Substrate Stiffness Regulates the Development of Left-Right Asymmetry in Cell Orientation

Helical Polymers as Drug Delivery Carriers

With the continuous development of nanotechnology, a variety of novel materials have been used to constitute drug carriers and have attracted much attention. Among them, helical polymers have great potential for application as drug carriers. Helical polymers enhance the efficiency of drug utilization due to their helical structure and interaction with drug molecules. Therefore, different helical polymers are designed to diversify their functions, such as controlling the drug release rate, ensuring high biocompatibility and degradability, and enhancing cell barrier penetration for specific diseases. This review surveys the advancements in research concerning the diverse types of drug carriers constructed from helical polymers for their practical use in biological and medical applications. The use of helical polymers as drug carriers is discussed and evaluated in terms of their structural design and monitoring drug loading and disease outcomes, as well as the future challenges and potential applications of helical polymers.

Combination of vancomycin and guanidinium-functionalized helical polymers for synergistic antibacterial activity and biofilm ablation

The emergence of various resistant bacteria and overuse of antibiotics have led to severe side effects. Therefore, developing efficient and safe antibacterial systems is important. Herein, well-defined antimicrobial material–helical poly(phenyl guanidinium isocyanide) block copolymers with different conformations (l-P3-van, d-P3-van, and dl-P3-van) that connect vancomycin (van) to the polymer through a disulfide bond were synthesized. The prepared antimicrobial materials exhibit broad-spectrum antimicrobial activity, low bacterial resistance, and good proteolytic stability. They also overcome the intrinsic resistance of Gram-negative bacteria to van with a 100-fold increase in antimicrobial activity. Interestingly, the conformation of the material promotes its antimicrobial activity. The left-handed helix conformation shows five-fold more antimicrobial activity than the right-handed helical conformation, thereby opening a path for the application of nanochirality in the field of antibiotics.

Helical poly(phenyl isocyanide)-based antibacterial materials have been developed, which have a broad antibacterial spectrum and high antibacterial activity and can effectively destroy preformed biofilms.

Insensitivity of dental pulp stem cells migration to substrate stiffness

Dental pulp stem cells (DPSCs) are a promising cell source for regeneration of dental pulp. Migration is a key event but influence of the microenvironment rigidity (5 kPa at the center of dental pulp to 20 GPa for the dentin) is largely unknown. Mechanical signals are transmitted from the extracellular matrix to the cytoskeleton, to the nuclei, and to the chromatin, potentially regulating gene expression. To identify the microenvironmental influence on migration, we analyzed motility on PDMS substrates with stiffness increasing from 1.5 kPa up to 2.5 MPa. We found that migration speed slightly increases as substrate stiffness decreases in correlation with decreasing focal adhesion size. Motility is relatively insensitive to substrate stiffness, even on a bi-rigidity PDMS substrate where DPSCs migrate without preferential direction. Migration is independent of both myosin II activity and YAP translocation after myosin II inhibition. Additionally, inhibition of Arp2/3 complex leads to significant speed decrease for all rigidities, suggesting contribution of the lamellipodia in the migration. Interestingly, the chromatin architecture remains stable after a 7-days exposure on the PDMS substrates for all rigidity. To design scaffold mimicking dental pulp environment, similar DPSCs migration for all rigidity, leaves field open to choose this mechanical parameter.

Advances in biomolecule inspired polymeric material decorated interfaces for biological applications

With the development of surface modification technology, interface properties have great effects on the interaction between biomedical materials and cells and biomolecules, which significantly affects the biocompatibility and functionality of materials. As an orderly and perfect system, biological organisms in nature effectively integrate all kinds of bio-interfaces with physiological functions, which shed light on the importance of biomolecules in organisms. It gives birth to a bio-inspiration strategy to design and fabricate smart materials with specific functionalities, e.g. osteogenic and chondrocytic induced materials inspired by bone sialoprotein and chondroitin sulfate. Through this mimicking approach, various functional materials were utilized to decorate the interfaces and further optimize the performance of biomedical materials, which would widely expand their applications. In this review, followed by a summary and brief introduction of surface modification methods, we highlight recent advances in the fabrication of functional polymeric materials inspired by a range of biomolecules for decorating interfaces. Then, the other applications of biomolecule inspired materials including tissue engineering, diagnosis and treatment of diseases and physiological function regulation are presented and the future outlook is discussed as well.

