Macrophage Polarization Related to Biomimetic Calcium Phosphate Coatings: A Preliminary Study

Osteoinductive micro-nano guided bone regeneration membrane for in situ bone defect repair

BACKGROUND

Biomaterials used in bone tissue engineering must fulfill the requirements of osteoconduction, osteoinduction, and osseointegration. However, biomaterials with good osteoconductive properties face several challenges, including inadequate vascularization, limited osteoinduction and barrier ability, as well as the potential to trigger immune and inflammatory responses. Therefore, there is an urgent need to develop guided bone regeneration membranes as a crucial component of tissue engineering strategies for repairing bone defects.

METHODS

The mZIF-8/PLA membrane was prepared using electrospinning technology and simulated body fluid external mineralization method. Its ability to induce biomimetic mineralization was evaluated through TEM, EDS, XRD, FT-IR, zeta potential, and wettability techniques. The biocompatibility, osteoinduction properties, and osteo-immunomodulatory effects of the mZIF-8/PLA membrane were comprehensively evaluated by examining cell behaviors of surface-seeded BMSCs and macrophages, as well as the regulation of cellular genes and protein levels using PCR and WB. In vivo, the mZIF-8/PLA membrane's potential to promote bone regeneration and angiogenesis was assessed through Micro-CT and immunohistochemical staining.

RESULTS

The mineralized deposition enhances hydrophilicity and cell compatibility of mZIF-8/PLA membrane. mZIF-8/PLA membrane promotes up-regulation of osteogenesis and angiogenesis related factors in BMSCs. Moreover, it induces the polarization of macrophages towards the M2 phenotype and modulates the local immune microenvironment. After 4-weeks of implantation, the mZIF-8/PLA membrane successfully bridges critical bone defects and almost completely repairs the defect area after 12-weeks, while significantly improving the strength and vascularization of new bone.

CONCLUSIONS

The mZIF-8/PLA membrane with dual osteoconductive and immunomodulatory abilities could pave new research paths for bone tissue engineering.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

Calcium phosphate coating enhances osteointegration of melt electrowritten scaffold by regulating macrophage polarization

The osteoimmune microenvironment induced by implants plays a significant role in bone regeneration. It is essential to efficiently and timely switch the macrophage phenotype from M1 to M2 for optimal bone healing. This study examined the impact of a calcium phosphate (CaP) coating on the physiochemical properties of highly ordered polycaprolactone (PCL) scaffolds fabricated using melt electrowritten (MEW). Additionally, it investigated the influence of these scaffolds on macrophage polarization and their immunomodulation on osteogenesis. The results revealed that the CaP coated PCL scaffold exhibited a rougher surface topography and higher hydrophilicity in comparison to the PCL scaffold without coating. Besides, the surface morphology of the coating and the release of Ca2+ from the CaP coating were crucial in regulating the transition of macrophages from M1 to M2 phenotypes. They might activate the PI3K/AKT and cAMP-PKA pathways, respectively, to facilitate M2 polarization. In addition, the osteoimmune microenvironment induced by CaP coated PCL could not only enhance the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in vitro but also promote the bone regeneration in vivo. Taken together, the CaP coating can be employed to control the phenotypic switching of macrophages, thereby creating a beneficial immunomodulatory microenvironment that promotes bone regeneration.

Potential effects of biomaterials on macrophage function and their signalling pathways

The use of biomaterials in biomedicine and healthcare has increased in recent years. Macrophages are the primary immune cells that induce inflammation and tissue repair after implantation of biomaterials. Given that macrophages exhibit high heterogeneity and plasticity, the influence of biomaterials on macrophage phenotype should be considered a crucial evaluation criterion during the development of novel biomaterials. This review provides a comprehensive summary of the physicochemical, biological, and dynamic characteristics of biomaterials that drive the regulation of immune responses in macrophages. The mechanisms involved in the interaction between macrophages and biomaterials, including endocytosis, receptors, signalling pathways, integrins, inflammasomes and long non-coding RNAs, are summarised in this review. In addition, research prospects of the interaction between macrophages and biomaterials are discussed. An in-depth understanding of mechanisms underlying the spatiotemporal changes in macrophage phenotype induced by biomaterials and their impact on macrophage polarization can facilitate the identification and development of novel biomaterials with superior performance. These biomaterials may be used for tissue repair and regeneration, vaccine or drug delivery and immunotherapy.

Mg, Zn Substituted Calcium Phosphates-Thermodynamic Modeling, Biomimetic Synthesis in the Presence of Low-Weight Amino Acids and High Temperature Properties

The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs' enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg2+ and Zn2+ ions and modified with glycine, alanine and valine were first evaluated using a thermodynamic equilibrium model. The influence of the type and concentration of amino acid on the incorporation degree of Mg and Zn into the solid phases was predicted. Experimental studies, designed on the basis of thermodynamic calculations, confirmed the predictions. Amorphous calcium phosphates double-doped with Mg and Zn were biomimetically precipitated and transformed into Mg, Zn-β-tricalcium phosphates (TCP) upon calcination. The Rietveld refinement confirmed that Mg2+ and Zn2+ substituted Ca2+ only at the octahedral sites of β-TCP, and in some cases, fully displacing the Ca2+ from them. The resulting Mg, Zn-β-TCP can serve as a reservoir for Mg and Zn ions when included in the formulation of a biomaterial for bone remodeling. The research conducted reveals the effect of combining mathematical models with experimental studies to pre-evaluate the influence of various additives in the design of materials with predetermined properties.

There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

A The present overview describes various production techniques for biocompatible calcium orthophosphate (abbreviated as CaPO4) deposits (coatings, films and layers) on the surfaces of various types of substrates to impart the biocompatible properties for artificial bone grafts. Since, after being implanted, the grafts always interact with the surrounding biological tissues at the interfaces, their surface properties are considered critical to clinical success. Due to the limited number of materials that can be tolerated in vivo, a new specialty of surface engineering has been developed to desirably modify any unacceptable material surface characteristics while maintaining the useful bulk performance. In 1975, the development of this approach led to the emergence of a special class of artificial bone grafts, in which various mechanically stable (and thus suitable for load-bearing applications) implantable biomaterials and artificial devices were coated with CaPO4. Since then, more than 7500 papers have been published on this subject and more than 500 new publications are added annually. In this review, a comprehensive analysis of the available literature has been performed with the main goal of finding as many deposition techniques as possible and more than 60 methods (double that if all known modifications are counted) for producing CaPO4 deposits on various substrates have been systematically described. Thus, besides the introduction, general knowledge and terminology, this review consists of two unequal parts. The first (bigger) part is a comprehensive summary of the known CaPO4 deposition techniques both currently used and discontinued/underdeveloped ones with brief descriptions of their major physical and chemical principles coupled with the key process parameters (when possible) to inform readers of their existence and remind them of the unused ones. The second (smaller) part includes fleeting essays on the most important properties and current biomedical applications of the CaPO4 deposits with an indication of possible future developments.