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Interfacial Energy Balance Governs Initial Cell Spreading Dynamics
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  • Jifeng Ren
    Jifeng Ren
    School of Biomedical Engineering, Capital Medical University, Beijing 100069, China
    Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing 100069, China
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
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  • Shuhuan Hu*
    Shuhuan Hu
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    BGI-Shenzhen, Shenzhen,Guangdong 518083, China
    *Email: [email protected]
    More by Shuhuan Hu
  • Yi Liu
    Yi Liu
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
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  • Siping Huang
    Siping Huang
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    More by Siping Huang
  • Jingqian Zhang
    Jingqian Zhang
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
  • Qi Gao
    Qi Gao
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
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  • King Wai Chiu Lai
    King Wai Chiu Lai
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
  • Raymond H. W. Lam*
    Raymond H. W. Lam
    Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    City University of Hong Kong Shenzhen Research Institute, Shenzhen Guangdong 518172, China
    *Email: [email protected]. Phone: +852-3442-8577. Fax: +852-3442-0172.
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Langmuir

Cite this: Langmuir 2025, 41, 44, 29494–29501
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https://doi.org/10.1021/acs.langmuir.5c03250
Published November 2, 2025

Copyright © 2025 American Chemical Society. This publication is licensed under these Terms of Use.

Abstract

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Cell spreading is a fundamental process in physiological and pathological contexts, including tissue formation, wound healing, and cancer cell extravasation. Previous studies have examined biophysical mechanisms governing early spreading (around 1–10 min) while biomolecular processes also begin to emerge, yet initial spreading in an even earlier stage (<1 min) remains largely unexplored. Here, we present a deterministic model based on interfacial energy balance─integrating strain energy, surface adhesion energy, and viscous dissipation─to quantitatively describe initial spreading dynamics. Using interference reflection microscopy (IRM), we characterize spreading behaviors of three breast cell lines (MCF-10A, MCF-7, and MDA-MB-231) on extracellular matrix-coated substrates. Model predictions, incorporating biomechanical and biochemical parameters measured through IRM and atomic force microscopy (AFM), show strong agreements with experimental observations. This work provides a universal framework for understanding initial spreading and offers insights into strategies to regulate initial cell spreading, with potential applications in cancer treatment and tissue engineering.

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Introduction

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Cell spreading plays a critical role in physiological and pathological processes, including tissue formation, wound healing, inflammation, and cancer cell extravasation. (1−4) In the earliest stage, initial spreading determines the yield of integrin binding, focal adhesion formation, actin filament extension, and subsequent cell spreading and migration.
Models describing cell spreading have been developed over the past few decades. Cuvelier et al. categorized the process into early spreading (1–10 min) and late spreading (>10 min), proposing power-law relationships that incorporate viscous dissipation of the cell cortex and cell–ECM adhesion (governed by effects such as integrin-ligand binding) to predict early spreading behaviors. (5) Frisch and Thoumine modeled late spreading as a viscous droplet wetting process to estimate the cell–substrate contact radius. (6) However, these models presume at the beginning of cell spreading a noticeable cell–substrate attachment area, which is not guaranteed. Biological responses over the attachment area also initiate during early spreading but not initial spreading. For example, the mechanosensitive protein paxillin begins to aggregate near integrins along the perimeter of the cell–substrate contact area starting approximately 3–5 min of cell spreading. (7,8) This suggests the dynamics of initial spreading without the involvement of biological responses can be different for those of early spreading. Hence, the initial spreading phase (<2 min) is required to further investigated to better understand the roles of the key biophysical properties governing initial spreading and formation of the attachment area.
Recent studies have explored the influence of biophysical cues on cell spreading. For example, coatings of various extracellular matrix proteins (ECMs) have been applied to modulate cell–substrate adhesion strength via integrin clustering, thereby affecting cell spreading behaviors. (8) Substrate stiffness has also been shown to affect late spreading, involving both the spreading rate and area. (9,10) Additionally, cell viscoelasticity plays a significant role in cell spreading, as cells deform under external stresses. (11,12) Prior to attachment and spreading on substrates, a cell can be modeled as a spherical soft-shell structure, (13) with its membrane contributing primarily to elasticity and its cytoplasmic liquid to viscosity. While previous studies have analyzed individual biophysical factors in early and late spreading, a comprehensive analytical framework for initial spreading, along with systematic parametric studies, remains lacking.
In this paper, we present a first-principles model based on interfacial energy balance to describe the dynamics of the initial cell–substrate contact area. The model integrates strain energy, surface adhesion energy, and viscous dissipation. The model can reveal the roles of a more comprehensive set of biophysical properties, including whole-cell elasticity and cell–substrate adhesion strength, which are sometimes overlooked. (5) To validate our approach, we conduct parametric studies by applying an interference reflection microscope (IRM) (14) to characterize initial spreading dynamics under various conditions. We examine three breast cell lines (MCF-10A, MCF-7, and MDA-MB-231), modulating cell–substrate binding strength through different ECM protein coatings and substrate stiffness through different substrate materials. Average cell properties (body size, viscosity, and elastic modulus) are measured by our previously developed microfluidic deformability cytometer, (15,16) while viscoelastic properties of individual cells are measured using atomic force microscopy (AFM) for further analysis. In essence, this work provides insights into how surface conditions can modulate cell growth and morphology on different surfaces for potential applications, such as cancer treatment and tissue engineering.

