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Superhydrophobic Polyhydroxyalkanoates: Preparation and Applications Xuemei CHE, Dai-xu Wei, and Guo-Qiang Chen Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.8b01176 • Publication Date (Web): 05 Sep 2018 Downloaded from http://pubs.acs.org on September 5, 2018
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Biomacromolecules
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Original paper
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5 6
Title:
Superhydrophobic Polyhydroxyalkanoates: Preparation and Applications
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Authors:
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Xue-Mei Chea,b, Dai-Xu Weia, and Guo-Qiang Chen*a,b,c
10 11
Affiliations
12
a
13
Center for Life Sciences, Tsinghua University, Beijing 100084, China
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b
Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
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c
MOE Key Lab for Industrial Biocatalysis, Tsinghua University, Beijing 100084,
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China
Center of Synthetic and Systems Biology, School of Life Science, Tsinghua-Peking
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KEYWORDS:
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PHB, Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), Superhydrophobicity, Oil
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absorbents, Anti-bioadhesion
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ABSTRACT
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Poly(R-3-hydroxybutyrate-co-R-3-hydroxyhexanoate) (PHBHHx), a family member
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of microbial polyhydroxyalkanoates (PHA), is a biodegradable and biocompatible
25
material with some hydrophobicity and reasonable strength for packaging and tissue
26
engineering applications. In this study, superhydrophobic PHBHHx is fabricated via a
27
simple non-solvent-assisted process. The material can absorb all tested hydrophobic
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solvents and oil up to six folds of the material weights from water, permitting
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applications for cleaning environmental oil or solvent pollutions with convenience of
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disposal after the usage due to its biodegradability. With an excellent combination of
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biodegradability and biocompatibility, superhydrophobic PHBHHx films are
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evaluated for anti-bioadhesion properities to exploit possible implant usages. Up to
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100% reductions for platelet adhesions on the superhydrophobic PHBHHx surfaces
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are observed compared with that on the control material surfaces. Superhydrophobic
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biodegradable and biocompatible PHBHHx films demonstrate promising low value
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and high-volume or high-value and low volume applications.
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1. INTRODUCTION
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Superhydrophobic surface has received increasing interest due to their tremendous
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potential in areas of batteries, oil–water separation, optical devices, self-cleaning,
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drug
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anti-bioadhesion1-8. Usually, superhydrophobic surface shows an apparent water
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contact angles larger than 150°9. Superhydrophobicity has been inspired by natural
delivery,
anti-icing
coatings,
microfluidic
devices,
sensors
and
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materials such as lotus leaves and butterfly wings9-10.
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Superhydrophobicity requires two essential features including a micro- or
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nanostructured surface or a nonpolar chemical molecular structures, to help trap a thin
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air layer that reduces the interaction between the surface and the water11. Approaches
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have been investigated to prepare superhydrophobic surfaces, such as self-assembly
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procedure, sol–gel process and phase separation et al9. Among these ways, phase
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separation is the simple one for creating superhydrophobic surfaces with rough
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topography, it takes advantage of the instability generated by the multi-component
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mixture, especially for polymers12. There are some methods to form phase separation,
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including thermal induction13, solvent induction14 and non-solvent induction15. Xue et
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al. reported a porous superhydrophobic PLA film fabricated via phase separation,
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utilizing 1, 4-dioxane as a solvent and ethanol as a non-solvent. The porous
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superhydrophobic PLA film showed a rough micro/nano-porous structure with a CA
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value of 153.5 ± 1.7°16. Similarly, superhydrophobic LDPE films with
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micro-/nanoscale hierarchical topography were also fabricated and the as prepared
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LDPE film had a CA value of 173.0 ± 2.5°17.
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Oil water separation and anti-bioadhesion are two of the main applications of
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superhydrophobic materials. Recently, oil–water separation has become an important
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method to solve environmental contamination issues18-19. Superhydrophobic materials
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together with other smart ones have been prepared and employed to separate oils from
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oil-and-water mixtures20-21. However, it remains a challenge to deal with the used
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superhydrophobic materials due to their non-degradable property in nature. The used
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superhydrophobic materials are burnt and abandoned resulting in secondary
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pollution22-23. Therefore, it is of vital importance to investigate biodegradable
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superhydrophobic materials for oil–water separation for sustainable developments.
