Regulation of Epithelial-to-Mesenchymal Transition Using Biomimetic

Jun 20, 2016 - structure of the basement membrane with an average fiber diameter of 0.5 and 5 ... fiber diameter of proteins found in the basement mem...
0 downloads 10 Views 6MB Size
Subscriber access provided by West Virginia University | Libraries

Article

Regulation of Epithelial-to-Mesenchymal Transition Using Biomimetic Fibrous Scaffolds Anitha Ravikrishnan, Tugba Ozdemir, Mohamed A Bah, Karen A Baskerville, S. Ismat Shah, Ayyappan K Rajasekaran, and Xinqiao Jia ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05646 • Publication Date (Web): 20 Jun 2016 Downloaded from http://pubs.acs.org on June 22, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



ACS Applied Materials & Interfaces

Regulation of Epithelial-to-Mesenchymal Transition Using Biomimetic Fibrous Scaffolds

2  3 

Anitha Ravikrishnan,1$ Tugba Ozdemir,1$ Mohamed Bah,1 Karen A. Baskerville,2 S. Ismat



Shah,1,3 Ayyappan K. Rajasekaran,1,4,5 and Xinqiao Jia1,4,6*

5  6 

1



USA



2



3

10 

4

11 

5

12 

6

Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716,

Department of Biology, Lincoln University, Lincoln University, PA 19352, USA Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA Department of Biological Sciences, University of Delaware, Newark, DE, 19716, USA Therapy Architects, LLC, Helen F Graham Cancer Center, Newark, DE, 19718, USA Department of Biomedical Engineering, University of Delaware, Newark, DE 19716, USA

13  14  15 

$

These two authors contributed equally to this work.

16  17  18 

*To whom correspondence should be addressed: Xinqiao Jia, 201 DuPont Hall, Department of

19 

Materials Science and Engineering, University of Delaware, Newark, DE, 19716, USA. Phone:

20 

302-831-6553, Fax: 302-831-4545, E-mail: [email protected].

21  22  23 

Keywords: Fibrous Scaffolds; MDCK Cells; Fiber Diameter; Hepatocyte Growth Factor;

24 

Epithelial-to-Mesenchymal Transition; Phenotype.

25  26  1   

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



Abstract.



Epithelial-to-mesenchymal transition (EMT) is a well-studied biological process that takes



place during embryogenesis,  carcinogenesis and tissue fibrosis. During EMT, the polarized



epithelial cells with a cuboidal architecture adopt an elongated fibroblast-like morphology. This



process is accompanied by the expression of many EMT-specific molecular markers. While the



molecular mechanism leading to EMT has been well established, the effects of matrix



topography and microstructure have not been clearly elucidated. Synthetic scaffolds mimicking



the mesh-like structure of the basement membrane with an average fiber diameter of 0.5 µm



and 5 µm were produced via electrospinning of poly(-caprolactone) (PCL) and were used to

10 

test the significance of fiber diameter on EMT. Cell-adhesive peptide motifs were conjugated to

11 

the fiber surface to facilitate cell attachment. Madin-Darby Canine Kidney (MDCK) cells grown

12 

on these substrates showed distinct phenotypes. On 0.5 µm substrates, cells grew as compact

13 

colonies with an epithelial phenotype. On 5 µm scaffolds, cells were more individually dispersed

14 

and appeared more fibroblastic. Upon addition of hepatocyte growth factor (HGF), an EMT

15 

inducer, cells grown on the 0.5 µm scaffold underwent pronounced scattering, as evidenced by

16 

the alteration of cell morphology, localization of focal adhesion complex, weakening of cell-cell

17 

adhesion, and upregulation of mesenchymal markers. By contrast, HGF did not induce a

18 

pronounced scattering of MDCK cells cultured on the 5.0 µm scaffold. Collectively, our results

19 

show that the alteration of the fiber diameter of proteins found in the basement membrane may

20 

create enough disturbances in epithelial organization and scattering that might have important

21 

implications in disease progression.

