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. Author manuscript; available in PMC: 2019 Jul 1.
Published in final edited form as: Mater Sci Eng C Mater Biol Appl. 2018 Feb 24;88:166–171. doi: 10.1016/j.msec.2018.02.019

Effects of Polycaprolactone on Alendronate Drug Release from Mg-Doped Hydroxyapatite Coating on Titanium

Susmita Bose 1, Ashley Vu 1, Khalid Emshadi 1, Amit Bandyopadhyay 1
PMCID: PMC5939600  NIHMSID: NIHMS955401  PMID: 29636132

Abstract

The scientific objective of this study was to understand the influence of PCL coating on alendronate drug release kinetics in vitro. Our hypothesis was PCL coating would minimize burst release of alendronate from plasma sprayed Mg-doped hydroxyapatite (HA) coated commercially pure titanium (CpTi) samples. In the US alone, over 44 million women and men aged 50 and older are affected by osteoporosis which can lead to replacement and /or revision surgeries. Alendronate is a widely-used drug for treating osteoporosis and would be an ideal drug to be loaded and released from these replacement systems. Initial burst release is a common phenomenon for the most drug loaded devices. To modulate the release kinetics, a biodegradable polymer, polycaprolactone (PCL), coating with slow degradable kinetics was employed. Samples with 2 and 4 wt.% PCL showed about 34% and 26% release of alendronate within the first 24 h, respectively, compared to 75% burst release without any PCL coating. With the addition of a PCL coating, a controlled release kinetics of alendronate was achieved from HA coated titanium implants, which can potentially impact millions of patients worldwide having compromised bone due to osteoporosis.

Keywords: Commercially pure titanium, hydroxyapatite coating, plasma spray, alendronate, drug delivery, polycaprolactone

Graphical abstract

graphic file with name nihms955401u1.jpg

(a) Pure CpTi substrate. (b) Deposition of Mg-HA on CpTi substrate using supersonic plasma nozzle. (c) Fully coated substrate loaded with alendronate then coated with PCL; both via drop by drop method. (d) Mg-HA coated CpTi implants with controlled alendronate release through PCL coating with initial burst release and sustained release over time.

Introduction

Osteoporosis is a medical condition that affects millions of patients worldwide. Osteoporosis causes more than 8.9 million fractures annually [1]. This figure relates to an osteoporotic fracture every 3 seconds [2]. Osteoporotic patients suffer from brittle bones and are susceptible to severe fractures from the loss of bone tissue. These fractures can lead to full replacement and/or revision surgeries. Osteoporosis can be caused by many factors such as hormonal changes, a deficiency of calcium or vitamin D, or simply the age of a patient. Alendronate is a bisphosphonate drug widely-used for a variety of diseases and has been demonstrated as useful for treating and preventing different forms of osteoporosis [3, 4]. Alendronate can also treat bone metastasis, hypercalcemia of malignancy, and Paget’s disease [5, 6]. Drugs incorporated with alendronate have shown to enhance proliferation and differentiation of human osteoblast cells thus increasing bone formation [7]. Alendronate is also widely-used and researched because of its ability to affect bone metabolism via both osteoblast and, in particular, osteoclast cells [8]. Bisphosphonates containing nitrogen are believed to inhibit farnesyl diphosphate synthase (FPP synthase). FPP synthase is found within the mevalonate to cholesterol synthesis pathway [9, 10]. Geranylgeranyl pyrophosphate is a downstream intermediate of the mevalonate to cholesterol synthesis pathway and has been shown to have a stimulatory effect on osteoclast (bone resorption) cell activities [11]. Alendronate can suppress osteoclast activity via inhibition of geranylgeranyl pyrophosphate synthesis.

Titanium (Ti) and its alloys are commonly utilized for bone implants due to their appropriate modulus for application, corrosion resistance, fatigue resistance, and biocompatibility [12, 13]. Hydroxyapatite (HA), a calcium phosphate with comparable chemical structure to bone, is a common coating used on Ti to enhance osteoconductivity, bonding to tissue, and bone tissue ingrowth [14–17]. Plasma spraying is the only process approved by the Food and Drug Administration (FDA), USA for biomedical coatings due to its excellent coating properties compared to other processes [18]. To enhance osteoconductivity, small amounts of dopants can be introduced to pure HA. In this study, magnesium (Mg) was used as a doping agent to significantly enhance osteoblast activity [19–21]. Alendronate was incorporated into Mg-doped HA coated samples to further osteoblast activity and reduce osteoclast activity.

