PCL-CNT nano-composites for bone tissue engineering application

Polymer
science: research advances, practical applications and educational aspects (A. Méndez-Vilas; A. Solano, Eds.)
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PCL-CNT nano-composites for bone tissue engineering application
Feng Luo1,2, Tong Wang1,2, Junyu Chen1,2, Lai Suo1,2, Lanlan Pan1,3 Xibo Pei1,2, Qianbing Wan1,2
1
State Key Laboratory of Oral Disease, Sichuan University, Chengdu 610041, China
Department of Prosthodontics, Sichuan University, Chengdu 61004, China
3
Department of Periodontics, the Affiliated Stomatology Hospital of Chongqing Medical University, Chongqing 400015,
China
2
Bone injuries and defects, caused by trauma, malformation, osteoporosis and tumours, are therapeutically challenging.
Autografts and allografts are ideal treatment approaches for bone regeneration. However, they may be associated with a
number of complications, and outcomes are variable. Therefore, bone substitute biomaterials, which not only effectively
solved the problem of limited supply, but also provided possibility for reducing immune-complications and enhancing
bone formation properties, have shown great potential for bone tissue engineering application. Currently, polycaprolactone
(PCL) are widely used for the production of scaffolds for tissue engineering thanks to its superior rheological and
viscoelastic properties. Nevertheless, some intrinsic drawbacks, hydrophobic chemical nature, interaction with biological
fluids prevent cells adhesion and proliferation, for instance, limited PCL’s application. Carbon nanotubes (CNTs), with
excellent osteoinductivity and osteoconductivity, offer a natural platform for obtaining composite micro-fabricated
scaffolds thanks to their outstanding mechanical properties and good biocompatibility, even they are not biodegradable.
Thus, PCL-CNT nanocomposites, combined PCL and CNTs to maintain their advantages as well as minimise their
drawbacks, could be used as effective bone substitute biomaterials for bone regeneration.
Keywords: Bone regeneration; Bone tissue engineering; polycaprolactone; Carbon nanotubes; PCL-CNT nanocomposites
1. Bone tissue engineering
Bone is a nano-composite made of the extracellular matrix (ECM), including organic (mainly collagen) and inorganic
(nano-crystalline hydroxyapatite) substances [1]. As a a hard tissue, bone’s main functions are to provide mechanical
support for our body, protect internal organs, produce and store blood cells in bone marrow. However, bone injuries and
defects, caused by trauma, malformation, osteoporosis and tumours, are therapeutically challenging [2]. Autografts and
allografts are ideal treatment approaches for bone regeneration [3]. Unfortunately, they may be associated with a
number of complications, and outcomes are variable.
Tissue engineering emerged in the early 1990s to address limitations of tissue grafting and alloplastic tissue repair
[4]. Bone tissue engineering offers a promising new approach for bone repair. As a scaffold applied in bone
regeneration, the scaffold supposed to meet a number of requirements to fullfill the function. Firstly, the scaffold should
have porous architecture design to provide sufficient space for cells growth-into and proliferation [5]. Furthermore, a
successful scaffold should balance mechanical function with biofactor delivery in the process of new bone formation
[4]. Bone scaffold materials have been improved by remarkable advances in the biomedical engineering in the past
decades, but still need better biocompatibility and biofunctionality.
2. PCL in bone tissue engineering
Recently, artificial materials, particularly polymers, have been of growing importance in various biomedical
technologies, including tissue engineering and transplantation medicine. Polycaprolactone (PCL) [Fig. 1], a
hydrophobic, semi-crystalline polymer, is one of the earliest polymers synthesised by the Carothers group in the early
1930s [6]. Currently, PCL is widely applied in the production of scaffolds for tissue engineering thanks to its superior
rheological and viscoelastic properties [7 - 9]. Shor and his co-workers fabricate PCL scaffolds with a controlled pore
size of 350 μm with designed structural orientations using a novel precision extruding deposition (PED) technique [10].
Their studies demonstrated the viability of the PED process to fabricate PCL scaffolds having the necessary mechanical
properties, structural integrity, and controlled pore size and interconnectivity desired for bone tissue engineering.
Similarly, Porter et al. used PCL nano-fibers as a replacement for common bone graft material, autogenous cancellous
bone, and found that the PCL nanofibers provided a biomimetic environment which are beneficial for the mesenchymal
stem cells (MSCs) performance [11]. Zanetti et al. also hold the opinion that PCL composites may have appropriate
mechanical and biocompatibility properties for use as bone tissue scaffolds [12].