Results and Discussion

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Model

Here, we hypothesize that initial cell spreading dynamics is a deterministic process governed by the biomechanical energy-balanced interactions between cells and ECMs, (6,17) as shown in Figure 1a. Briefly, cell deformation during initial spreading can be expressed by the radial displacement of this first contact point (δ). The cortical strain energy (ΔUs) corresponds to the cell deformation should vary with δ; and the viscous dissipation (Wv) cell deformation should be a function of δ̇ and the underlying shear strain rates (γ̇) generated in the cytoplasm. Cell–substrate adhesion energy change (ΔUb) is a function of the cell–substrate contact area (Ac), which increases with δ. We have derived dynamic Ac as a function of time (t) and other key factors based on the energy balance between ΔUb, ΔUs, and Wv:
ΔUb=ΔUs+Wv
(1)

Figure 1

Figure 1. Visualization of initial cell spreading. (a) Key parameters involved in the initial cell spreading process. (b) Configuration of IRM using a laser scanning confocal microscope. (c) Glass and PDMS substrates coated with fluorescent fibronectin. (d) IRM images of an initial spreading MCF-10A cell on fibronectin-coated glass (upper) and their cross-sectional views (lower, processed with intensity inversion and thresholding for better visualization), captured as 10s, 60s, and 300s. All other cases are available in Figure S1. (e) Transient spreading area (Ac) of MCF-10A cells spreading on fibronectin-coated glass substrates. Gray lines represent single-cell dynamics; and the black line represents the average Ac (t). Error bars are standard errors of the mean. All cases with N numbers are available in Figure S2. Scale bar: 10 μm.

ΔUb and ΔUs can be calculated by integrating the corresponding effective cell–substrate adhesion force (Fb) and compressive force to the substrate (Fs), respectively, over the maximum radial displacement (δ) of the cell. The rate of viscus dissipation (W˙v) is calculated based on effects of strain rate over the cytoplasmic region.
ΔUb is approximated as
ΔUbζb·Ac
(2)
where ζb is the cell–substrate adhesion energy per unit contact area and the instantaneous cell spreading area is denoted as Ac. ζb summarizes cell-ECM adhesion events, including integrin-ligand binding. For instance, integrins α5β1 and αvβ3 bind to fibronectin, and integrins α1β1 and α2β1 bind to collagen (type I), (18) and therefore ζb for collagen and fibronectin can have different values for the same cell type. During the initial spreading on flat surfaces, the cell shape can be considered to have a circular Ac, whereas the remaining cell surface maintains as spherical (radius: R). Ac is a function of R and the radial displacement of the first contact point (δ), for small deformation (δ ≪ R):
Ac=2πδR
(3)
The cell body stiffness is approximated to have consistent whole-cell mechanical properties over the cytoplasmic region. For small deformation, the pressure distribution Pc over the contact area can be approximated as a parabolic function of the radial position r, with r = 0 at the center of the circular contact area. (19) Previous studies suggest that the stiffness of the cell nucleus is at least 1 order of magnitude larger than that of the cytoplasmic region, (20,21) and hence we assume the cell nucleus (radius: Rn) does not deform during the initial spreading. Pc can then be approximated as a soft-shell deforming process:
Pc=E×Ac2πR(RRn)(1πr2Ac)
(4)
where E* (=E/(1–ν2)) is the effective elastic modulus of a cell, with E as the whole-cell elastic modulus and ν ≈0.4 as Poisson’s ratio. (22,23)
Recalling eq 3, the compressive force to the cell (Fc) can be derived by
Fc=0RcE×δRRn(1πr2Ac)·2πrdr=E×Acδ2(RRn)
(5)
On the other side of the cell–substrate interface, the substrate should deform together with the cell. The results displacement of the first contact point on the substrate side (δs) for the case δs ≪ δ can be approximated as δs ≈ δ•E*/Es*, where Es* is the effective elastic modulus of the substrate material. The compressive force to the substrate (Fs) can then be approximated as
Fs=πRRRn·Es*2E*·δs2
(6)
The change in total strain energy during the initial spreading (ΔUs) can then be derived by summing the integral of Fc over δ and the integral of Fs over δs:
ΔUs=0δπE×RRRnδ2dδ+0δsπRRRn·Es*2E*·δs2dδs
(7)
ΔUs=124π2(E*+E*2Es*)Ac3(RRn)R2
(8)
During cell deformation, flow presents between the cell nucleus and the cytoplasmic region. Based on the scaling argument, the viscous dissipation per volume during the cell deformation should be in the scale of μγ˙2, where μ is whole-cell viscosity and γ̇ is the average strain rate of cytoplasmic flow. (5) Hence, we estimate the rate of viscous dissipation W˙v during the initial spreading is an integrative effect over the cytoplasmic region as
W˙v=λ(4πR334πRn33)·μγ˙2
(9)
where λ is a correction factor, which is estimated by fitting the key expression with the least-squared error together with other parameters obtained by experiments as described in the next section. γ̇ should scale with variations in the angular velocity (Vθ) of cytoplasmic flow per radial thickness of the cell cytoplasmic region, i.e., γ˙Vθ/(RRn). By considering the conservation of mass/volume, one can obtain the following scaling relationship by comparing the radial velocity (in the scale of δ̇) over the deforming cell membrane and Vθ during cell deformation in the initial spreading process:
Ac·δ˙2πAc(RRn)·Vθ
(10)
Recalling eq 3, one can obtain
γ˙Ac·Ac˙4π3/2R(RRn)2
(11)
Substituting eq 11 into eq 9, W˙v can be expressed as
W˙v=λμR(R3Rn3)12π2R(RRn)4·AcAc2
(12)
By differentiating eq 1 with respect to time t and substituting with eqs 2, 8, and 12
ΦAcAc˙+Ac2=Ψ
(13)
where Φ=2λμ(R3Rn3)3πE*(1+E*/Es*)(RRn)3 and Ψ=8π2ζbR2(RRn)E*(1+E*/Es*).
Solving eq 14, one can obtain
Ac=α(1eβt)
(14)
where α = Ψ is defined as the “length scale” of spreading and β = 2/Φ is defined as the “time constant” of spreading.