Although the alendronate drug was successfully loaded into the system, the effectiveness of the local drug delivery system was still lacking due to the initial burst release phenomenon commonly exhibited by drug loaded devices [11]. This can cause a rapid depletion of drug supply and cannot provide a sustainable local delivery system. Previous studies have shown a polymer coating can modulate the release kinetics of alendronate from biomaterials. Polycaprolactone (PCL) is a well-known polymer used in bone tissue engineering due to its predictable and reproducible degradation characteristics [22]. One study showed sustained release of alendronate by using PCL coating on a 3D printed tricalcium phosphate scaffold [23]. Another study showed sustained release of alendronate by using another polymer, poly (lactic-co-glycolic acid) (PLGA), with hydroxyapatite (HA)-alendronate microspheres [24]. These studies successfully controlled an initial burst release of alendronate and provided a more sustainable release. However, those results do not address alendronate incorporation and release in load-bearing implants. Local alendronate delivery in load-bearing applications could significantly improve implant integration and longer term in vivo performance for patients suffering from osteoporosis.

The scientific objective of this study was to understand the influence of PCL coating on alendronate drug release kinetics in vitro in a load-bearing implant application. Our hypothesis was PCL coating would minimize burst release of alendronate from Mg-doped HA coated CpTi samples. To validate our hypothesis, we have worked on three specific aims – (1) processing of strongly adherent Mg-doped HA coating on CpTi using induction plasma spray, (2) loading of alendronate into Mg-doped HA coated CpTi implants, and (3) modulating alendronate release kinetics using PCL. To accomplish these aims, testing of coating bond strength was performed as well as surface characterizations including X-ray diffraction (XRD), Fourier Transform InfraRed (FTIR) spectroscopy, and Field Emission Scanning Electron Microscopy (FESEM). Finally, a release kinetic study was performed with PCL coating concentrations of 2 wt.% and 4 wt.% to measure its effects on the release of alendronate in a phosphate buffer solution. The results of this study could be incorporated in hip and dental implants to treat and prevent osteoporosis, enhance osteoconduction, and improve osseointegration (Figure 1).

Figure 1.

Figure 1

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CpTi is initially bioinert but deposition of Mg-HA coating and loaded with alendronate enhances bioactivity. PCL coating enables sustained release of alendronate which can be used in hip and dental implants to treat and prevent osteoporosis, enhance osteoconduction, and improve osseointegration. Images: Wolgin, MD, Orthopaedic Surgeon. The Osteoporosis Center. American Academy of Implant Dentistry.

Materials and Methods

Mg-doped HA coating preparation using induction plasma spray

CpTi (President Titanium, MA) was used as the substrate material. Circular samples of 12.5 mm diameter and 2 mm thick were machined using a waterjet. Prior to plasma coating, samples were sandblasted, washed ultrasonically in deionized (DI) water, and cleaned with acetone to remove any organic residue. Commercial grade HA powder (Monsanto, USA), with 150–212 µm particle size, was used in this study. HA was doped with 1.0 wt.% Mg as per previous optimization studies [20, 21] and will be referred to as Mg-HA.

A 30kW induction plasma system (Tekna Plasma System, Canada), equipped with powder feeding system, was used for coating (Figure 2). A supersonic plasma nozzle was used and coatings were made at plate power of 25 kW with a distance of 110 mm from the plasma torch to the samples (Table 1). Argon (Ar) gas was used as the central gas and carrier gas with a flow rate of 25 standard liter per minute (slpm) and 10 slpm, respectively. Sheath gas was mixed of Ar (60 slpm) and hydrogen (H) (6 slpm) with a 10:1 ratio. The pressure inside the deposition chamber was maintained at 5 psig. HA particles cross the plasma region in the supersonic plasma nozzle at a velocity of 510 m/s. HA particles reside in plasma for 290 µs which reduces heat exposure in comparison to 5 ms to a normal plasma nozzle.

Figure 2.

Figure 2

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Supersonic plasma nozzle schematic with finished product.

Table 1.

Experimental conditions for preparing doped HAp coatings [35].

