Effect of calcium carbonate on the compliance of an apatitic calcium phosphate bone cement

Biomaterials 18 (1997) 1535-1539 © 1997 Elsevier Science Limited Printed in Great Britain. All rights reserved PII:

ELSEVIER

S0142-9612

(97)

0142-9612/97/$17.00

00096-3

Effect of calcium carbonate on the compliance of an apatitic calcium phosphate bone cement I. Khairoun, M.G. Boltong, F.C.M. Driessens and J.A. Planell Department of Materials Science and Metallurgy, Universitat Polit~cnica de Catalunya, Avda. Diagonal 647, E- 08028, Barcelona, Spain Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time and the ultimate compressive strength. Three cement formulations were tested. The previously developed Biocement H was made of a powder containing c~-tertiary calcium phosphate and precipitated hydroxyapatite. Biocement B2 powder was made by adding some CaCO 3 to Biocement H, whereas Biocement B1 was made by adding some CaCO 3 but with simultaneous adjustment of the amount of precipitated hydroxyapatite.The liquid/ powder ratio of the cement paste and the accelerator concentrations (percentage Na2HPO4) in cement liquid were varied. For Biocement H there was no combination of LIP ratio and percentage Na2HPO4 for which all clinical requirements were satisfied. However, there was an area of full compliance for Biocements B1 and B2, of which that for B1 was the largest. Therefore, Biocement B1 may be applied in clinical situations as those in orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, even when early contact with blood is inevitable. © 1997 Elsevier Science Limited. All rights reserved Keywords: Calcium phosphate cement, bone cement, clinical requirements Received 2 January 1997; accepted 23 May 1997

Calcium phosphate bone cements CPBCs are materials consisting of a liquid being water or an aqueous solution, and a powder containing one or more solid c o m p o u n d s of calcium and/or phosphate salts so that if liquid and powder are mixed in an appropriate ratio they form a paste, which, at room or body temperature, sets by precipitation of one or more other solid compounds, of which at least one is a calcium phosphate. They have the advantage over calcium phosphate bioceramics in that they do not need to be delivered in prefabricated forms or as granules but that they can be molded during the operation or simply injected into the bone defect 1. Since the first CPBC was synthesized 2 some 20 different formulations have been published which set at room or body temperature into solid bodies with considerable mechanical strength 3, so that at the m o m e n t four types are k n o w n depending on the type of calcium phosphate formed during the setting. This can be either dicalcium phosphate dihydrate CaHPO4.2H20 (DCPD) or calcium deficient hydroxyapatite Cag(HPO4)(PO4)5OH (CDHA) or hydroxyapatite Calo(PO4)6(OH)2 (HA) or amorphous calcium phosphate (ACP) having no fixed stoichiometry. The CPBCs investigated in this study are of the CDHA type. Biocement H was developed earlier 4. Its powder consists of alpha-tertiary calcium phosphate ~-

TCP and some precipitated hydroxyapatite PHA. Its liquid is an aqueous solution of disodium hydrogen phosphate Na2HPO 4. It has been proven that its properties do not depend critically on the stoichiometry or the temperature treatment of the ~-TCP preparation used 5. Further, the setting characteristics and the strength are considerably improved w h e n going from room temperature to body temperature 6. During setting there is no dimensional change or any detectable thermal effect 7, neither exothermic nor endothermic. Biocement B2 is a formulation derived from Biocement H by adding some CaCO 3 to the powder, whereas the powder of Biocement B1 not only contains CaCO3 but also has a higher content of precipitated HA than Biocement H. The liquid of Biocements B1 and B2 is either water or an aqueous solution of Na2HPO4. During setting, the ~-TCP is transformed into a carbonated apatite so that the CaCO3 is involved in the setting reaction 8. As for dental stone the so-called Gillmore needles are suitable to measure the setting times of CPBCs. The light and thick needle is used to measure the initial setting time I, the heavy and thin needle for the final setting time 9, F. The clinical meaning of I is that it indicates the time from which the paste may not be deformed without damaging the structure of the solidifying cement. That of F indicates the time from when the cement can be touched without scratching it.

