We have prepared silicate based hard materials and have processed it with organic flux. Because of the bioactivities of hydroxyapatites with tissues, this class of materials have attracted interest for bone applications. We have utilized low temperature processing techniques. Organic melt was used and the directional solidification method to cast the shaped sample. This organic treated material has different characteristics than coarsened oxide materials. Our approach involved low temperature processing using nano and micron sized powders of the material system Na2O-K2O-CaO- MgO-Ga2O3-SiO2, and titanates were processed by sintering and grain growth. Our results indicate that substitution of gallium and magnesium or titanium with some variation in processing methods have great potential to improve the glassy characteristics without decreasing the mechanical properties of bones. Effect of radiation on bone was studied by exposing with commercially available Cs137 gamma ray source. It was observed that electrical resistivity increased due to radiation exposure for this system

Arnold, Brad

Bhavsar, Jayati

Choa, Fow-Sen

Cullum, Brian

Gautam, Pooja

Kelly, Lisa

Mandal, K. D.

Singh, N. B.

Smith, Paul

Su, Ching Hua

Tufail, Areeba

NASA Technical Reports Server

Design and characteristics of hydroxyapatites: Effect of radiation  
 
Jayati Bhavsar, Areeba Tufail, Pooja Gautam*, Brad Arnold, Fow-Sen Choa, Lisa Kelly, Brian 
Cullum, Paul Smith, Ching Hua Su+, K. D. Mandal*, and N. B. Singh 
 
University of Maryland, Baltimore County, Baltimore MD 21250 
+EM31, NASA Marshall Space Flight Center, Huntsville, AL 35812 
*IIT-Banaras Hindu University, Varanasi (UP) India 
 
ABSTRACT 
We have prepared silicate based hard materials and have processed it with organic flux. Because of the bioactivities 
of hydroxyapatites with tissues, this class of materials have attracted interest for bone applications. We have utilized 
low temperature processing techniques. Organic melt was used and the directional solidification method to cast the 
shaped sample. This organic treated material has different characteristics than coarsened oxide materials. Our 
approach involved low temperature processing using nano and micron sized powders of the material system Na2O-
K2O-CaO- MgO-Ga2O3-SiO2, and titanates were processed by sintering and grain growth. Our results indicate that 
substitution of gallium and magnesium or titanium with some variation in processing methods have great potential to 
improve the glassy characteristics without decreasing the mechanical properties of bones. Effect of radiation on bone 
was studied by exposing with commercially available Cs137 gamma ray source. It was observed that electrical 
resistivity increased due to radiation exposure for this system.  
   
Email: singna@umbc.edu 
 
Keywords: bones, hydroxyapatite, organic, solidification, oxides 
 
1. INTRODUCTION 
There is a continuous effort to develop process for tissue engineering for achieving bone compositions both crystalline 
composites and glasses for good mechanical properties, bioactivity, less degradability, and regeneration 
characteristics. This can be achieved by both understanding the stoichiometric composition and developing novel 
processes. Considerable efforts on biodegradable composites have been achieved by synthesizing organic-inorganic 
composites. The basic idea is to take the advantage of achieving good bone regeneration characteristics in organic-
inorganic composites by changing their stoichiometric compositions. The apatite type materials (hexagonal, space 
group P63/6) are found in nature and have been explored since past half century for their compositions and crystal 
structures. Hydroxyapatites are excellent materials and play very important role. Previous researches were focused 
ion calcium based phosphates and some silicates. But there is a great need for substitution of elements such as gallium 
to replace calcium and applications of silicates and titanates to replace phosphate to achieve slow degradation and to 
achieve high bone strength. The control of morphology more specifically micro, nanopororous strictures, cellular 
structures are governed by processes and by choosing proper components. Generally, organics (polymers) have high 
heat of fusion and grow with facets. It makes control of morphology very difficult. Growth by casting, solution 
crystallization and other methods make it very difficult. Hydroxyapatites single crystals have been investigated their 
applications as the laser host material. Czochralksi and flux growth methods have been utilized to achieve single 
crystals. With the increasing thrust to design hard and active bioactive glasses (BGs), it is important to understand the 
mechanism of bonding between BGs and soft and hard tissues. Chemical process which involves dissolution and 
precipitation reactions at BG surfaces upon contact with physiological fluids is very important and most important for 
regenerative tissues [1-4] . Other factors such as variation[5.6] in pH due to increased concentration of various ions at 
the BG-fluid interface affects the morphology at the interface. In many cases microcrystals are developed and provide 
interface between tissue and new implanted bones. This indicates that variations in ions affect the interactions of BGs 
with tissue is extremely important factor. Additionally, interaction of rough surfaces of BGs helps in attachment of 
tissues. The hardening behavior and mechanism and kinetic rate requires more study. The composition and local pH 
(and hence ion generation) locally vary a lot. This makes any quantitative prediction on growth rate and kinetics of 
growth very difficult.  
 
