Emergent membrane morphologies in relaxed and tense membranes in presence of reversible adhesive pinning interactions

et al. 2021

Preprint

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Physicochemical characteristics of nanoparticles (NPs) can be engineered for tuning their biological function in cellular delivery. How NP mechanical properties impact multivalent ligand-receptor mediated binding to cell surfaces, the avidity of NP adhesion to cells, propensity for internalization, and effects due to crowding remain unknown or unquantified. We report computational analyses of binding mechanisms of three distinct NPs that differ in type and rigidity (core-corona flexible NP, rigid NP, and rigid-tethered NP) but are otherwise similar in size and ligand surface density; moreover, for the case of flexible NP, we tune NP stiffness by varying the internal crosslinking density. We employ biophysical modeling of NP binding to membranes together with thermodynamic analysis powered by free energy calculations and show that efficient cellular targeting and uptake of NP functionalized with targeting ligand molecules can be shaped by factors including NP flexibility and crowding, receptor-ligand binding avidity, state of the membrane cytoskeleton, and curvature inducing proteins. Owing to this multitude of factors, we demonstrate that the binding avidity of a flexible NP depends on engineered changes in NP flexibility governed by significant enthalpy entropy compensations arising from multiple competing terms associated with NP, receptor density, and membrane. Analyses of the individual enthalpic and entropic contributions associated with NP, membrane, and receptor-ligand binding and receptor diffusion collectively illuminate this complex dependence of avidity on crosslinking. These findings provide strong evidence that NP flexibility is an important design parameter for rationally engineering NP targeting and uptake in a crowded cellular adhesion microenvironment.

Section: Resultsmentioning

confidence: 99%

Biophysical Considerations in the Rational Design and Cellular Targeting of Flexible Polymeric Nanoparticles

et al. 2021

Preprint

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“…The adhesion proteins, membrane-cytoskeleton linker proteins, and membrane-ECM attachment proteins play a significant role in defining cell membranes' morphology. The pinning of the membrane due to such proteins not only restricts membrane undulations but induce protrusions and invaginations 24 . The equilibrium conformations of a membrane patch under the influence of such interactions as a function of and pinning density is given in Supplementary Fig.…”

Section: Effect Of Membrane Morphologies In Np Adhesion and Uptakementioning

confidence: 99%

“…NP-cell adhesion is also expected to be influenced by the state of the cytoskeleton or the extracellular matrix, which (in the current study) is represented as the pinning of a deformable membrane with cytoskeletal proteins that bind the cell membrane to the substrate or extracellular matrix 23 . An earlier study demonstrates that the pinning induces confinement in the membrane undulations and, as a result, leads to novel and non-trivial membrane topographies, which could impact the binding and the uptake of the NP to the cell membrane 24 .…”

Section: Introductionmentioning

confidence: 99%

“…Quantitative characterization of mechanisms modulating NGP adhesion to the host cell membrane requires a model that accurately estimates the adhesion affinity from the underlying receptor-ligand binding parameters. In this context, we have recently developed a statistical mechanics based computational framework for multivalent adhesion of functionalized rigid, rigid-tethered, and flexible NPs to a membrane surface that takes into account mechanical properties of both the NP and the cell surfaces as well as the biophysical factors of membrane anchorage 21,24 . We have also proposed new thermodynamic methods to compute entropyenthalpy compensation for the related problem of binding affinity of NPs to the cell surface 21 .…”

Section: Introductionmentioning

confidence: 99%

“…The equilibrium conformations of the membranes are also determined by the state of cytoskeletal pinning and adhesive interactions between the membrane and extracellular matrix. The presence of these pinning or adhesion sites, their mobility, and bindingunbinding dynamics limit the out-of-plane fluctuations of the membrane and induces protrusions or invaginations in the membrane 24 . To understand the role of such membrane adhesions, we introduce pinning sites at randomly selected discrete points on the membrane and vary the density of pinning ( ).…”

mentioning

confidence: 99%

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Biophysical Considerations in the Rational Design and Cellular Targeting of Flexible Polymeric Nanoparticles

