AIE luminogen bridged hollow hydroxyapatite nanocapsules for drug delivery

Article abstract of DOI:10.1039/c3dt50243k

A new type of organophosphonic acid, (4,4′-(1,2-diphenylethene-1,2- diyl)bis(4,1-phenylene))bis(methylene)diphosphonic acid (PATPE), based on tetraphenylethene has been prepared, and its ester derivative exhibits the characteristic property of aggregation-induced emission (AIE) in DMSO-H ₂O solution. The PATPE is then fabricated into hydroxyapatite by a one-pot condensation process to form hollow mesoporous nanocapsules of ellipsoidal morphology. The AIE luminogen-bridged hollow hydroxyapatite nanocapsules emit strong blue light under UV irradiation, which is further used for drug delivery using ibuprofen (IBU) as a model drug. The fluorescence intensity of the materials varies greatly with the loading and release of IBU, suggesting that the drug release process may be tracked in terms of the change of luminescence intensity. The biocompatibility of AIE luminogen functionalized material is also evaluated on HUH7 human hepatoma cells using the MTT assay. The low cytotoxicity of the materials reveals that the as-prepared multifunctional hydroxyapatite will be a new candidate for simultaneous drug delivery and cell imaging in potential bioapplications. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt50243k

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AIE luminogen bridged hollow hydroxyapatite
nanocapsules for drug delivery†
Cite this: Dalton Trans., 2013, 42, 9877
Dongdong Li,a Zhiqiang Liang,a Jie Chen,b Jihong Yu*a and Ruren Xua
A new type of organophosphonic acid, (4,4’-(1,2-diphenylethene-1,2-diyl)bis(4,1-phenylene))bis(methy-
lene)diphosphonic acid (PATPE), based on tetraphenylethene has been prepared, and its ester derivative
exhibits the characteristic property of aggregation-induced emission (AIE) in DMSO–H2O solution. The
PATPE is then fabricated into hydroxyapatite by a one-pot condensation process to form hollow meso-
porous nanocapsules of ellipsoidal morphology. The AIE luminogen-bridged hollow hydroxyapatite
nanocapsules emit strong blue light under UV irradiation, which is further used for drug delivery using
ibuprofen (IBU) as a model drug. The fluorescence intensity of the materials varies greatly with the
loading and release of IBU, suggesting that the drug release process may be tracked in terms of the
change of luminescence intensity. The biocompatibility of AIE luminogen functionalized material is also
evaluated on HUH7 human hepatoma cells using the MTT assay. The low cytotoxicity of the materials
reveals that the as-prepared multifunctional hydroxyapatite will be a new candidate for simultaneous
drug delivery and cell imaging in potential bioapplications.
Received 24th January 2013,
Accepted 22nd April 2013
DOI: 10.1039/c3dt50243k
www.rsc.org/dalton
such as semiconductor quantum dots (QDs),14 metal
1. Introduction
nanoclusters,15 metal ions,16 organic dyes,17,18 etc. Among
Mesoporous materials, which have tunable pore size, large these materials, the high concentration of QDs may cause
specific surface area and internal volume, have become a class serious problems such as enhanced cytotoxicity, which limits
of promising material for immobilization of biologically active their further application in the area of living marking or
species, especially drug molecules.1–4 So far, many types of imaging.19 On the other hand, when more luminescent
mesoporous materials including silica,5 phosphates,6 carbon,7 organic dyes, such as rhodamine, fluorescein, and nile red are
and so on,8 have been employed for drug loading. Among incorporated into the solid materials, their emissions will be
these materials, hydroxyapatite (HAp, Ca10(PO4)6(OH)2), the weakened due to the notorious aggregation-caused quenching
main inorganic component of natural bone, has been inten- (ACQ) effect.20 Since the first anti-ACQ materials namely aggre-
sively studied as the drug delivery system, owing to its good gation-induced emission (AIE) were found by Tang and co-
biological compatibility and surface properties.9 Up to now, workers,21 they have aroused considerable attention because of
many works have been reported about the drug storage/release their striking turn-on fluorescence phenomenon mainly
systems based on mesoporous HAp, which show great advan- caused by restriction of intramolecular rotation in the aggrega-
tage in efficiently enhancing drug loading and slowing down tion state.22,23 These materials have been incorporated in silica
the release rate.10,11
nanoparticles and polymers, and used as fluorescent probes in
Recently, the design and synthesis of luminescent functio- intracellular imaging.24–26 More recently, we have introduced
nalized mesoporous materials have attracted more and more AIE luminogen tetraphenylethene (TPE) into mesoporous
attentions for their application in imaging guided therapy. SBA-15 through post-grafting methods.27,28 The synthesized
Several types of fluorescent nanomaterials have been intro- materials combine the unique properties of the AIE luminogen
duced into mesoporous materials for biomedical imaging,12,13 and porous materials, proving to be excellent fluorescence
probes for potential applications in drug delivery and explosive
detection.
aState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of
Chemistry, Jilin University, Changchun, 130012, P. R. China.