https://ntrs.nasa.gov/search.jsp?R=20180005408 2019-08-31T14:50:22+00:00Z
The objectives of this study were to develop novel composition containing gallium materials and surfaces to prevent 
wear and corrosion; using nano, micro and bulk materials and novel processes for designing structures to increase 
fatigue and fracture resistance; understanding the morphology and evaluate thermal properties which may throw light 
on performance function in that occur because of aging or disease. There are several other outstanding issues such as 
(a) activity of tissues for bone replacements (b) suitability of crystalline composites vs glass and (c) monolithic vs 
composites which need to be explored in detail. The focused objectives were to develop soft and hard tissues by doping 
heavy element (gallium) which may have less depletion compared to calcium as results of aging, understand glassy 
behavior and effect of radiation on properties.  
 
2. EXPERIMENTAL METHODS AND RESULTS 
 
As described in the previous section the goal was to understand the morphology specially to process samples free from 
precipitates for good, glassy behavior, several compositions were synthesized. The results of two compositions listed 
in Table 1 are presented in this paper.  The focus was to determine the morphology of two gallium containing samples 
with and without titanium. 
 
                               Table 1- Composition of two mixtures for synthesis 
 
Material Sample A Weight (g) Sample B Weight (g) 
Sodium carbonate 0.60 0.6 
Calcium oxide 2.0 2.0 
Magnesium oxide 0.2 0.2 
Potassium carbonate 1.2 1.2 
Silicon oxide 5.3 5.3 
Gallium oxide 0.4 0.4 
Titanium oxide 0.00 0.6 
 
2.1 Synthesis of samples: As supplied chemicals (Fig.1a) by Sigma Aldrich were listed for the range of 99+% purity. 
No further purification was performed. The stochiometric ration as listed in Table 1 was used to prepare two samples. 
Samples were mixed and grinded to achieve homogeneous mixture.  
  
 
 
(a)                                                                                   (b)   
               Fig. 1 Two compositions of mixtures (a) As supplied chemicals and (b) fine powder of mixture of chemicals. 
 
There were two approaches which we used for the processing of samples.  These processes are: 
(a) Sintering at high temperature: In the first approach we prepared pressed pellets of samples and annealed these 
samples at 700C for a period of 24 hours.  The samples were cooled by switching the power of the furnace. There 
was no control on cooling rate. Since cooling rate has pronounced effect on the morphology and glass formation, 
this requires further research to understand glassy and crystalline transition behavior in this material system. 
 
(b) Solution process: In this process mixture was placed in a solution of dilute nitric acid-water mixture at room 
temperature. After an hour of leaving the sample at room temperature, we heated the material and kept in the 
range of 70 -80 0C for several hours. The material does not dissolve completely. This material was heated to 
driveaway the solvent. Almost after 24 hours the sample dried and was filtered. This sample was also pressed 
into a pellet and was annealed for 24 hours in a furnace at 700C.  
 
                         
(a)                                                (b) 
Fig. 2 Pellets pressed at 8000 psi to prepare 12 mm diameter samples (a) as prepared and (b) annealed at 700C pellets 
 
2.2 Morphological Study: The morphology of the material was studied at low magnifications (50-200X) using 
microscope and scanning electron microscope using a NOVA NANOSEM 450 system for transitioning of 
particles into glassy morphology. We observed that material processed in solution followed by annealing 
showed excellent glassy matrix. Fig.3 shows morphology of sample which was placed at 150 0C for 24 hours. 
This sample showed some small size precipitates which may have resulted from insoluble species.  
 
