Thirdly, the PDA-NPs and PDA-decorated HA nanorods were alternately assembled to form a porous and hierarchical micro/nanostructured {PDA/HA} composite coating on the Ti surfaces.. [14]
Trang 1Biosurface and Biotribology ] (]]]]) ]]]–]]]
Mussel-inspired nanostructured coatings assembled using polydopamine nanoparticles and hydroxyapatite nanorods for biomedical applications
Zhenming Wanga,1, Pengfei Lia,1, Yanan Jianga, Zhanrong Jiaa, Pengfei Tanga, Xiong Lua,b,n,
Fuzen Renc, Kefeng Wangb, Huiping Yuand
a Key Lab of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu,
Sichuan 610031, China b
National Engineering Research Center for Biomaterials, Genome Research Center for Biomaterials, Sichuan University, Chengdu, Sichuan 610064, China c
Department of Materials Science and Engineering, South University of Science and Technology, Shenzhen, Guangdong 518055, China
d College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610064, China Received 2 September 2016; received in revised form 13 January 2017; accepted 25 January 2017
Abstract
Producing hierarchical nanostructured coatings with a biomimetic composition is an effective surface modification strategy to improve the bioactivity of biomaterials In this study, mussel-inspired polydopamine nanoparticles (PDA-NPs) and hydroxyapatite (HA) nanorods were used to modify Ti surfaces Firstly, the PDA-NPs were prepared via oxidative self-polymerization of dopamine Secondly, the HA nanorods were decorated with a PDA nanolayer in order to improve the adhesion of the HA nanorods Thirdly, the PDA-NPs and PDA-decorated HA nanorods were alternately assembled to form a porous and hierarchical micro/nanostructured {PDA/HA} composite coating on the Ti surfaces Finally, Bone morphogenetic protein-2 (BMP-2) was immobilized
on the {PDA/HA} composite coating using the functional groups of PDA The BMP-2-loaded {PDA/HA} composite coating exhibited excellent biocompatibility and promoted the adhesion, proliferation, and differentiation of bone marrow stromal cells The animal implantation tests indicated that the BMP-2-loaded {PDA/HA} composite coating promoted the formation of new bone tissue
& 2017 Southwest Jiaotong University Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Keywords: Polydopamine nanoparticle; Hydroxyapatite; BMP; Self-assembly; Hierarchical structure; Biocompatibility
1 Introduction
Nanostructured coatings with a biomimetic composition are an
effective surface modification method to improve the bioactivity
of biomaterials Previous studies indicate that substrate-decorated
polydopamine (PDA) coatings can significantly improve cell
affinity and promote cell behavior compared with bare substrates
[1,2] Most of the reported PDA coatings are dense and consist of
solidfilms that completely cover the substrates and do not have
micro/nanostructures to facilitate cell adhesion and tissue ingrowth Recently, PDA nanoparticles (PDA-NPs) have been studied in the energy [3], environmental [4], and biomedical fields [5] Some studies have revealed that PDA-NPs-decorated substrates promote cell behavior and tissue ingrowth due to the micro/nanostructures and cell affinity of the PDA-NPs Wang et
al.[6]used PDA-NPs to decorate aβ-tricalcium phosphate (TCP) scaffold, and the results demonstrated that the PDA-NPs provided multiple bioactive sites for the adsorption of proteins and peptides, while improving the adhesion of bone marrow stromal cells (BMSCs) on the TCP scaffold However, pristine PDA-decorated substrates lack the necessary osteoinductivity to be used for bone reparation
Several studies indicate that hydroxyapatite (HA) is the main inorganic component of the bone matrix and has excellent biocompatibility [7,8] Nevertheless, compared with
www.elsevier.com/locate/bsbt
http://dx.doi.org/10.1016/j.bsbt.2017.01.001
2405-4518/ & 2017 Southwest Jiaotong University Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).
n Corresponding author at: Key Lab of Advanced Technologies of Materials,
Ministry of Education, School of Materials Science and Engineering, Southwest
Jiaotong University, Chengdu, Sichuan 610031, China Tel.: þ86 28 87634023;
fax: þ86 28 87601371.
