superhydrophobic poly (lactic acid) membrane for controlled-release of oil soluble drugs

Accepted Manuscript Regular Article Tunable adhesion of superoleophilic/superhydrophobic Poly (lactic acid) membrane for controlled-release of oil soluble drugs Ailin Gao, Fu Liu, Zhu Xiong, Qing Yang PII: DOI: Reference:

S0021-9797(17)30600-8 http://dx.doi.org/10.1016/j.jcis.2017.05.071 YJCIS 22378

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

14 March 2017 27 April 2017 21 May 2017

Please cite this article as: A. Gao, F. Liu, Z. Xiong, Q. Yang, Tunable adhesion of superoleophilic/superhydrophobic Poly (lactic acid) membrane for controlled-release of oil soluble drugs, Journal of Colloid and Interface Science (2017), doi: http://dx.doi.org/10.1016/j.jcis.2017.05.071

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Tunable adhesion of superoleophilic/superhydrophobic Poly (lactic acid) membrane for controlled-release of oil soluble drugs Ailin Gao a, b, Fu Liu*a, b, Zhu Xiong a, Qing Yang a (a: Polymer and Composite Division, Ningbo Institute of Material Technology &Engineering, Chinese Academy of Sciences, No. 1219 Zhongguan West Rd, Ningbo, P.R. China 315201; b: University of Chinese Academy of Sciences, 19 A Yuquan Rd, Shijingshan District, Beijing, P.R. China 100049) Abstract : Superhydrophobic membranes with tunable adhesion have attracted intense interests for various engineering applications. In this work, superhydrophobic sustainable poly (lactic acid) (PLA) porous membrane with tunable adhesive force from 101 μN to 29 μN was successfully fabricated via one-step phase separation method. The incorporation of Perfluoro-1-decene (PFD) into the PLLA/PDLA membrane via the in situ polymerization can facilely tune the PLLA/PDLA stereocomplex crystallization during phase inversion, which consequently caused the unique morphology blooming evolution from bud to full-blown state. The resulted membrane showed tunable pore size, porosity, surface area, surface roughness and superhydrophobicity, which enabled the membrane with controlled-release of oil soluble drugs. Keyword: PLA superhydrophobic membrane, tunable adhesion, stereocomplex crystallization, in situ polymerization, controlled-release 1. Introduction Since the basic ideas of superhydrophobic wetting theory were proposed by Wenzel, [1, 2] Cassie and Baxter [3, 4] several decades ago, a plethora of articles have been published on this topic over the recent years.[5-8] Among these, superhydrophobic porous membranes have attracted intense interests and proved to be practically effective in various fields such as anti-fouling surface,[9, 10] membrane distillation,[11, 12] oil/water separation [13] and micro-fluid transportation [14] et al. Recently,

applications

in

biomedicine

and

healthcare

have

been

widely

explored.[15-18] Self-cleaning membranes were believed to show reduced blood platelets adhesion and better blood compatibility.[19] Polycaprolactone (PCL) membrane was used to load antibiotic drug tetracycline hydrochloride for the controlled drug delivery.[20] The biomimetic multiscale structure was found to be helpful for the drug loading and release. The hierarchical surface with high surface area ratio is facilitated to absorb and accommodate drug molecules. The rate of drug delivery can be determined by the displacement of the air trapped in the material.[21] The superoleophilicity/ superoleophobicity of the nanomaterials promote the adsorption-desorption of oil-soluble drugs and control the drug release kinetics accordingly. Therefore, feasible and efficient strategy to fabricate superwetting membrane with hierarchical surface for controlled drug release is of increasing importance. It is suggested that the wetting behavior of solid surface is governed by surface texture and energy.[22] Methods such as plasma treatment,[23] template replication,[24]

phase

separation,[25]

electrospinning[26]