Experimental Validation

To examine dynamics of initial cell spreading with experiments, we performed IRM imaging using a laser scanning confocal microscope (Figure 1b), visualizing the cell spreading for different breast cell types (MCF-10A, MCF-7, and MDA-MB-231) on collagen (type I)-coated glass, collagen-coated polydimethylsiloxane (PDMS), fibronectin-coated glass, and fibronectin-coated hexane-softened PDMS, as described in Methods. To examine ECM protein coating, we coated fibronectin conjugated with fluorescent molecules (50 μg/mL, Alexa Fluor 488 protein label kit, Thermo Fisher Scientific, Waltham, MA) on glass and PDMS substrates (2 h of immersion). No significant difference in fluorescence intensity was observed between the two substrate materials (Figure 1c), suggesting that the major difference of the substrate properties is the stiffness rather than the molecular conditions.
Next, we seeded cells on the substrate placed inside a confocal dish, followed by recording stacks of IRM images near the cell–substrate contacts at every 10s for 3 h after cell seeding to capture the cell spreading process occurring at any time within such period. We extracted the images showing the cells before attachment to measure cell radius (R) and then the first 5 min of cell spreading of different cells (Figures 1d and S1).
Results (Figures 1e and S2) confirm that the cell spreading area (Ac) is roughly a stabilizing function of time (t), agreeing with previous works. (17) Curve fitting of exponentially stabilizing functions over two spreading intervals (1 and 5 min) reveals that the 5 min fits do not match early stage dynamics (within 1 min). This indicates that initial cell spreading is primarily governed by a distinct mechanism, compared to early spreading occurring over 5 min–10 min.
To validate the biophysical model describing early cell spreading, one can determine α and β by obtaining the least-squared error of the measured Ac with the correction factor λ = 22.39 (eq 9) over the first 60s. The measured R and other premeasured bulk parameters (nuclear radius (Rn), effective elastic modulus (E*), cell–substrate adhesion energy per unit contact area (ζb), and whole-cell viscosity (μ)) are substituted in eq 14 to predict the length scale (α) and time constant (β) of spreading for each cell. The measurement procedures of these bulk parameters are described in Table I. The correlations between measured and predicted α and β (R2 ≈0.71 and R2 ≈0.80, respectively, for proportional fitting) demonstrate the representativeness of the reported biophysical model (Figure 2a).
Table I. Measured Key Parameters for MCF-10A, MCF-7, and MDA-MB-231 (MDA) Cells
 MCF-10AMCF-7MDA
E (kPa)1.30 ± SE0.060.74 ± SE0.040.66 ± SE0.04
η (kPa•s)2.62 ± SE0.162.55 ± SE0.173.89 ± SE0.25
ζb, Col (μJ/m2)1256 ± SE692218 ± SE4621892 ± SE259
ζb, FN (μJ/m2)529 ± SE1011185 ± SE651974 ± SE153
Rn (μm)3.52 ± SE0.084.01 ± SE0.074.12 ± SE0.16

Figure 2

Figure 2. Prediction and measurement of the cell spreading area (Ac). (a) Scatter plots of predicted and measured α (left) and β (right) for MCF-10A, MCF-7, and MDA-MB-231 cells spreading on different substrate materials coated with collagen type 1 (Col) or fibronectin (FN). N = 112 in total; and N for different cases are mentioned in Figure S2. (b) Power-law fittings of measured cell–substrate contact radius (Rc = √(Ac/π)) against scaled time βt for. The black dash line indicates the expected power–law relation (∼t1/4) predicted by the model.

The transient contact radius, defined as Rc = √(Ac/π), follows a power-law relationship with t. For example, previous studies have reported that Rct1/2 in early spreading (60s < t < 600s). (5) As analyzed in this work, initial spreading (0s < t < 60s) should correspond to roughly 0 < βt < 3, as 0.01 s–1 < β < 0.05 s–1 based on the experiment results. Recalling eq 14 that Ac (2) = π2Rc (4) = α(1 −et), one can expect that Rct1/4 as 1 – e–βt ≈ βt for βt < 1. Experimental results (Figures 2b and S3) confirm this scaling behavior, supporting the predictive capabilities of the model.

Parametric Study of Initial Spreading Rate

We further investigate the roles of key factors in influencing initial spreading. Theoretically, ∂Ac/∂t|t=0 → ∞ and therefore this expression fails to reflect the key interfacial properties according to eq 14. As a remedy, we consider the “spreading rate” as the rate of change of Ac (2) at t = 0:
Ac2t|t=0=αβ=KRR2(RRn)4(R3Rn3)
(15)
where KR = 24π3ζb/(λμ). For consistency throughout this paper, we present the spreading rate as the values obtained from IRM measurements, whereas α and β are computed from the measured R, and cellular and interfacial properties. We plot the measured spreading rate against αβ (Figure 3a) with a reasonable correlation coefficient (R2 ≈0.68). The measured spreading rate scaled with a factor of KR–1 Rn–3 should be a function of the body-nuclear radius ratio (r = R/Rn), i.e., r2(r – 1)4/(r3 – 1). Results show that the values of r for individual cells lie around the prediction (Figure 3b), confirming the role of cell size (presented with R) in initial spreading. Further comparisons of spreading rates across different conditions (Figure 3c) indicate that cells spread faster on collagen-coated surfaces, which exhibit higher ζb, than on fibronectin-coated surfaces. Additionally, spreading rates on glass are comparable to those on (hexane-softened) PDMS with the same ECM protein coating, suggesting that the ECM protein is a dominant factor over substrate stiffness. This can be explained by the fact that E* is canceled out in KR (eq 15). Notably, it has been reported that the spreading characteristics can be influenced by substrate stiffness in the later spreading stages (>1 min), owing to the occurrence of active intracellular processes such as focal complexes clustering and actin polymerization. (10) Results (Figure 3d) also show that cells with larger ratios of μ/ζb tend to exhibit faster spreading rates. Collectively, these trends align with the expression of αβ, supporting the reported biophysical model as a universal prediction approach for initial spreading across different cell–substrate interfacial conditions. Thus, the key cell and interfacial properties (e.g., μ) can be reflected by the initial spreading dynamics.