E-mail address: luxiong_2004@163.com (X Lu).
1 These two authors contributed equally to this work.
Peer review under responsibility of Southwest Jiaotong University.
Trang 2traditional HA, nanoscaled HA has a higher biocompatibility
and bioactivity, and is similar to the inorganic components of
natural bone tissue [9–11] Recently, Tsai et al [12] used a
deposition method based on dopamine polymerization to
prepare nanostructured PDA/HA coatings on Ti implants,
and their results indicated that the PDA/HA coatings enhanced
the proliferation and osteodifferentiation of human BMSCs
compared with pristine PDA coatings Chien et al [13]
prepared nanostructured PDA/HA coatings on Ti implants
using the adhesive properties of PDA, and their results
demonstrated that the incorporation of nanoscaled HA
enhanced the osteoinductivity of the PDA coatings and
promoted new bone formation In summary, the incorporation
of nanoscaled HA on PDA coatings can improve their
bioactivity and induce bone ingrowth
In addition, previous studies also demonstrated that porous
and hierarchical micro/nanostructured composite coatings have
high bioactivity and cell affinity Wang et al [14] prepared
porous micro/nanostructured PDA microcapsules/chitosan
composite coatings on Ti surfaces using a layer-by-layer
self-assembly technique; their results indicated that the porous
micro/nanostructures of the composite coatings promoted both
the adhesion and proliferation of BMSCs Wu et al [15]
fabricated porous nanostructured poly(L-lactide)/HA honey-combfilms using a self-assembly technique, and their results showed that the porous nanostructures of the honeycombfilms improved the affinity of a MC3T3-E1 cell line Based on previous studies, the development of a nanoscaled self-assembly technique for preparing porous and hierarchical micro/nanostructured functional coatings is of great interest
In this study, bioactive coatings with porous and hierarchical micro/nanostructures containing HA nanorods and PDA-NPs were self-assembled using the unique adhesive properties of PDA Firstly, the HA nanorods were synthesized using a chemical precipitation method To facilitate the self-assembly, the HA nanorods were decorated with a PDA nanolayer Secondly, the PDA-NPs were prepared via oxidative self-polymerization of dopamine Thirdly, the NPs and PDA-decorated HA nanorods were alternately assembled on the Ti surface to form a {PDA/HA} composite coating Finally, BMP-2 was immobilized on the {PDA/HA} composite coating
to improve the osteoinductivity of the Ti substrates The physicochemical properties of the composite coatings were analyzed, and the biological properties were evaluated using in vitro cell cultures and in vivo animal implantation The experimental procedure is illustrated inFig 1
Fig 1 Schematic of the {PDA/HA} composite coating self-assembly and characterization of the biological properties on the Ti surface (a) Preparation of PDA-NPs; (b) preparation of PDA-decorated HA nanorods; (c) self-assembly of the PDA-NPs and PDA-decorated HA nanorods; (d) immobilization of BMP-2 on the {PDA/HA} composite coating; (e) cytocompatibility and osteoinductivity of the coating were investigated via in vitro cell culture and in vivo implantation, respectively.