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Importantly, surface topography is also a property to tissue implants as it influences
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the interaction with surrounding cells exposed to24-26. Some implants require coating
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to minimize cell adhesion and blood coagulation27. Additionally, some implanted
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surfaces offer an ideal environment for adhesion of microbial cells, causing infection
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and implant failure28. To prevent these medical complications, numerous ideas have
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been proposed29-30, including coatings and changing material compositions.
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Superhydrophobic surfaces with extremely low wettability (CA > 150°) have emerged
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as a potential alternative, which could resist adhesions of microbial cells and
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platelets9. However, the studies are limited to the antifouling properties of a
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superhydrophobic biopolymer surface.
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Negative environmental issues of petroleum-based materials have promoted more
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interests for renewable biomaterials derived from natural resources31-33. The
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utilization of renewable materials can make a great contribution to sustainable
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development34. Polyhydroxylalkanoates (PHA) are a family of polyesters synthesized
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by many kinds of bacteria and some haloarchaea species33, 35-37. More than 150 kinds
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of PHA have been known till now. Because of their excellent biocompatibility,
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biodegradability and thermal-mechano-properties, PHA have attracted a lot of
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attentions38-42. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is one of
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a random copolymer consisting of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate
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(3HHx) monomers. Compared with homopolymer P3HB, PHBHHx has a lower
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melting point and more favorable properties43. Biodegradable PHBHHx has been
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investigated for industrial packaging and biomedical applications44. Sudesh et al.
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found that natural hydrophobic PHA has a significant oil-absorbing ability, which
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may have applications in the cosmetics and skin cares45. Recently, Tsujimoto et al.
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prepared porous PHBHHx monolith exhibiting strong plant oil absorption
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capability46. Dou et al made a micro-ball composed of P3HB for the absorption of
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spilled crude oil from water with adsorption capability of 1.8 g/g47. However, no
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study was found regarding superhydrophobic PHA for oil-water separation.
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This study aimed to develop technology for making superhydrophobic PHBHHx films
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and investigated their applications as environmentally friendly oil removal agent or
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blood clotting prevention implant.
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2. MATERIALS AND METHODS
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2.1. Materials
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Bacterial copolymer PHBHHx was kindly provided by Lukang Pharmaceutical Co.
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Ltd (Shandong, China). It showed a polydispersity of 2.14 and a number-average
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molecular weight (Mn) of 1.14×105 g/mol as measured by gel permeation
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chromatography
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Chromotography. Ethanol, octane, hexane, vegetable oil, silicon oil and chloroform
(GPC),
3HHx
content
of
28
mol-%
detected
via
Gas
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were obtained from Sinopharm Chemical Reagent Beijing Co., Ltd, China. Diesel and
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gasoline were purchased from PetroChina Petrochemical Research Institute.
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Phosphate
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(Sigma-Aldrich), fetal bovine serum (Sigma-Aldrich), cell counting kit-8 (CCK-8,
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Boya Biotech) and the above chemicals mentioned were used as received. The
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platelet-rich plasma (PRP) was obtained from fresh rabbit blood. Human bone
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marrow mesenchymal stem cells (hBMSCs) were supplied by Cyagen, China.
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2.2.
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PHBHHx was dissolved in chloroform and then the solution was poured onto a clean
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glass dish to allow evaporation of solvent at room temperature. Smooth PHBHHx
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films were obtained after storage of one week under vacuum. Superhydrophobic
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PHBHHx
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PHBHHx/chloroform solution with PHA concentrations of 5%, 7.5%, 10% and 12.5%
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were poured onto clean glass dishes, respectively. The dishes containing PHBHHx
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solutions were placed in ethanol for 6 hours to allow full phase separations. After a
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vacuum drying process in an oven at 40oC for 6 hours, PHBHHx films with
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hierarchical structures were successfully created.
buffered
saline
(PBS)
(Sigma-Aldrich)
and
sodium
citrate
Sample Preparation
films
were
fabricated
using
a
phase
separation
process.
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2.3. Contact Angle Measurements
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The PHBHHx/water contact angles were determined by Dataphysics OCA 15Pro
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optical contact angle meter (Dataphysics, Germany). A 2.0 µl aliquot of deionized
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water was dropped onto the PHBHHx films and the water contact angle was obtained
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by an average of parallel tests taken at three positions on each PHBHHx films at room
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temperature.
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2.4. Scanning Electron Microscope
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FEI Quanta 200 scanning electron microscopy (FEI, America) was used to observe
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the surface morphology of the PHBHHx films. Before observation, all of the
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PHBHHx films were coated with a layer of gold and the surface images were taken at
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an accelerated voltage of 10 kV.