22  23 

2   

ACS Paragon Plus Environment

Page 2 of 37

Page 3 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



ACS Applied Materials & Interfaces

1. Introduction



Epithelial to mesenchymal transition (EMT) is a complex biological process that takes



place during tissue development and disease progression. During development, successive



EMT events generate embryonic organs and tissues. In healthy adult epithelial tissues,



polarized epithelial cells bonded to the basement membrane are held together through



adherens junction complexes, consisting of F-actin, catenins and E-cadherin.1-3 Under



pathological conditions, in response to EMT-inducing signals, the epithelial cells weaken their



cell-cell adhesions and lose the apico-basal polarity as the EMT inducers suppress the genes



encoding proteins involved in both adherens junctions and cell polarity.2,

4

During EMT, cells

10 

also undergo cytoskeletal reorganization,5-6 adopt a more elongated cell morphology and

11 

become progressively more migratory and invasive.7-8 In chronic fibrosis, the transformed cells

12 

undergo abnormal remodeling of their extracellular matrix (ECM) and produce excessive

13 

proteins and proteoglycans,9 resulting in the thickening and scarring of the tissue. At the onset

14 

of carcinoma invasion, epithelial cells are released from the cell clusters into neighboring tissues

15 

with varying tissue structures, mechanical properties and dimensionality, spreading cancer to a

16 

distal organ.

17 

The basement membrane/extracellular matrix (ECM) composed mainly of fibrillar proteins,

18 

such as collagen and fibronectin, and amorphous fillers, such as glycosaminoglycans, provides

19 

structural support and contextual information to the resident cells, serving as a key regulator of

20 

cell functions. During EMT, the ECM undergoes drastic compositional, structural and

21 

mechanical changes to accommodate aberrant tissue growth.10-12 The ECM reorganization

22 

is associated with the alteration in the density and orientation of fibrillar proteins.16 The increase

23 

or decrease in fiber crosslinking not only affects the matrix stiffness but also alters the ligand

24 

density, thereby influencing cell migration.

25 

remodeled by the stromal cells to generate invasive pathways for cancer cell migration.18 By

17

During cancer metastasis, the interstitial matrix is

3   

13-15

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



contrast, increased deposition of fibrillar proteins prevents the normal wound healing process



and results in tissue fibrosis 19-20.



Paracrine effectors are potent inducers of EMT. Particularly, hepatocyte growth factor



(HGF), a fibroblast-derived protein known as the scatter factor, affects the intercellular



connections and mobility of normal epithelial cells, and thus might be involved in embryogenesis



or wound healing.  21 Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels



in the presence of exogenous HGF form branching tubules, whereas cells grown in control gels



without HGF or in fibroblast conditioned media with HGF antibody only develop into spherical



cysts.  22 It is known that HGF binds a tyrosine kinase receptor c-Met proto-oncogene with high 23

10 

affinity to induce epithelial morphogenesis.

11 

dependent not only on the target cell type but also the environmental context and culture

12 

conditions. Although a large body of literature  24-26 reports the HGF-induced scattering or

13 

tubulogenesis by culturing MDCK cells on planar substrates or in collagen gels or Matrigel, the

14 

roles of the ECM topography on the initial clustering and HGF-induced scattering have not been

15 

elucidated.

Of note, the morphogenetic effects of HGF are

16 

To gain a fundamental understanding on how physical features of the ECM define cellular

17 

behaviors and alter cell phenotypes, a straightforward and reliable method for producing

18 

biomimetic fibrous scaffolds with controlled diameter and surface chemistry is needed.

19 

Electrospinning is a powerful technique for the fabrication of synthetic scaffolds that closely

20 

mimic the structure, morphology and mechanical properties of the natural ECM.  27-29 These

21 

micro/nano fibrous scaffolds, with the interconnected porous network and high surface to

22 

volume ratio, provide a favorable environment for cell attachment, migration and proliferation.30-

23 

32

24 

caprolactone) (PCL) 33 has been electrospun into fibrous scaffolds for various tissue engineering

25 

applications.34-36 Various surface modification methods have been applied to the PCL fibers to

26 

improve the hydrophilicity and to promote cell-scaffold interactions without compromising the

Owing to its biocompatibility, high molecular weight and semi-crystalline nature, poly(-

4   

ACS Paragon Plus Environment

Page 4 of 37

Page 5 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

37-39



bulk properties.



scaffolds with varying fiber diameters to support the attachment, growth and differentiation of



MDCK cells. Because integrin signaling is important in EMT, the amino acid sequence



corresponding to integrin binding receptors at focal adhesion complexes



the PCL scaffold. We further evaluated how the fiber diameter affects the HGF-induced cell



scattering on the scaffold. Our results highlight the importance of the biophysical attributes of



the cellular microenvironment on the fundamental aspects of EMT in tissue morphogenesis and



wound healing.

