- Email: [email protected]
Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate
Biomateriols
16 (1995)
527-532
@ 1995
Elsevier Science Limited Printed in Great Britain. All rights reserved 0142-9612/95/$10.00
Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate Kunio Ishikawa, Youji Miyamoto”, Masayuki Kon, Masaru Nagayama* and Kenzo Asaoka Department
of Dentat
Non-decay
alginate
cement
paste
(c-FSCPC) mately
alginate
resulted
in distilled
completely
within
into conventional
in no setting
diffraction
when
analysis
any concentrations increased
rapidly
and kept in distilled
alginate’s
strength.
alginate
composite
surgery
where
Keywords: Received
of sodium
Calcium
of sodium
no significant
alginate
studied
of sodium
water
is exposed
phosphate
19 July 1994; accepted
alginate
alginate.
time
when
be of value
than
strength the cement
in orthodontics
1 wt%.
of
Powder
to apatite
for
of the cement paste
alginate
together
indicate
FSCPC approxi-
phase,
of cement
of sodium
taken
behaviour,
the
the introducti0.n
in the liquid
The mechanical addition
when
of the cement,
was more
up to 0.8 wt%
even
conventional
In contrast,
phosphate
in this investigation,
should
whereas
for the conversion
further
by introducing
was stable
The setting
introduced
and absorption
was
decreased
with sodium
that the use of sodium
and oral and maxillofacial
to blood.
cement,
non-decay,
21 September
1994
apatite,
alginate
However, the problem of decay with this cement limits the potential wider application of this bioactive material. For example, CPC is thought to have good potential value in orthodontics and in oral and maxillofacial surgery. In such fields, there is a good chance that pastes would be exposed to blood and thus decay of the cement paste would result in the failure of the operation or, at least, would decrease the effectiveness of the operation. Therefore, there is a requirement for a non-decaying type of FSCPC (nd-FSCPC) for the wider application of FSCPC. In this investigation, we prepared a nd-FSCPC by adding sodium alginate to the liquid phase of FSCPC. The in vitro findings obtained in this investigation are reported together with a discussion of the required properties for a nd-FSCPC based on these findings.
calcium phosphate cement (FSCPC) shows significantly shortened setting time compared with conventional CPC1-’ (c-CPC) - which consists of an equimolar mixture of tetracalcium phosphate (TTCP; CQ(PO,]~O) and dicalcium phosphate anhyclrous (DCPA; CaHPO,) or dicalcium phosphate dihydrate (CaHPO,.ZH,O)-going from 30-60 min to approximately 5 mini’. Although FSCPC shows the same excellent bioactivity as c-CPC, there are various problems involved in the wider clinical use of this cement. One of these problems is the decay of the cement when the cement paste is in contact with blood. apatite (HAP: The sets to form cement ambient under Ca10-,(~O~),(P04)~-,(OH)~-X) conditions. However, exposure of the paste to blood early after mixing results in the decay of the cement, the situation being similar to that observed for gypsum. Gypsum sets when mixed with water; however, gypsum paste also decays gradually when immersed in water just after mixing. Decay is not a problem when the cement paste is used in areas where there is no liquid in contact with the cement, such as in root filling materials.
Fast-setting
Correspondence
alginate difference
(O-2.0 wt%).
obtained
of Dentistry,
School
was prepared
mixing,
neutral
at 37” C, whereas
biocompatibility
Surgery,
nd-FSCPC
after
on the presence
FSCPC as nd-FSCPC
the cement
immediately immersion.
The results
excellent
(nd-FSCPC)
of FSCPC.
1 min upon
with the addition
known
cement
phase
water
the amount
of sodium
of Oral and Maxilfofaciaf
770 Japan
CPC, i.e. CPC without
revealed
immersed
the mechanical
phosphate
into the liquid
was immersed
decayed
Tokushima,
calcium
(O-2.0 wt%)
5 min, was not dependent
sodium X-ray
3-18-15 Kuramoto,
type fast-setting
sodium
and ‘First Department
Engineering,
Tokushima University,
MATERIALS AND METHODS Preparation
of calcium phosphate cement (CPC)
TTCP was made from CaHP04 and CaC03, as described previously7**s12. The solid was first crushed with a mortar and mill, and then ground for 1 h in dried
to Dr Kunio Ishikawa. 527
Biomaterials
1995, Vol. 16 No. 7
Non-decay type FSCPC: K. lshikawa
528 cyclohexane in an agate jar, using a ball mill (Retsch PM4, Brinkman, New York, USA) to obtain a median particle size of 4.11 pm. Commercial ultra-pure DCPA (J.T. Barker Chemical Co., NJ, USA) was ground for 24 h in 66% ethanol in the agate jar to a medium particle size of 0.7 pm. Although particle size distribution affects the properties of CPC such as mechanical strength and setting timel’, we did not examine any other particle size distribution in this study, in order to focus only on the effect of sodium alginate on the decay properties of the paste when exposed to a liquid phase. The particle size of TTCP and DCPA was measured in isopropanol by a sedimentation method based on Stokes’ law, using a centrifugal particle size analyser (SA-CP3, Shimazu, Kyoto, Japan). X-ray diffraction (XRD) revealed no other crystals after grinding. CPC powders, made by mixing equimolar amounts of TTCP and DCPA using a micro mill (Bel-Art Products, Pequannock, NJ, USA), were stored in a vacuum desiccator at 60” C. The liquid phase of the nd-FSCPC was made by dissolving sodium alginate (Nacalai Tesque, Kyoto, Japan) in 0.2 mol 1-l Na,H,_,PO,; 0.2 mol ll’ Na2HP04 and 0.2 mol 1-l NaH2P04 were mixed so that the solution had pH 7.4 at 37”C, and then sodium alginate was dissolved in this solution. No adjustment was made to the concentration of neutral phosphate due to the addition of sodium alginate, since the volume of sodium alginate was negligible, even at the maximum concentration used in the present investigation, i.e. 2 wt%.