  
 
Fig. 3 Sample prepared by solution method followed by drying at 150C showed small precipitates 
The sample processed in solution was also used to determine morphological change at 700oC. Annealing at high 
temperature dissolved the precipitates. As shown in Fig. 4 there was no sign of precipitates in the matrix. Also, there 
were no faceted grains or large voids and holes in the sample. There was no sign of crystals in this matrix. Also, the 
surface morphology consisted of smooth layers.  
For a comparison both samples were processed for grain growth using ceramic processes. There was no solvent used 
in this process. Samples were placed at 700oC for a period of 50 hours. A typical morphology of sample is shown in 
Fig. 5. Annealing of 12 mm diameter and 5 mm thick transformed completely into hard matrix. Surfaces of this 
sample were very rough with some hills and valley indicating significant shrinking during the annealing.   
 
    
(a)                                                                                      (b) 
Fig. 4 Morphology of sample containing titanium showing glassy behavior. 
 
 
 
Fig. 5 Sample annealed at 700oC did not show voids or any micron size precipitates 
2.4 Bioactivity and effect of radiation: In the field of bio glasses continuous attempts have been made [1-6] to 
increase the bioactivity by using copper, strontium and other dopants in phosphate composites. We have performed 
some experiments using both compositions (with and without titanium) to test the validity of organic-inorganic 
composites for increasing activity. In the preliminary tests we used low temperature organic eutectic mixtures.  A as 
casted sample in eutectic is shown in Fig. 6. This sample has annealed mixture and could be fabricated for desired 
shapes.  
 
Fig. 9 As casted large (4x 4 cm) sample using low melting organic eutectic. This sample has annealed mixture 
For the effect of radiation, we used a commercially available gamma-ray source Cs137.  The effect of radiation was 
estimated by measuring the resistivity of material.  The measured resistivity [7] is in the range of 10-3 ohm-cm. It 
was changing significantly in range of 100Hz to 1MHz range. After a radiation of >50 hours the resistivity increased 
significantly for all frequency. This indicates that radiation affects the ionization process of the prepared samples. 
Further tests are continuing using spectral techniques such as IR and Raman for as prepared and irradiated samples. 
Also, differential thermal analysis and mechanical tests are continuing.  
3. SUMMARY 
 
Two silicate hydroxyapatites were synthesized using solution and annealing methods. It was observed that reactive 
solution process followed by annealing produced glasses free from precipitates and voids. Effect of radiation on bone 
was studied by exposing with commercially available Cs137 gamma ray source. It was observed that electrical 
conductivity decreases due to its exposure.  
 
 
4. REFERENCES 
 
[1]. L.L Hench, J. Materials Science, mater, Med, 17, 967 (2006). 
[2]. Valentina Miguez-Pacheco, David Greenspan, Larry Hench and Aldo R. Boccaccini, American Ceramic 
Society Bulletin, 94, 27-31 (2015).  
[3]. A. Hoppe, N. S. Guldal and A. R. Boccaccini, Biomaterials 32 (11), 2757  (2011). 
[4] M. N. Rahaman, D. E. Day, B. S. Bal, Q. Fu, S. B. Jung, L. F. Bonewald and A. P. Tomsia, Acta Biomater., 
7 2355 (2011). 
[5]. A. A. Gorustovich, J. A. Roether and A. R. Boccaccini, Tissue Eng, Part B Rev. 16, 2, (2010)199. 
[6] Guilin, Luo, Yufei Ma, Xu Cui, Lixin Jiang, Mingming Wu, Yang Hu, Yanfeng Luo, Haobo Pan and 
Changshun Ruan, RCA Advances, 7, 11880  (2017). 
[7]. Areeba Tufail, Christopher Cooper, Stacey Sova, Eric Bowman, Bradley Arnold, Fow-Sen Choa, Brian 
Cullum, K. D. Mandal and N. B. Singh, Effect of radiation on bone materials” (To be communicated)  


Design and Characteristics of Hydroxyapatites: Effect of Radiation

Design and Characteristics of Hydroxyapatites: Effect of Radiation

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