate (TTCP/DCPA)/25 wt% CSH composite cement

It can be summarized from the data shown in Table 5 as follows:

1 . K₂HP0₄-derived hardened cement composites have too short WT/ST and low CS.

2. (NH₄) H2P04-derived hardened cement composites have reasonable WT/ST, but is dispersed after immersion in Hanks' solution.

3. NaH₂P0₄-2H₂0-derived hardened cement composites have reasonable WT/ST, but too acidic and low strength.

4. Among all setting solutions tested, (NH₄)₂HP0 results in the highest

CS.

5. Among all (NH )₂HP0₄ concentrations, 0.6 M gives the highest CS (41 MPa). Exam ple 2: TTCP/DCPA/CSH mixed with 0.60M (N H₄)₂H P0₄

Table 6. TTCP/DCPA/CSH mixed with 0.60 M (N H₄)₂HP0₄.

Summary of the results shown in Table 6 (TTCP/DCPA/CSH mixed with 0.60 M (N H₄)₂H P0₄):

(1 ) When CSH contents are higher than about 65 wt% in the

TTCP/DCPA/CSH cement powder, their CS values become too low (< 1 5 MPa). The appropriate CSH content under the test conditions should be less than about 65 wt%. To obtain a higher strength (CS > 30 MPa), the CSH content should be less than about 35 wt%.

(2) All cytotoxicity values are acceptably greater than 80% for all CSH

contents (from about 10 wt% to about 90 wt%) when 0.60 M (NH₄)₂H P0₄ is used as hardening solution. Exam ple 3: TTCP/DCPA/CSH mixed with 0.20-3.0 M (NH₄)₂HP0₄

Table 7. TTCP/DCPA/CSH (TTCP/DCPA : CSH = 90: 10) mixed with

0.20-3.00M (NH₄)₂HP0₄

Summary of the results shown in Table 7 (TTCP/DCPA/CSH

(TTCP/DCPA : CSH = 90: 10) mixed with 0.20-3.00M (NH₄)₂HP0₄):

(1 ) When the (NH₄)₂HP0₄ concentration is too low (0.25 M or lower under the present test conditions), the hardened paste is dispersed upon immersion in Hanks' solution and its strength cannot be measured.

(2) Although ammonium is a critical life-sustaining element, the (NH )₂HP0₄ concentration cannot be too high (2 M or higher under the present test conditions) for reducing cytotoxicity level.

(3) The appropriate (NH )₂HP0 concentration should be in the window of 0.25 M-2.0 M, preferably 0.5 M-1 .0 M. (or the NH₄ ⁺ ion concentration in the window of 0.50 M-4.0 M, preferably 1 .0 M-2.0 M) Example 4: TTCP/DCPA/CSH mixed with 0.20-3.0 M (NH₄)₂HP0₄

Table 8. TTCP/DCPA/CSH (TTCP/DCPA : CSH = 75:25) mixed with

0.20-3.00M (NH₄)₂HP0₄

Summary of the results shown in Table 8 (TTCP/DCPA/CSH

(TTCP/DCPA : CSH = 75:25) mixed with 0.20-3.00M (N H₄)₂HP0₄):

(2) Although ammonium is a critical life-sustaining element, the (NH₄)₂HP0 concentration cannot be too high (> 2 M under the present test conditions) for reducing cytotoxicity level.

(3) The appropriate (N H₄)₂HP0₄ concentration should be in the window of 0.25 M-2.0 M, preferably 0.5 M-1 .0 M. (or the NH₄ ⁺ ion concentration in the window of 0.50 M-4.0 M, preferably 1 .0 M-2.0 M) Example 5: TTCP/DCPA/CSH mixed with 0.25-1.0 M (NH₄)₂HP0₄

Table 9. TTCP/DCPA/CSH (TTCP/DCPA : CSH = 65:35) mixed with

0.25-1.0M (NH₄)₂HP0₄

Summary of the results shown in Table 9 (TTCP/DCPA/CSH

(TTCP/DCPA : CSH = 65:35) mixed with 0.25-1.0M (NH₄)₂HP0₄):

(1) When the (NH₄)₂HP0₄ concentration is too low (0.25M or lower under the present test conditions), the hardened paste is dispersed upon immersion in Hanks' solution and its strength cannot be measured.