In the present study, we have prepared mesoporous HAp
with (4,4′-(1,2-diphenylethene-1,2-diyl)bis(4,1-phenylene))bis-
(methylene)diphosphonic acid (PATPE) containing AIE-active
molecule TPE by a one-pot condensation process. Namely,
PATPE molecules are incorporated in the three-dimensional
network structure of HAp through P–O–Ca covalent bonds.
E-mail: jihong@jlu.edu.cn; Fax: +86 431 85168608; Tel: +86 431 85168608
bKey Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun, 130022, P. R. China
†Electronic supplementary information (ESI) available: Details of SEM, IR. See
DOI: 10.1039/c3dt50243k
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The obtained AIE luminogen-bridged mesoporous HAp 3.25 mmol) and PATPE (0.073 g, 0.14 mmol) were added to
materials exhibit ellipsoidal hollow nanocapsule morphology, water (5 mL) and the pH was adjusted to 10 with NH3·H2O.
and show strong fluorescence property and good biocompati- Subsequently, the latter solution was added dropwise to
bility. The drug loading and release process can also be moni- the former solution containing CTAB and Ca(NO3)2, yielding
tored by the change of luminescence intensity, showing great a milky suspension, which was continue to be stirred at
advantage over other traditional materials. The results suggest 40 °C for 2 h. The obtained mixture was transferred to a
that this multifunctional material may be used as an excellent Teflon-lined autoclave and crystallized statically at 80 °C under
drug carrier and the drug release process can be tracked by the autogenous pressure for about 24 h. The obtained precipitate
change of luminescence intensity in future bioapplications.
was filtered off and washed several times with deionized water,
DMSO and ethanol, and then refluxed in ethanol for 24 h to
remove the template. After drying at 60 °C, the material func-
tionalized with the AIE luminogen (PATPE), marked as MHAp-
FL, was obtained. The pure mesoporous HAp (MHAp) was syn-
thesized using the same method without adding PATPE.
2. Materials and methods
2.1 Materials
Cetyltrimethylammonium bromide (CTAB, Shanghai Huishi
Chemical Co., Ltd.), (NH4)2HPO4 (Beijing Beihua Chemical
Co., Ltd.), Ca(NO3)2·4H2O (Tianjin Guangfu Chemical Regent
Co., Ltd.), ibuprofen (IBU, Nanjing Chemical Regent Co., Ltd.),
triethyl phosphite (Chengdu Kelong Chemical Regent Co.,
Ltd.). All the initial chemicals in this work were used without
further purification, except THF was distilled from sodium
under nitrogen in the presence of benzophenone. 1,2-Bis-
[4-(bromomethyl)phenyl]-1,2-diphenylethene (BTPE) was pre-
pared according to the reported procedures.29
2.5 In vitro drug release and fluorescence spectra
The drug storage and in vitro release experiment using MHAp-
FL as a carrier was carried out as follows: MHAp-FL sample
(0.1 g) was dried at 80 °C for about 6 h and then was added to
hexane solution (15 mL) containing 60 mg mL−1 ibuprofen.