In addition, PCL’s rate of biodegradation is favourable for bone regeneration. The biodegradable nature of PCL may
be attributed to the hydrolytic degradation of its ester bond [13]. Degradation behaviours of porous scaffold play a
significant role in tissue regeneration via affecting cell vitality, cell growth, and even host response [14]. As living bone
constantly undergoes a couple resorptive-formative process known as bone remodelling [15]. The chosen polymer
suppose to degrade at a controlled rate in concert with tissue regeneration. However, the degradation behaviours are
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usually influenced by polymer structures and properties and environmental conditions (medium, temperature, and pH)
[16]. Wu et al. investigated the in vitro degradation behaviours of three-dimensional tissue engineering porous scaffolds
made from polymers systematically up to 26 weeks in phosphate buffer saline solution at 37 C [17]. It is believed that
the ideal in vivo degradation rate may be similar or slightly less than the rate of tissue formation [18]. Eventually, the
three-dimensional space occupied by porous scaffolds is replaced by newly formed tissue [16]. Furthermore, the
degradation products should not be toxic and must be easily excreted by metabolic pathways. For PCL, the nontoxic
degradation metabolites that are formed ultimately and either secreted directly or metabolised in the Krebs cycle [19].
Fig. 1 Structures made from PCL: Nanospheres (a,b). Nanofibres (c,d). Foams (e,f). Knitted textiles (g,h,i). Selective laser sintered
scaffold (j-o). Fused deposition modeled scaffolds (p–u) [5].
Nevertheless, some intrinsic drawbacks, hydrophobic chemical nature, interaction with biological fluids prevent cells
adhesion and proliferation, for instance, limited PCL’s application [20]. In addition, PCL does not have adequate
mechanical properties to be applied in high load bearing situation, particularly which has limited its use in bone tissue
engineering. As aforementioned, bone is a kind of hard tissue, normal trabecular bone’s mechanical strength stress is 5
MPa, while the compression modulus is 50 MPa [21]. To overcome these disadvantages, tissue engineering science has
focused efforts on developing PCL-based bone scaffolds, which must fulfil certain specific requirements such as
biocompatibility, osteointegration ability, biodegradability, and capacity of bioresorption [22]. Moreover, they should
have compatible mechanical properties (similar to those of bone) and simple processing [23].
3. CNTs in bone tissue engineering
As Lahiri et al. put forwarded, one of the most effective methods of increasing the mechanical properties (elastic
modulus and tensile strength) of a polymer is by reinforcing with a second-phase material [24]. In terms of
reinforcement, carbon nanotubes (CNTs) [Fig. 2] supposed to be the candidate with most potential, due to their high
mechanical properties (Young’s modulus 0.2-1 TPa, tensile strength 11-63 GPa) and fiberlike structure [25 - 27]. The
addition of CNTs to PCL results in an increase in the crystallisation temperature and a decrease in the percent
crystallinity confirming the heterogeneous nucleating effect of the nanotubes [28]. The CNT reinforced polymer
composites can be used as a new generation high load bearing applications [29 - 31 ].There are some reports on
preparation of MWCNT/PLLA composite and MWCNT/PCL composite to increase the mechanical proper- ties of
polymers [31, 32]. Lahiri et al. studied the use of CNTs as reinforcement to enhance the mechanical properties of a
polylactide-caprolactone copolymer (PLC) matrix. They attributed the increase in the viability of human osteoblast cells
compared to the PLC matrix to the combined effect of CNT content and surface roughness of the composite films [24].
Our previous studies also demonstrated that the MWNTs/PCL composite, fabricated via solution evaporation technique,
improved its mechanical properties with the addition of MWNTs (0.25-2 wt%) and enhanced the proliferation and
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differentiation of rat bone-marrow-derived stroma cells (BMSCs) [33]. Accordingly, we concluded that MWNTs/PCL
composite scaffolds have the potential for bone tissue engineering and the relatively low concentration of MWNTs (0.5
wt%) is preferred [Fig. 3].
Fig. 2 CNTs with controlled structures synthesised in CVD: (a) random SWCNT network; (b) vertically aligned MWCNTs; (c, d)
patterned growth of vertically aligned MWCNTs; (e) pyramid like structure of vertically aligned MWCNTs; (f, g) soybean
peroxidase (SBP) immobilised on (f) vertically aligned and (g) random CNTs [27].