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2.5. Atomic Force Microscopy
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To observe the surface morphologies of PHBHHx films, AFM (MFP-3D Infinity,
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Oxford Instruments, U.S.A.) scanning was carried out in a tapping mode with a
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standard ACTA AFM probe (AFM probe, U.S.A.). The film was scanned and images
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of scan size (30 µm × 30 µm) were collected for the PHBHHx film. AFM image
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processing software XEI (Park Systems, U.S.A.) was employed to analyze the images.
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2.6. Solvent and Oil Absorption Test
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The PHBHHx film was put on the surface of oil/water mixture in a glass dish. The oil
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was dyed with Oil Red. Various types of oils and organic solvents were used to
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evaluate the absorption ability of the PHA materials, including octane, hexane,
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vegetable oil, silicon oil, gasoline oil and diesel oil. The weights of the PHBHHx
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material before (W1) and after (W2) absorption were measured, then the weight gain 7
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G were evaluated by the formula of G = (W2 – W1)/W1.
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2.7. Cell adhesion Test
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Human bone marrow mesenchymal stem cells (hBMSCs) were provided by Cyagen
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and were cultured in human bone marrow mesenchymal stem cell basal medium
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(Cyagen, China) with 10% fetal bovine serum in an incubator with 5% CO2 at 37°C.
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Smooth PHBHHx films and superhydrophobic PHBHHx films were carefully placed
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on the bottom of the wells of a 96-well culture plate with the rough surfaces up.
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Before seeding, the plates were sterilized with 75% ethanol for 12 h. 5 × 104 of
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hBMSCs were respectively seeded onto the PHBHHx films and then cultured in the
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medium. After incubations lasting 1, 4 and 7 day, respectively, cell count kit-8
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solution was employed to each well to evaluate the cell viability quantitatively.
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Solution absorbance was measured at 450 nm with a Thermo Scientific Varioskan
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Flash microplate reader (Thermo, America) after incubation at 37°C for 1 h. Three
166
specimens were prepared for each sample. FEI Quanta 200 scanning electron
167
microscopy (SEM) was used to observe the morphology of in vitro cultured cells on
168
the PHBHHx films. A confocal laser microscopy (A1; Nikon) was employed to take
169
the Fluorescence images. Before cell staining, the films were washed with PBS. Alexa
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Fluor 555 Phalloidin (Invitrogen, CA, USA) was used to stain actin fibers and
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4,6-diamidino-2-phenylindole (DAPI) (Invitrogen, CA, USA) was used to stain cell
172
nuclei respectively.
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2.8. Platelet Adhesion Test
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The method for in vitro platelet adhesion test of the PHBHHx films was according to
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a previous method48-49. A plastic syringe with 3.8% (w/v) sodium citrate solution with
177
a final dilution ratio of 1:9 was used to collect fresh rabbit blood. The mixture of
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rabbit blood and sodium citrate solution was centrifuged at the speed of 1500 rpm for
179
10 min at 4 °C to obtain platelet-rich plasma (PRP) for the platelet adhesion study.
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The PHBHHx films in dishes were sterilized using 75% ethanol and then washed with
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PBS three times. The films were heated to 37°C, 1 mL of PRP was added to the tested
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films followed by incubation at 37°C for 3 h. The films were fixed with
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glutaraldehyde (2.5% v/v) after being washed with PBS three times. Then after being
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dehydrated in an ethanol–water solution at different ethanol concentrations for 15
185
min, including concentrations of 30%, 50%, 60%, 70%, 80%, 90%, 95% and 100%,
186
respectively, the platelets on the PHBHHx film were dried and visualized under the
187
SEM at a voltage of 10 kV.
188 189
2.9. Bacterial Adhesion Test
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Escherichia coli expressing green-fluorescent-protein (GFP) was cultured in LB
191
medium for 8 h at 37°C. Smooth PHBHHx films and superhydrophobic PHBHHx
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films were placed on the bottom of the wells of a 48-well culture plate with the rough
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surface up. Before seeding, the plates were sterilized with 75% ethanol for 12 h and a
194
bacterial suspension (1 mL) was seeded onto the films. After incubation at 37°C for 3
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h, the PHA based films were taken out and washed with PBS three times to remove
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the non-adhered bacteria, followed by fixation in 2.5% glutaraldehyde and step by 9
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step dehydration using 30%, 50%, 60%, 70%, 80%, 90%, 95% v/v water/ethanol
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solution and 100% ethanol at last. The samples were analyzed for adhered bacteria on
199
the surface. Fluorescence images were then taken with a confocal laser microscopy
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(A1; Nikon). FEI Quanta 200 scanning electron microscopy (SEM) was used to
201
observe the morphology of in vitro cultured cells on the PHBHHx films. The number
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of E. coli adhered on the PHBHHx film were obtained from the SEM images taken at
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6000x magnifications. Five images were used to get an average number for each
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sample.