and

ion-assisted

deposition[27] can effectively enhance surface water repellency by physically or chemically endow surface with regularly or irregularly arrayed pillar-like, spherical, fiber-like, needle-like or flower-like micro/nanostructures. Among these surface engineering methods, phase separation was considered to be simple, low-cost and easy to create various shaped substrates, especially for polymers.[28, 29] Various strategies have been proposed to promote the generation of hierarchical structures during phase transfer process from polymer solution to solidified membrane.[30] Phase separation could be induced by solvent evaporation, temperature change, solvent-nonsolvent exchange and even variation of polymer feature. Szczepanski etc. [31] used an approach called polymerization-induced phase separation (PIPS) to in situ generate surface roughness with rose petal-like morphology and properties. The PIPS method enhanced the incompatibility between polymer resin and solvent along with the polymerization. Within the solvent induced phase conversion, the stacking of polymer particles has been considered as the direct reason for the formation of micropapillaries. And the polymer crystal behavior during phase separation has been

further proved to be effective to enhancing the stacking of polymer particles. Solvent species, polymer concentration, vapor evaporation rate as well as synergetic additives would deeply tailor the speed of phase separation and final surface morphology. On the basis of various researches, it was found that the controllability of microstructure is indeterminate because the spherulites formation was a semi-spontaneous behavior and would be profoundly affected by the polymer category and phase separation conditions. For instance, flower-like micro- and nanoscale structure could be obtained by casting polycarbonate solution under 50% moisture.[32] The polystryrene membrane showed regular microspheres when ethanol and THF was used as co-solvents.[33]

It is commonly difficult to predict the formation of fine

morphologies for the mechanism of solution phase inversion and interaction between macromolecule and solvent are complicated.[34] Thus more investigations should be implemented on the essential relevance between crystal form and final morphology. In the present study, bio-resourced and bio-degradable intrinsic hydrophilic PLA was used as raw materials to construct superhydrophobic surface based on porous membrane. It is well-known that stereocomplex structure can form reverse configuration and stereocomplex crystallization among PLA molecular chains during solidification procedure.[35, 36] By taking advantage of special microspheres composed of PLLA/PDLA with nano-scaled folds, hydrophobic surface with high adhesion can be produced in our previous work.[37] However, only density and interval space of microspheres were adjusted while the microsphres kept their unaltered shape which limited the adjustment of surface water-repellency and adhesion force. Therefore, the present work aims to tune the adhesion force of superhydrophobic PLA membrane via phase inversion. Herein, the specific blooming process of micropapillae caused by stereocomplex crystallization could be finely controlled via in situ polymerization of Perfluoro-1-decene (PFD) monomers in PLLA/PDLA miscible solution. Owing to the very small atomic radius and strong polarity of F elements in PFD, hydrogen bonds may form between PFD and PLA. Coupled with the molecular entanglement between polymerized PFD (PPFD) and PLA, the stereoregularity of PLLA/PDLA was weakened to result in evolution of

crystalline behavior. XPS, SEM and LSCM were utilized to analyze the surface chemistry and micro-/nano- morphology of the membrane. The surface contact angle and the droplet adhesive force were measured to understand the superhydrophobicity and adhesion variation. The membrane was also measured by DSC to reveal the stereocomplex crystallization behavior. Finally, the loading and release kinetics of lipid soluble drugs in the produced membrane was investigated based on the varied adhesion force of the superoleophilic surface. 2. Experimental section 2.1 Materials Poly(L-lactic acid) (PLLA, REVODE 190, Mw 2.1×105 g/mol, Zhejiang Hisun Biomaterials) and Poly(D-lactic acid) (PDLA, Purac Co. Gorinchem, Netherlands) were used to fabricate membrane after 24 h vacuum drying at 70℃. 1-Methyl-2pyrrolidinone (NMP, AR), perfluoro-1-decene (PFD) monomers and initiator azodicarbonamide (AIBN) were purchased from Aladdin and directly used without further purification. Food grade cod liver oil was commercially purchased. 2.1 Membrane Preparation Superhydrophobic PLA membrane was prepared via non-solvent induced separation process. Fixed content ratio of PLLA and PDLA (4:1) were dissolved in NMP to form a homogenous solution at 85℃. Various contents of PFD monomers were added into the pre-formed homogenous solution and in situ polymerized for another 12 hours. Mass ratio of PLA/PFD was respectively set to 85:15, 80:20, 75:25 and 70:30. Primary membranes were produced by casting the solution onto a clean and dry ground glass with a blade (200 μm). Without any delay, the primary membrane was transferred into coagulation bath (water) at room temperature to complete the phase separation. The solidified membrane was stripped from the glass plate and kept in deionized water for another 48 h before dried in air for further testing. Detailed membrane preparation conditions are listed in Table 1.

