Optimization of functionalized polymer layers for specific targeting of mobile receptors on cell surfaces

Integrating osteoimmunology and nanoparticle-based drug delivery systems for enhanced fracture healing

Fracture healing is a complex interplay of molecular and cellular mechanisms lasting from days to weeks. The inflammatory phase is the first stage of fracture healing and is critical in setting the stage for successful healing. There has been growing interest in exploring the role of the immune system and novel therapeutic strategies, such as nanoparticle drug delivery systems in enhancing fracture healing. Advancements in nanotechnology have revolutionized drug delivery systems to the extent that they can modulate immune response during fracture healing by leveraging unique physiochemical properties. Therefore, understanding the intricate interactions between nanoparticle-based drug delivery systems and the immune response, specifically macrophages, is essential for therapeutic efficacy. This review provides a comprehensive overview of the relationship between the immune system and nanoparticles during fracture healing. Specifically, we highlight the influence of nanoparticle characteristics, such as size, surface properties, and composition, on macrophage activation, polarization, and subsequent immune responses. IMPACT STATEMENT: This review provides valuable insights into the interplay between fracture healing, the immune system, and nanoparticle-based drug delivery systems. Understanding nanoparticle-macrophage interactions can advance the development of innovative therapeutic approaches to enhance fracture healing, improve patient outcomes, and pave the way for advancements in regenerative medicine.

Bistable adhesion behavior of an anisotropic particle on a sliding polymer brush

Bistable adhesion behavior of an anisotropic particle adsorbed on a sliding polymer brush was found by a single chain in mean field theory (SCMFT) study. Adjacent to the normal adhesion state at which the entropy is depressed, an additional abnormal adhesion state appears. The numerical results demonstrate that the physical mechanism of the bistable adhesion behavior is from the cooperation of the reptation motion of the sliding polymers and the rotating motion of the anisotropic particle. In the abnormal adhesion state, the orientational entropy of the anisotropic particle dominates the adhesion behavior, although the translational entropy is depressed. This bistable adhesion behavior works like a lasso rope in that the abnormal state provides a wide, sensitive, and responsive range, and the normal state furnishes stable adhesion depending on the particle anisotropy.

Computational design of nanoparticle drug delivery systems for selective targeting

Ligand-functionalized nanoparticles capable of selectively binding to diseased versus healthy cell populations are attractive for improved efficacy of nanoparticle-based drug and gene therapies. However, nanoparticles functionalized with high affinity targeting ligands may lead to undesired off-target binding to healthy cells. In this work, Monte Carlo simulations were used to quantitatively determine net surface interactions, binding valency, and selectivity between targeted nanoparticles and cell surfaces. Dissociation constant, KD, and target membrane protein density, ρR, are explored over a range representative of healthy and cancerous cell surfaces. Our findings show highly selective binding to diseased cell surfaces can be achieved with multiple, weaker affinity targeting ligands that can be further optimized by varying the targeting ligand density, ρL. Using the approach developed in this work, nanomedicines can be optimally designed for exclusively targeting diseased cells and tissues.

Selectivity of ligand-receptor interactions between nanoparticle and cell surfaces

Selectivity of interactions between nanoparticles functionalized by tethered ligands and cell surfaces with different densities of receptors plays an essential role in biorecognition and its implementation in nanobiomedicine. We show that the onset of nanoparticle adsorption has a universal character for a range of nanoparticles: the onset receptor density decreases exponentially with the energy of ligand-receptor binding and inversely with the ligand density. We demonstrate that a bimodal tether distribution, which permits shielding ligands by longer nonfunctional tethers, leads to extra loss of entropy at the adsorption onset, enhancing the selectivity.

Anti-fouling bioactive surfaces

Bioactive surfaces refer to surfaces with immobilized bioactive molecules aimed specifically at promoting or supporting particular interactions. Such surfaces are of great importance for various biomedical and biomaterials applications. In the past few years, considerable effort has been made to create bioactive surfaces by forming specific biomolecule-modified surfaces on a non-biofouling "base" or "background". Hydrophilic and bioinert polymers have been widely used as anti-fouling layers that resist non-specific protein interactions. They can also serve as "spacers" to effectively move the immobilized biomolecule away from the surface, thus enhancing its bioactivity. In this review we summarize several successful approaches for the design and preparation of bioactive surfaces based on different types of anti-fouling/spacer materials. Some perspectives on future research in this area are also presented.

Nanoparticle design optimization for enhanced targeting: Monte Carlo simulations

Using computer simulations, we systematically studied the influence of different design parameters of a spherical nanoparticle tethered with monovalent ligands on its efficiency of targeting planar cell surfaces containing mobile receptors. We investigate how the nanoparticle affinity can be affected by changing the binding energy, the percent of functionalization by ligands, tether length, grafting density, and nanoparticle core size. In general, using a longer tether length or increasing the number of tethered chains without increasing the number of ligands increases the conformational penalty for tether stretching/compression near the cell surface and leads to a decrease in targeting efficiency. At the same time, using longer tethers or a larger core size allows ligands to interact with receptors over a larger cell surface area, which can enhance the nanoparticle affinity toward the cell surface. We also discuss the selectivity of nanoparticle targeting of cells with a high receptor density. Based on the obtained results, we provide recommendations for improving the nanoparticle binding affinity and selectivity, which can guide future nanoparticle development for diagnostic and therapeutic purposes.

Kinetics of nanoparticle targeting by dissipative particle dynamics simulations

Dissipative particle dynamics simulations are applied to study nanoparticle targeting to a cell surface containing a high concentration of receptors. We found that the normalized number of bound ligands follows an exponential growth function 1 - exp(-t/tau), with the lifetime tau increasing as a function of the binding strength. With increasing binding energy, the shape of the adsorbed nanoparticle becomes ellipsoidal due to a large number of stably bound ligands, most of which are positioned on the nanoparticle periphery. For a low degree of functionalization of homogeneously distributed ligands, the kinetics of nanoparticle attachment slows down due to interference by nonfunctional chains, the overall number of bound ligands at equilibrium decreases, although the stability of ligand attachment increases. Janus-like nanoparticles with functionalized chains positioned on one side of the nanoparticle exhibit more rapid binding to the cell surface with a large equilibrium number of stably bound ligands.