The resulting mixture was stirred in a vial for 24 h and sealed
to prevent the evaporation of organic solvent. Then the
material was centrifuged and fully dried at 60 °C in air,
marked as MHAp-FL-IBU. The amount of IBU adsorbed onto
the MHAp-FL was determined by thermogravimetry (TG) analy-
sis. Several samples of MHAp-FL-IBU of the same quality were
2.2 Preparation of tetraethyl(4,4′-(1,2-diphenylethene-1,2-
diyl)bis(4,1-phenylene))bis(methylene)diphosphonate (PETPE)
put into simulated body fluid (SBF) (142.0/5.0/2.5/1.5/147.8/
4.2/1.0/0.5
=
Na+/K+/Ca2+/Mg2+/Cl−/HCO3−/HPO42−/SO4
)
2−
BTPE (1.55 g, 3 mmol) was added to triethyl phosphite
(10 mL), and the resulting solution was refluxed for about
12 h. After solvent evaporation under reduced pressure, the
residue was purified by column chromatography on silica gel
(ethyl acetate). Yield: 1.1 g (58%). 1H NMR (300 MHz, CDCl3): δ
7.08 (m, 18H), 3.95 (m, 8H), 3.04 (d, 4H), 1.20 (m, 12H). 13C
NMR (75 MHz, CDCl3): 143.6, 142.1, 140.5, 131.4, 131.2, 129.5,
129.2, 127.6, 126.4, 62.1, 34.5, 32.7, 16.3. HRMS (micrOTOF):
m/z calcd for C36H42O6P2: 633.2529 [M + H]+; found: 633.2509.
(pH 7.4) at 37 °C under slow stirring, respectively. The volume
of SBF was determined by IBU adsorbed to the materials with
the ratio of 1 mL mg−1. After the IBU was released for a
specific time, the samples were centrifuged and dried. Then
the samples were filled into the circular groove, compacted as
much as possible and the fluorescence intensity of these
samples was tested under the same conditions (slit width,
voltage, etc.). The percentage of drug release at different times
can be obtained by UV-vis analysis at 220 nm. The release
system of MHAp was prepared through the same process.
2.3 Preparation of (4,4′-(1,2-diphenylethene-1,2-diyl)bis-
(4,1-phenylene))bis(methylene)diphosphonic acid (PATPE)
2.6 Cell viability (MTT assay)
PETPE (0.7 g, 1.1 mmol) and (CH3)3SiBr (0.87 mL, 6.6 mmol)
were dissolved in CH2Cl2 (30 mL) and stirred at room tempera-
ture for about 24 h, then the solvent was removed and MeOH
(20 mL) was added with stirring for 2 h. The solvent was
removed under reduced pressure and washed with CH2Cl2
thoroughly. The product was obtained as a yellow solid (0.57 g,
100%). 1H NMR (300 MHz, DMSO): δ 7.06 (m, 18H), 2.90 (d,
4H). 13C NMR (75 MHz, DMSO): 142.9, 141.2, 140.5, 131.8,
130.5, 130.2, 129.1, 127.8, 125.4, 35.5, 33.7. HRMS (micrOTOF):
m/z calcd for C28H26O6P2: 519.1126 [M − H]−; found: 519.1086.
To evaluate the biocompatibility of the MHAp and MHAp-FL,
cell viability was investigated using the method based on the
MTT assay which is a standard test for screening the toxicity of
biomaterials. Typically, MHAp-FL powder (300 mg) was added
into a glass bottle and sterilized by ultraviolet irradiation for
0.5 h, then Dulbecco’s modified Eagle’s medium (DMEM)
(3 mL) containing 10% fetal bovine serum (FBS) culture
medium was added, incubated at 37 °C for 24 h and filtered.
HUH7 human hepatoma cells were cultured in DMEM
medium with 10% FBS at 37 °C under a humidified atmos-
phere containing 5% CO2, the cell culture medium changed
once every other day until reached 95% confluence, then the
2.4 Synthesis of mesoporous HAp hybrid with AIE
luminogen PATPE
CTAB (0.2 g, 0.55 mmol) was dissolved in deionized water cells were trypsinized with buffered saline solution containing
(5 mL) containing Ca(NO3)2·4H2O (1.28 g, 5.42 mmol), then the 0.25% trypsin. After that, the cells were placed in a 96-well
solution was adjusted to pH = 10 using NH3·H2O and kept at plate at a density of 1.0 × 104 cells per well. Then the extract
40 °C water bath with stirring for about 1 h. (NH4)2HPO4 (0.43 g, solution was diluted to a specific concentration of 0.2, 0.3, 0.6,
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1.3, 2.5, 5, 10, 20 and 40 mg mL−1, respectively and immedi-
ately added into the cells with incubation for 24 h at 37 °C.
The culture medium and 20 µL MTT solution (5 mg mL−1
)
were added to each well. After cultured for 4 hours, the culture
medium was removed and 150 µL of DMSO was added to each
well, and then the plate was placed on a shaking table for
about 10 min, and the absorbance of the suspension was
measured at 492 nm.