Table1. Preparation conditions of PLA membranes code

PLLA (g)

PDLA (g)

M-0

4

1

M-15PFD

4

M-20PFD

PFD (g)

NMP (g)

AIBN(g)

0

20

0

1

0.88

19.12

0.0088

4

1

1.25

18.75

0.0125

M-25PFD

4

1

1.67

18.33

0.0167

M-30PFD

4

1

2.14

17.86

0.0214

2.3 Characterizations The chemical composition in membrane surface was assessed by an X-ray photoelectron spectroscopy analysis (XPS; AXIS ULTRA, UK). Membrane surface morphologies and roughness were analyzed according to the scanning electron microscopy (SEM; Hitachi, S4800, Japan) and laser scanning confocal microscope (LSCM; LSM700, Zeiss, Germany). The membrane surface area, porosity and pore size were determined by the automatic specific surface area and porosity analyzer (BET, ASAP2020m, Micromeritics Instrument corp. US). The degassing temperature was 80℃. Static water contact angles (WCA) and rolling angles in air were measured through a CA system (OCA20, Dataphysics, Germany). Their surface adhesive force was determined by a highly sensitive microelectromechanical balance system (Data-Physics DCAT11, Germany). The crystallization evolution of the PLA membranes was characterized by differential scanning calorimetry (DSC) on a PerkinElmer analyzer. Firstly, the samples were kept at 30℃ for 3 min before heating to 250℃ at 10 ℃/min, and then the degree of crystallinity (χc) were determined according to equation (1) and (2):[38]

 hc % 

H m  H c 100 93.6 J / g

(1)

 sc % 

H m 100 142 J / g

(2)

where ΔHm and ΔHc are the enthalpies (J/g) fusion at melt temperature and cold crystallization of the PLA membranes, respectively; 93.6 J/g is the standard melting enthalpy for homo-crystal (α-form) and 142 J/g for stereocomplex crystallinity. To investigate the adsorption kinetics of membranes with different surface texture and adhesive force, M-0 and M-30PFD samples with the same size were contacted with dyed water to observing their water repellency property. After that, the right membrane sample of M-0 and M-30PFD were contacted with cod liver oil/water emulsion to determine their adsorption rate by observing the wetting area versus time. The cod liver oil/water emulsion was formed via the assistance of ultrasonic dispersion. To investigate their adsorption capacity to cod liver oil, three pieces of 2.4× 2.4 cm2 PLA membranes were immersed in 1 wt% cod liver oil/water emulsion for 15 min to achieve the adequate adsorption-desorption equilibrium. After the removal of moisture by the vacuum oven, the mass difference of the membrane before and after adsorption was calculated as the adsorption capacity to cod liver oil. Afterwards, all samples were immersed into hexane/ethanol mixture (1:9 in volume) to release cod liver oil. The membrane was taken out at set intervals weighed after drying for calculating the release curve of cod liver oil.