Besides, it was well documented that carbon nanotubes (CNTs), including single-walled carbon nanotube (SWNT)
and multi-walled carbon nanotube (MWNT), offer a natural platform for obtaining micro-fabricated scaffolds for
cellular growth attributed to their outstanding mechanical properties, biocompatibility [34, 35] As bone-tissue
compatibility of CNTs and CNT influence on bone formation are important issues, the effects of CNTs on bone also
attract a lot of attention. In terms of bone regeneration, CNTs can be considered as osteoproductive material which can
elicit both intracellular and extracellular cell response at the material surface, which is desirable in bone regeneration
since they promote rapid bone integration performance [34]. It is reported that MWNTs adjoining bone show high
bone-tissue compatibility and accelerate bone formation stimulated by recombinant human bone morphogenetic
protein-2 (rhBMP-2) [36]. Li et al. evaluated the attachment, proliferation, osteogenic gene expression, ALP/DNA,
protein/DNA and mineralization of human adipose-derived stem cells cultured in vitro on MWNTs. The results
indicated that MWNTs might stimulate inducible cells in soft tissues to form inductive bone by concentrating more
proteins, including bone-inducing proteins [37]. Usui et al. demonstrated that MWCNT have very good bone-tissue
compatibility and help in the bone repair by accelerating its growth [36]. Furthermore, CNTs get closely integrated in
the grown bone without toxic effect [38]. CNTs also shows minimised local inflammatory reactions and is well
integrated into the newly formed bone after implantation for bone regeneration [36, 39]. These findings should
encourage development of clinical treatment modalities involving CNTs.
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Fig. 3 Experimental and computational effective moduli for (a) tensile and (b) compressive specimens. Data represents
mean±standard deviation for n=6, *P<0.05 (compared to pure PCL specimens) [33].
4. PCL-CNT nano-composites in bone tissue engineering
Thus, PCL-CNT nano-composites, combined PCL and CNTs together to maintain their advantages as well as minimise
their drawbacks, could be used as an effective bone substitute biomaterial for bone regeneration [20]. With this
materials combination, the achieved scaffolds are supposed to obtain bioactivity, biocompatibility, porosity, and size
pore, and mechanical properties compatible with the bone tissue, as well as electrical conductivity for inducing bone
healing. For instance, Sanchez-Garcia et al. present the properties of nano-bio-composites of PCL containing carbon
nanotubes as a function of filler content. It is found that carbon nanotubes can be used to enhance the conductivity,
thermal, mechanical and to enhance gas barrier properties of thermoplastic biopolyesters [40].
Otherwise, polymer-based nano-composites containing biocompatible and bioactive nano-components seem to be
excellent materials that could be used in many biomedical applications. The carbon nanotubes can modified the bone
cell growth and proliferation rate. Our previous work also reported the rat bone-marrow-derived stroma cells (BMSCs)
on the composite scaffolds differentiated down the osteogenic lineage and expressed high levels of bone marker ALP
[Fig. 4. 5] [33]. Wiecheć et al. seed the human osteoblast-like MG 63 cells with PCL/CNT nano-composites for
biological evaluation. Results of this study confirm that the PCL/CNT nano-composites are appropriate to the growing
and proliferation of human osteoblast-like cells [41]. Besides, by “grafting from” approach based on in-situ ringopening polymerisation, biodegradable PCL has been covalently grafted onto the surfaces of multi-walled carbon
nanotubes (MWNTs). It was convenient for us to control the grafted PCL content via adjusting the feed ratio of
monomer to MWNT-supported macro-initiators (MWNT-OH). When fabricating MWNT/PCL composite fibers by in
situ polymerisation, Saeed et al. found that the carbon nanotubes were well dispersed and oriented along the finer axes
[42]. More importantly, the carbon nanotubes retain their inherently tubelike characteristic and the PCL also hold its
own biodegradability in the biodegradation experiments. These results indicate possible application for PCL/CNT nanocomposites in biomaterials, biomedicine and artificial bones [43].
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Fig.4 SEM images of the BMSCs cultured on composite scaffolds (CNT-0.5 and CNT-2) and pure PCL scaffold under the same
culture condition. Magnification: (a) 600×, (b) 1200× [33].
Furthermore, besides the superior mechanical capacity as well as biocompatibility, another important feature for bone
substitute scaffolds, is that, after the implantation in the bone-defected site, the formation of layers of bio-active bonelike hydroxyapatite (Ca10(PO4)6(OH)2) (HA) between the surface of biomaterials and the bone tissue [44].
Hydroxyapatite, the main inorganic component of bone tissue, is the ideal candidate for enhancing bioactivity of
composites [45, 46]. The formation of hydroxyapatite in vitro of bone scaffolds can be implemented in simulated body
fluid (SBF), which has substantially identical ion composition and ion concentration as human plasma [47].