Central gas flow rate (Standard Liter per Minute slpm) 25 Ar
Sheath gas flow rate (Standard Liter per Minute slpm) 60 Ar + 6 H2
Carrier gas flow rate (Standard Liter per Minute slpm) 10 Ar
Power (kW) 25
Working distance (mm) 110
Chamber pressure (Psig) 5
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Mechanical properties of Mg-doped HA coatings

Standard tensile adhesion test was performed using ASTM C633 to test the bond strength of the Mg-HA coating. Two Mg-HA coated CpTi samples were attached to posts using quick set epoxy resin as an adhesive glue and placed in an oven for curing at 120°C for 2 h. The samples were slowly cooled down to room temperature and tested. The samples were larger than the samples used in the drug release kinetics with a surface area of 5.06 cm2. Bond strength was calculated using failure force / sample area. Pure HA coated CpTi samples were also tested as a control.

Phase analysis and surface characterization of Mg-doped HA coatings

To determine the different phases in the coating, Siemens D500 krystalloflex X-ray diffractometer using Cu Kα radiation at 35 kV and 30 mA at room temperature was used with a Ni-filter over the 2theta range from 20° to 55°, at a step size of 0.02° and count time of 0.5 seconds per step. FTIR spectra were obtained using an Attenuated Total Reflection (ATR-FTIR) spectrophotometer (Nicolet 6700, ThermoFisher, Madison, WI) in the 400 to 4000 cm−1 wave number range. Mg-HA coated CpTi samples were sectioned with a low speed diamond blade then ground with 1200 grit silicon carbide paper. Microstructural characterization of the coatings was performed using FESEM (DEI 200F, FEI, OR).

Alendronate loading onto Mg-doped HA coating and PCL coating

Mg-HA coated samples were loaded with 200 µg of alendronate (Pipeline Biotechnology, NJ, USA) via drop by drop method. Alendronate solution (4 mg/mL) was prepared by dissolving in DI water. The alendronate solution (50 µL) was pipetted onto the sample surfaces and gently spread to ensure uniform coverage. The samples were then allowed to dry overnight at room temperature.

PCL (Sigma, St. Louis, MO, USA) with an average molecular weight of 14000 g/mol was used in this study (Table 2). The PCL solution was prepared by dissolving 2 wt.%, and 4 wt.% in acetone (w/v). PCL was added via drop wise method using a pipette. Each drop spread and more drops were added until samples were coated thoroughly. Samples were dried overnight at room temperature before handling and used in the drug release study (Figure 3).

Table 2.

Thermal and mechanical properties of polycaprolactone [36].

Avg. Molecular
Weight		 Melting
Point		 Glass
Transition		 Strength
(modulus)		 Degradation
Time		 Degradation
Products
14000 g/mol 58 to 63 °C −60 to 60 °C 0.4 GPa >24 months Caproic acid
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Figure 3.

Figure 3

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Schematic of sample preparation: (a) pure CpTi substrate, (b) CpTi with Mg-HA coating, (c) CpTi coated Mg-HA loaded with alendronate, and (d) alendronate loaded CpTi coated Mg-HA with PCL coating.

Alendronate release study

The drug release study was performed in phosphate buffer solution (PBS) in a shaking incubator with 150 rpm under 37°C. Each sample loaded with alendronate was immersed in 5 mL of PBS (pH = 7.4) after the sample was coated with PCL. The sample media was replaced with new, fresh PBS after 2, 4, 6, 12, 24, 48, 72, 96, 120, 144, and 168 h time points. All compositions were tested in triplicate. The amount of alendronate released was determined spectrophotometrically using complex formation with Fe (III) ions using a Biotek Synergy 2 SLFPTAD microplate reader (Biotek, Winooski, VT, USA) [25]. The sample media was mixed with 5 mM of FeCl3 solution and absorbance was detected at 293 nm.

Results

Adhesive bond strength of Mg-doped HA coatings

Per ISO standard, bond strength must be at or above 15 MPa [26]. The adhesive bond strength of HA and Mg-HA coatings were found to be 17.4 ± 2.9 MPa and 16.73 ± 2.3 MPa, respectively [19]. No significant difference in adhesive bond strength was found between the pure and doped HA coatings.