3. Results and discussion 3.1 Chemical components and morphology evolution XPS was applied to analyze the variation of F element enrichment on PLLA/PDLA stereocomplex membrane surface. Fig. 1 shows that higher PFD mass ratio in the solution results in higher fluorine ratio on the solidified membrane, which can be clearly manifested by the gradually enhanced F1s spectrum in Fig. 1. In case of M-30PFD, the surface F ratio increases to 2.54%. The theoretical atomic percentage of F is calculated via the following formulas: (3)

where FPFD represents the total F atomic numbers in added PFD monomers; CPFD, CPLA and OPLA represent the total C atomic numbers in added PFD monomers, total C atomic numbers in PLA chains and total O atomic numbers in PLA chains involved with PLLA and PDLA. Compared with the theoretical F element contents in Table 2, measured results via XPS were much lower, which indicates that there was minute quantity of PPFD residue in PLA membranes after several days of soaking in water. The probable reasons for above phenomenon are that only PPFD oligomers were produced owing to the long side chains in PFD monomers and vast majority of PPFD will leach out along with NMP during solvent-nonsolvent exchange process. However, the phase inversion, morphology and crystallization could be well manipulated by the involvement of PPFD.

Fig. 1. XPS wide-scans of membrane M-15PFD, M-20PFD, M-25PFD and M-30PFD with various PFD content. Table 2. Element atomic fractions as determined by XPS analysis and theoretical fraction of F. Samples

XPS percentage of components (mol%) C

O

Theoretical contents of F (mol%)

F

M-15PFD

62.19

37.14

0.67

8.37

M-20PFD

63.35

35.39

1.26

11.2

M-25PFD

63.67

34.25

2.09

14.2

M-30PFD

63.65

33.81

2.54

17.1

Fig. 2. Top surface and pore walls in cross section SEM images of M-0 and M-15PFD, M-20PFD, M-25PFD and M-30PFD. The effects of PPFD on membrane micro-/nano-scaled texture in were determined by SEM and LSCM as presented in Fig. 2 and Fig. 3. All membrane top surfaces are relatively smooth, ascribed to the quickly solidified skin layer at the interface between solvent and coagulation bath. Different from the porous top surface of M-0, M-PFD membranes showed denser surface. With the incorporation of PPFD into the PLLA/PDLA membrane via the in situ polymerization, the viscosity of casting solution was improved due to the entanglement of polymers accordingly. The polymer-rich phase dominated the top skin-layer and caused the dense surface. The pore walls in cross section experience the similar morphology variation.

Fig. 3. SEM images of pristine M-0 and M-15PFD, M-20PFD, M-25PFD and M-30PFD membrane manipulated by various contents of PFD. More interestingly, the morphological evolution of bottom surface was substantially influenced by the in situ polymerization of PFD in PLLA/PDLA. As depicted in Fig. 3, for M-0 membrane without PPFD, the nano-scaled lamellar crystals are bundled closely to form the bud-like spherulites, which are distributed loosely with larger gap. The spherical crystals are mainly caused by the stereocomplex crystallization of PLLA/PDLA.[37] With manipulating the in situ polymerization of PFD in stereocomplex PLLA/PDLA membrane, the bud-like spherulites are blooming gradually. The expanding bloom-like spherulites are compacted and inter-connected closely for M-30PFD. Therefore, the arrangement and distribution of petal-like nano-scaled lamellar crystals on micro-scaled bud or bloom

are dominating the surface texture, by virtue of the stereocomplex crystallization behavior of PLLA/PDLA. LSCM measurements were also conducted to observe the 3D topography as shown in Fig. 3. M-0 displays granular humps with average surface roughness (Sa) of 1.3 μm. Upright fibers come into being and gradually bestrew overall membrane surface along with the increasing PFD monomers mass ratio. As a result, the average roughness presents a significant enhancement from initial 1.3 μm to 7.1 μm. The microstructure evolution on bottom surface was analogous to flowering process from bud state to half-blown state and finally to full-blown state, and resulted in the gradual increase of spherulites diameter and decrease of interval space. As shown in Fig. 4, every single spherulite was marked with yellow circle in SEM images to intuitively depict the spherulites diameter and density. The diameters increased from ~3.02 μm to ~5.73 μm and the interval space decreased from ~4.50 μm to ~1.29 μm. Therefore, the controllable microstructure evolution could be achieved via in situ polymerization of PFD in PLLA/PDLA membrane.