Percentage of remaining cement To investigate the potential value of nd-FSCPC against blood exposure, the percentage of remaining cement was measured by immersing the cement paste in distilled water immediately after mixing. Using a glass slab and spatula, we mixed the CPC powder with the liquid phase, at a powder to liquid ratio (P/L) of 4.0, and then packed the cement into a cylindrical mould (4.7 mm D x 8 mm H). The mould was made by cutting off the front portion of a 1 cm3 plastic syringe (Terumo, Tokyo, Japan). A force of approximately 3 kg per 6 mm D was applied for packing the cement into the moulds. After smoothing the surface of the cement on the open side, we pushed the piston of the syringe so that the paste was immersed in distilled water; this was done in an incubator kept at 37°C. After 24 h immersion, the largest mass of the cement was collected and dried with a freeze drier (FD-1, Tokyo Rikakiki Co., Ltd, Tokyo, Japan).
Setting time of the cement The setting time of the CPC samples was measured according to the method set out in international standard Is01566 for dental zinc phosphate cements. In this method, the cement is considered set when a 400 g weight loaded on to a Vicat needle with a tip diameter of 1 mm fails to make a perceptible circular indentation on the surface of the cement. The Standard requires that the cement be maintained at a temperature of 37” C and relative humidity of at least 37%; in the present investigation, the conditions were 37” C and 100% humidity. Biomaterials
1995, Vol. 16 No. 7
et al.
X-ray powder diffraction The XRD patterns of the vacuum-dried samples were recorded with a vertically mounted diffractometer system (ADG-301; Toshiba Co. Ltd, Tokyo, Japan), radiation Cu Ka monochromatized using Ni (A= 0.1540 nm) generated at 30 kV and 10 mA. The specimens were scanned from 3 to 60” 20 (where 1” is the Bragg angle) in a continuous mode. Standard HAP used for comparison was prepared at room temperature as described previously13.
Mechanical strength measurements To evaluate the mechanical strength of the set FSCPC in the presence and absence of sodium alginate, we measured the diametral tensile strength (DTS). Two different methods were employed to evaluate the effect of sodium alginate. In one method, we used set CPC; the paste was immersed in distilled water immediately after mixing, similar to the method used for the measurement of percentage remaining cement. A plastic tube with an inner diameter of 6 mm and a plastic rod with a diameter of 6 mm were used to make the paste, which was 6 mm in diameter (D) and 3 mm thick (H). In the other method, the paste was kept from direct exposure to the water. The paste was placed in a split mould (6 mm D x 3 mm H), using a force of approximately 3 kg per 6 mm D. Both sides of the mould were covered with glass and clamped, and the mould was kept in an incubator for 24 h at 37” C and 100% humidity. CPC specimens prepared by these methods were kept in an incubator for 24 h and then subjected to DTS measurement, the measurement being done within 30 min after the specimens were taken out of the incubator. The wet DTS value was measured to simulate body conditions, even though the dry specimen had a higher value. The DTS values were measured on an Instron (Universal Testing Machine, United Calibration Corp., Garden Grove, CA, USA). The diameter and length of each specimen were measured with a micrometer. The samples were later placed on steel platens, which were then covered with one thickness of wet filter paper, and tested at a loading rate of 1.0 mm min-’ The DTS value used was the average value of at least ten specimens.
RESULTS Figure I shows the effects of sodium alginate on the percentage of remaining cement in c-CPC and FSCPC when the cement was immersed in distilled water immediately after mixing. Both c-CPC and FSCPC decayed completely within 24 h in the absence of sodium alginate. When the cement paste was immersed in the distilled water, it decayed gradually, the rate of decay being much faster with c-CPC (within 1 min) than with FSCPC. The addition of sodium alginate, approximately 0.5 wt%, to the liquid phase of the cement increased the amount of remaining paste to 100%. The percentage of remaining paste was similar for c-CPC and FSCPC, except at 0.2 wt% of sodium alginate; the c-CPC paste decayed completely, whereas a mass of approximately 25% of the FSCPC paste remained and set.
Non-decay
type FSCPC: K. lshikawa
et al.
529
z 100 E E” 80 8 f .IE
60
E” 40 d E 8 20 $ a
0 0
0.5
1
2.0
Sodium Alginate (%) Figure 1
Effects of sodium alginate on the percentage of remaining cement paste after 24 h. The cement paste was immersed in distilled water at 37°C immediately after mixing (mixing ratio of 4.0, powder/liquid): 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
The setting time of the nd-FSCPC and nd-CPC in the presence of various concentrations of sodium alginate in the liquid phase (O-2.0 wt%) is summarized in Table 1 with that for c-FSCPC and c-CPC. The setting time of the c-CPC was approximately 30-40 min, the same value was obtained for the c-CPC whose liquid phase contained less than 1% sodium alginate. However, mixing with a sodium alginate solution of 1% or more resulted in no setting within 3 h, the longest time checked for setting. The surface of the paste seemed to adsorb water and became slippery. In contrast, the
setting time of FSCPC was 5-6 min, regardless of the sodium alginate concentration (O-LO%). The XRD patterns of c-FSCPC and nd-FSCPC kept in distilled water at 37” C for 24 h are shown in Figure 2, with those of the powder phase of CPC, an equimolar mixture of TTCP and DCPA, and poorly crystallized HAP for comparison. The XRD patterns of nd-FSCPC after 24 h were similar to those of c-FSCPC, and conversion to HAP was confirmed. The DTS values of the cements are summarized in Figure 3 for cement pastes immersed in distilled water at 37” C immediately after mixing. In both FSCPC and c-CPC, the DTS value increased rapidly with the addition of sodium alginate, the value being maximal at around 0.8% of sodium alginate in both cases; the addition of further sodium alginate resulted in a slight decrease in the DTS value. The DTS value was much higher for FSCPC than for c-CPC. Shown in Figure 4 is the DTS value of cement when the paste was kept in the mould. The mould was kept in an incubator at 37” C and relative humidity of 100% but the paste was not in direct contact with water. The DTS value decreased with the addition of sodium alginate for both FSCPC and c-CPC. Similar to these results shown in Figure 3, FSCPC had higher DTS values both in the absence and presence of sodium alginate (o-2.0%).