Phase and chemical analysis of Mg-doped HA coatings

A concern for plasma spray HA coatings is the high temperature application can cause phase decomposition and amorphous phase formation. HA (JCPDS no. 09-0432) was identified as the major phase in both pure HA and Mg-HA coatings (Figure 4). The three characteristic peaks of HA are distinctly visible in the diffraction pattern: HA (211), HA (112), and HA (300). The supersonic plasma nozzle used in this study helped make highly crystalline HA phase and this can be seen by the level baseline and the sharpness and distinctness of the peaks within the XRD spectra. Presence of Mg in the coating does not appear to have affected phase composition or crystallinity in the Mg-HA coating. Additionally, crystalline HA coatings can be characterized by the sharp and distinct FTIR spectra. HA was identified as the major component in both pure HA and Mg-HA coatings within the FTIR spectra (Figure 5). The symmetric (v1) P–O stretching mode of HA phosphate groups appeared at 960 cm−1, and the antisymmetric (v3) P–O stretching modes were noticed between 970 and 1190 cm−1. The antisymmetric (v4) P–O bending modes of the phosphate groups were found in the region of 540 to 660 cm−1. A weak H2PO4 2- band was identified at 870 cm−1.

Figure 4.

Figure 4

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XRD spectra of HA and 1wt.% Mg-HA coatings.

Figure 5.

Figure 5

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ATR-FTIR spectra of Mg-HA coating.

Cross sectional microstructure of Mg-doped HA coatings

Cross sectional microstructure of the plasma sprayed Mg-HA coating on CpTi show an average thickness of about 280 µm with no gaps or cracks between coating and CpTi substrate indicating strong bonding (Figure 6).

Figure 6.

Figure 6

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Cross section of plasma sprayed Mg-HA coated samples.

Alendronate release study

Alendronate drug was released from Mg-HA on CpTi with 0 wt.%, 2 wt.%, and 4 wt.% PCL coating while immersed in PBS (Figure 7). Two time scales can be seen: short time scale to show burst release kinetics and a long-term release scale to show sustained release. With no PCL coating, a release of about 75% of alendronate was seen in the first 12 hours. Samples with 2 and 4 wt.% PCL coating showed slower burst release at about 34% and 26% respectively. After 24 hours, samples without PCL coating released more than 75% of alendronate. Samples with PCL coating released about 50% of alendronate.

Figure 7.

Figure 7

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Alendronate release kinetics profile from Mg-doped HA samples coated with PCL.

Discussion

Drug loaded devices exhibit the initial burst release phenomenon and alendronate is no exception [11]. An effective treatment of a local drug delivery system cannot have large initial burst release or uncontrolled release. Chemical and electrostatic interactions between the surface of calcium phosphates and drug molecules highly affect the drug adsorption and release from the system [27–29]. Bisphosphonates, like alendronate, can strongly bind to calcium phosphate surfaces resulting from the chemical exchange of the phosphate group [30]. Drug entities tend to stay bound to adsorbed surfaces via weak electrostatic interactions. After the first layer of phosphate group exchange, the subsequent layers are bound by these weak electrostatic interactions leaving the system susceptible to burst release [11, 27]. The use of a biodegradable polymer, like PCL, can effectively sustain and control drug delivery by preventing the burst release kinetics [11, 23, 31].

Diffusion, chemical processes, matrix degradation, and external or electronic processes control drug release kinetics [23, 27, 32]. Diffusion processes tend to dominate the release kinetics because matrix degradation happens at a slower rate than diffusion [11]. Tarafder et al. reported that the release of alendronate at a pH of 7.4 is diffusion dominated [23]. Alendronate is hydrophilic (soluble in water) and can cause unfavorable interactions with PCL. These unfavorable interactions cause the diffusion of alendronate from the PCL coating (Figure 8).

Figure 8.

Figure 8

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Alendronate in the form of alendronic acid (hydrophilic) and PCL (hydrophobic) cause an unfavorable drug-polymer hydrophilic-hydrophobic interaction causing a diffusion dominated release of alendronate through PCL coating.

PCL is a biodegradable polymer that is easy to process. PCL is non-immunogenic, non-carcinogenic, non-toxic, and biocompatible [23]. PCL degrades at a low rate and is a useful base polymer for developing long-term implantable drug delivery systems [33]. Our previous work using lovastatin (an osteogenic drug) showed a sustained release controlled by PCL drugpolymer interactions [11]. This was dependent on the drug-polymer hydrophilic-hydrophobic interactions. In this work, a PCL coating was applied on the surface of the alendronate loaded Mg-doped HA coated CpTi samples at different concentrations to study its influence on alendronate drug release kinetics. Results in this study have shown with the aid of a PCL coating, a sustained alendronate drug release can occur. A higher concentration of PCL coating (4 wt.%) showed slower burst release and more sustained drug release comparatively than lower concentration (2 wt.%) and no coating at all (Figure 7). 2 wt.% PCL coating showed 54% and 4 wt.% PCL coating showed 65% less burst release compared to no PCL coating. This shows that PCL as a coating helps control burst release and therefore the drug is not depleted too quickly within the first 12 h (Figure 7). After 24 h of shaking incubation, samples with PCL coating released about 33% less drug than without a coating at all. Similar works have also reported PCL coating concentration can control drug release [11, 23, 34].