Figure 3

Figure 3. Roles of key parameters. (a) Scatter plot of αβ against measured initial spreading rate. The dash line indicates proportional linear fitting of all points (legends are shared with the same one in Figure 2a). (b) Scatter plot of measured initial spreading rate against R/Rn. The solid line indicates the prediction based on the model with average cell properties (legends are shared with the same one in Figure 2a). (c) Average initial spreading rates of cells spreading on different substrate conditions. Asterisks represent p < 0.05. (d) Correlations between initial spreading rate and the derived μ/ζb for all cases. The dash line indicates the linear regression of the average values. Error bars are standard errors of the mean. N = 112 in total; and N for different cases are mentioned in Figure S2.

Individual Cell Viscoelasticity

To further examine the roles of body viscoelasticity, we integrated IRM and AFM to quantify cell properties during initial spreading, as shown in Figure 4a. Because of a technical challenge that both measurements cannot be conducted simultaneously, we first employed IRM to quantify cell spreading, followed by measuring body viscoelasticity using AFM. Considering also that both IRM and AFM needed to be applied on the same cell, we reduced the magnification to enable more cells to be captured in each IRM image. Substrates containing the cells were then transferred to an AFM machine for force relaxation analysis (see Methods) to obtain cell biomechanical properties (R, E*, and μ). ζb and Rn are assumed to be constant.

Figure 4

Figure 4. Characterization of single-cell viscoelasticity. (a) IRM (left) and AFM (right) measurements of MDA-MB-231 cells during the initial spreading process. Scale bar: 20 μm. (b) Scatter plots of single-cell E*/μ against R for individual cells. (c) Scatter plots of αβ against single-cell E*. Blue dash lines indicate fitting results of “fast spreading” cells, and red dash lines indicate fitting results of “slow spreading” cells. (d) Correlation of μ and E* for different individual cells. Each dash line indicates the linear fitting of individual cells with the same cell type.

Afterward, we examined micrographs for IRM and AFM to identify the matching individual cells. We classify two groups of cells for each cell type based on the value of β. The cells with time constants of initial spreading, i.e., measured 1/β, above the average level (0.0348 s–1 for MCF-10A, 0.03 s–1 for MCF-7, and 0.0355 s–1 for MDA-MB-231) are considered as the “fast-spreading” cells; otherwise, they are the “slow-spreading” ones. Results (Figure 4b) agree with the reported model (eq 14) in which the fast-spreading cells possess larger values of R and E*/μ. The fast-spreading cells also exhibit larger αβ values on average (Figure 4c). Furthermore, it can be observed that αβ is negatively correlated with E*, despite that the expression of αβ (eq 15) is inversely proportional to μ but not a function of E*. This can be explained by the fact that the measured E* and μ tend to correlate with each other (Figure 4d), consistent with our previous works. (16) Collectively, these findings confirmed the involvement of different key cells and interfacial properties in initial spreading.

Methods

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Substrate Preparation and Cell Seeding

Confocal culture dishes with coverslips as their bases were used as the glass substrates. For PDMS substrates, a prepolymer mixture containing monomer and curing agent (weight ratio 10:1) was poured onto a coverslip, followed by spin-coating at 800 rpm for 30s and baking at 80 °C overnight. The PDMS-coated coverslip was then glued onto a culture dish with a precut hole at its base. The “soft-PDMS” substrates were prepared by mixing PDMS monomer and curing agent at a 50:1 weight ratio, achieving an equivalent stiffness in the scale of ∼10 kPa based on our AFM measurements, also agreeing with the reported values. (24) This mixture was poured into confocal culture dishes and baked at 80 °C overnight.
Afterward, the fabricated substrates were immersed with 50 μg/mL of fibronectin (FN; Invitrogen) or collagen type I (from rat tail; Sigma-Aldrich) for 2 h, then briefly rinsed with PBS. Cells were seeded onto the substrates at a density of 6 × 103 cells/cm2 for IRM imaging.

Interference Reflection Microscopy

IRM offers high sensitivity and resolution for visualizing the close contact between cells and the substrate. IRM was implemented using a laser scanning confocal microscope (TCS-SP8, Leica Microsystems, Wetzlar, Germany), as shown in Figure 1b. A 555 nm laser source generated a high-coherence light beam, which was directed by a reflection/transmission lens. Imaging was performed using a 63× oil immersion objective, enabling high-resolution time-lapse acquisition. Two photomultiplier tubes (PMTs) were utilized: one captured interference reflection light to track cell spreading dynamics, while the other recorded transmitted light to measure the cell diameter. Incident light is reflected at both the substrate-medium and medium–cell interfaces, generating an interference beam detected by the PMT. Due to interference effects, closely contacted regions appear dark, while noncontact regions appear bright. This contrast allows precise visualization of the cell–substrate adhesion, enabling direct observation of cell spreading dynamics with high fidelity.

IRM Image Processing

IRM images were analyzed by using a customized MATLAB (MathWorks, Natick, MA) script. The Canny algorithm (25) was applied to detect the spreading edge of cells in each time frame captured by IRM. Individual cells were then segmented by dissecting the image into multiple subimages, each containing a single cell. Following intensity thresholding, the spreading area was quantified.