Investigators have fabricated a bone-like apatite layer on various types of organic polymer substrates and titanium metal
by soaking in SBF solution [48 - 50]. Costa et al. further studied the differential regulation of osteoblast and osteoclast
activity of hydroxyapatite coatings by incubation of polycaprolactone with SBF, which is a straight-forward method to
directly modify surface complexity and roughness [51]. As the chemical composition of molecular structures of
minerals formed are similar to the minerals of natural bone, the bioactive layer is supposed to promote the integration
between biomaterials and bone tissue as well as bone healing [52 - 54]. Therefore, once the synthetic biomaterial is able
to exchange via ion and remineralisation in SBF, and induce the formation of bone-like apatite layer on its surface, the
material can be considered to own a relatively superior bioactivity [55]. It is a convenient way to evaluate whether the
material is bioactivity or not. Fortunately, it was reported that the surface of PCL, both two-dimensional (2 D) and
three-dimensional (3 D), formed a dense and uniform bone-like apatite layer, which is strongly adhered to the PCL
surface and remained intact after a tape-detachment test, by immersing into SBF for 24 h [17, 48, 51]. In this regard, it
is concluded that the scaffold also shows great potential for bone tissue engineering.
Currently, some papers also try to using PCL/CNT composites in various fields regarding tissue engineering. The
diversity of applications for which PCL/CNTs composites can be used for is greatly increased by the addition of surface
functionalisations; addition of functional groups to the surface can alter the solubility, dispersion and cellular uptake of
composites [56 - 58]. For example, as reported, the myocardium is unable to regenerate itself after infarct, resulting in
scarring and thinning of the heart wall. Wickham et al. [Fig. 6] devoted to develop a patch to buttress and bypass the
scarred area, while allowing regeneration by incorporated cardiac stem/progenitor cells (CPCs) [59]. With further
development, PCL/T-CNT meshes or similar patches may become a viable strategy to aid restoration of the
postmyocardial infarction myocardium. The CNT/PCL conductive polymer composite, developed by layer by layer
spray, also showed promising results as a possible sensor for the identification of organic vapours [60]. Rana et al.
prepared films consisted of chitosan grafted (CNT-CS) and chitosan-co-polycaprolactone grafted (CNT-CS-PCL)
multiwalled carbon nanotubes using a spray layer-by-layer technique for Vapor Sensing [61]. Kim et al. described a
one-pot method for the mass production of polymeric microspheres containing water-soluble carbon-nanotube (wCNT)-taxol complexes as a sustained drug delivery system [62].
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Fig. 5 A. Live/dead staining of BMSCs cultured for 1 day. (a) Live cells on pure PCL. (b) Live cells on MWNTs/PCL composite
(CNT-0.25). (c) Dead cells on MWNTs/PCL composite. The live BMSCs were stained green and appeared to have adhered and
attained a normal polygonal morphology on all materials. Dead cells were stained red and were very few on all materials. B. BMSCs
proliferation on pure PCL and MWNTs/PCL composite scaffolds. (a) Cells on pure PCL; and (b) cells on MWNTs/PCL composite
(CNT-0.25); (c) confluent monolayer of BMSCs on MWNTs/PCL composite (CNT-0.5). C. Percentage of live BMSCs, PLive. Each
value is mean ± deviation, n = 5. [33]
Another promising field, nano-materials refer to the size of those material which are less than 100 nanometers in
diameter. Due to their size, nanoparticles exhibit properties like high surface area, functionalizable surface chemistry
and controllable structure, which are unlike that of the same material in bulk size. Nanoparticles themselves have the
potential to have therapeutic benefit. Through manipulation of their elemental composition, size, shape, charge and
surface modification or functionalisation it may be possible to target particles to specific organs where they may elicit
their therapeutic effect [63]. With truly nanometric features, CNTs show exceptional mechanical, thermal, optical and
electrical properties which may facilitate better structural and interfacial integrity in biomedical devices. In addition,
CNTs could be potentially assembled into complex, multifunctional and three-dimensional (3D) structure. These
advantages suggest carbon nanostructures with well defined shapes and functions as a next-generation material to repair
and regenerate hard tissues both in vitro and in vivo [27].
5. 3 D structure of PCL-CNT nano-composites
When talking about 3D structure, it is well documented that porosity and pore size of biomaterial scaffolds play a
critical role in bone formation in vitro and in vivo [64]. Bone is a structure composed of cancellous and cortical bone.
Cancellous is spongy in nature having 50–90 vol% porosity, while cortical bone with less than 10 vol% porosity [65].
Scaffolds for osteogenesis should mimic the ECM properties in order to optimise integration into surrounding tissue.