Trang 32 Material and methods
2.1 Preparation of the PDA-decorated HA nanorods
The HA nanorods were synthesized using a previously
reported chemical precipitation method [16] Briefly, Ca
(NO3)2 4H2O and (NH4)2HPO4 were first dissolved in
dis-tilled water to prepare a 0.5 mol L1Ca(NO3)2solution and a
0.3 mol L1 (NH4)2HPO4 solution, respectively Then, the
(NH4)2HPO4solution (100 mL) was added dropwise to the Ca
(NO3)2 solution (100 mL) at a rate of 5 mL min1 under
vigorous stirring Ammonium hydroxide was immediately
added to adjust the pH of the mixed solution to 11 After
vigorous stirring for 12 h, the suspension was centrifuged
(8800 g, 15 min) three times The HA suspension was cooled
at20 1C in a freezer for 24 h, and then subsequently
freeze-dried at 40 1C for 36 h using a freeze dryer The dopamine
hydrochloride (DA, 0.05 g) was dissolved in a Tris–HCl
solution (100 mL, pH¼8.5) The HA nanorods (0.4 g) were
then dispersed in the DA solution (100 mL) After vigorous
stirring for 12 h in the dark, the PDA-decorated HA nanorods
were obtained via centrifugation (8800 g, 15 min) and
freeze-drying (40 1C, 36 h)
2.2 Preparation of the PDA-NPs
PDA-NPs were synthesized according to a modified
proce-dure previously reported[17,18] Briefly, an ammonia aqueous
solution (0.8 mL, NH4OH, 28–30%) was mixed with
deio-nized water (90 mL) and ethanol (40 mL) under mild stirring at
room temperature for 10 min DA (0.5 g) was dissolved in
deionized water (10 mL) Then, the DA solution was injected
on the previously mixed solution and the reaction proceeded
for 48 h under vigorous stirring The PDA-NPs were obtained
by centrifugation (13,000g , 15 min) and washed with
deio-nized water three times Finally, the PDA-NPs were dried
under vacuum at 601C
2.3 Coating of the Ti surfaces
Various coatings were prepared on Ti surfaces using a
self-assembly technique，including bare Ti, {PDA} coating, {HA}
coating and {PDA/HA} composite coating Briefly, the
PDA-NPs and PDA-decorated HA nanorods were separately
dis-solved in distilled water to prepare 2 mg mL–1 suspensions of
PDA-NPs and PDA-decorated HA nanorods The Ti plates
(Ф 10 1 mm) were then immersed on the PDA-NP
suspen-sion for 10 min at room temperature, and the PDA-NPs
assembled on the Ti surface after washing for three times
Finally, the PDA-NPs-coated Ti substrates were immersed in
the PDA-decorated HA nanorod suspension These steps were
repeatedfive times to obtain a {PDA/HA} composite coating
on the Ti substrates For the preparation of the {PDA} and
{HA} coating, the Ti substrates were immersed on the
corresponding PDA-NPs and PDA-decorated HA nanorod
suspensions ten times, as previously described
2.4 Characterization of the HA nanorods, PDA-decorated HA nanorods, PDA-NPs, and various coatings
The particle size distribution and zeta potential of the HA nanorods, PDA-decorated HA nanorods, and PDA-NPs were evaluated using a laser particle analyzer (ZETA-AIZER, Malvern Instruments Ltd., UK) The crystal phase of the PDA-decorated HA nanorods was determined by X-ray diffraction (XRD, X’pert PRO, Philips, The Netherlands) over the 2θ range of 15–751, with a rate of 0.1 1 s1. The morphology of the HA nanorods, PDA-decorated HA nanorods, PDA-NPs, {PDA} coating, {HA} coating, and {PDA/HA} composite coating was investigated using scan-ning electron microscopy (SEM, JSM 6390, JEOL, Japan) and transmission electron microscopy (TEM, JEOL, Japan) 2.5 BMP-2 adsorption and release
BMP-2 was first dissolved in distilled water to prepare a BMP-2 solution (10μg mL–1) Then, the various composite coatings (bare Ti, {PDA}, {HA} and {PDA/HA}) were immersed in the BMP-2 solution (200 μL) to absorb BMP-2 for 24 h at room temperature The adsorbed BMP-2 was obtained by subtracting the amount of BMP-2 left in the distilled solution from the initial amount The BMP-2 loaded bare Ti and {PDA/HA} composite coating are denoted as Ti/BMP-2 and {PDA/HA}/BMP-2, respectively To determ-ine the BMP-2 release kdeterm-inetics from the Ti/BMP-2 and {PDA/HA}/BMP-2, the BMP-2-loaded samples were placed
in phosphate buffer saline (PBS, 2 mL) and agitated at 371C The BMP-2 concentration in the solution was analyzed at different times (1, 5, 8, and 12 days) using the human BMP-2 ELISA kits
2.6 In vitro cell experiments BMSCs were cultured on various coatings, including bare Ti plates (Ф 10 1 mm) and {PDA}, {HA}, {PDA/HA}, and {PDA/HA}/BMP-2 coated Ti plates, to evaluate their cyto-compatibility The detailed process for the cell adhesion, proliferation, and differentiation of BMSCs on the various coatings was described in Supporting Information, as reported
in Ref.[19] 2.7 In vivo animal experiments Five groups of implant materials, including bare Ti bars (Ф 1 20 mm) and {PDA}, {HA}, {PDA/HA}, and {PDA/
Table 1 Particle size and zeta potential of different particles.