(2) Except a few cases, all 1-d CS values are higher than 20 MPa, and, under certain conditions, higher than 30 MPa. Example 6: TTCP/DCPA/CSH mixed with 0.40-1 .0 M (NH₄)₂HP0₄ Table 10. TTCP/DCPA/CSH (TTCP/DCPA : CSH = 55:45) mixed with

0.40-1.00M (NH₄)₂HP0₄

Summary of the results shown in Table 10 (TTCP/DCPA/CSH

(TTCP/DCPA : CSH = 55:45) mixed with 0.40-1 .00M (NH₄)₂HP0₄):

(1 ) All 1 -d CS values are higher than 20 MPa, and, under certain conditions, higher than 30 MPa.

(2) For higher concentration (1 .0M) and lower L/P values (lower than 0.33 cc/g), the WT/ST are a little too short. Example 7: TTCP/DCPA/CSH mixed with 0.40-0.60 M (NH₄)₂HP0₄

Table 11 . TTCP/DCPA/CSH (TTCP/DCPA : CSH = 45:55) mixed with 0.40-0.60 M (NH₄)₂HP0₄

Summary of the results shown in Table 11 (TTCP/DCPA/CSH

(TTCP/DCPA : CSH = 45:55) mixed with 0.40-0.60M (NH₄)₂HP0₄):

(1 ) All 1 -d CS values are higher than 20 MPa

(2) Working times are longer than 5.5 min and setting times are longer than 7.5 min under all testing conditions.

Table 12. CS (MPa) of TTCP/DCPA/CSH after immersion in Hanks' solution for different days

Summary of the results shown in Table 12:

(1 ) Except the "55:45" composite, all 42d-CS values are higher than 20 MPa, indicating a mild decay in strength even after immersion in Hanks' solution for 42 days. When the CSH content is increased to 45 wt%, however, the CS value of the composite decreases very significantly.

Example 8: Effects of addition of organic acids on TTCP/DCPA/CSH mixed with 1 .0 M (N H₄)₂HP0₄ Table 13. Effects of addition of organic acids (tartaric acid, citric acid and malic acid) on properties of TTCP/DCPA/CSH (TTCP/DCPA : CSH = 75:25) mixed with 1 M (NH₄)₂HP0₄

Summary of the results shown in Table 13:

(1 ) Addition of malic acid in 1 M (NH₄)₂HP0₄ setting solution decreases the CS value of the hardened composite cement

(2) Addition of citric acid in 1 M (NH )₂HP0₄ setting solution increases the CS value of the hardened composite cement (from about 28 MPa to about 32 MPa)

(3) Addition of tartaric acid in 1 M (NH₄)₂HP0₄ setting solution increases the CS value of the hardened composite cement (from about 28 MPa to 35 MPa) Preparation of a TTCP/DCPA/CSH com posite dense block

Appropriate amounts of TTCP and DCPA powders were uniformly mixed in a ball miller, followed by uniformly mixing with appropriate amount of CSH powder. The resultant TTCP/DCPA/CSH mixed powders were mixed uniformly with a desirable setting solution (e. g . , 0.6M (N H₄)₂H P0₄) at a desirable UP ratio (e.g. , 0.28 cc/g) to form a TTCP/DCPA/CSH paste.

Prior to being fully hardened , the paste was placed in a mold under a desirable pressure (at a maximum pressure of 1 50, 300 or 450 Kgf) to squeeze a portion of the liquid out of the paste. After being removed from the mold, one group of the hardened composite samples were placed in a moisture-proof container for 1 day. Another group of samples were further impregnated in an impregnation solution ( 1 M ( N H₄)₂H P0₄ or 1 M K₂H P0 ) at a desirable temperature (37°C) for 1 day, followed by drying in an oven at 50°C for 1 day.