2.7 Characterizations
Powder X-ray diffraction (XRD) patterns were recorded on a
Rigaku D/MAX 2500/PC X-ray diffractometer with CuKα radi-
ation (λ = 0.15405 nm). N2 adsorption–desorption isotherms
were measured on a Micromeritics ASAP 2010 M apparatus at
77 K. Surface areas were estimated according to the Brunauer–
Emmett–Teller (BET) method, and the pore-size distributions
were calculated based on the adsorption branch of the
isotherm with Barrett–Joyner–Halenda (BJH) method. Trans-
mission-electron-microscopy (TEM) images were recorded with
a Tecnai F20 electron microscope. CHN elemental analyses
were carried out on a varioMICRO elemental analyzer. Infrared
(IR) measurements of the samples dispersed in KBr pellets
were performed on a Perkin-Elmer spectrum 430 FT-IR
spectrometer. UV-Vis adsorption spectra were obtained on
a
Shimadzu UV-2550 spectrophotometer. The photo-
luminescence (PL) emission spectra were obtained on a
Shimadzu RF-5301PC spectrofluorometer. Thermogravimetric
(TG) measurement was produced by a TGA Q500 system in air
Fig. 1 (a) Plot of I/I0 values versus the compositions of aqueous mixtures, I0
=
emission intensity in pure DMSO solution. (b) PL spectra changes of PETPE
depending on the water fractions in DMSO. Excitation wavelength: 360 nm.
Inset shows the fluorescence emission of PETPE taken under the UV light
(365 nm).
with a heating rate of 10 K min−1
.
3. Results and discussion
Table 1 Textural parameters of MHAp, MHAp-FL, and MHAp-FL-IBU samples
The compound PETPE was prepared according to the synthetic
route shown in Scheme 1. To investigate the AIE property of
PETPE, we added different amounts of water, a poor solvent
SBET
DBJH
IBU
PATPE
Samples
V (cm3 g−1
)
(m2 g−1
)
(nm) (wt%) (mmol g−1
)
for the luminogen, to its pure DMSO solutions (3 × 10−5 mol L−1
)
MHAp
MHAp-FL
MHAp-FL-IBU 0.14
0.16
0.32
42.0
119.7
51.5
2
24
2–30 73
2–30
—
0.09
—
and monitored the PL changes (Fig. 1). The PL intensity
of PETPE increases slowly when the volume fraction of water is
lower than 60%, while increases dramatically when more water
was added. The mixture emits intense blue light with the PL
peak centered at 475 nm. The PL intensities increase by 106
fold from the pure DMSO solution to DMSO–H2O mixture with
90% water.
—
using CTAB as the surfactant. After removing the surfactant,
the material functionalized with the AIE luminogen was
obtained, marked as MHAp-FL. The content of PATPE intro-
duced in MHAp-FL determined by elemental analysis was
0.09 mmol g−1 (Table 1). Fig. 2 shows the representative wide
angle XRD patterns of MHAp-FL, and pure mesoporous HAp
(MHAp) as compared with the standard data for hydroxyapa-
tite. All the materials display typical diffraction peaks of HAp,
which are consistent with the standard database (JCPDS No.
09-0432), indicating that the obtained samples are HAp crys-
tals. However, the slight increase of the peak broadening of
MHAp-FL suggests a modest increase of structural disorder.30
Fig. S1† presents the typical SEM images of as-synthesized
MHAp and MHAp-FL samples. It can be seen from Fig. S1a†
that MHAp are mostly uniform rod-like nanoparticles with
The PATPE molecules were introduced into HAp through
P–O–Ca covalent bonds by a one-pot condensation process by
Scheme 1 The synthetic route of PETPE and PATPE.
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Fig. 2 Wide angle XRD patterns of (a) MHAp-FL, (b) MHAp, (c) the standard
data for HAp.
Fig. 4 (a) N2 adsorption/desorption isotherms of MHAp-FL, MHAp, and
MHAp-FL-IBU, respectively. (b) Corresponding pore size distributions based on
the adsorption branch of the isotherm with the Barrett–Joyner–Halenda (BJH)
method.
PATPE to MHAp expands the pore size of the resulting
materials.