Cell Properties Quantification

An elasticity microcytometer, as previously reported, (15) was utilized to quantify key cellular and interfacial properties of three breast cell lines (MCF-10A, MCF-7, and MDA-MB-231). These properties include cell radius (R), whole-cell elasticity (E), whole-cell viscosity (μ), and cell–substrate adhesion energy per contact area (ζb), as summarized in Table I.
Cell suspensions were injected into confining microchannels in the device using a controlled driving pressure (P), as shown in Figure S4a. Cells were captured along the microchannels at positions (L) dependent on E and R over time (t). R of a captured cell was measured with its deformed shape, while E was determined from R and L using Hertz and Tatara’s theories. (26) By tracking dynamic cell deformation (R and L) along the confining channel, we quantified μ based on a standard linear solid (SLS) model. (16) Our measured μ were comparable to previously reported values. (16)
To determine ζb, additional experiments were conducted. (15) The elastic microcytometer was coated with 50 μg/mL fibronectin or collagen (type I) as the substrate preparation procedure. Cells were injected into the device under a low-pressure level, such that the cells were captured along the confining microchannels. After a 30 min incubation period, facilitating cell adhesion to the channel walls, contact area (Ac) was measured. P was then gradually increased to dislodge the cells (Figure S4b). The minimal P required to remove a captured cell (with a projected cross-section area along the confining channel at L) reflected the cell–substrate binding force (Fb). ΔUb was then obtained by ΔUb = Fb/Fligand × Uligand, where Fligand (=45 pN) (27) represents the binding force per ligand and Uligand (=50 × 10–18 J) corresponds to the binding energy per ligand. (6) ζb was subsequently determined as ζb = ΔUb/Ac, aligning with previously reported values (∼103 μJ/m2). (27)
Additionally, the cell nuclear radius (Rn) was measured from fluorescence micrographs of Hoechst 33342-stained cells (Sigma-Aldrich).

Measurement of In Situ Single-Cell Viscoelasticity

Measurements on single-cell viscoelasticity were conducted using AFM. An AFM system (BioScope Catalyst; Bruker Nano, Santa Barbara, CA) with a conical tip (tilt angle: 20°; tip radius: 60 nm; spring constant 0.06 N/m) was applied to conduct stress-relaxation nanoindentation on an attached cell. (28) The tip approached the cell at a velocity of 6 μm/s until a trigger force of 2 nN, followed by keeping the tip at a static position and recording the force relaxation for 2s.

Cell Culture

Human breast epithelial cells (MCF-10A) and breast cancer cells (MCF-7 and MDA-MB-231) were obtained from ATCC (Manassas, VA). MCF-10A cells were cultured in Mammary Epithelial Growth Medium (MEGM; CC-3150, Lonza, Walkersville, MD) supplemented with 0.4% (v/v) bovine pituitary extract (BD, Franklin Lakes, NJ), 0.1% (v/v) human epithelial growth factor (hEGF; Cell Signaling Technology, Beverly, MA), 0.1% (v/v) hydrocortisone (Sigma-Aldrich, St. Louis, MO), 0.1% (v/v) insulin (Sigma-Aldrich), and 0.1% (v/v) of a reagent containing 30 mg/mL gentamicin and 15 μg/mL amphotericin (GA-1000, Lonza). MCF-7 cells were cultured in high-glucose Dulbecco’s modified Eagle’s medium (DMEM; Invitrogen, Carlsbad, CA) supplemented with 10% fetal bovine serum (Atlanta Biologicals, Atlanta, GA), 0.5 μg/mL fungizone (Invitrogen), 5 μg/mL gentamicin (Invitrogen), 100 units/mL penicillin, and 100 μg/mL streptomycin. MDA-MB-231 cells were maintained in DMEM-F12 (Invitrogen) with 10% fetal bovine serum and 100 units/ml of penicillin.
All cells were cultured at 37 °C with 5% CO2 in a humidified incubator. For experimental preparation, cells were detached using 0.25% trypsin–EDTA in phosphate-buffered saline (PBS; Sigma-Aldrich), followed by centrifugation and replacement with fresh culture medium. The cell suspension was then diluted to a target density of 4 × 104 cells/mL by adding additional medium, ensuring optimal conditions for biochemical adhesion measurements.

Statistics

p-values were calculated using the two-tailed unpaired Student’s t-test. Significant differences are indicated by p < 0.05.

Conclusion

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In summary, we present a theoretical model grounded in viscoelastic cell deformation to quantitatively describe the initial spreading dynamics. This model is derived based on the energy balance of strain energy, surface adhesion energy, and viscous dissipation. The model accurately predicts the initial spreading dynamics across various cell types and substrate conditions. A parametric study incorporating IRM and AFM measurements further elucidates the roles of key cell properties (e.g., viscosity, elastic modulus, and body size) and interfacial factors (e.g., binding strength and substrate stiffness). Possible improvements of the measurement include (1) the higher imaging rate for capturing any more rapid dynamic effects during initial cell spreading and (2) hardware integration of AFM and confocal microscopy, such that any dynamics in viscoelastic properties of the cell body can also be captured.
Collectively, these findings establish a universal scheme for understanding the initial spreading of individual cells as a process governed by the interfacial energy balance. Noted, successful initial cell spreading can offer sufficient contact area downstream biological events, such as aggregation of focal adhesion molecules and subsequent actin filament formation, determining cell morphology and survival on the surface. The initial spreading characteristics can be guided by modulating the key factors, offering broad potential bioapplications such as suppression of cancer cell spreading and improved prediction of early tissue formation.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.langmuir.5c03250.

  • Representative IRM images for selected cell types spreading on different substrate conditions; fitting of cell spreading area; power-law relationship of the spreading radius; and cell properties measurement using an elasticity microcytometer (PDF)

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Author Information

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  • Corresponding Authors
  • Authors
    • Jifeng Ren - School of Biomedical Engineering, Capital Medical University, Beijing 100069, ChinaBeijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing 100069, ChinaDepartment of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    • Yi Liu - Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    • Siping Huang - Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, ChinaOrcidhttps://orcid.org/0000-0001-8721-5255
    • Jingqian Zhang - Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, ChinaOrcidhttps://orcid.org/0009-0008-6016-2390
    • Qi Gao - Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, China
    • King Wai Chiu Lai - Department of Biomedical Engineering, College of Biomedicine, City University of Hong Kong, Hong Kong 999077, ChinaOrcidhttps://orcid.org/0000-0001-5002-2273
  • Author Contributions

    J.R. and S.H. contributed equally to this work.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We thank financial supports from the Hong Kong Research Grant Council (GRF 11217323 and 11206324) and the National Natural Science Foundation of China (NSFC 12402380).