UHMWPE-MWCNT-nHA based hybrid trilayer nanobiocomposite: Processing approach, physical properties, stem/bone cell functionality, and blood compatibility

The development of polymeric nanocomposites for biomedical applications remains a major challenge in terms of tailored addition of nanoparticles to realize the simultaneous enhancement of fracture resistance and cell/blood compatibility. To address this, the present work has been planned to determine whether small addition of surface functionalized multiwalled-carbon-nanotube, MWCNT (<1.5 wt%) and egg-shell derived nanosized hydroxyapatite, nHA (<10 wt%) to ultrahigh-molecular-weight-polyethylene (UHMWPE) can significantly improve the physical properties as well as biocompatibility. The difference in mouse osteoblast and human mesenchymal stem cell (hMSc) proliferation has been validated using both the monolithic composite and a trilayered composite with two different UHMWPE nanocomposites on either face with pure polymer at the middle. The combination of rheology and micro-CT with fractography reveals the homogeneous dispersion of nanofillers, leading to mechanical property enhancement. The quantitative analysis of cell viability and cell spreading by immunocytochemistry method, using vinculin and vimentin expression, establish significant cytocompatibility with hMSc and osteoblast cells onto the trilayer hybrid nanobiocomposite substrates. The hemocompatibility of the investigated composites under the controlled flow of rabbit blood in a microfluidic device reveals the signature of reduced thrombogenesis with reduction of platelet activation on UHMWPE nanocomposite w.r.t. unreinforced UHMWPE. An attempt has been made to discuss the blood compatibility results in the backdrop of the bovine serum albumin adsorption kinetics. Summarizing, the present study establishes that the twin requirement of mechanical property and cyto/hemo-compatibility can be potentially realized in developing trilayer composites in UHMWPE-nHA-MWCNT system.

Fabrication of elastomer pillar arrays with elasticity gradient for cell migration, elongation and patterning

The elasticity of the cell and that of the supporting extracellular matrices (ECMs) in tissue are correlated. In some cases, the modulus of the ECM varies with a high spatial gradient. To study the effect of such a modulus gradient on the cell culture behavior, we proposed a novel yet straightforward method to fabricate elastomeric micropillar substrates with different height gradients, which could provide a large range of elasticity gradient from 2.4 kPa to 60 kPa. The micropillars were integrated into a microfluidic chip to demonstrate the elasticity variation, with the theoretical results proving that the elasticity of the two micropillar substrates was in the same range but with distinguished gradient strengths. Fibroblast seeded on the micropillar substrates showed migration toward the stiffer area but their elongation highly depended on the strength of the elasticity gradient. In the case of high gradient strength, cells could easily migrate to the stiffer area and then elongated perpendicularly to their migration direction. Otherwise, cells were mostly elongated in the direction of the gradient. Our results also showed that when the cell density was sufficiently high, cells tended to be oriented in the same direction locally, which was affected by both underneath pillars and cell-cell contact. The elasticity gradients could also be generated in a ripple shape, and the cell behavior showed the feasibility of using the micropillars for cell patterning applications. Moreover, the gradient pillar substrates were further used for the aggregate formation of induced pluripotent stem cells, thus providing an alternative substrate to study the effect of substrate elasticity on stem cell behavior and differentiation.