Fig. 4. 3D LSCM images of pristine M-0 membrane, M-15PFD, M-20PFD, M-25PFD and M-30PFD membranes manipulated by various PFD contents. 3.2 Surface properties The surface area, porosity and pore size measured by BET are shown in Table 3. Compared with the pristine M-0, modified membranes exhibit much higher surface area, higher porosity and smaller pore size. The relatively dense top surface and pore

walls in cross section account for the lower surface area, porosity and pore size of M-15PFD. The evolution of the bottom surface morphology from bud-like to bloom-like spherulites enhanced the surface area and porosity as an air cushion, which will consequently influence the interaction with water or oil. Table 3. BET measurement results of M-0 and M-15PFD, M-20PFD, M-25PFD and M-30PFD. Samples M-0

Surface area (m2/g) 17.55

Porosity (cm3/g) 0.1150

Pore size (nm) 17.38

M-15PFD

14.09

0.0859

12.51

M-20PFD

22.24

0.1203

15.78

M-25PFD

22.80

0.1349

16.72

M-30PFD

22.91

0.1398

16.72

The static water contact angle (WCA) and sliding angle of M-0 and modified PLLA/PDLA membranes are illustrated in Fig. 5. It was shown that M-0 membrane presents “petal effect” surface properties, strong hydrophobicity with a high contact angle of ~139o and very high adhesion. The water droplet was adhered to the bottom surface without dropping even the membrane was placed upside down. The base of the water droplet was pin-pointed into the micro-scaled space among bud-like spherulites to form the Wenzel state. With the manipulation of PPFD on surface texture of PLLA/PDLA membrane, membrane M-20PFD perform surperhydrophobic characteristics with a WCA of 150o and the as-prepared surface can no longer fix the water droplet and the sliding contact angle is 35o. The sliding contact angle further decreased to 21o owing to the high roughness. The full-blown spherulites with higher porosity were able to confine more air inside to form the stable air cushion. Besides, the presence of fluorine-containing components on the membrane surface promoted the decrease of surface tension and contributed to the enhanced superhydrophobicity.

Fig. 5. Water contact angles and sliding angles in air of M-0 and M-15PFD, M-20PFD, M-25PFD and M-30PFD membrane manipulated by various content of PFD. The adhesion force of M-0 and M-30PFD was measured with a highly sensitive dynamic contact angle detector to further determine the water repellency. In the experiments, a water droplet (5μL) was controlled to approach and squeeze against membrane surface, and then allowed to relax. During the relaxing process, water droplet gradually broke away from membrane surface. As shown in Fig. 6 (a), for M-0 presenting “petal effect”, the water droplet was severely distorted from spherical to rectangular strip and then broken into two parts, caused by a high adhesion force of 101 μN. The ever reported highest value of adhesion force is ～127 μN.[39] In comparison, the water droplet was easily divorced from M-30PFD membrane with no residual left behind, and the adhesion force is only 29 μN (13.2 μN has been previously defined as ultralow adhesion force value [40]) based on the real-time

recorded force-distance curves in Fig. 6 (b). As discussed above, the bud-like spherulites with micro-scaled space promoted the penetration of droplet, while the expanding bloom with nano-scaled lamellar crystals prevented the intrusion of water droplet more effectively.