References

Click to copy section linkSection link copied!

This article references 28 other publications.

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    Nisenholz, N.; Rajendran, K.; Dang, Q.; Chen, H.; Kemkemer, R.; Krishnan, R.; Zemel, A. Active Mechanics and Dynamics of Cell Spreading on Elastic Substrates. Soft Matter 2014, 10 (37), 72347246,  DOI: 10.1039/C4SM00780H
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    Li, J.; Han, D.; Zhao, Y.-P. Kinetic Behaviour of the Cells Touching Substrate: The Interfacial Stiffness Guides Cell Spreading. Sci. Rep. 2014, 4 (1), 3910,  DOI: 10.1038/srep03910
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    Bonakdar, N.; Gerum, R.; Kuhn, M.; Spörrer, M.; Lippert, A.; Schneider, W.; Aifantis, K. E.; Fabry, B. Mechanical Plasticity of Cells. Nat. Mater. 2016, 15 (10), 10901094,  DOI: 10.1038/nmat4689
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    Sackmann, E.; Smith, A.-S. Physics of Cell Adhesion: Some Lessons from Cell-Mimetic Systems. Soft Matter 2014, 10 (11), 16441659,  DOI: 10.1039/c3sm51910d
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    Liu, Y.; Ren, J.; Zhang, R.; Hu, S.; Pang, S. W.; Lam, R. H. Spreading and Migration of Nasopharyngeal Normal and Cancer Cells on Microgratings. ACS Appl. Bio Mater. 2021, 4 (4), 32243231,  DOI: 10.1021/acsabm.0c01610
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    Hu, S.; Liu, G.; Chen, W.; Li, X.; Lu, W.; Lam, R. H.; Fu, J. Multiparametric Biomechanical and Biochemical Phenotypic Profiling of Single Cancer Cells Using an Elasticity Microcytometer. small 2016, 12 (17), 23002311,  DOI: 10.1002/smll.201503620
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    Hu, S.; Lam, R. H. W. Characterization of Viscoelastic Properties of Normal and Cancerous Human Breast Cells Using a Confining Microchannel. Microfluid. Nanofluidics 2017, 21 (4), 68,  DOI: 10.1007/s10404-017-1903-x
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    Chamaraux, F.; Fache, S.; Bruckert, F.; Fourcade, B. Kinetics of Cell Spreading. Phys. Rev. Lett. 2005, 94 (15), 158102,  DOI: 10.1103/PhysRevLett.94.158102
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    Lerche, M.; Elosegui-Artola, A.; Kechagia, J. Z.; Guzmán, C.; Georgiadou, M.; Andreu, I.; Gullberg, D.; Roca-Cusachs, P.; Peuhu, E.; Ivaska, J. Integrin Binding Dynamics Modulate Ligand-Specific Mechanosensing in Mammary Gland Fibroblasts. iScience 2020, 23 (9), 101507,  DOI: 10.1016/j.isci.2020.101507
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    Ghaednia, H.; Wang, X.; Saha, S.; Xu, Y.; Sharma, A.; Jackson, R. L. A Review of Elastic–Plastic Contact Mechanics. Appl. Mech. Rev. 2017, 69, 060804,  DOI: 10.1115/1.4038187
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    Ren, J.; Li, Y.; Hu, S.; Liu, Y.; Tsao, S. W.; Lau, D.; Luo, G.; Tsang, C. M.; Lam, R. H. W. Nondestructive Quantification of Single-Cell Nuclear and Cytoplasmic Mechanical Properties Based on Large Whole-Cell Deformation. Lab Chip 2020, 20 (22), 41754185,  DOI: 10.1039/D0LC00725K
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    Varner, H.; Cohen, T. Explaining the Spread in Measurement of PDMS Elastic Properties: Influence of Test Method and Curing Protocol. Soft Matter 2024, 20 (46), 91749183,  DOI: 10.1039/D4SM00573B
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    Cao, Y.; Wu, D.; Duan, Y. A New Image Edge Detection Algorithm Based on Improved Canny. J. Comput. Methods Sci. Eng. 2020, 20 (2), 629642,  DOI: 10.3233/JCM-193963
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    Zhang, Z. L.; Kristiansen, H.; Liu, J. A Method for Determining Elastic Properties of Micron-Sized Polymer Particles by Using Flat Punch Test. Comput. Mater. Sci. 2007, 39 (2), 305314,  DOI: 10.1016/j.commatsci.2006.06.009
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    Wysotzki, P.; Sancho, A.; Gimsa, J.; Groll, J. A Comparative Analysis of Detachment Forces and Energies in Initial and Mature Cell-Material Interaction. Colloids Surf. B Biointerfaces 2020, 190, 110894,  DOI: 10.1016/j.colsurfb.2020.110894
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    Chim, Y. H.; Mason, L. M.; Rath, N.; Olson, M. F.; Tassieri, M.; Yin, H. A One-Step Procedure to Probe the Viscoelastic Properties of Cells by Atomic Force Microscopy. Sci. Rep. 2018, 8 (1), 14462,  DOI: 10.1038/s41598-018-32704-8

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  • Abstract

    Figure 1

    Figure 1. Visualization of initial cell spreading. (a) Key parameters involved in the initial cell spreading process. (b) Configuration of IRM using a laser scanning confocal microscope. (c) Glass and PDMS substrates coated with fluorescent fibronectin. (d) IRM images of an initial spreading MCF-10A cell on fibronectin-coated glass (upper) and their cross-sectional views (lower, processed with intensity inversion and thresholding for better visualization), captured as 10s, 60s, and 300s. All other cases are available in Figure S1. (e) Transient spreading area (Ac) of MCF-10A cells spreading on fibronectin-coated glass substrates. Gray lines represent single-cell dynamics; and the black line represents the average Ac (t). Error bars are standard errors of the mean. All cases with N numbers are available in Figure S2. Scale bar: 10 μm.