Gradient platform for combinatorial screening of thermoset polymers for biomedical applications

The goal of this work was to design a device for rapid screening of crosslinked thermoset polymers. This gradient curing platform is capable of yielding a library of polyesters with systematically varying mechanical and physicochemical properties and the resultant cellular response. A library of poly(xylitolsebacate) polyesters was prepared in this device by differential curing to yield a gradient polymer. The resultant polymer exhibits a gradient in the storage modulus (1 to 5 MPa), wettability (70° < water contact angle < 110°), degree of crosslinking, degradation rate (3-25% in 7 days), drug release and biological response (ability to support stem cell proliferation and differentiation) from one end of the polymer to the other. Primary human mesenchymal stem cells were cultured to assess the cellular response in vitro. Maximal stem cell proliferation and osteogenesis was observed on the highly crosslinked polyester segments that provide high stiffness, are hydrophobic and are slow degrading as compared to the lower cured counterparts. Under in vivo conditions, this material showed differential response across the gradient without displaying significant concerns for inflammation or infection. This gradient curing device is capable of ascertaining suitable curing conditions to obtain appropriate polymers for application specific requirements. This gradient platform was further used to identify optimal processing parameters to prepare three-dimensional tissue scaffolds such as electrospun fiber mats and porous foams. Thus, this versatile combinatorial platform is well suited for rapid screening of thermoset polymers for biomedical applications.

Synthesis of Redox-Responsive Core Cross-Linked Micelles Carrying Optically Active Helical Poly(phenyl isocyanide) Arms and Their Applications in Drug Delivery

In this manuscript, we designed and synthesized three core cross-linked micelles (M-5L, P-5L, and P-5D) with redox-responsive disulfide bonds in the core and carrying optically active helical polyisocyanide arms. Their arms were different in the helicity of the main chain and the chirality of the side groups. These micelles showed excellent redox-responsiveness to reducing agent. However, because of the different chiralities of the arms, the three micelles exhibited different performances in drug delivery and controlled release. The M-5L micelle carrying left-handed helical arms showed better therapeutic effect than the other two due to the rapid cell membrane permeability.

Chiral Orientation of Skeletal Muscle Cells Requires Rigid Substrate

Reconstitution of tissue morphology with inherent left–right (LR) asymmetry is essential for tissue/organ functions. For skeletal muscle, the largest tissue in mammalian organisms, successful myogenesis requires the regulation of the LR asymmetry to form the appropriate muscle alignment. However, the key factor for reproducing the LR asymmetry of skeletal tissues in a controllable, engineering context remains largely unknown. Recent reports indicate that cell chirality may underlie the LR development in tissue morphogenesis. Here, we report that a rigid substrate is required for the chirality of skeletal muscle cells. By using alternating micropatterned cell-adherent and cell-repellent stripes on a rigid substrate, we found that C2C12 skeletal muscle myoblasts exhibited a unidirectional tilted orientation with respect to the stripe boundary. Importantly, such chiral orientation was reduced when soft substrates were used instead. In addition, we demonstrated the key role of actin stress fibers in the formation of the chiral orientation. This study reveals that a rigid substrate is required for the chiral pattern of myoblasts, paving the way for reconstructing damaged muscle tissue with inherent LR asymmetry in the future.

Nonmonotonic Self-Deformation of Cell Nuclei on Topological Surfaces with Micropillar Array

Cells respond to the mechanical signals from their surroundings and integrate physiochemical signals to initiate intricate mechanochemical processes. While many studies indicate that topological features of biomaterials impact cellular behaviors profoundly, little research has focused on the nuclear response to a mechanical force generated by a topological surface. Here, we fabricated a polymeric micropillar array with an appropriate dimension to induce a severe self-deformation of cell nuclei and investigated how the nuclear shape changed over time. Intriguingly, the nuclei of mesenchymal stem cells (MSCs) on the poly(lactide-co-glycolide) (PLGA) micropillars exhibited a significant initial deformation followed by a partial recovery, which led to an "overshoot" phenomenon. The treatment of cytochalasin D suppressed the recovery of nuclei, which indicated the involvement of actin cytoskeleton in regulating the recovery at the second stage of nuclear deformation. Additionally, we found that MSCs exhibited different overshoot extents from their differentiated lineage, osteoblasts. These findings enrich the understanding of the role of the cell nucleus in mechanotransduction. As the first quantitative report on nonmonotonic kinetic process of self-deformation of a cell organelle on biomaterials with unique topological surfaces, this study sheds new insight into cell-biomaterial interactions.