DISCUSSION One of the problems with c-FSCPC is that the cement decays when in contact with blood. When CPC sets,
a) Powder
T: l-rCP
pha8e
Table 1
Setting time of non-decay type fast-setting calcium phosphate cement and non-decay type calcium phosphate cement in the presence of various concentrations of sodium alginate (02.0%) in the liquid phase. The setting time of fastsetting calcium phosphate cement (FSCPC) and conventional calcium phosphate cement (c-CPC) is shown for comparison. The cement was mixed at a powder to liquid ratio of 4.0 CPC
Sodium alginate (wt%)
Setting time (min)
FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC
0.0 0.2 0.4 0.6 0.8 1.0 1.5 2.0 0.0 0.2 0.4 0.6 0.8 1.0 1.5 2.0
5.3 It 0.5 5.2 * 0.4 5.8 f 0.7 5.5 f 0.5 5.3 f- 0.5 5.3 Ib 0.5 5.2 f 0.4 5.5 It 0.5 38.8 i 3.9 41.5 f 4.1 39.7 * 4.1 40.0 f 4.1 42.5 f 4.0 no setting no setting no setting
c) nd-FSCPC
I...‘.......““‘,......“..
25
30
36
26 (degree) Figure 2 Powder X-ray diffraction patterns of conventional fast-setting calcium phosphate cement (c-FSCPC) and nondecay type fast-setting calcium phosphate cement (ndFSCPC) kept in distilled water at 37°C for 24 h. The powder phase of calcium phosphate cement and poorly crystallized hydroxyapatite (HAP) are shown for comparison (TTCP = tetracalcium DCPA = dicalcium phosphate; phosphate anhydrous). Biomaterials 1995. Vol. 16 No. 7
Non-decay
530
8
T T
Sodium Alginate (%) Figure 3 Effects of sodium alginate on mechanical strength (wet diametral tensile strength (DTS) value) of cement when the paste was immersed in distilled water (37°C) immediately after mixing and kept in distilled water for 24 h: 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
the set mass is stable even in contact with a liquid phase. However, CPC paste is easily decayed by contact with the liquid phase. Once the paste decays, it does not set, since under these circumstances the setting reaction cannot occur. The setting reaction involves the interlocking of formed HAP1”,14; HAP crystals interlock, showing similar setting behaviour to that seen for the setting reaction of gypsum. As shown in Figure 1, the cement paste decayed completely in the absence of sodium alginate in both cases, FSCPC and c-CPC. It should be noted that this is an in vitro study, and the immersion conditions used may be more severe than would be the actual case for cement paste when used for surgery. In fact, even c-FSCPC did not decay completely w6en it was packed in the mould with the upper and bottom ends open, and was immersed in distilled water (data not shown). When the paste was immersed in distilled water in the mould, the upper and lower faces of the cement were in contact with water, but not the side face, which faced the mould. c-CPC decayed completely even in that case. This difference of percentage of remaining cement, based on whether the paste was immersed with or without the mould, is thought to reflect differences in the amount of paste in which the setting reaction can proceed. As stated above, interlocking of HAP crystals must occur for setting to take place. For this crystal the distance between the interlocking to occur, crystals has to be short, and thus contact with water is not preferable. However, the setting reaction can proceed partially in the part facing the mould. Thus, some of the mass remained, even in the case Biomaterials
1995, Vol. 16 No. 7
type
FSCPC: K. lshikawa
et al.
of c-FSCPC, i.e. FSCPC not containing sodium alginate, when the mass was immersed in distilled water immediately after mixing, if it was kept in the mould. The immersion liquid used in this study was distilled water. In practice, the liquid phase in contact with the paste is blood. Blood may show behaviour that is a little different from distilled water. One reason for the decay of cement paste may be the penetration of water into the cement paste by osmosis. Since the combination of cement paste with blood gives a lower osmotic pressure than that with water, the percentage of remaining cement would be higher in blood. The percentage of remaining FSCPC was higher (approximately 25%) than that of c-CPC (0%) when 0.2% sodium alginate was incorporated into the liquid phase. This difference can be explained in terms of differing degrees of crystal interlocking. FSCPC set within approximately 5 min, in contrast to the 30 min setting time for c-CPC1’. This is because FSCPC is converted to HAP much faster than c-CPC. Thus, the introduction of only a small amount of sodium alginate (0.2%) may work well to prevent the complete decay of FSCPC paste. Differences in nd-FSCPC and nd-CPC can be seen more clearly in Figure 3. In both cements, FSCPC and c-CPC, the introduction of sodium alginate resulted in a rapid increase in the mechanical strength. However, the DTS value of nd-FSCPC was much higher than that of nd-CPC. This difference can be explained similarly to the above explanation; FSCPC set much faster than c-CPC; thus the setting reaction proceeded faster than the decay of the cement. The addition of sodium alginate, unfortunately, has a drawback in that, as
15
G 10 % P 0
5
0 0.0
0.5
1.0
1.5
2.0
Sodium Alginate (%) Figure 4 Effects of sodium alginate on mechanical strength (wet diametral tensile strength (DTS) value) of cement when paste was packed in a mould and kept in an incubator at 37°C and relative humidity of 100% for 24 h: 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
Non-decay
type
FSCPC:
K. lshikawa
531
et al.