In the current investigation, we assessed the ability of electrospun PCL

40-41

was conjugated to

9  10 

2. Materials and Methods

11 

2.1. Chemicals and reagents.

12 

Poly(-caprolactone) (PCL, ~80 kDa), hexamethylenediamine (HMD) and ethylene-

13 

diaminetetraacetic acid (EDTA.4Na) were purchased from Sigma-Aldrich (St. Louis, MO).

14 

Organic solvents, including chloroform, N, N-dimethyl formamide (DMF), methylene chloride,

15 

dichloromethane

(DCM)

16 

sulfosuccinimidyl

4-(N-maleimidomethyl)

17 

obtained from Thermo-Fisher (Rockford, IL) and were used without further purification.

18 

Deionized water (DI H2O) was sourced from a NANOpure Diamond water purification system

19 

(Thermo Scientific, Barnstead, NH). Phosphate buffered saline (PBS) was purchased from

20 

Gibco (Life Technologies Carlsbad, CA). Monoclonal anti-vinculin antibody was purchased from

21 

Sigma-Aldrich (St. Louis, MO), monoclonal mouse anti-vimentin antibody was purchased from

22 

GenWay Biotech, Inc., (San Diego, CA) and purified mouse anti-E-cadherin antibody was

23 

purchased from BD Biosciences (San Diego, CA). Alexa 488, Alexa 647 and Alexa 488-

24 

conjugated goat anti-mouse or rabbit IgG, as well as Alexa 568-conjugated Phalloidin, were

25 

purchased from Molecular Probes (Eugene, OR). Recombinant human hepatocyte growth factor

and

isopropanol,

as

well

as

difunctional

cyclohexane-1-carboxylate

5   

the

ACS Paragon Plus Environment

crosslinker,

(sulfo-SMCC),

were

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



(HGF), DAPI, Syto 13 and propidium iodide (PI) were obtained from Invitrogen (Grand Island,



NY). CellTrackerTM red was purchased from Life Technologies (Carlsbad, CA).

3  4 

2.2. Scaffold fabrication and modification



2.2.1. Scaffold fabrication. Fibrous PCL scaffolds with varying fiber diameter were



fabricated using different solvents and electrospinning parameters. To produce a nonwoven mat



of uniform submicron fibers, PCL was dissolved in DCM/DMF (7:3, v/v) at a concentration of 12



wt%. The solution was transferred to a 3 mL syringe capped with a 21G blunt ended needle



(Becton Dickinson, Franklin Lakes, NJ). The syringe was suspended horizontally adjacent to a

10 

grounded aluminum collector plate at a fixed distance of 21 cm and a power supply was wired to

11 

the metal needle with an alligator clip to establish a constant electric potential of 12 kV. The

12 

PCL solution was spun at a flow rate of 1 mL/h using an automatic syringe pump (New Era

13 

Pump Systems, Farmingdale, NY). To produce micron-sized fibers, a 15 wt% PCL/chloroform

14 

solution was spun from a 16G needle at a flow rate of 1.5 mL/h with a needle-to-collector

15 

distance of 16 cm. The collected fiber mats, with an average thickness of 130 µm, were dried

16 

overnight under vacuum.

17  18 

2.2.2. Surface functionalization. A cell-adhesive peptide with a sequence of

19 

CGGWGRGDSPG (RGD-SH) was prepared on a PS3 peptide synthesizer (Protein

20 

Technologies Tucson, AZ) using the Rink Amide resin (EMD Millipore, Billerica, MA) following

21 

standard Fmoc solid phase peptide synthesis protocols, with the N-terminus was acetylated and

22 

the C-terminus amidated.

23 

with a Phenomenex® C18 preparative column and lyophilized to obtain dry powder. The HPLC

24 

traces of the purified peptide are shown in Fig. S1. The molecular weight of the purified peptide

25 

was analyzed by electrospray ionization mass spectrometry (ESI-MS, Fig. S2) (Thermo LCQ

42-44

The crude peptide was purified using the Waters HPLC equipped

6   

ACS Paragon Plus Environment

Page 6 of 37

Page 7 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces



LC-MS system with ion trap mass analyzer, San Jose, CA). ESI-MS m/z ([M+H]⁺): 1089.0



(calculated), 1089.7 (found).