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3. RESULTS AND DISCUSSION
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3.1 Fabrication and Characterization of Superhydrophobic PHBHHx Surface
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PHBHHx films with multi-scale topography were fabricated via a facial phase
210
separation method as described16. Typical SEM micrographs of PHBHHx films
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prepared by different PHBHHx concentrations were shown (Fig. 1): the surface
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wettability is largely dependent on their topography50.
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Figure 1. Chemical structure of PHBHHx and SEM studies on surface morphologies
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of PHBHHx films.
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(a)
217
Superhydrophobic PHBHHx films prepared using solutions of different PHBHHx
218
concentrations, respectively (b) 5%; (c) 7.5%; (d) 10%; (e) 12.5%; CA values of
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87.7±1.3 o, 134.25±0.15o, 133.25±2.15o, 149.75±0.25o and 151.25±0.35o were
220
obtained from corresponding surfaces, respectively.
Chemical
structure
of
PHBHHx;
(b)
Smooth
PHBHHx
film;
(c-f)
221
222
With an increasing concentration, these samples demonstrated quite different surfaces
223
morphologies with contact angle (CA) varying from 134.25±0.15o and 133.25±2.15o
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to 149.75±0.25o and 151.25±0.35o (Fig. 1). The morphology characterized by
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micro-porous structures and the size of the pores varying from a few microns to tens
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of microns (Fig. 1c), led to a higher CA value of the surface (134.25±0.15°) than that
227
of the smooth PHBHHx film (87.4±1.3°) reported46. With increasing PHBHHx
228
concentrations, structures of leaf-shapes, flowers-like patterns, domains and
229
microspheres were formed, respectively (Figs. 1d, 1e and 1f). Micro-porous and leafy
230
structures were obtained at low PHBHHx concentrations (Figs 1c and 1d) while at
231
high PHBHHx concentration flower-like patterns and spheres were observed (Figs 1e
232
and 1f). This structure transition has been found in other polymers attributing to the
233
nucleation and increased crystal growth rate with increasing polymer concentration51.
234
Flower-like structures were revealed to contain nano-fibrilar-like patterns, while
235
microspheres were shown with deep grooves in a nano-scale. The micro-nano binary
236
structure has been known to significantly increase the hydrophobicity of a surface
237
compared with the surface of only micro-scaled domains51. When scaling down the
238
domain size of a surface, a significant increase in the CA value was found (Fig. 1f).
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The surface became superhydrophobic with a CA value of 151.25±0.35o when
240
micro-nano scale hierarchical structures were observed there (Fig. 1f).
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Figure 2. Roughness of PHBHHx films characterized by AFM.
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(a) Smooth PHBHHx film; (b-e) Superhydrophobic PHBHHx films prepared by
244
solutions of different PHBHHx concentrations, respectively (b) 5%; (c) 7.5%; (d)
245
10 %; (e) 12.5%; (f) Surface roughness of PHBHHx films in a-e.
246
247
We also carried out the atomic force microscopy (AFM) test and typical AFM surface
248
topography pictures were shown in Fig 2. It could be observed that the
249
superhydrophobic PHBHHx films had a quite roughness which may contributed to
250
increase of water contact angle and anti-adhension ability (Fig. 2f). Superhydrophobic
251
materials have been investigated for separating oil-in-water mixtures and some
252
medical applications1-3. In this study, a multi-scale PHBHHx film exhibiting a very
253
high CA value (Fig. 1f) was successfully prepared and explored for both oil
254
absorption and anti-bioadhesion studies. It is emphasized that the superhydrophobic
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PHBHHx film was not chemically modified.
256 257
3.2 Solvent and/or Oil Absorption by Superhydrophobic PHBHHx
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The oil absorption materials can concentrate oil and then transform them by the
259
removal of the oils containing absorption materials52. To achieve this goal, porous
260
superhydrophobic structure is required to gain high absorption capacity and selectivity.