shown in Figure 4 and Table 1, it resulted in a decrease of mechanical strength and inhibited the setting reaction. Sodium alginate is considered to form insoluble calcium alginate gel in the presence of calcium ions, which may be supplied horn the dissolution of TTCP or DCPA, as shown in Equation (1). 2Na-Alg + Ca2+ + Ca-Alg,
+ 2Na+
(1)
The insoluble hydrogel, calcium alginate, may inhibit the decay of cement paste in distilled water. However, calcium alginate does not increase the interlocking of HAP crystals, and thus can be taken just as an impurity from the interlocking reaction. Only this phenomenon was examined when the cement paste was allowed to set without contact with distilled water, as shown in Figure 4. Comparison of the DTS values in Figures 3 and 4 revealed that sodium alginate does not completely exclude the effect of distilled water. The DTS value of nd-FSCPC containing 0.8% sodium alginate in the liquid phase was approximately 9 MPa when it was kept from water contact, whereas the DTS value decreased to approximately 6 MPa when the paste was immediately immersed in distilled water. There may be better additives for the preparation of nd-FSCPC. Therefore, this may be a good opportunity to consider the requirements for such an additive. These are: 1. It should inhibit the decay of cement paste in liquid. 2. It should not inhibit the conversion of cement to HAP. 3. It should not decrease the mechanical strength of the set cement. 4. It should not decrease the handling properties of the cement paste. 5. It should show excellent biocompatibility, at least similar to that of apatite. 6. It should be adsorbed within a relatively short time. We showed here that sodium alninate satisfied the first requirement. Sodium alginatg also satisfies the second requirement. Although the nd-FSCPC may slow down the conversion of cement to HAP, since the addition of more than 1% sodium alginate resulted in no setting of c-CPC (Table z), this effect may be negligible for the nd-FSCPC if the content of sodium alginate is less than 2.6%. In addition, the XRD results showed no significant inhibition with the addition of sodium alginate (Figure 2). The third requirement was not completely satisfied by sodium alginate (Figure 2). As shown in Figure 4, the addition of sodium alginate resulted in a decrease of mechanical strength. However, with respect to this requirement, we believe that the benefit is greater than the drawback. Sodium alginate satisfies requirement 4. Moreover, the addition of sodium alginate increases the handling properties if the sodium alginate content is less than 2%. This may be because sodium alginate is viscous. Requirements 5 and 6 were not within the scope of this investigation. These features are very important, and thus, should be confirmed by an in vivo study based on the results of this basic study. Sodium
alginate and calcium alginate are known to show excellent biocompatibility. In 1963, the FAO/WHO joint community announced that a daily intake of alginic acid and its NH4, Ca, K and Na salts was safe15. Calcium alginate is often used for the capsule of cells such as liver cells, and is thought to show excellent biocompatibility at the cell level. Not only the cell’s natural response but also absorption can be expected, based on the results reported with the use of dried calcium alginate as an absorption string and as artificial skin16-‘r. In conclusion, a non-decay type FSCPC (nd-FSCPC) was proposed and some of its basic mechanical characteristics were studied by introducing sodium alginate to the liquid phase of c-FSCPC. The introduction of sodium alginate to the liquid phase of FSCPC resulted in nd-FSCPC, which did not decay even when the paste was immersed in distilled water immediately after mixing; this compound can thus be used for areas exposed to blood. This nd-FSCPC seemed to have potential value for the wider application of FSCPC.
ACKNOWLEDGEMENT This study was supported in part by a Grant-in-Aid K.I.) for Scientific Research from the Ministry Education, Science and Culture, Japan.
(to of
REFERENCES 1
2
Brown W, Chow L. Combinations of sparingly soluble calcium phosphates in slurries and paste as mineralizers and cements. US Patent 4,612,053, 1986. Brown WE, Chow LC. A new calcium phosphate, watersetting cement. In: Brown PW, ed. Cements Research Progress. Westerville, OH: American Ceramic Society, 1986:
3
4 5
6
7
8
9
10
351-379.
Chohayeb AA, Chow LC, Tsaknins PJ. Evaluation of calcium phosphate as a root canal sealer-filler material. JEndodont 1987; 13: 384-387. Development Chow Lc. of self-setting calcium phosphate cements. ] Ceram Sot Jpn 1991; 99: 954-964. Costantino PD, Friedman CD, Jones K, Chow LC, Pelzer HJ, Sisson GA. Hydroxyapatite cement I. Basic chemistry and histologic properties. Arch Otolaryngol Head Neck Surg 1991; 117: 379-384. Friedman CD, Costantino PD, Jones K, Chow LC, Pelzer HJ, Sisson GA. Hydroxyapatite cement II. Obliteration and reconstruction of the cat frontal sinus. Arch Otolaryngol Head Neck Surg 1991; 117: 385-389. Fukase Y, Eanes ED, Takagi S, Chow LC, Brown WE. Setting reactions and compressive strength of calcium phosphate cement. ] Dent Res 1990; 69: 1852-1856. Sugawara A, Chow LC, Takagi S, Chohayeb H. In vitro evaluation of the sealing ability of a calcium phosphate cement when used as a root canal sealer-filler. I Endodont 1990; 16: 162-165. Sugawara A, Nishiyama M, Kusama K, et al. Histopathological reaction of calcium phosphate cement. Dent MaterJ 1992; 11: 11-16. Ishikawa K, Tagaki S, Chow LC, Ishikawa Y. Properties and mechanisms of fast-setting calcium phosphate cements. J Mater Sci: Mater Med (manuscript
submitted]. Biomaterials
1995. Vol. 16 No. 7
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12
13
14
15 16
Non-decav twe Ishikawa K, Sanin N, Takagi S, Chow LC, Eanes ED, Matusya S. Effects of particle size on pH and mechanical strength of calcium phosphate cement. I Mater Sci: Mater Med (manuscript submitted). Ishikawa Y, Ishikawa K, Takagi S, Chow LC, Eanes ED, Friedman CD. Release of antibiotics from calcium phosphate cement. I Mater Sci: Mater Med (manuscript submitted). Ishikawa K, Kon M, Tenshin S, Kuwayama N. Effect of preparation conditions in aqueous solution on properties of hydroxyapatite. Dent Mater J 1990; 9: 58-69. Ishikawa K. Effects of porosity on mechanical strength of calcium phosphate cement. I Biomed Mater Res (manuscript submitted). Announcement. WHO Techn Pep Ser 1974; 281: 381. Gensheimer D. A review of calcium alginates. Ostomy/ Wound Management 1993; 39: 34-43.