Correspondence to Dr I. Khairoun. 1535

Biomaterials 1997, Vol. 18 No. 23

1536

Clinical requirements for calcium phosphate bone cements: I. K h a i r o u n et al.

So the cement must be applied before I and the w o u n d may be closed after F. In an early stage of the development of CPBCs it was noticed that some CPBCs disintegrate on early contact with water, aqueous solutions and body fluids like blood. We designed a test to measure the so-called cohesion time (CT) of a CPBC, i.e. the time from which it does not disintegrate any more when immersed in Ringer s solution 1°. From this definition it is clear that a CPBC must be applied to a wound after CTbut before I. The first serious attempt to formulate clinical requirements for the CPBCs in terms of setting times and cohesion times came from our working group 11' 12. At the m o m e n t we have had some practical experience with clinicians. On the basis of that experience we can express the following handling requirements 3~
C T ~> 1

F <~ 15

(1) (2) (3)

in which the numbers express minutes. Requirement (2) means in effect that C T must be at least I min before I so that the clinician has at least I min to apply and to mold the material. As the mixing in a mortar is about I min the shortest C T that can be allowed is about 2 min so that the clinician has at least I min to collect the paste from the mortar and to put it on the pallet knife or in the syringe with which it is to be transferred to the w o u n d after C T and before /. For dental applications, I must be close to 3 min whereas for orthopedic applications it must be close to 8 min. However, in no case is it tolerable for the clinician that F is greater than 15 min. For m a n y dental cements and also for CPBCs, it is suitable to measure the compressive strength (CS) and the diametral tensile strength DTS after immersion of the cement in Ringer s solution at 37°C during some time 13. Usually CPBCs. reach ultimate strength within 5 days of immersion 4. As in most clinical applications the CPBCs are applied in direct contact with h u m a n trabecular bone, it may be stated as a mechanical requirement that the strength of a CPBC must be at least as high as that of h u m a n trabecular bone. As in most applications the CPBC will be occluded between bone and metal implant surfaces, one may presume that CS is most relevant. As the m a x i m u m CS of h u m a n trabecular bone is 30MPa 14 the main mechanical requirement for CPBCs is expected to be: CS >~ 30 MPa

(4)

From the previous studies on Biocement H and Biocement F 4-7 it was presumed that there were certain areas for the liquid/powder ratio L/P and the accelerator concentration (per cent NazHPO4) in the cement liquid for which requirements (1) through (4) were simultaneously satisfied. The purpose of the present study was to investigate the limitations of this area without and with additions of C a C O 3 to Biocement H in order to enable conclusions as to whether 1. A clinically suitable high-viscosity paste can be formulated which can be applied as a dough. 2. A clinically suitable low-viscosity paste can be formulated which can be applied by injection from a syringe. Biomaterials 1997, Vol. 18 No. 23

3. Both a high-viscosity and a low-viscosity paste can be formulated using the same cement powder but eventually using different L/P ratios and/or accelerator concentrations in the liquid.

M A T E R I A L S A N D METHODS ~-TCP was prepared by using an appropriate mixture of CaHPO4 (Merck, Darmstadt, Catalogue n u m b e r 2144) and C a C O 3 (Merck 2076), heating it at 1300°C for at least 6 h and quenching it in air down to room temperature. The PHA was a commercial product called Tri-calcium phosphate (Merck 2143) but in fact being apatitic. The powder of Biocement H contained 98% ~-TCP and 2% PHA. The powder of Biocement B1 contained 90% ~-TCP, 5% PHA and 5% C a C O 3 whereas that of Biocement B2 contained 90% ~-TCP, 2% PHA and 8% C a C O 3. The liquid/powder ratio L/P of the three cements was taken to be 0.30, 0.32, 0.35 or 0 . 4 0 m l g -1. The values chosen for the accelerator concentration were 0, 1, 2.5 and 4% Na2HPO4 in water. The setting times I and F were determined as usual 9 and C T with the method developed previously 1°. L F and C T were measured in triplicate. Teflon molds were used to prepare cement cylinders with a height of 1 2 m m and a diameter of 6 m m and soaking was carried, out during 1, 2 and 5 days in Ringer's solution at 37°C prior to determination of CS with an Instron Universal Testing Machine Type 4507 at a compression rate of l m m m i n -1 (n = 8). The results were screened on their area of compliance with each of the requirements (1)-(4). For those conditions, for which requirements (1) through (4) were satisfied simultaneously it was investigated whether the paste was enough of a low-viscosity type to be injectable at time C T or whether is was of a high-viscosity type to be applied as a dough.