Trang 4HA}/BMP-2 coated Ti bars, were implanted in the femoral
bone marrow cavity of SD rats to evaluate their
osteoinduc-tivity in vivo Each group contained four parallel samples The
detailed process for the intramedullary implantation,
histolo-gical staining (toluidine blue and magenta), and new bone area
ratio (NBAR) around the implant materials was described in
Supporting Information, as reported in Ref.[20]
3 Results
3.1 Characterization of the HA nanorods, PDA-decorated HA
nanorods, and PDA-NPs
The particle size and zeta potential of different particles (HA
nanorods, PDA-decorated HA nanorods, and PDA-NPs,) are
shown inTable 1 The average particle size of the PDA-NPs is
46279 nm, and their zeta potential is 25.4170.95 mV
The average particle size of HA nanorods is 18378 nm and
the average particle size of PDA-decorated HA nanorods is
18676 nm, which indicates that the size of HA nanorods is
not significantly change after HA nanorods were decorated by
PDA However, the zeta potential of the HA nanorods is
4.5170.27 mV After decoration with PDA, the zeta potential
of the HA nanorods is changed to 18.5370.44 mV These
results show that PDA was successfully grafted on the surface
of the HA nanorods
The morphologies of the PDA-NPs and PDA-decorated HA nanorods are shown in Fig 2(a)–(c) The SEM and TEM images reveal that the PDA-NPs are spherical with a rough surface, and possess a diameter of 450 nm (Fig 2(a) and (b)) The TEM micrographs reveal that the HA nanorods have
a rod-like structure, with a length and width of 100 and
10 nm, respectively (Fig 2(c)) The selected area electron diffraction (SAED) patterns of the PDA-decorated HA nanor-ods show distinct diffraction rings, representing the (002), (211), (310), and (213) crystallographic planes (Fig 2(c)) The XRD patterns of the PDA-decorated HA nanorods show intense diffraction peaks at 25.81, 32.11, 39.81, 46.81, and 49.51, which can be assigned to the (0 0 2), (2 1 1), (3 1 0), (2
2 2), and (2 1 3) lattice planes of HA, respectively
3.2 Characterization of various coatings The SEM images shown inFig 3reveal the morphology of the {PDA} coating, {HA} coating, and {PDA/HA} composite coating on the Ti surface If only PDA-NPs are assembled, the distribution of the PDA-NPs on the {PDA} coating is uneven and the Ti substrate can be observed (Fig 3(a)) If only PDA-decorated HA nanorods are assembled, the {HA} coating is compact and dense (Fig 3(b)) However, if the PDA-NPs and PDA-decorated HA nanorods are alternately assembled, the spherical PDA-NPs and rod-like HA nanorods result in porous
Fig 2 (a) SEM and (b) TEM images of the NPs; (c) TEM image of the decorated HA nanorods (the inset shows the SAED patterns of the PDA-decorated HA nanorods); and (d) XRD pattern of the PDA-PDA-decorated HA nanorods.