Biomaterials 1995, Vol. 16 No. 7
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21
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Guobo N, Mingzhu G. Design and application study of cell microcapsulation instrument. Chin J Biotechnol 1989; 5: 97-104. Klein CPAT, van de1 Lubbe HBM, de Groot K. A plastic of alginate composite with calcium phosphate granulate as implant material: an in viva study. Biomaterials 1987: 8: 308-310. O’Sullivan DG, Sherman IW, Phillips DE. The role of calcium alginate swabs in adenotonsillectomy. Clin Otolaryngoll992; 17: 403405. Sirimanna KS, Todd GB, Madden GJ. A randomized study to compare calcium sodium alginate fibre with two commonly used materials for packing after nasal surgery. Clin Otolaryngol 1992; 17: 237-239. Pirone LA, Bolton LL, Monte KA, Shannon RJ. Effect of calcium alginate dressings on partial-thickness wounds in swine. J Invest Surg 1992; 5: 149-153.
16 (1995)
527-532
@ 1995
Elsevier Science Limited Printed in Great Britain. All rights reserved 0142-9612/95/$10.00
Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate Kunio Ishikawa, Youji Miyamoto”, Masayuki Kon, Masaru Nagayama* and Kenzo Asaoka Department
of Dentat
Non-decay
alginate
cement
paste
(c-FSCPC) mately
alginate
resulted
in distilled
completely
within
into conventional
in no setting
diffraction
when
analysis
any concentrations increased
rapidly
and kept in distilled
alginate’s
strength.
alginate
composite
surgery
where
Keywords: Received
of sodium
Calcium
of sodium
no significant
alginate
studied
of sodium
water
is exposed
phosphate
19 July 1994; accepted
alginate
alginate.
time
when
be of value
than
strength the cement
in orthodontics
1 wt%.
of
Powder
to apatite
for
of the cement paste
alginate
together
indicate
FSCPC approxi-
phase,
of cement
of sodium
taken
behaviour,
the
the introducti0.n
in the liquid
The mechanical addition
when
of the cement,
was more
up to 0.8 wt%
even
conventional
In contrast,
phosphate
in this investigation,
should
whereas
for the conversion
further
by introducing
was stable
The setting
introduced
and absorption
was
decreased
with sodium
that the use of sodium
and oral and maxillofacial
to blood.
cement,
non-decay,
21 September
1994
apatite,
alginate
However, the problem of decay with this cement limits the potential wider application of this bioactive material. For example, CPC is thought to have good potential value in orthodontics and in oral and maxillofacial surgery. In such fields, there is a good chance that pastes would be exposed to blood and thus decay of the cement paste would result in the failure of the operation or, at least, would decrease the effectiveness of the operation. Therefore, there is a requirement for a non-decaying type of FSCPC (nd-FSCPC) for the wider application of FSCPC. In this investigation, we prepared a nd-FSCPC by adding sodium alginate to the liquid phase of FSCPC. The in vitro findings obtained in this investigation are reported together with a discussion of the required properties for a nd-FSCPC based on these findings.
calcium phosphate cement (FSCPC) shows significantly shortened setting time compared with conventional CPC1-’ (c-CPC) - which consists of an equimolar mixture of tetracalcium phosphate (TTCP; CQ(PO,]~O) and dicalcium phosphate anhyclrous (DCPA; CaHPO,) or dicalcium phosphate dihydrate (CaHPO,.ZH,O)-going from 30-60 min to approximately 5 mini’. Although FSCPC shows the same excellent bioactivity as c-CPC, there are various problems involved in the wider clinical use of this cement. One of these problems is the decay of the cement when the cement paste is in contact with blood. apatite (HAP: The sets to form cement ambient under Ca10-,(~O~),(P04)~-,(OH)~-X) conditions. However, exposure of the paste to blood early after mixing results in the decay of the cement, the situation being similar to that observed for gypsum. Gypsum sets when mixed with water; however, gypsum paste also decays gradually when immersed in water just after mixing. Decay is not a problem when the cement paste is used in areas where there is no liquid in contact with the cement, such as in root filling materials.
Fast-setting
Correspondence
alginate difference
(O-2.0 wt%).
obtained
of Dentistry,
School
was prepared
mixing,
neutral
at 37” C, whereas
biocompatibility
Surgery,
nd-FSCPC
after
on the presence
FSCPC as nd-FSCPC
the cement
immediately immersion.
The results
excellent
(nd-FSCPC)
of FSCPC.
1 min upon
with the addition
known
cement
phase
water
the amount
of sodium
of Oral and Maxilfofaciaf
770 Japan
CPC, i.e. CPC without
revealed
immersed
the mechanical
phosphate
into the liquid
was immersed
decayed
Tokushima,
calcium
(O-2.0 wt%)
5 min, was not dependent
sodium X-ray
3-18-15 Kuramoto,
type fast-setting
sodium
and ‘First Department
Engineering,
Tokushima University,
MATERIALS AND METHODS Preparation
of calcium phosphate cement (CPC)
TTCP was made from CaHP04 and CaC03, as described previously7**s12. The solid was first crushed with a mortar and mill, and then ground for 1 h in dried
to Dr Kunio Ishikawa. 527
Biomaterials
1995, Vol. 16 No. 7
Non-decay type FSCPC: K. lshikawa
528 cyclohexane in an agate jar, using a ball mill (Retsch PM4, Brinkman, New York, USA) to obtain a median particle size of 4.11 pm. Commercial ultra-pure DCPA (J.T. Barker Chemical Co., NJ, USA) was ground for 24 h in 66% ethanol in the agate jar to a medium particle size of 0.7 pm. Although particle size distribution affects the properties of CPC such as mechanical strength and setting timel’, we did not examine any other particle size distribution in this study, in order to focus only on the effect of sodium alginate on the decay properties of the paste when exposed to a liquid phase. The particle size of TTCP and DCPA was measured in isopropanol by a sedimentation method based on Stokes’ law, using a centrifugal particle size analyser (SA-CP3, Shimazu, Kyoto, Japan). X-ray diffraction (XRD) revealed no other crystals after grinding. CPC powders, made by mixing equimolar amounts of TTCP and DCPA using a micro mill (Bel-Art Products, Pequannock, NJ, USA), were stored in a vacuum desiccator at 60” C. The liquid phase of the nd-FSCPC was made by dissolving sodium alginate (Nacalai Tesque, Kyoto, Japan) in 0.2 mol 1-l Na,H,_,PO,; 0.2 mol ll’ Na2HP04 and 0.2 mol 1-l NaH2P04 were mixed so that the solution had pH 7.4 at 37”C, and then sodium alginate was dissolved in this solution. No adjustment was made to the concentration of neutral phosphate due to the addition of sodium alginate, since the volume of sodium alginate was negligible, even at the maximum concentration used in the present investigation, i.e. 2 wt%.