RESULTS Standard deviations of/, F and C T were i min. Those of the strength were 15% of the value of CSo Strength data for 1 and 2 day old samples will not be mentioned because they are not relevant for further discussion. For Biocement H the results are given in Tables 1 to 4. For none of the combinations of L/P and per cent Na2HPO4 investigated was there compliance with the requirements (1) through (4) simultaneously. This means that Biocement H is not suitable for clinical applications. For Biocement B1 the results are given in Tables 5 to 8. Table 9 indicates for which combinations of L/P and per cent Na2HPO4 there is full compliance with the requirements (1) through (4). Further investigations of the pastes in question showed that all three can be handled as doughs and none of them is really injectable. For Biocement B2, the results are given in Tables 10 to 13. Table 14 shows that only one of the investigated combinations of L/P and per cent Na2HPO 4 complied with the clinical requirements (1) through (4) simultaneously. The cement paste in ~nUeStion could only be handled as a dough and was ot injectable.

Clinical r e q u i r e m e n t s for calcium p h o s p h a t e bone cements: I. K h a i r o u n et al.

1537

Table 1 The initial setting time, I (min), for Biocement H as a function of the L/P ratio (ml g-r) and the accelerator concentration percentage Na2HPO4 (n = 3)

Table 6 The final setting time, F (min), of Biocement B1 as a function of the L/P ratio (ml g - l ) and the accelerator concentration percentage Na2HPO4 (n = 3)

Na2HPO,~

Na2HPO4

(%) 0 1 2.5 4

L/P ratio 0.30

0.32

0.35

0.40

28 10 7 4.25

32 8.5 6.5 5

35 12 9 6.5

38 20 11 9

Table 2 The final setting time, F (min), for Biocement H as a function of the L/P ratio (ml g-r) and the accelerator concentration percentage Na2HPO4 (n = 3) Na2HPO4

(%) 0 1 2.5 4

0.30 70 28 15 22

0.32 76 28 17 17

Na2HPO4

0 1 2.5 4

0.35 78 30 28 30

0.40 80 58 35 56

0.32

0.35

0.40

9.5 4.5 0 -21

13 3 0.5 0

14 4 4 1.5

15 9 7 4.5

Na2HPO4

L/P ratio 0.30

0.32

0.35

0.40

50 44 47 n.d.

50 52 51 39

51 50 35 n.d.

(%)

0.40

45 20 13 11

60 23 14.5 11

76 34 19 15

>80 42 22 19

L/P ratio 0.30

0 1 2.5 4

<7 <1 <-0.5 0.5

0.32

0.35

0.40

<0 2 1 2

0 7 1.5 2

0 7.5 5 3

Table 8 The 5-day compressive strength CS-5 (MPa) of Biocement B1 (n = 8) as a function of the LIP ratio (ml g-r) and the accelerator concentration percentage Na2HPO, (n = 8) Na2HPO,

(%) 0 1 2.5 4

Na2HPO4

L/P ratio 0.30

0.32

0.35

0.40

n.d. 40 45 40

n.d. 43 36 35

n.d. 32 42 35

n.d. 43 34 27

n.d., not determined. T a b l e 9 Compliance (+) with the four requirements (1) through (4) for Biocement B1 as a function of the L/P ratio (ml g - l ) and the accelerator concentration percentage Na2HPO~ Na2HPO,

L/P ratio 0.30

0.32

0.35

0.40 m

2.5 4

Table 5 The initial setting time, I (min), of Biocement B1 as a function of the L/P ratio (ml g - l ) and the accelerator concentration percentage Na2HPO4 (n = 3)

0 1 2.5 4

0.35

Na2HPO4

35 39 34 28

n.d., not determined.