The N2 adsorption–desorption isotherms and pore size dis-
tributions of MHAp, MHAp-FL and MHAp-FL-IBU are shown
in Fig. 4. The BET surface area and pore volume of MHAp are
42 m2 g−1 and 0.16 cm3 g−1, respectively, and the pore size dis-
tribution is between 2 and 5 nm, in agreement with the TEM
observation. Besides the well-defined mesopores, this material
shows interparticle (textural) porosity with the pore size distri-
bution at 5–30 nm as evidenced by the adsorption step at high
relative pressures of >0.9 (Fig. 4a). While MHAp-FL shows
similar IV isotherm and typical H1 hysteresis loops when P/P0
is over 0.5, revealing the typical character of mesoporous
materials. The respective BET surface area, pore volume, and
pore size of MHAp-FL are 120 m2 g−1, 0.32 cm3 g−1, and
Fig. 3 TEM images of (a) MHAp, (b) MHAp-FL.
average diameter of 20–40 nm in width and 100–200 nm in 2–30 nm, respectively, which are much higher than those of
length. When doped with PATPE, the particle size of MHAp-FL MHAp. It is noticed that after introducing IBU molecules into
has been greatly reduced with a length of about 50 nm MHAp-FL, both the BET surface area and pore volume are
(Fig. S1b†). The difference in crystal dimension as well as remarkably reduced, implying that the mesoporous channels
shape may be attributed to the introduction of PATPE during have been filled with IBU. All the textural parameters of the
the synthesis of MHAp-FL.
corresponding materials are summarized in Table 1.
The TEM images of MHAp and MHAp-FL are shown in
The FT-IR spectra of MHAp, MHAp-FL, PATPE, IBU, and
Fig. 3, which provide fine details of the crystal morphology MHAp-FL-IBU are displayed in Fig. S2.† The bands at 567 and
and the pore information. It is found that the pores of MHAp 603 cm−1 can be assigned to the ν4 bending vibration of P–O
are irregular with an average pore size of 2–5 nm. Interestingly, bond, and the 961 cm−1 band is due to the ν1 symmetric P–O
the MHAp-FL exhibits ellipsoidal hollow nanocapsule mor- stretching vibration. The strong bands at 1044 and 1100 cm−1
phology with the pore size of 2–30 nm. Obviously, introducing are assigned to the ν3 stretching vibration of P–O bond. The
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Fig. 6 The release curves of IBU from (a) MHAp-IBU, (b) MHAp-FL-IBU in SBF.
Fig. 5 Fluorescence spectra of (a) MHAp-FL, (b) PATPE, (c) MHAp. Excitation
wavelength: 400 nm. Insert photos were taken under the UV light (365 nm).
band at 3435 cm−1 corresponds to the vibration mode of OH
groups, while the peak at 3572 cm−1 to the stretching vibration
of OH− ions in the HAp lattice. All the above bands are charac-
teristic for the typical HAp FT-IR spectrum.31 For MHAp-FL,
the new bands appeared between 1400–1600 cm−1 can be
assigned to the stretching vibration of CvC of aromatic rings
(Fig. S2b†), confirming that PATPE was successfully incorpo-
rated into the material.32 Pure IBU (Fig. S2d†) shows a strong
band at 1720 cm−1, which is attributed to the vibration of car-
boxyl group (COOH) present in IBU. It is found that for the
IBU loaded MHAp-FL-IBU (Fig. S2e†), the band at 1720 cm−1 is
still obvious and the IR bands of HAp can also be observed,
indicating that IBU has been adsorbed into MHAp-FL and the
material can be used as a drug carrier.
Fig. 7 Fluorescence spectra of MHAp-FL and MHAp-FL-IBU with ibuprofen
released at different percentages.
The pure MHAp shows no luminescence under the UV
irradiation (Fig. 5). However, after the incorporation of PATPE,
MHAp-FL emits strong blue luminescence centered at 487 nm,
with a little red shift compared to pure PATPE (470 nm). showed much slower and sustained release of IBU, which can
This is because when PATPE molecules were loaded in the avoid the explosive release of IBU and prolong the drug effect.
framework of MHAp, the internal rotations of the molecules The reason can be explained by the formation of hydrogen
are largely restricted, thus block the nonradiative relaxation bonds between –COO− groups of IBU and –OH groups of
channel and populate the radioactive decay to the ground MHAp-FL hollow capsules. Meanwhile, the porous texture is
state, making the material emissive. Therefore such bioactive also important for slowing down or holding back the release of
material may be a new candidate for simultaneous drug carry- loaded IBU.
ing and cell imaging in potential bioapplications, and this will
be further discussed in the next section.