Preparation of TTCP/DCPA/CSH com posite porous blocks

Appropriate amounts of TTCP and DCPA powders were uniformly mixed in a ball miller, followed by uniformly mixing with appropriate amount of CSH powder. The resultant TTCP/DCPA/CSH mixed powders were mixed uniformly with a desirable setting solution (e.g . , 0.6M (NH₄)₂H P0₄) at a desirable UP ratio (e.g . , 0.28 cc/g) to form a TTCP/DC PA/CSH paste.

The composite paste was then uniformly mixed with a pore-forming agent (e.g. KCI particles) with a desirable weight ratio (e.g.

TTCP/DCPA/CSH : KCI = 1 : 1 or 1 :2) to form a TTCP/DCPA/CSH/KCI paste.

Prior to being fully hardened , the composite paste was placed in a mold under a desirable pressure (at a maximum pressure of 450 Kgf) to squeeze a portion of the liquid out of the paste. After being removed from the mold, one group of the hardened composite blocks were immersed in de-ionized water at 37°C for 3 days to allow KCI particles to dissolve, forming a porous composite block, followed by drying in an oven at 50°C for 1 day. Another group of samples were further impregnated in an impregnation solution (e.g. 1 M (NH₄)₂HP0₄ or 1 M K₂HP0₄) at a desirable temperature (37°C) for 1 day to allow the strength of the porous block to increase, followed by drying in an oven at 50°C for 1 day. To remove the residual impregnation solution from inside the pores, the impregnated porous samples were further rinsed in de-ionized water at 37°C for 3 days.

Measurement of porosity

The porosity of the various samples was measured according to ASTM C830-00 (2006) method, "Standard Test Methods for Apparent Porosity, Liquid Absorption, Apparent Specific Gravity, and Bulk Density of Refractory Shapes by Vacuum Pressure".

Example 9: Dense block

Table 14. Compressive strengths (MPa) of TTCP/DCPA/CSH composite dense blocks prepared from TTCP/DCPA/CSH mixed powders mixed with

0.6 M (NH₄)₂HP0₄ (L/P=0.28 cc/g)

Summary of the results shown in Table 14 (Compressive strengths of TTCP/DCPA/CSH composite dense blocks):

(1 ) Impregnation-treated samples have significantly higher CS values under all conditions

(2) CS values significantly increase with higher molding pressure under all conditions Example 10: Porous block

Table 15. Porosity values (vol%) of TTCP/DCPA/CSH composite porous blocks prepared from TTCP/DCPA/CSH/KCI (pore-forming agent)-mixed powders mixed with 0.6 M (NH₄)₂HP0₄ (L/P=0.33 cc/g)

Summary of the results shown in Table 15 (TTCP/DCPA/CSH composite porous blocks prepared from TTCP/DCPA/CSH/KCI (pore-forming agent)-mixed powders mixed with 0.6 M (NH₄)₂HP0₄):

(1) The porosity values are in. the range 46-63% at TTCP/DCPA/CSH : KCI = 1:1, and 81-89% at TTCP/DCPA/CSH : KCI = 1:2, which are ideal for use as a tissue-engineered scaffold.

(2) The porosity value generally increases with increasing CSH content in the composite.

Table 16. Compressive strength (MPa) values of TTCP/DCPA/CSH composite porous blocks prepared from TTCP/DCPA/CSH/KCI

!-forming agent)-mixed powders mixed with 0.6 M (NH₄)₂HP0₄ (L/P=0.33cc/g)

Summary of the results shown in Table 16 (TTCP/DCPA/CSH composite porous blocks prepared from TTCP/DCPA/CSH/KCI (pore-forming

agent)-mixed powders mixed with 0.6M (N H₄)₂HP0₄):

(1 ) The CS strength of the porous blocks decreases with increasing CSH content in the composite under all test conditions.

(2) The CS values of the porous blocks (w/o impregnation treatment)

prepared from TTCP/DCPA/CSH/KCI are in the range about 2-5 MPa at TTCP/DCPA/CSH : KCI= 1 : 1 , and about 0.4-0.9 MPa at

TTCP/DCPA/CSH : KCI= 1 :2.