Trang 5and hierarchical micro/nanostructures (Fig 3(c)) The
decorated HA nanorods are attached to the surface of the
PDA-NPs, as shown in the high magnification SEM image (inset of
Fig 3(c)), which is ascribed to the intrinsic adhesion of the
PDA-NPs A cross-section image of the {PDA/HA} composite coating shows a coating thickness of 4 μm after five assembly cycles (Fig 3(d)), and a uniform distribution of both PDA-NPs and PDA-decorated HA nanorods in the coating In summary, the biomimetic {PDA/HA} composite coating with
a porous and hierarchical micro/nanostructure can be prepared
by alternately assembling PDA-NPs and PDA-decorated HA nanorods on the Ti surface
3.3 BMP-2 adsorption and release The Table 2 showed the BMP-2 loading ability of various coatings after soaking in the BMP-2 solution (10μg mL1, 200μL) for 24 h The BMP-2 loading ability of {PDA} and {HA} coatings was significantly higher than that of bare Ti, which indicated that the PDA increased the BMP-2 loading ability of the coatings More-over, the BMP-2 loading ability of {PDA/HA} was the highest among all coatings, which revealed that adhesive PDA and the microporous structures synergistically enhanced the BMP-2 loading ability of the functional coatings
The cumulative BMP-2 release performance from Ti/BMP-2 and {PDA/HA}/BMP-2 was investigated by immersing the BMP-2-containing samples in PBS (Fig 4) Ti/BMP-2 shows a burst release, with more than 80% of BMP-2 being released during the first day In contrast, {PDA/HA}/BMP-2 showed sustained release, and only 35% of BMP-2 was released during thefirst day This result demonstrates that the {PDA/HA} coating
Fig 3 SEM images of various coatings (a) {PDA} coating, (b) {HA} coating, and (c) {PDA/HA} composite coating (the inset shows a magni fied image of the {PDA/HA} composite coating morphology); and (d) cross-section view of the {PDA/HA} composite coating.
Table 2
The BMP-2 loading ability of various composite coatings.
The amount of adsorption
(ng cm2)
Fig 4 Cumulative BMP-2 release from Ti/BMP-2 and {PDA/HA}/BMP-2.
Trang 6is excellent BMP-2 release carrier The main reason is attributed
to the {PDA/HA} coating that possesses porous
micro/nanos-tructures, providing multiple BMP-2 adsorption sites
3.4 Cell adhesion, proliferation, and differentiation
The morphology and adhesion of BMSCs after 3 days of
culture on various coatings were examined using SEM (Fig 5)
BMSCs on bare Ti surfaces (Fig 5(a)) showed scarcefilopodia
formation However, BMSC adhesion was better on the
{PDA} and {HA} coatings (Fig 5(b) and (c)) Specifically,
BMSCs on the {PDA/HA} composite coating with a porous
and hierarchical micro/nanostructure produced various filopo-dia to attach on these coating surfaces (Fig 5(d)–(f)) In summary, porous and hierarchical micro/nanostructures enhanced the adhesion of BMSCs
Alamar blue assays indicated that the {PDA/HA} composite coating favored the proliferation of BMSCs (Fig 6(a)) The number of BMSCs on various coatings increased after 7 days, which reveals that all coatings promoted the proliferation of BMSCs The number of BMSCs on the {PDA} and {HA} coatings was significantly higher than that on bare Ti surfaces Furthermore, the number of BMSCs on the {PDA/HA} composite coating was higher than that on the {PDA} and
Fig 5 SEM micrographs of BMSCs after 3 days of culture on various coatings (a) Bare Ti; (b) {PDA} coating; (c) {HA} coating; (d) {PDA/HA} coating; (e) {PDA/HA}/BMP-2 coating; and (f) high-magni fication micrographs of BMSCs on the {PDA/HA}/BMP-2 coating.