(%)

0.32

Table 7 The initial setting time, I (min), minus the cohesion time CT (min) of Biocement B1 as a function of the L/P ratio (mlg-1) and the accelerator concentration percentage Na2HPO4 (n = 3)

(%)

0 1 2.5 4

0.30

L/P ratio 0.30

Table 4 The 5-day compressive strength CS-5 (MPa) of Biocement H (n = 8) as a function of the L/P ratio (ml g - l ) and the accelerator concentration percentage Na2HPO~

(%)

0 1 2.5 4

L/P ratio

L/P ratio

Table 3 The initial setting time, I (min), for the cohesion time CT (min) for Biocement H as a function of the L/P ratio (ml g 1) and the accelerator concentration percentage Na2HPO4 (n = 3)

(%)

(%)

-

+ +

+

Table 10 The initial setting time, I (min), of Biocement B2 as a function of the LIP ratio (ml g - l ) and the accelerator concentration percentage Na2HPO4 (n = 3)

L/P ratio 0.30

0.32

0.35

0.40

30 10 5.5 5.5

37 11 7 6

41 16 7.5 6.5

45 21 11.5 9

DISCUSSION It was shown that Biocement H is not suitable for clinical applications. The main cause is that requirement (2) is not fulfilled. For the most promising combinations of the L/P ratio and accelerator concentrations, per cent Na2HPO4 CT coincided practically with the initial setting time I so that there is

% Na2HPO4

(%) 0 1 2.5 4

L/P ratio 0.30

0.32

0.35

0.40

n.d. 14.5 10 6

n.d. 17 11.5 7.5

n.d. 23.5 16.5 8.5

n.d. 30 19 11.5

n.d., not determined.

virtually no time period in which the clinician can apply and mold the material. According to Miyamoto e t a]. 15 t h e HA type cement invented by Brown and Chow 2 has the same problem, even when phosphate solutions are used as accelerator. Ishikawa e t a ] . 16 solved this problem by the addition of Biomaterials 1997, Vol. 18 No. 23

Clinical r e q u i r e m e n t s for calcium p h o s p h a t e bone cements: I. K h a i r o u n et al.

1538

Table 11 The final setting time, F (min), of Biocement B2 as a function of the L/P ratio (ml g 1) and the accelerator concentration percentage Na2HPO,~ (n = 3) Na2HPO~

L/P ratio

(%)

0 1 2.5 4

0.30

0.32

0.35

0.40

n.d. 34 17 12.5

n.d. 40 22 15

n.d. 43 27 20

n.d. 61 36 28

n.d., not determined. Table 12 The initial setting time, I (min), minus the cohesion time CT (min) of Biocement B2 as a function of the L/P ratio (mlg-1) and the accelerator concentration percentage Na2HPO4 (n = 3) Na2HPO4

(%)

L/P ratio 0.30

0 1 2.5 4

<-105 <-1 1.5 -1

0.32

0.35

0.40

<-120 3.5 2.5 1

<-120 9.5 3.5 1.5

<-120 4.5 4.5 4.5

Table 13 The 2-day compressive strength, CS-2 (MPa), of Biocement B2 as a function of the L/P ratio (mlg 1) and the accelerator concentration percentage Na2HPO4 (n = 8) Na~HPO4

(%) 0 1 2.5 4

L/P ratio 0.30

0.32

0.35

0.40

n.d. 42 44 41

n.d. 47 41 38

n.d. 33 37 39

n.d. 33 30 37

n.d., not determined. Table 14 Compliance (+) with the four requirements (1) through (4) for Biocement B2 as a function of the L/P ratio (ml g 1) and the accelerator concentration o)/o Na2HPO4 Na2HPO,~

(%)