(3) The impregnation treatment significantly enhances the strength of the porous blocks. The CS values of (N H₄)₂HP0₄-impregnated porous blocks significantly increase to 4.8-8.9 M Pa at TTCP/DCPA/CSH. : KCI = 1 : 1 , and about 0.5-1 .2 MPa at TTCP/DCPA/CSH : KCI = 1 : 2. The CS values of K₂H P0₄-impregnated porous blocks significantly increase to 4.8-8.8 MPa at TTCP/DCPA/CSH : KCI = 1 : 1 , and about 0.5- 1 .2 MPa at TTCP/DCPA/CSH : KCI = 1 : 2.

Exam ple 11 : Animal study and measurement of composite implant resorption ratios

Animal study was performed at National Cheng-Kung University Medical College Animal Center, Tainan, Taiwan. Adult (weighing 2.8-3.5 kg), healthy, male New Zealand white rabbits were used as experimental animals. The rabbits were housed individually in stainless steel cages which had free access to food and water. An acclimation period of a minimum of 7 days was allowed between receipt of the animals and the start of the study. I njection sites were shaved and cleansed with 70% ethanol and Betadine™

(povidone iodine 1 0%). All animals were operated under general anesthesia. Pentobarbital sodium (0. 1 ml/1 00 g, Tokyo Kasei Kogyo, Tokyo, Japan) was used as general anesthesia, while xylocaine (Fujisawa Pharmaceutical CO. , Tokyo, Japan) was used as local anesthesia. To implant cement paste in the medial condyle of femur, a longitudinal incision was made on the anterior surface of the femur. The inner side of knee joint of the rabbit was cut to^' expose the femur. After exposure of the femur, the periosteum was reflected and a 2 mm pilot hole was drilled. The hole was gradually widened with drills of increasing size until a final diameter of 5 mm was reached. A special 5 mm diameter drill burr was used and a ring was inserted at a depth of 10mm to ensure appropriate length (10 mm) of the drill hole.

Two kinds of calcium phosphate/calcium sulfate composite cement paste (90wt% TTCP/DCPA: 10wt% CSH and 55wt% TTCP/DCPA: 45wt% CSH) were implanted in the prepared bone cavity. After filling of the paste, subcutaneous tissues and skin were closed up layer by layer with silk threads. To reduce the risk of peri-operative infection, the rabbits were treated with antibiotics injection subcutaneously at a dose of 40 mg/kg. The animals were sacrificed after 12 week post-operation.

After the animals were sacrificed, the femur portions were excised immediately and excess tissue was removed. Photographs of the slices by a single-lens reflex camera and an image analysis system was used to calculate the areas of residual implant. The implant resorption ratios were determined by the equation, implant resorption ratio = (cross-sectional area of original implant - cross-sectional area of residual implant)/cross-sectional area of original implant.

Summary:

The average residual implant ratios for "90/10" and "55/45" samples are 81 .1 % (resorption ratio: 18.9%) and 67.7% (resorption ratio: 32.3%), respectively, as shown in the photographs mentioned above. That means the healing speed for the 55/45 implant is about 70% faster than for the 90/10 implant.

Claims

Claims:

1. A bone cement formula comprising a powder component and a setting liquid component with a liquid to powder ratio of 0.20 cc/g to 0.50 cc/g, preferably 0.25 cc/g to 0.35 cc/g, wherein the powder component comprises a calcium sulfate source and a calcium phosphate source with a weight ratio of the calcium sulfate source less than 65%, based on the total weight of the calcium sulfate source and the calcium phosphate source, and the setting liquid component comprises ammonium ion (NH₄ ⁺) in a concentration of about 0.5 M to 4 M, wherein the calcium phosphate source comprises tetracalcium phosphate (TTCP) and dicalcium

phosphate in a molar ratio of TTCP to dicalcium phosphate of about 0.5 to about 2.5, preferably about 1 .0, and the calcium sulfate source is calcium sulfate hemihydrate (CSH), calcium sulfate dehydrate (CSD), or anhydrous calcium sulfate, and preferably, CSH, wherein the calcium sulfate source of the powder component is greater than 5%, and more preferably is of 10% to 55%, based on the total weight of the calcium sulfate source and the calcium phosphate source powder.