PCL scaffolds were cut into circular disks of 10 mm diameter using an Acuderm punch



(Fort Lauderdale, FL). Individual disks were immersed in an ethanol/water mixture (1/1, v/v)



under gentle shaking for 2 h to remove any residual contaminants. Scaffolds were then allowed



to react with hexamethylenediamine (HMD) in 2-propanol (10 wt%) at ambient temperature for



24 h,



scaffolds were then washed with PBS (0.1 M) containing 0.15 M NaCl at pH 7.2 three times (5



min each). Next, the scaffolds were incubated with a sulfo-SMCC solution (4 mg/mL in PBS, pH

10 

7.4) at room temperature for 1 h. The sulfo-SMCC-treated scaffolds were washed three times

11 

with a PBS buffer containing 0.1 M EDTA at pH 7.0. Finally, the scaffold was incubated with

12 

RGD-SH at 0.2 mg/mL in PBS at 4 C overnight to immobilize the cell adhesive peptide.46

13 

Scaffolds were washed thoroughly with PBS to remove excess unbound peptides and dried

14 

under vacuum.

45

and unreacted HMD was removed by a thorough wash with DI H2O. The HMD-treated

15  16 

2.3. Scaffold characterization

17 

2.3.1. Scanning electron microscopy (SEM). Scaffold morphology was characterized

18 

using a Hitachi S4700 Scanning Electron Microscope. Samples were mounted on aluminum

19 

stubs using carbon tape and were sputter coated with platinum using Leica EM ACE600. The

20 

average diameter and pore size of the fibrous scaffolds were analyzed using DiameterJ,

21 

ImageJ 48 software, respectively.

47

and

22  23 

2.3.2. Contact angle analysis. For contact angle analysis, spun-cast films were used in

24 

place of the fibrous mats to eliminate topography related complications in data analysis and to

25 

unambiguously confirm the changes of surface chemistry. Specifically, PCL was spun cast from

7   

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



a 5 wt% chloroform solution onto a silicon wafer with a 300 nm-thick oxide layer, freshly clean



using a Piranha solution. The as-spun films were annealed at 60 C for 1 h. The silicon wafer



supported PCL film (3.6 µm thick, as determined by profilometry) was subjected to the same



surface modifications described above for PCL fibers. Water contact angle was measured at



room temperature using the sessile drop method on a Ramé-Hart contact angle Goniometer



(Succasunna, NJ). A distilled water droplet was placed on five different regions of the test



substrates and the measured angles were averaged.

8  9 

2.3.3. X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectroscopic

10 

(XPS) spectra of the spun-cast films, before and after various steps of surface modification,

11 

were recorded using Surface Science Instruments Model 301 ESCA with monochromatic Al

12 

Kα and Mg Kα X-rays dual source, with a resolution of 0.4 eV. The C 1s standard at 284.6 eV

13 

was used for the correction of the obtained spectra, in order to account for peak shifting due to

14 

charging. Data reported represents the chemical composition of the surface of the polymer film

15 

at a sampling depth of 3 to 10 nm, depending on the intensity of the emitted electron. The x-ray

16 

source is located perpendicular to the analyzer, while the sample is located 50 from the

17 

analyzer.

18  19 

2.3.4. Fourier transform infrared spectroscopy (FT-IR). A Fourier Transform Infrared

20 

Spectrometer (Nexus 670 FT-IR, Thermo Nicolet, Waltham, MA) was used to confirm the

21 

aminolysis on the surface of PCL films. Spun-cast films, before and after surface modification,

22 

were analyzed. The absorption spectra at the mid-infrared region (500 to 4000 wavenumbers)

23 

were recorded.

24 

8   

ACS Paragon Plus Environment

Page 8 of 37

Page 9 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces



2.3.5. Confocal microscopy. The as-spun fibers and the peptide modified fibers were



imaged using an LSM880 Multiphoton Confocal Microscope (Zeiss). For confocal imaging of



the as-spun scaffolds, the collected fibers were immersed in a PBS solution of CellTrackerTM



Red (1:1000) for 30 min. Separately, a multi-photon confocal microscope, operated at 30% laser



power, was used to confirm the peptide conjugation on PCL scaffolds based on tryptophan



fluorescence. Briefly, virgin PCL scaffolds, RGD-conjugated PCL scaffolds and RGD-coated



clean glass slides were imaged separately in order to get sample specific fluorescence emission



spectra. All samples were excited at 280 nm with an argon laser source and the unfiltered



emission spectra were collected. The fluorescence signal associated with tryptophan residue on

10 

RGD-modified PCL scaffolds was obtained by subtracting the background fluorescence from

11 

PCL.