Conclusion

The objective of this study was to understand the role of PCL concentration in controlling alendronate drug release kinetics in a stable Mg-doped HA coating on CpTi system. Highly crystalline Mg-doped HA coatings were successfully prepared on CpTi samples using induction radio frequency plasma spray with a supersonic nozzle. Mg showed no influence on crystallinity of HA and showed no significant change to the adhesive bond strength comparatively to a pure HA coating. Mg-HA coatings were loaded with 200 µg of alendronate and coated with 0 wt.%, 2 wt.%, and 4 wt.% of PCL. The results showed PCL did lower burst release kinetics in early time points and showed a sustained release over time. This work has the potential to be incorporated into future implants to provide a sustainable and effective local drug delivery system of alendronate to enhance early on set osseointegration, osteoconductivity, and ultimately change the lives of millions of osteoporotic patients worldwide.

Highlights.

Mg-HA coatings were prepared using induction plasma system on Ti.

PCL coating on Mg-HA minimized burst release of alendronate (AD).

The Mg-HA coatings on Ti showed good adhesion strength.

PCL helped with controlled release kinetics of AD from HA.

Acknowledgments

Authors would like to acknowledge financial support from the National Institute of Health under the grant number R01 AR066361. The authors would also like to thank Dr. Solaiman Tarafder for his contributions to this work. This content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Health.