261
Several biodegradable polymers are employed to fabricate porous structures for oil
262
absorption53. Cervin et al. prepared the superhydrophobic nanocellulose aerogels and
263
used the aerogels as a separation medium for separating oil from water54. As
264
mentioned above (Fig 1), a superhydrophobic PHBHHx film was prepared via a facile
265
phase separation.
266
267
Figure 3. Oil absorption studies.
268
Absorption of a colored oil (dyed with Oil Red O) in the mixture of oil/water using a
269
smooth PHBHHx films (a) and superhydrophobic PHBHHx films (b), respectively.
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Coming into contact with a layer of colored oil on the water layer, the
272
superhydrophobic PHBHHx film floated on the surface and absorbed all oils from the
273
mixture of oil/water in a very short period of time (Fig. 3b), while the smooth
274
PHBHHx film could only absorb small amount of oil (Fig. 3a). It shows absorption
275
ability of up to 4~6 times its own weight for absorption of oil and other solvents
276
including octane, hexane, vegetable oil, silicon oil, gasoline oil and diesel oil (Fig. 4).
277
278
Figure 4. Absorption capacity of smooth PHBHHx films and superhydrophobic
279
PHBHHx films investigated using six types of oils and organic solvents.
280
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Because of the rough structures and superhydrophobic property, the PHBHHx films
282
have high oil-absorption capacity, which are 3~6 times higher than that of smooth
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PHBHHx films. PHBHHx films can be directly buried then biodegraded in soil when
284
completing their usages, this promises the superhydrophobic PHBHHx films as an
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environmentally friendly candidate for cleaning oil-contaminating water.
286 287
3.3 Adhesion of Cells on Superhydrophobic PHBHHx
288
Superhydrophobic surfaces are actively studied also in biomedical areas to control
289
cellular interaction1, 55. Adhesion of cells on a material surface is usually related to the
290
surface wettability1. To investigate cell adhesions on smooth PHBHHx film and
291
superhydrophobic PHBHHx films, hBMSCs were used as model cells. Morphology
292
of hBMSCs were visible after 1 day of culture on the smooth PHBHHx film and
293
superhydrophobic PHBHHx surfaces, respectively.
294
295
Figure 5. Comparison of hBMSCs (Human bone marrow mesenchymal stem cells)
296
adhesion on the smooth and superhydrophobic PHBHHx surfaces after 1 day (24 h) of
297
incubation. SEM images of cells attached on (a) smooth PHBHHx surface and (b)
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superhydrophobic PHBHHx surface. Insets: Fluorescent microscopy images of cells
299
attached to the surfaces. Inset scale bar: 50 µm.
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On the smooth PHBHHx surface, a significant amount of cells were clearly observed,
301
indicating that cells could adhere and spread well on the surface (Figs. 5a and 5b),
302
with normal morphology (Fig. 5a), indicating good compatibility of PHBHHx. This
303
agrees with previous study related to significant cell growth on a smooth PHBHHx
304
film55. On the superhydrophobic PHBHHx surface, the amount of cells adhered is
305
considerably lower than that on the smooth PHBHHx surface. Moreover, shapes of
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the cells adhering to the superhydrophobic PHBHHx surface were abnormal with only
307
a few hBMSCs grown individually (Fig. 5b).
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309
Figure 6. Viability of hBMSCs on the smooth and superhydrophobic PHBHHx
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surfaces at different culture times assayed via CCK-8.
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The spread of hBMSCs on the superhydrophobic PHBHHx surface is limited due to
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the fact that cells were not in full contact with the surfaces in the growth medium, as
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indicated by the Cassie−Baxter model for the superhydrophobic surfaces56. Song et al
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also observed that very few cells were able to adhere to the superhydrophobic PLLA
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surfaces in comparison with the smooth ones57. SEM results are consistent with
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fluorescent microscopy images, both demonstrates that fewer cells adhered onto the
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superhydrophobic PHBHHx surface than that on the smooth PHBHHx surface.
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Quantitative results of cell culture for different days are displayed (Fig. 6). The cell
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count kit-8 solution was used to measure the cell adhesion on different substrates. It
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was obvious that the viability of hBMSCs on the superhydrophobic PHBHHx surface
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was much lower than that on smooth PHBHHx surfaces, only a few cells were
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observed capable of adhering onto the superhydrophobic PHBHHx surfaces.