Porous bone scaffolds, or 3D structure scaffolds, can be made by lots of methods, e.g. chemical/gas foaming [66],
solvent casting, particle/salt leaching [67], foam-gel [68]. Park et al. devised a new method for biosynthesis of CNTbased 3D scaffold by in situ hy
bridising CNTs with bacterial cellulose (BC), which has a structure ideal for tissue-engineering scaffolds [39]. This 3D
scaffold was achieved simply by culturing Gluconacetobacter xylinus, Bc-Synthesising bacteria, in medium containing
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CNTs. An amphiphilic comb-like polymer (APCLP) was adsorbed on CNTs to overcome CNT’s aggregation problem.
The APCLP-adsorbed CNT-BC hybrid scaffold (CNT-BC-Syn) showed homogeneously distributed CNTs throughout
the 3D microporous structure of BC. More importantly, the CNT-BC-Syn scaffolds also showed excellent
osteoconductivity and osteoinductivity that led to high bone regeneration efficacy.
Fig. 6 SEM images showing topological difference between (A) PCL sheets and (B) PCL fibers. Scale bar, 20 lm. The
incorporation of thiophene-conjugated carbon nanotubes (T-CNTs) did not alter the morphology of the meshes, as seen
in SEM micrographs of electrospun PCL (C) and PCL/T-CNT (D) fibrous meshes. Scale bar, 10 lm. [59]
Among the different technology methods, three dimensional printing (3DP) is becoming more and more popular due
to the ability to directly print porous scaffolds with designed shape, controlled chemistry and interconnected porosity.
Bose et al. reviewed recent advances in 3D printed bone tissue engineering scaffolds along with current challenges and
future directions [66]. Gonçalves et al. produced a three-phase composite scaffold via 3D printing, including
nanocrystalline hydroxyapatite (HA), carbon nanotubes (CNT), mixed in a polymeric matrix of polycaprolactone
(PCL), aimed at bringing together the properties of all into a unique material to be used in tissue engineering as support
for cell growth [23]. The 3D printing technique allows producing composite scaffolds having an interconnected network
of square pores in the range of 450-700 μm [Fig. 7]. The three-phase composites composites show typical
hydroxyapatite bioactivity, good cell adhesion and spreading at the scaffolds surface, indicating that the scaffolds with
CNT and PCL are promising materials in the field of bone regenerative medicine.
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Fig. 7 Technical drawing (A); 3D simulation (B); 10CNT scaffold (C); and final configurations of the 0CNT scaffold
(D-side view, E-top view) [23].
6. 3 D structure of PCL-CNT nano-composites
In summary, both CNTs and PCL have superior properties which are favourable for tissue engineering application. The
PCL-CNT nano-composites, have excellent mechanical properties, biocompatibility as well as osteogenesis ability,
indicating CNT/PCL have great potential in bone regeneration application. In addition, We predicted that the CNT/PCL
scaffold with 3D structure which can mimic the ECM properties is very promising. Finally, as an emerging field, we
need pay more attention supposed to the long-term degradation and biocompatibility about the CNT/PCL nanocomposites.
References
[1]
McMahon RE, Wang L, Skoracki R, et al. Development of nanomaterials for bone repair and regeneration. Journal of
Biomedical Materials Research Part B: Applied Biomaterials, 2013, 101(2): 387-397.
[2] Suenaga H, Furukawa K S, Suzuki Y, et al. Bone regeneration in calvarial defects in a rat model by implantation of human bone
marrow-derived mesenchymal stromal cell spheroids[J]. Journal of Materials Science: Materials in Medicine, 2015, 26(11): 1-9.
[3] Zimmermann G, Moghaddam A. Allograft bone matrix versus synthetic bone graft substitutes[J]. Injury, 2011, 42: S16-S21.
[4] Hollister SJ. Porous scaffold design for tissue engineering. Nature materials, 2005, 4(7): 518-524.
[5] Sahithi K, Swetha M, Ramasamy K, et al. Polymeric composites containing carbon nanotubes for bone tissue engineering.
International journal of biological macromolecules, 2010, 46(3): 281-283.
[6] Woodruff MA, Hutmacher DW. The return of a forgotten polymer—polycaprolactone in the 21st century. Progress in Polymer
Science, 2010, 35(10): 1217-1256.
[7] Shalumon KT, Sowmya S, Sathish D, et al. Effect of incorporation of nanoscale bioactive glass and hydroxyapatite in
PCL/chitosan nanofibers for bone and periodontal tissue engineering. Journal of biomedical nanotechnology, 2013, 9(3): 430440.