Fig. 6. (a) Photographs of the dynamic water adhesion measurement on M-0 and M-30PDF; (b) real-time recorded force-distance curves for M-0 and M-30PDF. 3.3 Mechanism exploration of micro/nano structure formation The influence of the in situ polymerization of PFD on the PLLA/PDLA stereocomplex crystallization was investigated via DSC. The scanning curves and calculated crystallinity are shown in Fig. 7 and Table 4. There are two intense endothermic peaks in Fig. 7, which can be assigned to the homo-crystal (hc) melting at 173.6℃ and stereocomplex crystal (sc) melting at 226.5℃.Because of the unequal in quality of PLLA and PDLA (4:1), there was a competition between homo-crystallization of PLLA and PDLA respectively and stereocomplex crystallization

caused

by PLLA/PDLA

stereocompex

structures.[41]

It

is

demonstrated that all PLA membranes possess both hc (α form) and sc. As presented in Table 4, the intensity of Xhc and Xsc both decreased along with increasing PFD amounts. And Xsc suffered a more obvious decline, which was interfered by the

presence of PPFD. Near the location of sc melting temperature, there is a weak peak at 217℃ which can be assigned to the sc melting enthalpy with discrepant crystal region or lamellar thickness due to the incomplete stereocomplex crystal.[42] The peak intensity was also decreased with increasing the content of PPFD. The stereocomplex structure of PLLA/PDLA is mainly determined by the strong hydrogen-bond interaction between PLLA and PDLA (-CH3···O=C).[43] The entangled PPFD chains adjacent to the pristine stereocomplex structure were inclined to disturb the compact array of PLLA/PDLA and caused decreasing crystallinity owning to the strong electron withdrawing ability of F atoms.

Fig. 7. DSC heating curves of M-0 and M-15PFD, M-20PFD, M-25PFD and M-30PFD membrane manipulated by various contents of PFD.

Table 4. Thermal properties of the neat PLLA/PDLA membrane and modified PLLA/PDLA membranes during first heating. PFD contents △Hc (J/g) △Hm (J/g) (hc) Xhc (%) △Hm (J/g) (sc) Xsc (%)

0

15%

20%

25%

30%

-4.08

-3.80

-2.85

-3.68

-3.11

26.35

23.67

23.09

23.40

23.08

23.79

21.23

21.62

21.06

21.33

43.82

40.21

38.89

38.24

35.92

30.86

28.32

27.38

26.93

25.29

It has been reported that the tight integration between the opposite chiral molecule chains of PLLA/PDLA promoted the formation of stereocomplex structure, which consequently improved the crystallinity of PLLA solution system.[36] Enhanced crystal behavior during phase separation is responsible for generation of numerous micro/nanostructures. Inherently, crystalline behavior indicates that compact parallel arrangement of uncoiled macromolecules induced the nucleus formation and polymer chains aggregation. The chains regularity and mobility are key factors that determine the degree of crystallinity. However, violent molecular entanglement and strong hydrogen bonds occurs between the in situ polymerized PPFD and PLLA/PDLA chains, which would disturb the PLA chains regularity and mobility and especially would intervene the steric regularity between PLLA and PDLA. The function mechanism of PPFD in PLLA/PDLA crystallization is illustrated in Fig. 8. The PFD monomers were first uniformly dispersed in PLA molecular chains. In situ polymerized PPFD was allowed to have better compatibility and entanglement with PLLA and PDLA chains especially compared with simple blending. Owing to the very small atomic radius and strong polarity, fluorine atoms easily combine with other elements by taking their electrons to form the stable electronic shell structure. Therefore, the strong hydrogen-bond interaction between PLLA and PDLA

stereocomplex structure was weakened and even broken by hydrogen-bond between F and ester carbonyl and therefore impaired the stereoregularity of PLLA/PDLA. The aggregated nucleus of stereocomplex PLLA/PDLA intends to form the closely packed bud-like spherulites after phase inversion, while the irregular stereocomplex disturbed by PPFD is inclined to form the bloom-like spherulites.