Footnotes

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References

  • 1.Johnell O, Kanis JA. An estimate of the worldwide prevalence and disability associated with osteoporotic fractures. Osteoporos Int. 2006;17(12):1726–1733. doi: 10.1007/s00198-006-0172-4. [DOI] [PubMed] [Google Scholar]
  • 2.Kanis JA. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis: synopsis of WHO report. Osteoporos Int. 1994;4(6):368–381. doi: 10.1007/BF01622200. [DOI] [PubMed] [Google Scholar]
  • 3.Liberman UA, et al. Effect of Oral Alendronate on Bone Mineral Density and The Incidence of Fractures in Postmenopausal Osteoporosis. N. Engl. J. Med. 1995;333:1437–1444. doi: 10.1056/NEJM199511303332201. [DOI] [PubMed] [Google Scholar]
  • 4.Watts NB, Harris ST, Genant HK, Wasnich RD, Miller PD, Jackson RD, Licata AA, Ross P, Woodson GC, 3rd, Yanover MJ. Intermittent cyclical etidronate treatment of postmenopausal osteoporosis. N. Engl. J. Med. 1990;323(2):73–79. doi: 10.1056/NEJM199007123230201. [DOI] [PubMed] [Google Scholar]
  • 5.Douglas DL, Duckworth T, Russell RG, Kanis JA, Preston CJ, Preston FE, Prenton MA, Woodhead JS. Effect of dichloromethylene diphosphonate in Paget’s disease of bone and in hypercalcaemia due to primary hyperparathyroidism or malignant disease. Lancet. 1980;1(8177):1043–1047. doi: 10.1016/s0140-6736(80)91496-8. [DOI] [PubMed] [Google Scholar]
  • 6.Mundy GR. Bisphosphonates as anticancer drugs. Expert Opin. Investig. Drugs. 1999;8(12):2009–2015. doi: 10.1517/13543784.8.12.2009. [DOI] [PubMed] [Google Scholar]
  • 7.García-Moreno C, Serrano S, Nacher M, Farré M, Díez A, Mariñoso ML, Carbonell J, Mellibovsky L, Nogués X, Ballester J, Aubía J. Effect of alendronate on cultured normal human osteoblasts. Bone. 1998;22(3):233–239. doi: 10.1016/s8756-3282(97)00270-6. [DOI] [PubMed] [Google Scholar]
  • 8.Moon HJ, Yun YP, Han CW, Kim MS, Kim SE, Bae MS, Kim GT, Choi YS, Hwang EH, Lee JW, Lee JM, Lee CH, Kim DS, Kwon IK. Effect of heparin and alendronate coating on titanium surfaces on inhibition of osteoclast and enhancement of osteoblast function. Biochem. Biophys. Res. Commun. 2011;413(2):194–200. doi: 10.1016/j.bbrc.2011.08.057. [DOI] [PubMed] [Google Scholar]
  • 9.Rodan GA, Reszka AA. Bisphosphonate Mechanism of Action. Curr. Mol. Med. 2002;2(6):571–577. doi: 10.2174/1566524023362104. [DOI] [PubMed] [Google Scholar]
  • 10.Cozon FP, Thompson K, Rogers MJ. Recent Advances in Understanding the Mechanism of Action of Bisphosphonates. Curr. Opin. Pharmacol. 2006;6:307–312. doi: 10.1016/j.coph.2006.03.005. [DOI] [PubMed] [Google Scholar]
  • 11.Tarafder S, Nansen K, Bose S. Lovastatin Release from Polycaprolactone Coated β-Tricalcium Phosphate: Effects of pH, Concentration and Drug-Polymer Interactions. Mater. Sci. Eng. C. 2013;33:3121–3128. doi: 10.1016/j.msec.2013.02.049. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Sun Y, Chang J, Huang H. Corrosion resistance and biocompatibility of titanium surface coated with amorphous tantalum pentoxide. Thin Solid Films. 2012;528:130–135. [Google Scholar]
  • 13.Das K, Bose S, Bandyopadhyay A. TiO2 nanotubes on Ti: Influence of nanoscale morphology on bone cell-materials interaction. J Biomed. Mater. Res. A. 2009;90A(1):225–237. doi: 10.1002/jbm.a.32088. [DOI] [PubMed] [Google Scholar]
  • 14.Gu YW, Khor KA, Cheang P. In vitro studies of plasma-sprayed hydroxyapatite/Ti-6Al-4V composite coatings in simulated body fluid (SBF) Biomaterials. 2003;24(9):1603–1611. doi: 10.1016/s0142-9612(02)00573-2. [DOI] [PubMed] [Google Scholar]
  • 15.Yoshinari M, Oda Y, Inoue T, Matsuzaka K, Shimono M. Bone response to calcium phosphate-coated and bisphosphonate-immobilized titanium implants. Biomaterials. 2002;23(14):2879–2885. doi: 10.1016/s0142-9612(01)00415-x. [DOI] [PubMed] [Google Scholar]
  • 16.Teixeira S, Rodriguez MA, Pena P, De Aza AH, De Aza S, Ferraz MP, Monteiro FJ. Physical characterization of hydroxyapatite porous scaffolds for tissue engineering. Mater. Sci. Eng. C. 2009;29(5):1510–1514. [Google Scholar]
  • 17.Leukers B, Gülkan H, Irsen SH, Milz S, Tille C, Schieker M, Seitz H. Hydroxyapatite scaffolds for bone tissue engineering made by 3D printing. J Mater. Sci. Mater. Med. 2005;16(12):1121–1124. doi: 10.1007/s10856-005-4716-5. [DOI] [PubMed] [Google Scholar]