Trang 7{HA} coatings After the BMP-2 was loaded, {PDA/HA}
showed the highest number of BMSCs These results
demon-strate that the PDA-NPs and HA nanorods can synergistically
enhance the proliferation of BMSCs
The ALP (alkaline phosphatase) activity test indicated that the
{PDA/HA} composite coating induced the BMSC differentiation
(Fig 6) The ALP activity of BMSCs on the {HA} and {PDA/HA}
coatings was significantly higher than that on the surface of bare Ti
and {PDA}; this is because HA in the {PDA/HA} composite
coating had a good osteoinductivity Moreover, the ALP activity of
BMSCs on the {PDA/HA}/BMP-2 composite coating was even
higher because BMP-2 improved the osteoinductivity of the
coat-ings In summary, the {PDA/HA} composite coating with a porous
and hierarchical micro/nanostructure enhanced BMSC proliferation
and differentiation
3.5 In vivo evaluation
Intramedullary tests showed that the {PDA/HA} composite
coating could induce bone regeneration in the bone marrow
cavity of SD rats after 12 weeks of implantation.Fig 7shows the
histological section stained with toluidine blue and magenta
There is almost no new bone tissue formation around the bare Ti
(Fig 7(a) and (b)) and {PDA} coating (Fig 7(c) and (d)), which
indicates that the bare Ti and {PDA} coating could not induce
bone regeneration However, new bone tissue formed around the
{HA} (Fig 7(e) and (f)) and {PDA/HA} composite coatings (Fig 7(g) and (h)) After BMP-2 was loaded, the new bone tissue formation increased significantly (Fig 7(i) and (j))
A quantitative analysis (Fig 8) indicated that the NBAR around the bare Ti and {PDA} coating was 0% However, the NBAR for the {HA} and {PDA/HA} composite coatings was
15% This result indicates that the osteoinductivity was significantly improved due to the addition of HA nanorods to the coating After the BMP-2 loading, the NBAR of the {PDA/ HA}/BMP-2 coating increased to 30% In summary, these results show that the incorporation of both HA and BMP-2 to the coatings synergistically enhanced the bone formation
4 Discussion The self-assembled {PDA/HA} composite coating can enhance the behavior of BMSCs and bone regeneration, which could be ascribed to three reasons Thefirst reason is the intrinsic cell affinity of PDA Previous studies have reported that PDA coatings can promote cell adhesion Cho et al.[21]reported that PDA coatings of the surfaces of polyethylene glycol adipate and polystyrene substrates could promote the proliferation and spreading of human neural stem cells She et al.[22]reported that PDA coatings of polylactic acid scaffold surfaces increased the adhesion, proliferation, and differentiation of human adipose-derived stem cells PDA can adsorb extracellular (ECM) proteins, such as fibronectin and collagen, providing a favorable environ-ment for cell proliferation and spreading[12,23]
The second reason is the porous and hierarchical micro/ nanostructure produced by self-assembly of PDA-NPs and PDA-decorated HA nanorods It should be noted that most of the previous studies focused on dense PDA films [24,25] In this study, the {PDA/HA} composite coating containing PDA-NPs and PDA-decorated HA nanorods, has a porous and hierarchical micro/nanostructure that facilitates cell adhesion
It is commonly accepted that porous and hierarchical micro/ nanostructures can improve the adsorption of ECM biomole-cules, which can enhance the osteoinductivity of the coatings
[26,27] Thus, the self-assembled PDA-NP-based porous and hierarchical micro/nanostructure reported in this study can promote cell activity
The third reason for the good bioactivity of the {PDA/HA} composite coating is attributed to the presence of PDA-decorated
HA nanorods It has been reported that nanoscaled HA has good bioactivity [9,10] PDA-decorated nanoscaled HA can signi fi-cantly enhance the differentiation and mineralization of osteo-blasts [28] Note that PDA decoration had no effect on Ca ion release from on HA nanorods, as demonstrated by the cumulative ion release experiments (Fig S1, Supporting information) In this study, we used PDA-decorated HA nanorods to assemble composite coatings Compared with pure PDA coatings, the in vitro study demonstrated that the HA nanorods promoted cell differentiation, and the in vivo study indicated that the HA nanorods accelerated the bone tissue regeneration The PDA-decorated HA nanorods reported in this study have the following advantages: (1) the preparation process of the PDA-decorated HA nanorods is simple and effective, and does not require complex
Fig 6 (a) Proliferation of BMSCs after 3 and 7 days of culture on various
coatings (b) ALP activity of BMSCs after culturing for 14 days * Indicates
the signi ficant difference (p o 0.05).
Trang 8Fig 7 Histological section stained with toluidine blue and magenta of different implant materials after they were implanted in the bone marrow cavity of SD rats for 12 weeks (a) and (b) bare Ti; (c) and (d) {PDA} coating; (e) and (f) {HA} coating; (g) and (h) {PDA/HA} composite coating; and (i) and (j) {PDA/HA}/BMP-2 coating The right column shows magnified images of the left column S represents the implanted samples, and NB represents the new bone around the implanted samples.