et al. 2021

Preprint

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It is becoming evident that engineered physicochemical characteristics of nanoparticles (NPs) are essential to improve their biological function for their cellular delivery and uptake. How NP mechanical properties impact multivalent ligand-receptor mediated binding to cell surfaces, the avidity of NP adhesion to cells, and cooperative effects due to crowding remain largely unknown or unquantified, and how tuning NPs' stiffness impacts their propensity for internalization is not clear. Here we focus on exploring the binding mechanisms of three distinct NPs that differ in type and rigidity (core-corona flexible NP, rigid NP, and rigid-tethered NP) but are otherwise similar in size and ligand surface density; moreover, for the case of flexible NP, we tune NP stiffness by varying the internal crosslinking density. We employed our recent spatial biophysical modeling of NP binding to membranes together with thermodynamic analysis powered by free energy calculations and show that efficient cellular targeting and uptake of NP functionalized with targeting ligand molecules can be shaped by factors including NP flexibility and crowding, receptor-ligand binding avidity, state of the membrane cytoskeleton, and curvature inducing proteins. Owing to this multitude of factors, we demonstrate that the binding avidity of a flexible NP depends on engineered changes in NP flexibility in a non-intuitive fashion because of significant enthalpy entropy compensations arising from multiple competing terms associated with NP, receptor density, and membrane. Analyses of the individual enthalpic and entropic contributions associated with NP, membrane, and receptor-ligand binding and receptor diffusion collectively illuminate this complex dependence of avidity on crosslinking. We find that the NP binding avidity can be engineered in a crowded environment by tuning their flexibility. We also find that when the cell membrane is bound to the cytoskeletal proteins via the pinning sites, the pinning sites' presence does not limit the binding avidity of both flexible and rigid-tethered NPs. Furthermore, we show that the membrane tension and pinning density, and the stiffness of flexible NPs can be tuned to alter the adhesion energy landscape and eventually improve the adhesion efficiency of flexible NPs. We also probed the effects of curvature-inducing proteins and receptor-ligand binding interactions on NP uptake. We found that complete uptake of both rigid-tethered NPs, and flexible NPs can be achieved by tuning NP stiffness and membrane tension even under moderate levels of ligand-densities in use for physiologically relevant applications. These findings provide strong evidence that NP flexibility is an important design parameter for rationally engineering NP targeting and uptake in a crowded cellular adhesion microenvironment.

Biophysical Considerations in the Rational Design and Cellular Targeting of Flexible Polymeric Nanoparticles

et al. 2021

Adv Materials Inter

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gene therapy [1][2][3] and their application as biomarkers for imaging and detection. [4][5][6] Functional nanoparticles are finding applications in genome editing, immune modulation, cell therapies, and molecular diagnostics to stratify patients based on biomarkers. However, the functional NPs' design, optimization, and deployment are hampered by our lack of understanding of their biological barriers and pharmacokinetics. [7] While such barriers have contributions that are systemic and span multiple scales, the specificity for a given application has essential contributions from the cellular scale. Cellular targeting is governed by avidity (adhesion) and uptake (internalization), which depend on the properties of the NPs and the cellular microenvironment.Adhesion between an NP and a cell surface typically involves the simultaneous binding [8,9] of many hundreds of ligands on the NP's surface to a similar number of receptors on the cell surface. [9][10][11][12][13] The physiological outcome of such multivalent adhesion, which can mediate diverse phenomena, including cell crowding and cell uptake, [14] depends on the strength of ligandreceptor binding interactions. Other factors that can modulate multivalent adhesion strength include physiochemical properties of both the NPs and the cell surfaces. [15] Previous How nanoparticle (NP) mechanical properties impact multivalent ligandreceptor-mediated binding to cell surfaces, the avidity, propensity for internalization, and effects due to crowding remains unknown or unquantified. Through computational analyses, the effects of NP composition from soft, deformable NPs to rigid spheres, effect of tethers, the crowding of NPs at the membrane surface, and the cell membrane properties such as cytoskeletal interactions are addressed. Analyses of binding mechanisms of three distinct NPs that differ in type and rigidity (core-corona flexible NP, rigid NP, and rigid-tethered NP) but are otherwise similar in size and ligand surface density are reported; moreover, for the case of flexible NP, NP stiffness is tuned by varying the internal crosslinking density. Biophysical modeling of NP binding to membranes together with thermodynamic analysis powered by free energy calculations is employed, and it is shown that efficient cellular targeting and uptake of NP functionalized with targeting ligand molecules can be shaped by factors including NP flexibility and crowding, receptor-ligand binding avidity, state of the membrane cytoskeleton, and curvature inducing proteins. Rational design principles that confer tension, membrane excess area, and cytoskeletal sensing properties to the NP which can be exploited for cellspecific targeting of NP are uncovered.