L/P ratio 0.30

0.32

-

÷

0.35

adding CaCO3. This combined change of formulation has the best effect on the compliance with the clinical requirements. The histology of CPBC implants in bone shows a very good osteointegration (which is a matter of days) followed by a gradual osteotransduction, i.e. the cement is transformed into new bone tissue 18. This osteotransduction occurs within some months in rabbits 19"2a whereas in goats it takes longer 18. On the contrary, w h e n the CPBC is implanted subcutaneously in rats so that cellular contact is inhibited while contact with the extracellular fluid is provided 21, it is mechanically and chemically stable during several months, which means that the apatite formed during setting of the cement is in physico-chemical equilibrium with the extracellular fluid. This in viyo behaviour of CDHA type CPBCs has led to the hypothesis that the above mentioned osteotransduction is caused by the fact that the Biocements are taken up in the normal bone remodelling process, whereby osteoclasts decrease the local pH and, hence, dissolve the mineral and the matrix of old bone, after which the osteoblasts deposit new matrix and increase the local pH so that this new matrix becomes mineralised 22. This hypothesis is being tested in in vitro cell culture experiments. It is already proven that osteoclasts resorb CDHA type CPBCs 23. Experiments with osteoblasts and osteoprogenitor cells are ongoing. The biocompatibility of CDHA type CPBCs is excellent 24, mainly owing to the fact that their pH during and after setting is close to 7.4. A further advantage is that there is no dimensional change nor any heat effect during setting 7. For these reasons, especially Biocement B1 has good potential value for use in orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, where the cement is exposed to blood. But obviously this exposition should be allowed after CT, whereas the molding and application must be finished before/. In conclusion, the addition of C a C 0 3 to Biocement H results in some compliance of this CDHA type calcium phosphate cement, but not enough to make it injectable.

0.40

ACKNOWLEDGEMENTS 2.5 4

sodium alginate to the cement liquid. This addition does not adversely affect the biocompatibility of this material 17. In this case Biocement H set faster at body temperature than at room temperature 6. Further, it was found that early contact with aqueous solutions resembling blood and other body fluids at and after the initial setting time I had no effect on its further setting behaviour 5. Yet, Jansen et al. 1~ noticed some problems with early blood contact of Biocement H before the initial setting time I in animal experimentation. No such problems occur with Biocement B1 or B2 which apparently is due to the addition of CaC03. By comparison of Tables 9 and 14 one can observe that the area of compliance is larger for Biocement B1 in which the amount of PHA is adjusted together with Biomaterials 1997, Vol. 18 No. 23

This study was supported by a grant from the Direcci6n Cientffica y Tecnica of Spain. The authors would also like to thank the CICYT for funding this work through project MAT 94-0911.

REFERENCES 1.

Driessens, F. C. M., Planell, J.A. and Gil, F.J., Calcium phosphate bone cements. In Encyclopedic Handbook of

Biomaterials and Bioengineeing Part B, Applications, Vol. 2, eds D.L. Wise et al. Marcel Dekker, New York, 2.

3. 4.

1995, pp. 855-877. Brown, W.E. and Chow, L.C., A new calcium phosphate setting cement. J. Dent. Res., 1983, 62, 672.

Driessens, F.C.M., Chemistry of calcium phosphate cements. Fourth Euro Ceramics, 1995, 8, 77-83. Driessens, F.C.M., Boltong, M.G., Planell, J.A., Bermudez, O., Ginebra, M. P. and Fernandez, E., A new apatitic calcium phosphate bone cement: preliminary results. Bioceramics, 1993, 6, 469-473.

Clinical requirements for calcium phosphate bone cements: I. K h a i r o u n et al.

5.

6.

7.

8. 9.

10.

11.

12.

13.

14.