After loaded with IBU, the PL intensity of MHAp-FL-IBU is
largely increased compared with MHAp-FL (Fig. 7). This is due
As there are a large number of OH groups on the surface of to that the intramolecular rotations of the TPE core are further
MHAp-FL, which can form hydrogen bonds with the carboxyl restricted inside the mesopore of MHAp-FL-IBU. Notably,
groups, we choose IBU as a drug marker to study the drug when IBU was released, the PL intensity of MHAp-FL-IBU
loading and release properties of MHAp-FL. It can be seen that decreases because the inhibition of AIE molecules rotation is
MHAp-FL shows much higher drug loading amount (73 wt%) gradually reduced. After the drug release balances, there still
compared to MHAp (24 wt%) due to its higher surface area remains a certain amount of molecules in the materials,
and larger-sized pore in the hollow ellipsoidal capsule struc- leading to their PL intensity a little higher than that of MHAp-
ture (Table 1).
FL. Fig. 8 shows the plot of PL intensity of MHAp-FL-IBU as a
The release behaviors of MHAp-IBU and MHAp-FL-IBU in function of cumulative release amount of ibuprofen. Other
the SBF are shown in Fig. 6. They both gave an initial burst drugs, such as metoprolol, gentamycin sulfate, were also
release of about 50% in the first few minutes which is ascribed attempted for the adsorption in MHAp-FL, all of which
to the weak interaction between IBU and the outer surface of showed enhanced fluorescence (Fig. 9). Notice that the
MHAp or MHAp-FL. As the time extended, MHAp-FL-IBU increase of PL intensity of MHAp-FL loaded with metoprolol is
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Fig. 10 Cell viabilities of HUH7 human hepatoma cells incubated with the
extract solutions of MHAp and MHAp-FL at different concentrations.
Fig. 8 The plot of PL intensity of MHAp-FL-IBU as a function of cumulative
release amount of ibuprofen.
4. Conclusions
In summary, organophosphonic acid (PATPE) based on AIE-
active tetraphenylethene has been synthesized and its ester
derivative shows the characteristic AIE property in DMSO–H2O
solution. Then PATPE was incorporated into HAp via P–O–Ca
covalent bonds by a co-condensation approach forming ellip-
soidal hollow nanocapsules. The as-prepared AIE luminogen
bridged mesostructured hydroxyapatite (MHAp-FL) exhibits
strong blue luminescence and good biocompatibility, and
shows a high IBU storage capacity and favorable drug release
behavior compared to pure MHAp. More importantly, the fluo-
rescence intensity changes with the amount of drug molecules
adsorbed to the materials, suggesting that the drug release
may be tracked and monitored by the change of luminescence
intensity. The multifunctionality of the materials presented
here offers new opportunities for the simultaneous bioimaging
and drug transports in potential bioapplications. Although the
resultant materials are excited by UV light, which may limit
their practical application in drug delivery systems, this study
provides a general concept for designing multifunctional bio-
active materials for applications. Further work in developing
such materials with long-wavelength emission is undergoing.
Fig. 9 Fluorescence spectra of MHAp-FL after adsorption of (a) metoprolol,
(b) gentamycin sulfate, (c) MHAp-FL. Excitation wavelength: 400 nm.
higher than that with gentamycin sulfate. This is due to the
smaller molecular structure of metoprolol, which can be easily
adsorbed into the materials. Above studies indicate that the
AIE functionalized mesoporous materials may have the poten-
tial application as drug delivery and can be further used to
track and monitor the drug release in terms of the change of
PL intensity in future bioapplications.
To further evaluate MHAp-FL that can be potentially
applied as an effective drug delivery system, in vitro cytotoxicity
against HUH7 human hepatoma cells was investigated by the
MTT assay to determine the toxicity of biomaterials based on
the formation of dark-red formazan by the metabolically active
cells. After the extract solutions of MHAp-FL incubated with
HUH7 human hepatoma cells for 24 h, the cell viabilities were
above 95% even when the concentration of the extract solution
was about 40 mg mL−1 (Fig. 10). As a comparison, the viabil-
ities of HUH7 human hepatoma cells incubated with MHAp at
different concentrations were also studied. The above experi-
mental results demonstrate that the AIE luminogen functiona-
lized mesoporous HAp has good biocompatibility as with
MHAp, which is an important prerequisite for imaging guided
carriers for bioapplications.
Acknowledgements
This work is supported by the National Natural Science Foun-
dation of China and the State Basic Research Project (Grant:
2011CB808703) of China.
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