[8] Binulal NS, Natarajan A, Menon D, et al. PCL–gelatin composite nanofibers electrospun using diluted acetic acid–ethyl acetate
solvent system for stem cell-based bone tissue engineering. Journal of Biomaterials Science, Polymer Edition, 2014, 25(4): 325340.
[9] Yao Q, Wei B, Guo Y, et al. Design, construction and mechanical testing of digital 3D anatomical data-based PCL–HA bone
tissue engineering scaffold. Journal of Materials Science: Materials in Medicine, 2015, 26(1): 1-9.
[10] Shor L, Güçeri S, Chang R, et al. Precision extruding deposition (PED) fabrication of polycaprolactone (PCL) scaffolds for
bone tissue engineering. Biofabrication, 2009, 1(1): 015003.
[11] Porter J R, Henson A, Popat K C. Biodegradable poly (ɛ-caprolactone) nanowires for bone tissue engineering applications.
Biomaterials, 2009, 30(5): 780-788.
376
Polymer science: research advances, practical applications and educational aspects (A. Méndez-Vilas; A. Solano, Eds.)
_______________________________________________________________________________________________
[12] Zanetti AS, McCandless GT, Chan JY, et al. Characterization of novel akermanite: poly‐ ‐caprolactone scaffolds for human
adipose‐derived stem cells bone tissue engineering. Journal of tissue engineering and regenerative medicine, 2015, 9(4): 389404.
[13] Cao H, Liu T, Chew SY. The application of nanofibrous scaffolds in neural tissue engineering. Advanced drug delivery reviews,
2009, 61(12): 1055-1064.
[14] Babensee JE, Anderson JM, Melntire LV, Mikos AG. Host response to tissue engineered devices. Adv Drug Deliv Rev 1998;
33:111–39.
[15] Ferraz M P, Monteiro F J, Manuel C M. Hydroxyapatite nanoparticles: a review of preparation methodologies. Journal of
Applied Biomaterials and Biomechanics, 2004, 2(2): 74-80.
[16] Martina M, Hutmacher D W. Biodegradable polymers applied in tissue engineering research: a review. Polymer International,
2007, 56(2): 145-157.
[17] Wu L, Ding J. In vitro degradation of three-dimensional porous poly (D, L-lactide-co-glycolide) scaffolds for tissue engineering.
Biomaterials, 2004, 25(27): 5821-5830.
[18] Holy CE, Dang SM, Davies JE, Shoichet MS. In vitro degradation of a novel poly(lactide-co-glycolide) 75/25 foam.
Biomaterials 1999; 20:1177–85.
[19] Nair L S, Laurencin C T. Biodegradable polymers as biomaterials. Progress in polymer science, 2007, 32(8): 762-798.
[20] Luo F, Pan L, Pei X, et al. PCL–CNT Nanocomposites[M]//Handbook of Polymer Nanocomposites. Processing, Performance
and Application. Springer Berlin Heidelberg, 2015: 173-193.
[21] Thomson RC, Yaszemski MJ, Powers JM, et al. Fabrication of biodegradable polymer scaffolds to engineer trabecular bone.
Journal of Biomaterials Science, Polymer Edition, 1996, 7(1): 23-38.
[22] Rezwan K, Chen Q, Blaker J, Boccaccini A. Biodegradable and bio- active porous polymer/inorganic composite scaffolds for
bone tis- sue engineering. Biomaterials 2006;27:3413–3431.
[23]Gonçalves EM, Oliveira FJ, Silva RF, et al. Three‐dimensional printed PCL‐hydroxyapatite scaffolds filled with CNTs for bone
cell growth stimulation. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2015.
[24] Lahiri D, Rouzaud F, Namin S, et al. Carbon nanotube reinforced polylactide− caprolactone copolymer: mechanical
strengthening and interaction with human osteoblasts in vitro. ACS applied materials & interfaces, 2009, 1(11): 2470-2476.
[25] Ju YM, Yu B, Koob TJ, Moussy Y, Moussy F. A novel porous col- lagen scaffold around an implantable biosensor for
improving biocompatibility. I. In vitro/in vivo stability of the scaffold and in vitro sensitivity of the glucose sensor with
scaffold. J Biomed Mater Res A 2008; 87: 136–146.
[26] Ercan B, Webster T. The effect of biphasic electrical stimulation on osteoblast function at anodized nanotubular titanium
surfaces. Biomaterials 2010; 31: 3684–3693.
[27] Han ZJ, Rider AE, Ishaq M, et al. Carbon nanostructures for hard tissue engineering. RSC Advances, 2013, 3(28): 11058-11072.