Percentage of remaining cement To investigate the potential value of nd-FSCPC against blood exposure, the percentage of remaining cement was measured by immersing the cement paste in distilled water immediately after mixing. Using a glass slab and spatula, we mixed the CPC powder with the liquid phase, at a powder to liquid ratio (P/L) of 4.0, and then packed the cement into a cylindrical mould (4.7 mm D x 8 mm H). The mould was made by cutting off the front portion of a 1 cm3 plastic syringe (Terumo, Tokyo, Japan). A force of approximately 3 kg per 6 mm D was applied for packing the cement into the moulds. After smoothing the surface of the cement on the open side, we pushed the piston of the syringe so that the paste was immersed in distilled water; this was done in an incubator kept at 37°C. After 24 h immersion, the largest mass of the cement was collected and dried with a freeze drier (FD-1, Tokyo Rikakiki Co., Ltd, Tokyo, Japan).
Setting time of the cement The setting time of the CPC samples was measured according to the method set out in international standard Is01566 for dental zinc phosphate cements. In this method, the cement is considered set when a 400 g weight loaded on to a Vicat needle with a tip diameter of 1 mm fails to make a perceptible circular indentation on the surface of the cement. The Standard requires that the cement be maintained at a temperature of 37” C and relative humidity of at least 37%; in the present investigation, the conditions were 37” C and 100% humidity. Biomaterials
1995, Vol. 16 No. 7
et al.
X-ray powder diffraction The XRD patterns of the vacuum-dried samples were recorded with a vertically mounted diffractometer system (ADG-301; Toshiba Co. Ltd, Tokyo, Japan), radiation Cu Ka monochromatized using Ni (A= 0.1540 nm) generated at 30 kV and 10 mA. The specimens were scanned from 3 to 60” 20 (where 1” is the Bragg angle) in a continuous mode. Standard HAP used for comparison was prepared at room temperature as described previously13.
Mechanical strength measurements To evaluate the mechanical strength of the set FSCPC in the presence and absence of sodium alginate, we measured the diametral tensile strength (DTS). Two different methods were employed to evaluate the effect of sodium alginate. In one method, we used set CPC; the paste was immersed in distilled water immediately after mixing, similar to the method used for the measurement of percentage remaining cement. A plastic tube with an inner diameter of 6 mm and a plastic rod with a diameter of 6 mm were used to make the paste, which was 6 mm in diameter (D) and 3 mm thick (H). In the other method, the paste was kept from direct exposure to the water. The paste was placed in a split mould (6 mm D x 3 mm H), using a force of approximately 3 kg per 6 mm D. Both sides of the mould were covered with glass and clamped, and the mould was kept in an incubator for 24 h at 37” C and 100% humidity. CPC specimens prepared by these methods were kept in an incubator for 24 h and then subjected to DTS measurement, the measurement being done within 30 min after the specimens were taken out of the incubator. The wet DTS value was measured to simulate body conditions, even though the dry specimen had a higher value. The DTS values were measured on an Instron (Universal Testing Machine, United Calibration Corp., Garden Grove, CA, USA). The diameter and length of each specimen were measured with a micrometer. The samples were later placed on steel platens, which were then covered with one thickness of wet filter paper, and tested at a loading rate of 1.0 mm min-’ The DTS value used was the average value of at least ten specimens.
RESULTS Figure I shows the effects of sodium alginate on the percentage of remaining cement in c-CPC and FSCPC when the cement was immersed in distilled water immediately after mixing. Both c-CPC and FSCPC decayed completely within 24 h in the absence of sodium alginate. When the cement paste was immersed in the distilled water, it decayed gradually, the rate of decay being much faster with c-CPC (within 1 min) than with FSCPC. The addition of sodium alginate, approximately 0.5 wt%, to the liquid phase of the cement increased the amount of remaining paste to 100%. The percentage of remaining paste was similar for c-CPC and FSCPC, except at 0.2 wt% of sodium alginate; the c-CPC paste decayed completely, whereas a mass of approximately 25% of the FSCPC paste remained and set.
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529
z 100 E E” 80 8 f .IE
60
E” 40 d E 8 20 $ a
0 0
0.5
1
2.0
Sodium Alginate (%) Figure 1
Effects of sodium alginate on the percentage of remaining cement paste after 24 h. The cement paste was immersed in distilled water at 37°C immediately after mixing (mixing ratio of 4.0, powder/liquid): 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
The setting time of the nd-FSCPC and nd-CPC in the presence of various concentrations of sodium alginate in the liquid phase (O-2.0 wt%) is summarized in Table 1 with that for c-FSCPC and c-CPC. The setting time of the c-CPC was approximately 30-40 min, the same value was obtained for the c-CPC whose liquid phase contained less than 1% sodium alginate. However, mixing with a sodium alginate solution of 1% or more resulted in no setting within 3 h, the longest time checked for setting. The surface of the paste seemed to adsorb water and became slippery. In contrast, the
setting time of FSCPC was 5-6 min, regardless of the sodium alginate concentration (O-LO%). The XRD patterns of c-FSCPC and nd-FSCPC kept in distilled water at 37” C for 24 h are shown in Figure 2, with those of the powder phase of CPC, an equimolar mixture of TTCP and DCPA, and poorly crystallized HAP for comparison. The XRD patterns of nd-FSCPC after 24 h were similar to those of c-FSCPC, and conversion to HAP was confirmed. The DTS values of the cements are summarized in Figure 3 for cement pastes immersed in distilled water at 37” C immediately after mixing. In both FSCPC and c-CPC, the DTS value increased rapidly with the addition of sodium alginate, the value being maximal at around 0.8% of sodium alginate in both cases; the addition of further sodium alginate resulted in a slight decrease in the DTS value. The DTS value was much higher for FSCPC than for c-CPC. Shown in Figure 4 is the DTS value of cement when the paste was kept in the mould. The mould was kept in an incubator at 37” C and relative humidity of 100% but the paste was not in direct contact with water. The DTS value decreased with the addition of sodium alginate for both FSCPC and c-CPC. Similar to these results shown in Figure 3, FSCPC had higher DTS values both in the absence and presence of sodium alginate (o-2.0%).