  • 18.Mohseni E, Zalnezhad E, Bushroa AR. Comparative investigation on the adhesion of hydroxyapatite coating on Ti–6Al–4V implant: A review paper. Int. J. Adhes. Adhes. 2014;48:238–257. [Google Scholar]
  • 19.Roy M, Bandyopadhyay A, Bose S. Induction plasma sprayed Sr and Mg doped nano hydroxyapatite coatings on Ti for bone implant. J Biomed Mater Res Part B. 2011;99B(2):258–265. doi: 10.1002/jbm.b.31893. [DOI] [PubMed] [Google Scholar]
  • 20.Banyopadhyay A, Bernard S, Xue W, Bose S. Calcium phosphate based resorbable ceramics: Influence of MgO, ZnO, and SiO2 dopants. J Am Ceram Soc. 2006;89(9):2675–2688. [Google Scholar]
  • 21.Banerjee SS, Tarafder MS, Davies NM, Bandyopadhyay A, Bose S. Understanding the influence of MgO and SrO binary doping on mechanical and biological properties of β-TCP ceramics. Acta Biomater. 2010;6(10):4167–4174. doi: 10.1016/j.actbio.2010.05.012. [DOI] [PubMed] [Google Scholar]
  • 22.Rezwan K, Chen QZ, Blaker JJ, Boccaccini AR. Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering. Biomaterials. 2006;27(18):3413–3431. doi: 10.1016/j.biomaterials.2006.01.039. [DOI] [PubMed] [Google Scholar]
  • 23.Tarafder S, Bose S. Polycaprolactone-Coated 3D Printed Tricalcium Phosphate Scaffolds: In Vitro Alendronate Released Behavior and Local Delivery Effect on In Vivo Osteogenesis. ACS applied materials & interfaces. 2014;6(13):9955–9965. doi: 10.1021/am501048n. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Shi X, Wang Y, Ren L, et al. Pharm Res. 2009;26(422) doi: 10.1007/s11095-008-9759-0. [DOI] [PubMed] [Google Scholar]
  • 25.Kuljanin J, Janković I, Nedeljković J, Prstojević D, Marinković V. Spectrophotometric determination of alendronate in pharmaceutical formulations via complex formation with Fe(III) ions. J. Pharm. Biomed. Anal. 2002;28(6):1215–1220. doi: 10.1016/s0731-7085(02)00021-3. [DOI] [PubMed] [Google Scholar]
  • 26.Implants for Surgery – Hydroxyapatite – Part 4: Determination of coating adhesion strength. 2002 ISO 13779-4. [Google Scholar]
  • 27.Bose S, Tarafder S. Calcium Phosphate Ceramic Systems in Growth Factor and Drug Delivery for Bone Tissue Engineering: A Review. Acta Biomater. 2012;8:1401–1421. doi: 10.1016/j.actbio.2011.11.017. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Tarafder S, Banerjee S, Bandyopadhyay A, Bose S. Electrically Polarized Biphasic Calcium Phosphates: Adsorption and Release of Bovine Serum Albumin. Langmuir. 2010;26:16625–16629. doi: 10.1021/la101851f. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Dasgupta S, Bandyopadhyay A, Bose S. Reverse Michelle-Mediated Synthesis of Calcium Phosphate Nanocarriers for Controlled Release of Bovine Serum Albumin. Acta Biomater. 2009;5(8):3112–3121. doi: 10.1016/j.actbio.2009.04.031. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Roussiere H, Fayon F, Alonso B, Rouillon T, Schnitzler V, Verron E, Guicheux J, Petit M, Massiot D, Janvier P, Bouler JM, Bujoli B. Reaction of Zoledronate with β-Tricalcium Phosphate for the Design of Potential Drug Device Combined Systems. Chem. Mater. 2008;20(1):182–191. [Google Scholar]
  • 31.Kim HW, Knowles JC, Kim HE. Hydroxyapatite/Poly(Caprolactone) Composite Coatings on Hydroxyapatite Porous Bone Scaffold for Drug Delivery. Biomaterials. 2004;25(7–8):1279–1287. doi: 10.1016/j.biomaterials.2003.07.003. [DOI] [PubMed] [Google Scholar]
  • 32.Ginebra MP, Traykova T, Planell JA. Calcium Phosphate Cements: Competitive Drug Carriers for Musculoskeletal System? Biomaterials. 2006;27:2171–2177. doi: 10.1016/j.biomaterials.2005.11.023. [DOI] [PubMed] [Google Scholar]
  • 33.Agrawal CM, Ray RB. Biodegradable polymeric scaffolds for musculoskeletal tissue engineering. J. Biomed. Mater. Res. 2001;55(2):141–150. doi: 10.1002/1097-4636(200105)55:2<141::aid-jbm1000>3.0.co;2-j. [DOI] [PubMed] [Google Scholar]
  • 34.Xue W, Bandyopadhyay A, Bose S. Polycaprolactone coated porous tricalcium phosphate scaffolds for controlled release of protein for tissue engineering. J. Biomed. Mater. Res. B Appl. Biomater. 2009;91(2):831–838. doi: 10.1002/jbm.b.31464. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Roy M. Thesis PhD. Washington State University; 2010. Calcium phosphate coating on titanium using laser and plasma spray. [Google Scholar]
  • 36.Gunatillake PA, Adhikari R. Biodegradable synthetic polymers for tissue engineering. Eur. Cell. Mater. 2003;5:1–16. doi: 10.22203/ecm.v005a01. [DOI] [PubMed] [Google Scholar]

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