    Figure 2

    Figure 2. Prediction and measurement of the cell spreading area (Ac). (a) Scatter plots of predicted and measured α (left) and β (right) for MCF-10A, MCF-7, and MDA-MB-231 cells spreading on different substrate materials coated with collagen type 1 (Col) or fibronectin (FN). N = 112 in total; and N for different cases are mentioned in Figure S2. (b) Power-law fittings of measured cell–substrate contact radius (Rc = √(Ac/π)) against scaled time βt for. The black dash line indicates the expected power–law relation (∼t1/4) predicted by the model.

    Figure 3

    Figure 3. Roles of key parameters. (a) Scatter plot of αβ against measured initial spreading rate. The dash line indicates proportional linear fitting of all points (legends are shared with the same one in Figure 2a). (b) Scatter plot of measured initial spreading rate against R/Rn. The solid line indicates the prediction based on the model with average cell properties (legends are shared with the same one in Figure 2a). (c) Average initial spreading rates of cells spreading on different substrate conditions. Asterisks represent p < 0.05. (d) Correlations between initial spreading rate and the derived μ/ζb for all cases. The dash line indicates the linear regression of the average values. Error bars are standard errors of the mean. N = 112 in total; and N for different cases are mentioned in Figure S2.

    Figure 4

    Figure 4. Characterization of single-cell viscoelasticity. (a) IRM (left) and AFM (right) measurements of MDA-MB-231 cells during the initial spreading process. Scale bar: 20 μm. (b) Scatter plots of single-cell E*/μ against R for individual cells. (c) Scatter plots of αβ against single-cell E*. Blue dash lines indicate fitting results of “fast spreading” cells, and red dash lines indicate fitting results of “slow spreading” cells. (d) Correlation of μ and E* for different individual cells. Each dash line indicates the linear fitting of individual cells with the same cell type.

  • References


    This article references 28 other publications.