Trang 9and expensive equipment; (2) HA nanorods modified by PDA
can improve the bonding strength of the composite coatings;
(3) the assembly process is conducted under a mild aqueous
environment and does not use organic solvents, avoiding
chemical toxicity of cells and tissues; and (4) the
PDA-decorated HA nanorods, along with the PDA-NPs, impart the
composite coatings with nanoporous structures, enhancing the
biomolecule adsorption ability of the coatings In conclusion, the
PDA-decorated HA nanorods have excellent biocompatibility and
osteogenic activity, and are excellent building blocks for
prepar-ing nanostructured materials with improved bioactivities
The {PDA/HA} composite coating had a high growth factor
loading ability and provided a sustained release of BMP-2, which
was attributed to two reasons First, the PDA-NPs in the coating
provided multiple bioactive sites for the BMP-2 immobilization Pan
et al [29] immobilized BMP-2 on a PDA-coated
poly(lactic-co-glycolic acid) polymer scaffold, and their results showed that PDA
provided multiple bioactive sites for BMP-2 immobilization, and
that BMP-2 improved the osteoinductivity of the scaffold Shin et al
[30] immobilized BMP-2 on the surface of PDA-decorated
poly-lactic acid nanofibers, and their results indicated that the
incorpora-tion of BMP-2 increased significantly the ALP activity and
calcification of human mesenchymal stem cells In this study, the
PDA-NPs were more favorable for BMP-2 immobilization because
of the amounts of functional groups exposed on the surface Second,
the porous and hierarchical structures of the composite coating
facilitate the BMP-2 adsorption Wang et al.[14]reported that PDA
capsules assembled on Ti surfaces had large specific surface areas,
effectively immobilizing a high dose of BMP-2 Li et al [31]
prepared a nanoporous structured Mg/Zn/Si xerogel for BMP-2
immobilization using a sol-gel method, and their results indicated
that the nanoporous structure could provide a sustained release of
BMP-2 and promote the proliferation and differentiation of
osteo-blasts, compared with a xerogel without a nanoporous structure In
summary, both PDA and microporous structures impart a growth
factor immobilization ability to the composite coatings
In summary, the {PDA/HA} composite coating showed
good osteoinduction and accelerated the in vivo bone tissue
formation, which consisted of a synergistic effect of three
coating features, including PDA-NP cell affinity and growth
factor affinity, bioactive HA nanorods, and hierarchical micro/ nanostructures Firstly, the PDA-NPs improved both cell adhesion and proliferation; secondly, the PDA-decorated HA nanorods promoted the osteoinductivity of the coatings; and thirdly, the self-assembled porous and hierarchical micro/ nanostructure provided a favorable microenvironment to recruit and host new cells Furthermore, the PDA-NPs, HA nanorods, and porous micro/nanostructures are beneficial for the BMP-2 immobilization [26,32] The incorporation of BMP-2 on the {PDA/HA} composite coating further enhanced the cell activity and bone regeneration [33,34] Hence, the {PDA/HA} composite coating with a porous and hierarchical micro/nanostructure closely mimics ECM microenvironments, promoting cell growth and tissue regeneration
5 Conclusions
In this study, a {PDA/HA} composite coating with a porous and hierarchical micro/nanostructure was prepared on the Ti surface by self-assembly of PDA-NPs and PDA-decorated HA nanorods The composite coating provided both a high loading and a sustained release of BMP-2 due to the porous micro/nanostructure and PDA growth factor affinity The BMP-2-loaded {PDA/HA} composite coating possessed an excellent cytocompatibility and it could significantly promote the adhesion, proliferation, and differentiation
of BMSCs In addition, the BMP-2-loaded {PDA/HA} composite coating was implanted in vivo, and exhibited excellent osteoinduc-tivity due to the synergistic effect of the porous micro/nanostruc-ture, HA-nanorods, and BMP-2
Acknowledgements The work was financially supported by the National Key Research and Development Program of China (2016YFB-0700802), the 863 Program (2015AA034202), NSFC (81671824), Open fund of Key Lab of Advanced Technologies
of Materials (MOE), Fundamental Research Funds for the Central Universities (2682016CX075)
Appendix A Supporting information Supplementary data associated with this article can be found in the online version athttp://dx.doi.org/10.1016/j.bsbt.2017.01.001
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