Sree Chitra Tirunal Institute for Medical Sciences and Technology ... precipitation followed by freeze drying and spray drying techniques. The spray dried.
Phosphorus
Research
Bulletin
Vol. 6 (1996), 35 - 38
PREPARATION AND CHARACTERIZATION HYDROXY APATITE POWDERS
OF FREE FLOWING
HARIKRISNA
SIVAKUMAR
VARMA
and RAJAGOPALAN
Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Thiruvananthapuram - 695012 INDIA
Sciences
and Technology
Abstract: Free flowing hydroxy apatite (HAP)powders have been synthesized by precipitation followed by freeze drying and spray drying techniques. The spray dried HAP powder (5-25 microns spheres) showed improved sintering characteristics compared to freeze dried powders, which were irregular in shape and their agglomerate sizes were in the range 5-100 microns. It also found that surface impurities on the freshly prepared powders show toxicity effects towards Red Cells, and L.929 fibroblast cells.
INTRODUCTION Synthetic implants
because
calcium
phosphate
materials
of their close resemblance
there are a number of HAP based materials of bone replacement treatment
of osteomytitis,
highlights adopted
procedures
the
characteristics
at our institute
towards
to the minerals are available
like alveolar
maxillofacial
have been identified
of tooth
in the market
ridge reconstruction,
and orthognathic
of hydroxy
apatite
the development
as potential and bone intended
a variety
bone filling,
etc. The present
derived
of HAP materials
1,2. Today
for
periodontal
implantation
powders
hard tissue
by different intended
work
methods
for bone filling
applications.
EXPERIMENTAL The HAP dihydrogen
PROCEDURES
was prepared ammonium
by a precipitation phosphate.
hours. Then it was filtered and washed or dispersed
in distilled
water
route
involving
The precipitate
was
ammoniated
aged in the mother
to get a filter cake which
and then spray dried.
-35-
calcium
nitrate
liquor
was then either freeze
It is important
to mention
and
for 24 dried
here that the
filter
cake
impurities
was
adequately
washed
such as nitrate and ammonium
a few times
ions. Both powders
were then heated at 300 degree C for 1 hr and then discs
a pressure
temperatures were measured
of 75
ranging
MPa
from
by Archimedes
in a uniaxial
1100-1300 method.
degree
press.
evaluation
and cytotoxicity
out according
The
water
to get rid of surface
were free flowing.
compacted
of the powders to standard
The powders
to 10 mm dia and 2mm thick
discs
were
C for 1 hr. The density
The wicker's
carried out. The toxicological was carried
with distilled
sintered
of the sintered
microhardness
measurement
with respect
to Haemolytic
procedures
at various discs
was also potential
3.
RESULTS AND DISCUSSION Fig 1 a,b,c shows the morphology of the powders. The freeze dried powder was irregular in shape while the spray dried one is spherical. At high magnification, these particles are found as agglomerates of submicron HAP crystallites ( 200nm). The densification characteristics of these powders are given in Fig.2 as a function of temperature. The spray dried powders showed improved sintered density compared to the freeze dried counterparts . This could be due to the better and uniform packing of the spherical powder particles . The microhardness values also show a similar trend (Fig .3) like the sintered density till 1250 degree C. Beyond 1250 degree C, the decrease in the hardness could be due to the increase in grain size 4,5The polished micrographs of the samples sintered at 1250 degree C (Fig.4) clearly shows that spray dried powders provide a uniform microstructure than freeze dried ones . Toxicological Evaluation The processing conditions, especially surface impurities can elicit adverse toxicological reactions. For example, in this study it was observed that thorough washing of the precipitate was required for making HAP less haemolytic . Fig.5 shows the effect of number of washing of the HAP precipitate on the haemolytic potential. Similar was the effect on L 929 fibroblast cells.Fig 6a shows a number of dead cells(rounded) along with unwashed HAP powders while with washed powders the cells were intact(Fig .6b). Further work is in progress to study the effect of reactions of powders and porous granules on the osteoblast cells as well as on the soft and hard tissues.
-36-
FIGURE 1 (a) Spray dried HAP powder (b) Freeze dried powder (c ) sample (b) at high magnification
FIGURE.
FIGURE3.
2. Sintered density Vs. Sintering temperature
Microhardness temperature
Vs. Sintering
FIGURE 4. Polished SEM pictures of sintered samples (a) Spray dried (b) Freeze dried
-37-
FIGURE
5. Effect Haemolysis
of washing behaviour
dried powder
on the of freeze
FIGURE 6. Fibroblast cells with (a) unwashed HAP powder . The rounded shapes are dead cells and (b) thoroughly washed HAP powder and intact cells
CONCLUSION
Free flowing HAP powders were prepared by freeze drying and spray drying techniques. Spray dried powder showed improved sintering properties . The microhardness values of the sintered samples derived from the spray dried powders were better than the freeze dried counterpart. The haemolysis and cytotoxicity study revealed that the surface impurities have got a deleterious effect need to be addressed while developing biological applications. ACKNOWLEDGEMENT The authers wish to thank Director, SCTIMST for the onstant encouragement and the permission to publish this work. The authers are also thankful to Dr. K.Rathinam and Dr.T.V.Kumari for the help rendered during the haemolysis and cytotoxicity studies respectively. One of the authors(HKV) would like to thank Department of Science and Technology for the financial support under the SERCYS scheme REFERENCES 1.M.Jarcho, Clin.Orthop., 157, 256 (1981) 2.L.L.Hench, J.Amer.Ceram.Soc., 74, 1487 (1991) 3.ISO Standard, CASE Pos Pale 56, CH-1211 Geneva 20, Switzerland- ISO/TR 7405-1984 (E) 16-17 4. S. Puajindanetr, S.M.Best and W.Bonfield, British Ceram .Trans., 93, 96 (1994) 5. H.K.Varma and R.Sivakumar, Materials Letters ( in press)
-38-