DISCUSSION One of the problems with c-FSCPC is that the cement decays when in contact with blood. When CPC sets,
a) Powder
T: l-rCP
pha8e
Table 1
Setting time of non-decay type fast-setting calcium phosphate cement and non-decay type calcium phosphate cement in the presence of various concentrations of sodium alginate (02.0%) in the liquid phase. The setting time of fastsetting calcium phosphate cement (FSCPC) and conventional calcium phosphate cement (c-CPC) is shown for comparison. The cement was mixed at a powder to liquid ratio of 4.0 CPC
Sodium alginate (wt%)
Setting time (min)
FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC FSCPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC c-CPC
0.0 0.2 0.4 0.6 0.8 1.0 1.5 2.0 0.0 0.2 0.4 0.6 0.8 1.0 1.5 2.0
5.3 It 0.5 5.2 * 0.4 5.8 f 0.7 5.5 f 0.5 5.3 f- 0.5 5.3 Ib 0.5 5.2 f 0.4 5.5 It 0.5 38.8 i 3.9 41.5 f 4.1 39.7 * 4.1 40.0 f 4.1 42.5 f 4.0 no setting no setting no setting
c) nd-FSCPC
I...‘.......““‘,......“..
25
30
36
26 (degree) Figure 2 Powder X-ray diffraction patterns of conventional fast-setting calcium phosphate cement (c-FSCPC) and nondecay type fast-setting calcium phosphate cement (ndFSCPC) kept in distilled water at 37°C for 24 h. The powder phase of calcium phosphate cement and poorly crystallized hydroxyapatite (HAP) are shown for comparison (TTCP = tetracalcium DCPA = dicalcium phosphate; phosphate anhydrous). Biomaterials 1995. Vol. 16 No. 7
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8
T T
Sodium Alginate (%) Figure 3 Effects of sodium alginate on mechanical strength (wet diametral tensile strength (DTS) value) of cement when the paste was immersed in distilled water (37°C) immediately after mixing and kept in distilled water for 24 h: 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
the set mass is stable even in contact with a liquid phase. However, CPC paste is easily decayed by contact with the liquid phase. Once the paste decays, it does not set, since under these circumstances the setting reaction cannot occur. The setting reaction involves the interlocking of formed HAP1”,14; HAP crystals interlock, showing similar setting behaviour to that seen for the setting reaction of gypsum. As shown in Figure 1, the cement paste decayed completely in the absence of sodium alginate in both cases, FSCPC and c-CPC. It should be noted that this is an in vitro study, and the immersion conditions used may be more severe than would be the actual case for cement paste when used for surgery. In fact, even c-FSCPC did not decay completely w6en it was packed in the mould with the upper and bottom ends open, and was immersed in distilled water (data not shown). When the paste was immersed in distilled water in the mould, the upper and lower faces of the cement were in contact with water, but not the side face, which faced the mould. c-CPC decayed completely even in that case. This difference of percentage of remaining cement, based on whether the paste was immersed with or without the mould, is thought to reflect differences in the amount of paste in which the setting reaction can proceed. As stated above, interlocking of HAP crystals must occur for setting to take place. For this crystal the distance between the interlocking to occur, crystals has to be short, and thus contact with water is not preferable. However, the setting reaction can proceed partially in the part facing the mould. Thus, some of the mass remained, even in the case Biomaterials
1995, Vol. 16 No. 7
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FSCPC: K. lshikawa
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of c-FSCPC, i.e. FSCPC not containing sodium alginate, when the mass was immersed in distilled water immediately after mixing, if it was kept in the mould. The immersion liquid used in this study was distilled water. In practice, the liquid phase in contact with the paste is blood. Blood may show behaviour that is a little different from distilled water. One reason for the decay of cement paste may be the penetration of water into the cement paste by osmosis. Since the combination of cement paste with blood gives a lower osmotic pressure than that with water, the percentage of remaining cement would be higher in blood. The percentage of remaining FSCPC was higher (approximately 25%) than that of c-CPC (0%) when 0.2% sodium alginate was incorporated into the liquid phase. This difference can be explained in terms of differing degrees of crystal interlocking. FSCPC set within approximately 5 min, in contrast to the 30 min setting time for c-CPC1’. This is because FSCPC is converted to HAP much faster than c-CPC. Thus, the introduction of only a small amount of sodium alginate (0.2%) may work well to prevent the complete decay of FSCPC paste. Differences in nd-FSCPC and nd-CPC can be seen more clearly in Figure 3. In both cements, FSCPC and c-CPC, the introduction of sodium alginate resulted in a rapid increase in the mechanical strength. However, the DTS value of nd-FSCPC was much higher than that of nd-CPC. This difference can be explained similarly to the above explanation; FSCPC set much faster than c-CPC; thus the setting reaction proceeded faster than the decay of the cement. The addition of sodium alginate, unfortunately, has a drawback in that, as
15
G 10 % P 0
5
0 0.0
0.5
1.0
1.5
2.0
Sodium Alginate (%) Figure 4 Effects of sodium alginate on mechanical strength (wet diametral tensile strength (DTS) value) of cement when paste was packed in a mould and kept in an incubator at 37°C and relative humidity of 100% for 24 h: 0, fast-setting calcium phosphate cement; 0, conventional calcium phosphate cement.