[28] Taghizadeh A, Favis BD. Carbon nanotubes in blends of polycaprolactone/thermoplastic starch. Carbohydrate polymers, 2013,
98(1): 189-198
[29] Pantiru M, Iojoiu C, Hamaide T, et al. Influence of the chemical structure of transfer agents in coordinated anionic ring‐opening
polymerization: application to one‐step functional oligomerization of ε‐caprolactone. Polymer international, 2004, 53(5): 506514.
[30] Báez J E, Marcos-Fernández Á, Galindo-Iranzo P. Exploring the effect of alkyl end group on poly (L-lactide) oligo-esters.
Synthesis and characterization. Journal of Polymer Research, 2011, 18(5): 1137-1146.
[31] Wu D, Zhang Y, Zhang M, et al. Selective localization of multiwalled carbon nanotubes in poly (ε-caprolactone)/polylactide
blend. Biomacromolecules, 2009, 10(2): 417-424.
[32] Chen GX, Kim HS, Park BH, et al. Synthesis of Poly (L‐lactide)‐Functionalized Multiwalled Carbon Nanotubes by Ring‐
Opening Polymerization. Macromolecular Chemistry and Physics, 2007, 208(4): 389-398.
[33] Pan L, Pei X, He R, et al. Multiwall carbon nanotubes/polycaprolactone composites for bone tissue engineering application.
Colloids and Surfaces B: Biointerfaces, 2012, 93: 226-234.
[34] Tran PA, Zhang L, Webster TJ. Carbon nanofibers and carbon nanotubes in regenerative medicine. Advanced drug delivery
reviews, 2009, 61(12): 1097-1114.
[35] Li X, Liu X, Huang J, et al. Biomedical investigation of CNT based coatings. Surface and Coatings Technology, 2011, 206(4):
759-766.
[36] Usui Y, Aoki K, Narita N, et al. Carbon Nanotubes with High Bone‐Tissue Compatibility and Bone‐Formation Acceleration
Effects. Small, 2008, 4(2): 240-246.
[37] Li X, Liu H, Niu X, et al. The use of carbon nanotubes to induce osteogenic differentiation of human adipose-derived MSCs in
vitro and ectopic bone formation in vivo. Biomaterials, 2012, 33(19): 4818-4827.
[38] Yang ST, Wang X, Jia G, et al. Long-term accumulation and low toxicity of single-walled carbon nanotubes in intravenously
exposed mice. Toxicology letters, 2008, 181(3): 182-189.
[39] Park S, Park J, Jo I, et al. In situ hybridization of carbon nanotubes with bacterial cellulose for three-dimensional hybrid
bioscaffolds. Biomaterials, 2015, 58: 93-102.
[40] Sanchez-Garcia MD, Lagaron JM, Hoa SV. Effect of addition of carbon nanofibers and carbon nanotubes on properties of
thermoplastic biopolymers. Composites science and technology, 2010, 70(7): 1095-1105.
[41] Wiecheć A, Stodolak-Zych E, Frączek-Szczypta A, et al. The study of human osteoblast-like MG 63 cells proliferation on
resorbable polymer-based nanocomposites modified with ceramic and carbon nanoparticles. Acta Physica Polonica A, 2012,
121(2): 546-550.
377
Polymer science: research advances, practical applications and educational aspects (A. Méndez-Vilas; A. Solano, Eds.)
_______________________________________________________________________________________________
[42] Saeed K, Park SY, Lee HJ, et al. Preparation of electrospun nanofibers of carbon nanotube/polycaprolactone nanocomposite.
Polymer, 2006, 47(23): 8019-8025.
[43] Zeng HL, Gao C, Yan DY. Poly ( ‐caprolactone)‐Functionalized Carbon Nanotubes and Their Biodegradation Properties.
Advanced Functional Materials, 2006, 16(6): 812-818.
[44] Bose S, Roy M, Bandyopadhyay A. Recent advances in bone tissue engineering scaffolds[J]. Trends in biotechnology, 2012,
30(10): 546-554.
[45] Stevens M M. Biomaterials for bone tissue engineering[J]. Materials today, 2008, 11(5): 18-25.
[46]Khan Y, Yaszemski M J, Mikos A G, et al. Tissue engineering of bone: material and matrix considerations[J]. The Journal of
Bone & Joint Surgery, 2008, 90(Supplement 1): 36-42.
[47] Costa D O, Allo B A, Klassen R, et al. Control of surface topography in biomimetic calcium phosphate coatings[J]. Langmuir,
2012, 28(8): 3871-3880.
