Clinical Application of Bone Morphogenetic Protein-2 Microcarriers Fabricated by the Cryopolymerization of Gelatin Methacrylate for the Treatment of Radial Fracture in Two Dogs

Development of nanocomposite hydrogel using citrate-containing amorphous calcium phosphate and gelatin methacrylate

Nanocomposite hydrogels are suitable in bone tissue engineering due to their resemblance with the extracellular matrix, ability to match complex geometries, and ability to provide a framework for cell attachment and proliferation. The nanocomposite hydrogel comprises organic and inorganic counterparts. Gelatin methacrylate (GELMA) is an extensively used organic biomaterial in tissue engineering due to its excellent biocompatibility, biodegradability, and bioactivity. The photo-crosslinking of GELMA presents a challenge when aiming to create thicker nanocomposite hydrogels due to opacity induced by fillers, which obstructs the penetration of ultraviolet (UV) light. Therefore, using a chemical crosslinking approach, we have developed nanocomposite GELMA hydrogel in this study by incorporating citrate-containing amorphous calcium phosphate (ACP_CIT). Ammonium persulfate (APS) and Tetramethylethylenediamine (TEMED) were deployed to crosslink the methacrylate group of GELMA. The oscillatory shear tests have confirmed that crosslinking enhances both storage (G') and loss modulus (G″) of GELMA. Subsequently, incorporation of ACP_CIT in GELMA hydrogel shows further enhancement in G' and G″ values. In vitro analysis of the developed hydrogels revealed that chemical crosslinking and incorporation of ACP_CIT do not compromise the cytocompatibility of the GELMA. Hence, for developing nanocomposite GELMA hydrogels employing APS/TEMED crosslinking emerges as a promising alternative to photo-crosslinking.

An Overview on Collagen and Gelatin-Based Cryogels: Fabrication, Classification, Properties and Biomedical Applications

Decades of research into cryogels have resulted in the development of many types of cryogels for various applications. Collagen and gelatin possess nontoxicity, intrinsic gel-forming ability and physicochemical properties, and excellent biocompatibility and biodegradability, making them very desirable candidates for the fabrication of cryogels. Collagen-based cryogels (CBCs) and gelatin-based cryogels (GBCs) have been successfully applied as three-dimensional substrates for cell culture and have shown promise for biomedical use. A key point in the development of CBCs and GBCs is the quantitative and precise characterization of their properties and their correlation with preparation process and parameters, enabling these cryogels to be tuned to match engineering requirements. Great efforts have been devoted to fabricating these types of cryogels and exploring their potential biomedical application. However, to the best of our knowledge, no comprehensive overviews focused on CBCs and GBCs have been reported currently. In this review, we attempt to provide insight into the recent advances on such kinds of cryogels, including their fabrication methods and structural properties, as well as potential biomedical applications.

Potential and recent advances of microcarriers in repairing cartilage defects

Articular cartilage regeneration is one of the challenges faced by orthopedic surgeons. Microcarrier applications have made great advances in cartilage tissue engineering in recent years and enable cost-effective cell expansion, thus providing permissive microenvironments for cells. In addition, microcarriers can be loaded with proteins, factors, and drugs for cartilage regeneration. Some microcarriers also have the advantages of injectability and targeted delivery. The application of microcarriers with these characteristics can overcome the limitations of traditional methods and provide additional advantages. In terms of the transformation potential, microcarriers have not only many advantages, such as providing sufficient and beneficial cells, factors, drugs, and microenvironments for cartilage regeneration, but also many application characteristics; for example, they can be injected to reduce invasiveness, transplanted after microtissue formation to increase efficiency, or combined with other stents to improve mechanical properties. Therefore, this technology has enormous potential for clinical transformation. In this review, we focus on recent advances in microcarriers for cartilage regeneration. We compare the characteristics of microcarriers with other methods for repairing cartilage defects, provide an overview of the advantages of microcarriers, discuss the potential of microcarrier systems, and present an outlook for future development.

Translational potential of this article

We reviewed the advantages and recent advances of microcarriers for cartilage regeneration. This review could give many scholars a better understanding of microcarriers, which can provide doctors with potential methods for treating patients with cartilage injure.

Macrophage Polarization and Osteoporosis: A Review

Over 200 million people suffer from osteoporosis worldwide. Individuals with osteoporosis have increased rates of bone resorption while simultaneously having impaired osteogenesis. Most current treatments for osteoporosis focus on anti-resorptive methods to prevent further bone loss. However, it is important to identify safe and cost-efficient treatments that not only inhibit bone resorption, but also stimulate anabolic mechanisms to upregulate osteogenesis. Recent data suggest that macrophage polarization may contribute to osteoblast differentiation and increased osteogenesis as well as bone mineralization. Macrophages exist in two major polarization states, classically activated macrophages (M1) and alternatively activated macrophage (M2) macrophages. The polarization state of macrophages is dependent on molecules in the microenvironment including several cytokines and chemokines. Mechanistically, M2 macrophages secrete osteogenic factors that stimulate the differentiation and activation of pre-osteoblastic cells, such as mesenchymal stem cells (MSC’s), and subsequently increase bone mineralization. In this review, we cover the mechanisms by which M2 macrophages contribute to osteogenesis and postulate the hypothesis that regulating macrophage polarization states may be a potential treatment for the treatment of osteoporosis.

Overcoming barriers confronting application of protein therapeutics in bone fracture healing

Bone fracture is a major contributor to debilitation and death among patients with bone diseases. Thus, osteogenic protein therapeutics and their delivery to bone have been extensively researched as strategies to accelerate fracture healing. To prevent morbidity and mortality of fractures, which occur frequently in the aging population, there is a critical need for development of first-line therapeutics. Bone morphogenic protein-2 (BMP-2) has been at the forefront of bone regeneration research for its potent osteoinduction, despite safety concerns and biophysiological obstacles of delivery to bone. However, continued pursuit of osteoinductive proteins as a therapeutic option is largely aided by drug delivery systems, playing an imperative role in enhancing safety and efficacy. In this work, we highlighted several types of drug delivery platforms and their biomaterials, to evaluate the suitability in overcoming challenges of therapeutic protein delivery for bone regeneration. To showcase the clinical considerations for each type of platform, we have assessed the most common route of administration strategies for bone regeneration, classifying the platforms as implantable or injectable. Additionally, we have analyzed the commonly utilized models and methodology for safety and efficacy evaluation of these osteogenic protein-loaded systems, to present clinical opinions for future directions of research in this field. It is hoped that this review will promote research and development of clinically translatable osteogenic protein therapeutics, while targeting first-line treatment status for achieving desired outcomes of fracture healing. Graphical abstract.

Recent advances in the use of microcarriers for cell cultures and their ex vivo and in vivo applications

Microcarriers are 100- to 300-micron support matrices that permit the growth of adherent cells in bioreactor systems. They have a larger surface area to volume ratio in comparison to single cell monolayers, enabling cost-effective cell production and expansion. Microcarriers are composed of a solid matrix that must be separated from expanded cells during downstream processing stages. The detachment method is chosen on the basis of several factors like cell type, microcarrier surface chemistry, cell confluency and degree of aggregation. The development of microcarriers with a range of physiochemical properties permit controlled cell and protein associations that hold utility for novel therapeutics. In this review, we provide an overview of the recent advances in microcarrier cell culture technology. We also discuss its significance as an ex vivo research tool and the therapeutic potential of newly designed microcarrier systems in vivo.