Non-decay
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FSCPC:
K. lshikawa
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et al.
shown in Figure 4 and Table 1, it resulted in a decrease of mechanical strength and inhibited the setting reaction. Sodium alginate is considered to form insoluble calcium alginate gel in the presence of calcium ions, which may be supplied horn the dissolution of TTCP or DCPA, as shown in Equation (1). 2Na-Alg + Ca2+ + Ca-Alg,
+ 2Na+
(1)
The insoluble hydrogel, calcium alginate, may inhibit the decay of cement paste in distilled water. However, calcium alginate does not increase the interlocking of HAP crystals, and thus can be taken just as an impurity from the interlocking reaction. Only this phenomenon was examined when the cement paste was allowed to set without contact with distilled water, as shown in Figure 4. Comparison of the DTS values in Figures 3 and 4 revealed that sodium alginate does not completely exclude the effect of distilled water. The DTS value of nd-FSCPC containing 0.8% sodium alginate in the liquid phase was approximately 9 MPa when it was kept from water contact, whereas the DTS value decreased to approximately 6 MPa when the paste was immediately immersed in distilled water. There may be better additives for the preparation of nd-FSCPC. Therefore, this may be a good opportunity to consider the requirements for such an additive. These are: 1. It should inhibit the decay of cement paste in liquid. 2. It should not inhibit the conversion of cement to HAP. 3. It should not decrease the mechanical strength of the set cement. 4. It should not decrease the handling properties of the cement paste. 5. It should show excellent biocompatibility, at least similar to that of apatite. 6. It should be adsorbed within a relatively short time. We showed here that sodium alninate satisfied the first requirement. Sodium alginatg also satisfies the second requirement. Although the nd-FSCPC may slow down the conversion of cement to HAP, since the addition of more than 1% sodium alginate resulted in no setting of c-CPC (Table z), this effect may be negligible for the nd-FSCPC if the content of sodium alginate is less than 2.6%. In addition, the XRD results showed no significant inhibition with the addition of sodium alginate (Figure 2). The third requirement was not completely satisfied by sodium alginate (Figure 2). As shown in Figure 4, the addition of sodium alginate resulted in a decrease of mechanical strength. However, with respect to this requirement, we believe that the benefit is greater than the drawback. Sodium alginate satisfies requirement 4. Moreover, the addition of sodium alginate increases the handling properties if the sodium alginate content is less than 2%. This may be because sodium alginate is viscous. Requirements 5 and 6 were not within the scope of this investigation. These features are very important, and thus, should be confirmed by an in vivo study based on the results of this basic study. Sodium
alginate and calcium alginate are known to show excellent biocompatibility. In 1963, the FAO/WHO joint community announced that a daily intake of alginic acid and its NH4, Ca, K and Na salts was safe15. Calcium alginate is often used for the capsule of cells such as liver cells, and is thought to show excellent biocompatibility at the cell level. Not only the cell’s natural response but also absorption can be expected, based on the results reported with the use of dried calcium alginate as an absorption string and as artificial skin16-‘r. In conclusion, a non-decay type FSCPC (nd-FSCPC) was proposed and some of its basic mechanical characteristics were studied by introducing sodium alginate to the liquid phase of c-FSCPC. The introduction of sodium alginate to the liquid phase of FSCPC resulted in nd-FSCPC, which did not decay even when the paste was immersed in distilled water immediately after mixing; this compound can thus be used for areas exposed to blood. This nd-FSCPC seemed to have potential value for the wider application of FSCPC.
ACKNOWLEDGEMENT This study was supported in part by a Grant-in-Aid K.I.) for Scientific Research from the Ministry Education, Science and Culture, Japan.
(to of
REFERENCES 1
2
Brown W, Chow L. Combinations of sparingly soluble calcium phosphates in slurries and paste as mineralizers and cements. US Patent 4,612,053, 1986. Brown WE, Chow LC. A new calcium phosphate, watersetting cement. In: Brown PW, ed. Cements Research Progress. Westerville, OH: American Ceramic Society, 1986:
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Non-decav twe Ishikawa K, Sanin N, Takagi S, Chow LC, Eanes ED, Matusya S. Effects of particle size on pH and mechanical strength of calcium phosphate cement. I Mater Sci: Mater Med (manuscript submitted). Ishikawa Y, Ishikawa K, Takagi S, Chow LC, Eanes ED, Friedman CD. Release of antibiotics from calcium phosphate cement. I Mater Sci: Mater Med (manuscript submitted). Ishikawa K, Kon M, Tenshin S, Kuwayama N. Effect of preparation conditions in aqueous solution on properties of hydroxyapatite. Dent Mater J 1990; 9: 58-69. Ishikawa K. Effects of porosity on mechanical strength of calcium phosphate cement. I Biomed Mater Res (manuscript submitted). Announcement. WHO Techn Pep Ser 1974; 281: 381. Gensheimer D. A review of calcium alginates. Ostomy/ Wound Management 1993; 39: 34-43.
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Guobo N, Mingzhu G. Design and application study of cell microcapsulation instrument. Chin J Biotechnol 1989; 5: 97-104. Klein CPAT, van de1 Lubbe HBM, de Groot K. A plastic of alginate composite with calcium phosphate granulate as implant material: an in viva study. Biomaterials 1987: 8: 308-310. O’Sullivan DG, Sherman IW, Phillips DE. The role of calcium alginate swabs in adenotonsillectomy. Clin Otolaryngoll992; 17: 403405. Sirimanna KS, Todd GB, Madden GJ. A randomized study to compare calcium sodium alginate fibre with two commonly used materials for packing after nasal surgery. Clin Otolaryngol 1992; 17: 237-239. Pirone LA, Bolton LL, Monte KA, Shannon RJ. Effect of calcium alginate dressings on partial-thickness wounds in swine. J Invest Surg 1992; 5: 149-153.