[48] Oyane A, Uchida M, Yokoyama Y, et al. Simple surface modification of poly ( ‐caprolactone) to induce its apatite‐forming
ability[J]. Journal of Biomedical Materials Research Part A, 2005, 75(1): 138-145.
[49] Mikael P E, Amini A R, Basu J, et al. Functionalized carbon nanotube reinforced scaffolds for bone regenerative engineering:
fabrication, in vitro and in vivo evaluation[J]. Biomedical Materials, 2014, 9(3): 035001.
[50] Holzwarth J M, Ma P X. Biomimetic nanofibrous scaffolds for bone tissue engineering[J]. Biomaterials, 2011, 32(36): 96229629.
[51] Costa D O, Prowse P D H, Chrones T, et al. The differential regulation of osteoblast and osteoclast activity by surface
topography of hydroxyapatite coatings[J]. Biomaterials, 2013, 34(30): 7215-7226.
[52] Subramaniam S, Fang Y H, Sivasubramanian S, et al. Hydroxyapatite-calcium sulfate-hyaluronic acid composite encapsulated
with collagenase as bone substitute for alveolar bone regeneration[J]. Biomaterials, 2016, 74: 99-108.
[53] Jin H H, Kim D H, Kim T W, et al. In vivo evaluation of porous hydroxyapatite/chitosan–alginate composite scaffolds for bone
tissue engineering[J]. International journal of biological macromolecules, 2012, 51(5): 1079-1085.
[54] Pei X, Wang J, Wan Q, et al. Functionally graded carbon nanotubes/hydroxyapatite composite coating by laser cladding[J].
Surface and Coatings Technology, 2011, 205(19): 4380-4387.
[55] Kokubo T, Takadama H. How useful is SBF in predicting in vivo bone bioactivity?[J]. Biomaterials, 2006, 27(15): 2907-2915
[56] Antonelli, A., Serafini, S., Menotta, M., Sfara, C., Pierige, F., Giorgi, L., et al. . Improved cellular uptake of functionalized
single-walled carbon nanotubes. Nanotechnology, 2010, 21(42): 425101.
[57] Chen L, Xie H, Wei Y. Functionalization Methods of Carbon Nanotubes and Its Applications. In: Marulanda JM, editors.
Carbon nanotubes applications on electron devices. Rijeka: InTech; 2011. p. 213-232.
[58] Kraszewski S, Bianco A, Tarek M, Ramseyer C. Insertion of short amino-functionalized single-walled carbon nanotubes into
phospholipid bilayer occurs by passive diffusion. PLoS One, 2012, 7(7): e40703.
[59] Wickham AM, Islam MM, Mondal D, et al. Polycaprolactone–thiophene‐conjugated carbon nanotube meshes as scaffolds for
cardiac progenitor cells. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2014, 102(7): 1553-1561.
[60] Castro M, Lu J., Bruzaud S., Kumar B, Feller JF. Carbon nanotubes/poly (ε-caprolactone) composite vapour sensors. Carbon,
2009, 47(8): 1930-1942.
[61] Rana VK, Akhtar S, Chatterjee S, et al. Chitosan and Chitosan-co-Poly (ε-caprolactone) Grafted Multiwalled Carbon Nanotube
Transducers for Vapor Sensing. Journal of nanoscience and nanotechnology, 2014, 14(3): 2425-2435.
[62] Kim SY, Hwang JY, Seo JW, et al. Production of CNT-taxol-embedded PCL microspheres using an ammonium-based room
temperature ionic liquid: As a sustained drug delivery system. Journal of colloid and interface science, 2015, 442: 147-153.
[63] Thorley AJ, Tetley TD. New perspectives in nanomedicine. Pharmacology & therapeutics, 2013, 140(2): 176-185.
[64] Karageorgiou V, Kaplan D. Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials, 2005, 26(27): 5474-5491.
[65] Bose S, Vahabzadeh S, Bandyopadhyay A. Bone tissue engineering using 3D printing. Materials Today, 2013, 16(12): 496-504.
[66] Kucharska M, Butruk B, Walenko K, et al. Fabrication of in-situ foamed chitosan/β-TCP scaffolds for bone tissue engineering
application. Materials Letters, 2012, 85: 124-127.
[67] Cao H, Kuboyama N. A biodegradable porous composite scaffold of PGA/β-TCP for bone tissue engineering. Bone, 2010,
46(2): 386-395.
[68] Yoshikawa H, Tamai N, Murase T, et al. Interconnected porous hydroxyapatite ceramics for bone tissue engineering. Journal of
the Royal Society Interface, 2009: rsif. 2008.0425. focus.
378