Modulation of Macrophages Differentiation by Nanoscale-Engineered Geometric and Chemical Features

Tuning foreign body response with tailor-engineered nanoscale surface modifications: fundamentals to clinical applications

Biomaterials are omnipresent in today's healthcare services and are employed in various applications, including implants, sensors, healthcare accessories, and drug delivery systems. Unfavorable host immunological responses frequently jeopardize the efficacy of biomaterials. As a result, surface modification has received much attention in controlling inflammatory responses since it helps camouflage the biomaterial from the host immune system, influencing the foreign body response (FBR) from protein adsorption to fibrous capsule formation. Surfaces with controlled nanotopography and chemistry, among other surface modification methodologies, have effectively altered the immune response to biomaterials. However, the field is still in its early stages, with only a few studies showing a synergistic effect of surface chemistry and nanotopography on inflammatory and wound healing pathways. Therefore, this review will concentrate on the individual and synergistic effects of surface chemistry and nanotopography on FBR modulation and the molecular processes known to modulate these responses. This review will also provide insights into crucial research gaps and advancements in various tactics for modulating FBR, opening new paths for future research. This will further aid in improving our understanding of the immune response to biomaterials, developing advanced surface modification techniques, designing immunomodulatory biomaterials, and translating discoveries into clinical applications.

Nanotopographical cues for regulation of macrophages and osteoclasts: emerging opportunities for osseointegration

Nanotopographical cues of bone implant surface has direct influences on various cell types during the establishment of osseointegration, a prerequisite of implant bear-loading. Given the important roles of monocyte/macrophage lineage cells in bone regeneration and remodeling, the regulation of nanotopographies on macrophages and osteoclasts has arisen considerable attentions recently. However, compared to osteoblastic cells, how nanotopographies regulate macrophages and osteoclasts has not been properly summarized. In this review, the roles and interactions of macrophages, osteoclasts and osteoblasts at different stages of bone healing is firstly presented. Then, the diversity and preparation methods of nanotopographies are summarized. Special attentions are paid to the regulation characterizations of nanotopographies on macrophages polarization and osteoclast differentiation, as well as the focal adhesion-cytoskeleton mediated mechanism. Finally, an outlook is indicated of coordinating nanotopographies, macrophages and osteoclasts to achieve better osseointegration. These comprehensive discussions may not only help to guide the optimization of bone implant surface nanostructures, but also provide an enlightenment to the osteoimmune response to external implant.

Recent advances in nanomedicines for regulation of macrophages in wound healing

Macrophages are essential immune cells and play a major role in the immune response as pro-inflammatory or anti-inflammatory agents depending on their plasticity and functions. Infiltration and activation of macrophages are usually involved in wound healing. Herein, we first described macrophage polarization and their critical functions in wound healing process. It is addressed how macrophages collaborate with other immune cells in the wound microenvironment. Targeting macrophages by manipulating or re-educating macrophages in inflammation using nanomedicines is a novel and feasible strategy for wound management. We discussed the design and physicochemical properties of nanomaterials and their functions for macrophages activation and anti-inflammatory signaling during wound therapy. The mechanism of action of the strategies and appropriate examples are also summarized to highlight the pros and cons of those approaches. Finally, the potential of nanomedicines to modulate macrophage polarization for skin regeneration is discussed.

Catalpol modulating the crosstalking between mesenchymal stromal cells and macrophages via paracrine to enhance angiogenesis and osteogenesis

Due to the inflammatory responses associated with defect occurrence and materials implantation, immunoregulation has emerged as a promising strategy to enhance bone regeneration. It has been widely reported that a material could facilitate osteogenesis if it can guide macrophages to anti-inflammatory M2 phenotype, vice versa, a substrate will influence macrophage phenotype if it is osteoinductive. However, few studies have looked into the intercellular crosstalking directly. Herein, the compound catalpol was selected for its multiple functions to study the interactions between bone marrow mesenchymal stromal cells (BMSCs) and macrophages. This iridoid glucoside exhibits excellent anti-inflammatory and osteoinductive activities. The effects of catalpol on mediating M1/M2 polarization of macrophages, inhibiting osteoclast differentiation, promoting osteogenesis and angiogenesis were systematically investigated to correlate the biological responses of BMSCs and macrophages. To extend its in vivo application, the catalpol was then loaded onto an electrospun polylactide/gelatin composite fibrous mesh and subcutaneously implanted to evaluate the local inflammation and ectopic osteogenesis. The results revealed that the functions of catalpol displayed in modulating cellular behaviors are via cell paracrine to strengthen intercellular crosstalking, hence demonstrating that catalpol itself could serve as a promising bioactive stimulator for bone tissue engineering.

Applications of biomaterials for immunosuppression in tissue repair and regeneration

The immune system plays an essential role in tissue repair and regeneration. Regardless of innate or adaptive immune responses, immunosuppressive strategies such as macrophage polarization and regulatory T (Treg) cell induction can be used to modulate the immune system to promote tissue repair and regeneration. Biomaterials can improve the production of anti-inflammatory macrophages and Treg cells by providing physiochemical cues or delivering therapeutics such as cytokines, small molecules, microRNA, growth factors, or stem cells in the damaged tissues. Herein, we present an overview of immunosuppressive modulation by biomaterials in tissue regeneration and highlight the mechanisms of macrophage polarization and Treg cell induction. Overall, we foresee that future biomaterials for regenerative strategies will entail more interactions between biomaterials and the immune cells, and more mechanisms of immunosuppression related to T cell subsets remain to be discovered and applied to develop novel biomaterials for tissue repair and regeneration. STATEMENT OF SIGNIFICANCE: Immunosuppression plays a key role in tissue repair and regeneration, and biomaterials can interact with the immune system through their biological properties and by providing physiochemical cues. Here, we summarize the studies on biomaterials that have been used for immunosuppression to facilitate tissue regeneration. In the first part of this review, we demonstrate the crucial role of macrophage polarization and induction of T regulatory (Treg) cells in immunosuppression. In the second part, distinct approaches used by biomaterials to induce immunosuppression are introduced, which show excellent performance in terms of promoting tissue regeneration.