Ginebra, M.P., Boltong, M.G., Fernandez, E., Planell, J.A. and Driessens, F. C. M., Effect of various additives and temperature on some properties of an apatitic calcium phosphate cement. J. Mater. Sci. Mater. Med, 1995, 6, 612-616. Ginebra, M. P., Fernandez, E., Driessens, F. C. M., et at., The effects of temperature on the behaviour of an apatitic calcium phosphate cement. J. Mater. Sci. Mat. Med., 1995, 6, 857-860. Fernandez, E., Ginebra, M.P., Bermudez, O., Boltong, M. G., Driessens, F. C. M. and Planell, J. A., Dimensional and thermal behaviour of calcium phosphate cements during setting compared to PMMA bone cements. J. Mater. Sci. Lett., 1995, 14, 4-5. Fernandez, E., private communication, 1996. Driessens, F.C.M., Boltong, M.G., Bermudez, O. and Planell, J.A., Formulation and setting times of some calcium orthophosphate cements: a pilot study. J. Mater. Sci. Mat. Med. 1993, 4, 503-508. Fernandez, E., Boltong, M.G., Ginebra, M. P, Driessens, F. C. M., Bermudez, O. and Planell, J.A., Development of a method to measure the period of swelling of calcium phosphate cements. J. Mater. Sci. Lett., 1996, 15, 1004-1005. Ginebra, M.P., Fernandez, E., Boltong, M.G., Planell, J.A., Bermudez, O. and Driessens, F.C.M., Compliance of a calcium phosphate cement with some short-term clinical requirements. Bioceramics, 1994, 7, 273-278. Ginebra, M.P., Fernandez, E., Boltong, M.G., Bermudez, O., Planell, J.A. and Driessens, F.C.M., Compliance of an apatitic calcium phosphate cement with the short-term clinical requirements in bone surgery, orthopaedics and dentisry. Clin. Mater., 1994, 17, 99-104. Bermudez, O., Boltong, M.G., Driessens, F.C.M. and Planell, J.A., Compressive strength and diametral tensile strength of some calcium-orthophosphate cements: a pilot study. J. Mater. Sci. Mater. Med., 1993, 4, 389-393. Yaszemski, M.J., Payne, R.G., Hayes, W.C., Langer, R and Mikos, A.G., Evolution of bone transplantation:

15.

16.

17.

18.

19.

20.

21.

22. 23.

24.

1539

molecular, cellular and tissue strategies to engineer human bone. Biomaterials, 1996, 17, 175-185. Miyamoto, Y., Ishikawa, K., Fukao, H., et al. In vivo setting behaviour of fast-setting calcium phosphate cement. Biomaterials, 1995, 16, 855-860. Ishikawa, K, Miyamoto, Y., Kon, M., Nagayama, M. and Asaoka, K., Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate. Biomaterials, 1995, 16, 527-532. Miyamoto, Y., Ishikawa, K., Takechi, M. et al., Nondecay type fast-setting calcium phosphate cement: setting behaviour in calf serum and its tissue response. Biomaterials, 1996, 17, 1429-1435. Jansen, J.A., de Ruijter, J.E., Schaecken, H.G., van der Waerden, J.P.C.M., Planell, J.A. and Driessens, F. C. M., Evaluation of tricalcium phosphate/hydroxyapatite cement for tooth replacement: an experimental animal study. J. Mater. Sci. Mater. Med., 1995, 6, 653657. Vasconselos, M., Afonso, A., Branco, R., Planell, ~., Driessens, F. and Cavalheiro, J., Histological evaluation of two bioactive cements. 5th World Biomaterials Congress, Toronto, 1996, p. 61. Jansen, J. A., Wolke, J. G. C., Hayakawa, T., Planell, J. A. and Driessens, F.C.M., A histological and mechanical evaluation of the effect of Ca-P cement on bone apposition. 5th World Biomaterials Congress, Toronto, 1996, p. 65. Driessens, F. C. M., Boltong, M. G., Zapatero, M. I., eta]., In vivo behaviour of three calcium phosphate cements and a magnesium phosphate cement. J. Mater. Sci. Mater. Med., 1995, 6, 272-278. Driessens, F. C. M. and Verbeeck, R. M. H., Biominerals, CRC Press, Boca Raton, 1990. De Bruijn, J.D., Bovell, Y.P., Planell, J.A. and Driessens, F. C. M., Osteoclast responses to two types of experimental calcium phosphate bone cements. 5th World Biomaterials Congress, Toronto, p. 121. Driessens, F.C.M., van Loon, J.A., van Sliedregt and Planell, J.A., Cytotoxicity testing of five calcium and one magnesium phosphate cement in vitro. 11th Eur. Conf. on Biomaterials. Pisa, 1994, pp. 344-346.

Biomaterials 1997, Vol. 18 No. 23