Fig. 8. Schematic illustrations of the function mechanism of PFD in situ polymerization in PLLA/PDLA crystallization via phase inversion: (a) Molecules dissolving; (b) In situ polymerization; (c) Phase separation and nucleus formation; (d) Macromolecules aggregation. 3.4 Controlled-release of oil-soluble drugs The superhydrophobic PLA membrane with tunable adhesion can be used to adsorb-desorb oil or lipid soluble drugs such as cod liver oil, which is mainly

composed of Vitamin A and Vitamin D. The hierarchical bottom surface of M-0 and modified PLA membrane M-30PFD were contacted with cod liver oil/water emulsion for adsorption-desorption equilibrium. Due to their extreme oil affinity, cod liver oil preferentially infiltrated into the membranes and confined inside the hierarchical structure.

Fig. 9. Graphic showing depiction of the water anti-adhesion property (a) and cod liver oil adsorption kinetic (b) of M-0 and M-30PFD. However, the surface adhesion discrepancy would intensively determine their adsorption and desorption performances. As depicted in Fig. 9 (a), the bottom surfaces of M-0 and M-30PFD show different anti-adhesion property while directly contacting with dyed water. There is completely no water droplet residue on M-30PFD surface while red water spots can be obviously observed on M-0 surface. The adsorption kinetics was implemented by contacting the bottom surface of M-0 and M-30PFD membrane simultaneously with cod liver oil/water emulsion. It can be observed from Fig. 9 (b) that cod liver oil can rapidly go through the bottom surface of M-30PFD and wet the top surface in a large area within 2 s, while the vast majority of top surface of M-0 kept white despite contacting with cod liver oil/water emulsion for the

same duration. The wetted area of top surface of both M-0 and M-30PFD developed with the extension of contacting time. And M-30PFD can be fully wetted within 13 min 10 s, while a fraction of M-0 still kept white even contacting for 29 min 40 s. The highly adhesive surface of M-0 for water droplets hinders the intrusion of cod liver oil by the hydro-interface, while the lowly adhesive surface of M-30PFD repels the water and opens the oleophilic micro-structure for cod liver oil, displaying the good oleophilicity. Besides, the more porous surface with higher surface area allows the membrane with higher capacity for the accommodation of small molecules. M-PFD membranes with plentiful bloom-like nanostructures were enabled to load more cod liver oil than M0 membrane as shown in Fig. 10 (a). Afterwards, the membranes were immersed in the hexane/ethanol solution to evaluate the controlled-release performance. The cod liver oil mass in M-0 rapidly decreased from 31.5 mg to 3.9 mg within 10 mins followed by further slow desorption within another 50 mins, while it cost 20 mins for M-30PFD to release cod liver oil from 40.9 mg to 5.9 mg, as shown in Fig. 10 (b). The release of cod liver oil was significantly delayed with the content of PPFD. The decrease of adhesion force for water，increase of oleophilicity are mainly responsible for the controlled-release of cod liver oil.

Fig. 10. Cod liver oil adsorbing capacity (a) and controlled-release performance (b) of M-0 and fluorinated membrane M-15PFD, M-20PFD, M-25PFD and M-30PFD.

Conclusion Superhydrophobic sustainable PLA membranes with a multiscaled micro-/nanostructure and tunable surface adhesion force were manufactured by a facile one-step phase inversion method. Perfluoro-1-decene was in situ polymerized in PLLA/PDLA stereocomplex to control the surface morphology evolution via phase inversion. The stereocrystallization of PLLA/PDLA composite was tuned to realize the bloom-like micro/nano structure from bud to full-blown state. The membrane surface area, porosity, pore size, surface roughness was also tuned accordingly. As a result, the PLLA/PDLA composite membrane exhibited tunable water contact angle from quasi-superhydrophobicity to superhydrophobicity and tunable adhesion force from 29 μN to 101 μN. As-prepared superhydrophobic/superoleohphilic PLLA/PDLA membranes with bloom-like micro/nanostructure demonstrated high adsorption capacity and controlled-release for cod liver oil.

Acknowledgements Financial support is acknowledged from National Nature Science Foundation of China (5161101025, 51603215, 51673209) and Youth Innovation Promotion Association of Chinese Academy of Science (2014258).

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