2. The formula of claim 1 , wherein the dicalcium phosphate is dicalcium phosphate anhydrous (DCPA).

3. The formula of claim 1 , wherein the setting liquid component comprises ammonium ion (NH₄ ⁺) in a concentration of about 1 .0 M to 2.0 M.

4. The formula of claim 3, wherein the setting liquid component is a solution of NH4H2PO4, (ΝΗ₄)₂ΗΡθ₄, (ΝΗ₄)₃Ρ0₄· 3Η₂0 or a mixture of them.

5. The formula of claim 4, wherein the setting liquid component is an aqueous solution of (NH₄)₂HP0₄.

6. The formula of claim 2, wherein the calcium phosphate source is composed of TTCP and DCPA.

7. The formula of claim 1 further comprising a pore-forming agent which is to be dissolved in a solution when a hardened bone cement composite prepared therefrom is immersed in the solution.

8. A process for preparing a hardened bone cement composite comprising forming a bone cement paste by mixing the powder component and the setting liquid component of the bone cement formula set forth in claim 1 ; shaping the paste in a mold; and removing the mold to form a block of hardened bone cement composite.

9. The process of claim 8 further comprising pressurizing said paste in said mold before said paste becomes set to remove a portion of liquid from said paste, so that a liquid to powder ratio of said paste decreases, wherein the pressure applied to the paste in the mold is form about 1 MPa to 500 MPa, preferably from 100 MPa to 500 MPa.

10. The process of claim 8 further comprising impregnating the block with an impregnating liquid for a period of time, so that a compressive strength of the resulting impregnated block removed from the impregnating liquid is increased compared to that of said block without said impregnating treatment.

11 . The process of claim 10, wherein the impregnating liquid is a phosphate-containing solution having a phosphate concentration from about 0.1 M to about 6 M, preferably from about 1 M to about 3 M.

12. The process of claim 8, wherein the powder component of the bone cement formula contains a pore-forming agent, or a pore-forming agent is added during the mixing or is mixed with the paste before shaping the paste in a mold, and said process further comprises immersing said block of hardened bone cement composite in an immersing liquid to dissolve said pore-forming agent in the immersing liquid, creating pores therein, so that a porous block is formed, and preferably the porous block has a porosity of 50-90 vol%.

13. The process of claim 12, wherein the pore forming agent is selected from the group consisting of LiCI, KCI, NaCI, MgCI₂, CaCI₂, Nal0₃, Kl, Na₃P0₄, K3PO4, Na₂C0₃, amino acid-sodium salt, amino

acid-potassium salt, glucose, polysaccharide, fatty acid-sodium salt, fatty acid-potassium salt, potassium bitartrate (KHC₄H₄O6), potassium

carbonate, potassium gluconate (KCeH Oy), potassium-sodium tartrate (KNaC₄H₄0₆-4H₂0), potassium sulfate (K₂S0₄), sodium sulfate, sodium lactate and mannitol.

14. The process of claim 12, wherein the immersing liquid is a phosphate-containing solution having a phosphate concentration from about 0.1 M to about 6 M, preferably from about 1 M to about 3 M, or water.

1 5. The process of claim 12 further comprising impregnating the porous block with an impregnating liquid for a period of time, so that a compressive strength of the resulting impregnated porous block removed from the impregnating liquid is increased compared to that of said porous block without said impregnating treatment.

16. The process of claim 15, wherein the impregnating liquid is a phosphate-containing solution having a phosphate concentration from about 0.1 M to about 6 M, preferably from about 1 M to about 3 M.

17. The process of claim 8 further comprising breaking up the block into pellets.

18. The process of claim 10 further comprising breaking up the porous block into pellets.