    1. 1
      Gout, S.; Tremblay, P.-L.; Huot, J. Selectins and Selectin Ligands in Extravasation of Cancer Cells and Organ Selectivity of Metastasis. Clin. Exp. Metastasis 2008, 25 (4), 335344,  DOI: 10.1007/s10585-007-9096-4
    2. 2
      Min, B.-M.; Lee, G.; Kim, S. H.; Nam, Y. S.; Lee, T. S.; Park, W. H. Electrospinning of Silk Fibroin Nanofibers and Its Effect on the Adhesion and Spreading of Normal Human Keratinocytes and Fibroblasts in Vitro. Biomaterials 2004, 25 (7–8), 12891297,  DOI: 10.1016/j.biomaterials.2003.08.045
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      Grinnell, F. Fibronectin and Wound Healing. J. Cell. Biochem. 1984, 26 (2), 107116,  DOI: 10.1002/jcb.240260206
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      Babcock, D. T.; Brock, A. R.; Fish, G. S.; Wang, Y.; Perrin, L.; Krasnow, M. A.; Galko, M. J. Circulating Blood Cells Function as a Surveillance System for Damaged Tissue in Drosophila Larvae. Proc. Natl. Acad. Sci. U.S.A. 2008, 105 (29), 1001710022,  DOI: 10.1073/pnas.0709951105
    5. 5
      Cuvelier, D.; Théry, M.; Chu, Y.-S.; Dufour, S.; Thiéry, J.-P.; Bornens, M.; Nassoy, P.; Mahadevan, L. The Universal Dynamics of Cell Spreading. Curr. Biol. 2007, 17 (8), 694699,  DOI: 10.1016/j.cub.2007.02.058
    6. 6
      Frisch, T.; Thoumine, O. Predicting the Kinetics of Cell Spreading. J. Biomech. 2002, 35 (8), 11371141,  DOI: 10.1016/S0021-9290(02)00075-1
    7. 7
      Ibata, N.; Terentjev, E. M. Development of Nascent Focal Adhesions in Spreading Cells. Biophys. J. 2020, 119 (10), 20632073,  DOI: 10.1016/j.bpj.2020.09.037
    8. 8
      Fouchard, J.; Bimbard, C.; Bufi, N.; Durand-Smet, P.; Proag, A.; Richert, A.; Cardoso, O.; Asnacios, A. Three-Dimensional Cell Body Shape Dictates the Onset of Traction Force Generation and Growth of Focal Adhesions. Proc. Natl. Acad. Sci. U.S.A. 2014, 111 (36), 1307513080,  DOI: 10.1073/pnas.1411785111
    9. 9
      Chaudhuri, O.; Gu, L.; Darnell, M.; Klumpers, D.; Bencherif, S. A.; Weaver, J. C.; Huebsch, N.; Mooney, D. J. Substrate Stress Relaxation Regulates Cell Spreading. Nat. Commun. 2015, 6 (1), 6365,  DOI: 10.1038/ncomms7365
    10. 10
      Nisenholz, N.; Rajendran, K.; Dang, Q.; Chen, H.; Kemkemer, R.; Krishnan, R.; Zemel, A. Active Mechanics and Dynamics of Cell Spreading on Elastic Substrates. Soft Matter 2014, 10 (37), 72347246,  DOI: 10.1039/C4SM00780H
    11. 11
      Li, J.; Han, D.; Zhao, Y.-P. Kinetic Behaviour of the Cells Touching Substrate: The Interfacial Stiffness Guides Cell Spreading. Sci. Rep. 2014, 4 (1), 3910,  DOI: 10.1038/srep03910
    12. 12
      Bonakdar, N.; Gerum, R.; Kuhn, M.; Spörrer, M.; Lippert, A.; Schneider, W.; Aifantis, K. E.; Fabry, B. Mechanical Plasticity of Cells. Nat. Mater. 2016, 15 (10), 10901094,  DOI: 10.1038/nmat4689
    13. 13
      Sackmann, E.; Smith, A.-S. Physics of Cell Adhesion: Some Lessons from Cell-Mimetic Systems. Soft Matter 2014, 10 (11), 16441659,  DOI: 10.1039/c3sm51910d
    14. 14
      Liu, Y.; Ren, J.; Zhang, R.; Hu, S.; Pang, S. W.; Lam, R. H. Spreading and Migration of Nasopharyngeal Normal and Cancer Cells on Microgratings. ACS Appl. Bio Mater. 2021, 4 (4), 32243231,  DOI: 10.1021/acsabm.0c01610
    15. 15
      Hu, S.; Liu, G.; Chen, W.; Li, X.; Lu, W.; Lam, R. H.; Fu, J. Multiparametric Biomechanical and Biochemical Phenotypic Profiling of Single Cancer Cells Using an Elasticity Microcytometer. small 2016, 12 (17), 23002311,  DOI: 10.1002/smll.201503620
    16. 16
      Hu, S.; Lam, R. H. W. Characterization of Viscoelastic Properties of Normal and Cancerous Human Breast Cells Using a Confining Microchannel. Microfluid. Nanofluidics 2017, 21 (4), 68,  DOI: 10.1007/s10404-017-1903-x
    17. 17
      Chamaraux, F.; Fache, S.; Bruckert, F.; Fourcade, B. Kinetics of Cell Spreading. Phys. Rev. Lett. 2005, 94 (15), 158102,  DOI: 10.1103/PhysRevLett.94.158102
    18. 18
      Lerche, M.; Elosegui-Artola, A.; Kechagia, J. Z.; Guzmán, C.; Georgiadou, M.; Andreu, I.; Gullberg, D.; Roca-Cusachs, P.; Peuhu, E.; Ivaska, J. Integrin Binding Dynamics Modulate Ligand-Specific Mechanosensing in Mammary Gland Fibroblasts. iScience 2020, 23 (9), 101507,  DOI: 10.1016/j.isci.2020.101507
    19. 19
      Ghaednia, H.; Wang, X.; Saha, S.; Xu, Y.; Sharma, A.; Jackson, R. L. A Review of Elastic–Plastic Contact Mechanics. Appl. Mech. Rev. 2017, 69, 060804,  DOI: 10.1115/1.4038187
    20. 20
      Guilak, F.; Tedrow, J. R.; Burgkart, R. Viscoelastic Properties of the Cell Nucleus. Biochem. Biophys. Res. Commun. 2000, 269 (3), 781786,  DOI: 10.1006/bbrc.2000.2360
    21. 21
      Ren, J.; Li, Y.; Hu, S.; Liu, Y.; Tsao, S. W.; Lau, D.; Luo, G.; Tsang, C. M.; Lam, R. H. W. Nondestructive Quantification of Single-Cell Nuclear and Cytoplasmic Mechanical Properties Based on Large Whole-Cell Deformation. Lab Chip 2020, 20 (22), 41754185,  DOI: 10.1039/D0LC00725K
    22. 22
      Trickey, W. R.; Baaijens, F. P. T.; Laursen, T. A.; Alexopoulos, L. G.; Guilak, F. Determination of the Poisson’s Ratio of the Cell: Recovery Properties of Chondrocytes after Release from Complete Micropipette Aspiration. J. Biomech. 2006, 39 (1), 7887,  DOI: 10.1016/j.jbiomech.2004.11.006
    23. 23
      Lam, R. H. W.; Weng, S.; Lu, W.; Fu, J. Live-Cell Subcellular Measurement of Cell Stiffness Using a Microengineered Stretchable Micropost Array Membrane. Integr. Biol. 2012, 4 (10), 12891298,  DOI: 10.1039/c2ib20134h
    24. 24
      Varner, H.; Cohen, T. Explaining the Spread in Measurement of PDMS Elastic Properties: Influence of Test Method and Curing Protocol. Soft Matter 2024, 20 (46), 91749183,  DOI: 10.1039/D4SM00573B
    25. 25
      Cao, Y.; Wu, D.; Duan, Y. A New Image Edge Detection Algorithm Based on Improved Canny. J. Comput. Methods Sci. Eng. 2020, 20 (2), 629642,  DOI: 10.3233/JCM-193963
    26. 26
      Zhang, Z. L.; Kristiansen, H.; Liu, J. A Method for Determining Elastic Properties of Micron-Sized Polymer Particles by Using Flat Punch Test. Comput. Mater. Sci. 2007, 39 (2), 305314,  DOI: 10.1016/j.commatsci.2006.06.009
    27. 27
      Wysotzki, P.; Sancho, A.; Gimsa, J.; Groll, J. A Comparative Analysis of Detachment Forces and Energies in Initial and Mature Cell-Material Interaction. Colloids Surf. B Biointerfaces 2020, 190, 110894,  DOI: 10.1016/j.colsurfb.2020.110894
    28. 28
      Chim, Y. H.; Mason, L. M.; Rath, N.; Olson, M. F.; Tassieri, M.; Yin, H. A One-Step Procedure to Probe the Viscoelastic Properties of Cells by Atomic Force Microscopy. Sci. Rep. 2018, 8 (1), 14462,  DOI: 10.1038/s41598-018-32704-8
  • Supporting Information

    Supporting Information


    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.langmuir.5c03250.

    • Representative IRM images for selected cell types spreading on different substrate conditions; fitting of cell spreading area; power-law relationship of the spreading radius; and cell properties measurement using an elasticity microcytometer (PDF)


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