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3.4 Adhesion of Platelets on Superhydrophobic PHBHHx
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Surface properties of a material are important for platelet adhesion35. Platelet adhesion
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on superhydrophobic PHBHHx was conducted using the platelet-rich plasma (PRP)
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method27. SEM was employed to visualize the morphology and calculate the number
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of the platelets adhered on the PHBHHx surface (Fig. 7). After 3 h of inoculation, the
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platelets spread over the entire smooth PHBHHx surface, yet too few platelets were
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observed on the superhydrophobic PHBHHx surface (Fig. 7).
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Figure 7. Comparison of platelet adhesion on the smooth PHBHHx and
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superhydrophobic PHBHHx. (a) SEM image of the platelet adhesion on the smooth
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PHBHHx surface (scale bar 10 µm). (b) SEM image of the platelet adhesion on the
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superhydrophobic PHBHHx surface (scale bar 10 µm).
337
338
Results in this study agree with other studies demonstrating that a hydrophobic
339
surface prohibits platelet adhesion while a smooth one tends to promote platelet
340
adhesion48.
341 342 343
3.5 Adhesion of Bacteria on Superhydrophobic PHBHHx
344
Due to the potential harm of intensive usage of biocides and antibacterial Ag+,
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superhydrophobicity has attracted increasing interests especially for reduction on
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bacterial adhesion.55 In current study, the ability of superhydrophobic PHBHHx film
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to prevent bacterial adhesion was studied by culturing E. coli on the surface.
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Comparison of bacterial adhesion on the smooth and superhydrophobic
349
Figure 8.
350
PHBHHx surfaces after 3h of incubation.
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SEM images of bacteria attached on (a) smooth PHBHHx surface and (b)
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superhydrophobic PHBHHx surface; Insets: Fluorescent microscopy images of
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bacteria attached to the surfaces. Inset scale bar: 100 µm. (c) Corresponding bacterial
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numbers on different PHBHHx film, averaged from 5 images for each film.
355
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Fluorescence microscopy images of bacterial adhered onto PHBHHx surface (Fig. 8)
357
shows a sharp reduction on bacterial adhesion on the superhydrophobic PHBHHx
358
compared with the smooth PHBHHx film, as also evidenced by morphology changes
359
and bacterial number (Fig. 8). The E. coli were clearly observed in good shapes and
360
number on the smooth PHBHHx film, while only few bacteria were found on the
361
superhydrophobic PHBHHx film. Quantitative estimation of adhered bacteria was
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conducted using SEM to show a clear reduction of adhered E. coli (Fig. 8c). The
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combination of micro-nanostructure and superhydrophobicity may lead to the
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improved anti-adhesion ability. This outcome is of great significance to further
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promote the use of superhydrophobic PHBHHx.
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CONCLUSION
367
4
368
For the first time, the superhydrophobic surfaces of PHBHHx containing a
369
micro-nano binary rough structure have been successfully prepared. The
370
superhydrophobic PHBHHx materials exhibit high selectivity and high separation
371
efficiency for oils-in-water and some solvents-in-water. Because of their
372
biodegradability, the used PHBHHx can be easily disposed, promising the
373
superhydrophobic PHBHHx as an environmentally friendly material for separation of
374
oil from water. A sharp reduction of adhered hBMSCs, platelets and bacteria on the
375
superhydrophobic PHBHHx surface was observed compared with the smooth
376
PHBHHx surface. A superhydrophobic PHBHHx may be an excellent candidate for
377
implant applications.
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AUTHOR INFORMATION
381 382
Corresponding Author
383
* Guo-Qiang CHEN (Chen GQ)
384
* E-mail:
[email protected] 385
Author Contributions
386
X.M.C. conducted the studies and prepared the draft paper. D.X. W. assisted the biological study. G.Q.C.
387
supervised the study.
388
Notes
389
The authors declare no competing financial interest.
390
Funding sources
391
This research was financially supported by a grant from Ministry of Sciences and Technology (Grant No.
392
2016YFB0302504), and grants from National Natural Science Foundation of China (Grant No. 31430003 and No.
393
31600072). Tsinghua President Fund also supported this project (Grant No. 2015THZ10).
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Superhydrophobic Polyhydroxyalkanoates: Preparation and Applications
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Authors:
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Xue-Mei Chea,b, Dai-Xu Weia, and Guo-Qiang Chen*a,b,c
576 577
Affiliations
578
a
579
Center for Life Sciences, Tsinghua University, Beijing 100084, China
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b
Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
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c
MOE Key Lab for Industrial Biocatalysis, Tsinghua University, Beijing 100084,
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China
Center of Synthetic and Systems Biology, School of Life Science, Tsinghua-Peking
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