12  13 

2.4. Cell culture

14 

Madin-Darby canine kidney (MDCK) NBL2 cells (ATCC, Manassas, VA) were cultured in

15 

Eagle's minimum essential medium (EMEM) (ATCC, Manassas, VA) supplemented with 10%

16 

fetal bovine serum (FBS) and 100 IU/mL penicillin/streptomycin in a humidified 37 C incubator

17 

maintained at 5% CO2 and 95% air. Cell culture media was changed every other day, and cells

18 

were routinely passaged using 0.25% (w/v) trypsin containing 0.02% EDTA. Prior to cell culture,

19 

the fibrous scaffolds were gently agitated in 70% ethanol overnight. After washing with fresh,

20 

serum free media, the scaffolds were exposed to germicidal UV light for 15 min, followed by a 3-

21 

h equilibration in cell culture media. MDCK cells were plated on the scaffold at a seeding density

22 

of 10,000 cells/scaffold and were incubated in media containing 0.5 % FBS for 2 h.

23 

Subsequently, the low serum media was replaced by EMEM containing 10% FBS. After 36-h

24 

incubation, the media was supplemented with HGF (50 ng/mL) and cells were cultured for an

25 

additional 12 h before individual constructs were collected and processed for immunostaining

26 

and confocal imaging. 9   

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1  2 

2.5. Biological characterization of cell-laden scaffolds



2.5.1. Live/dead staining. MDCK cells were cultured on scaffolds of different fiber



diameters in the presence or absence of HGF, as described above. After a total of 48 h of



culture, the constructs were rinsed with PBS and incubated with a mixture of Syto13 (1:1000)



and propidium iodide (1:2000) in PBS for 15 min to stain live and dead cells, respectively. After



an additional PBS wash to remove the unbound staining reagents, the constructs were imaged



using a Zeiss LSM 710 confocal microscope. Five different confocal images were taken per



sample and the number of clustered cells is defined as a group of more than five cells in close

10 

proximity.49

11  12 

2.5.2. Immunofluorescence. MDCK cells were fixed using an ice-cold cytoskeleton

13 

stabilization buffer for 1 min, incubated in freshly prepared with 4% paraformaldehyde/PBS

14 

solution for 15 min, washed three times with PBS and finally incubated overnight in a

15 

permeabilization buffer (2% BSA, 0.1% Triton X-100). Focal adhesions and cell-cell contacts

16 

were detected via immunostaining for vinculin, vimentin and E-cadherin, respectively. To this

17 

end, constructs were first incubated with primary antibodies (prepared in permeabilization

18 

buffer), monoclonal mouse anti-vinculin, monoclonal mouse anti-vimentin and purified mouse

19 

anti-E-cadherin, respectively for 90 min. After a 3-min wash with PBS, samples were incubated

20 

with the secondary antibodies (1:200, in 2% BSA), Alexa 488, Alexa 647 and Alexa 488-

21 

conjugated goat anti-mouse IgG (1:100 in 2% BSA) for 45 min, respectively. After washing with

22 

copious PBS to remove unbound antibodies, the constructs were incubated with DAPI (1:5000)

23 

and Alexa-conjugated phalloidin (1: 1000) for 5 and 30 min, respectively to counter stain cell

24 

nuclei and F-actin. The stained constructs were placed in Nunc chambers (Thermo Scientific,

25 

Rockford, IL) for imaging using a Zeiss LSM880 Multiphoton Confocal Microscope.

26  10   

ACS Paragon Plus Environment

Page 10 of 37

Page 11 of 37

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



ACS Applied Materials & Interfaces

2.6. Statistical analysis



All the quantitative data obtained were analyzed using one-way analysis of variance



(ANOVA) to compare the means of different data sets within each experiment from at least



three repeats. Errors were expressed as the standard error of the mean. A value of p