Bone Scaffolds Based on Degradable Vaterite/PEG-Composite Microgels

Polydopamine-mediated immobilization of BMP-2 onto electrospun nanofibers enhances bone regeneration

Dealing with bone defects is a significant challenge to global health. Electrospinning in bone tissue engineering has emerged as a solution to this problem. In this study, we designed a PVDF-b-PTFE block copolymer by incorporating TFE, which induced a phase shift in PVDF fromαtoβ, thereby enhancing the piezoelectric effect. Utilizing the electrospinning process, we not only converted the material into a film with a significant surface area and high porosity but also intensified the piezoelectric effect. Then we used polydopamine to immobilize BMP-2 onto PVDF-b-PTFE electrospun nanofibrous membranes, achieving a controlled release of BMP-2. The scaffold's characters were examined using SEM and XRD. To assess its osteogenic effectsin vitro, we monitored the proliferation of MC3T3-E1 cells on the fibers, conducted ARS staining, and measured the expression of osteogenic genes.In vivo, bone regeneration effects were analyzed through micro-CT scanning and HE staining. ELISA assays confirmed that the sustained release of BMP-2 can be maintained for at least 28 d. SEM images and CCK-8 results demonstrated enhanced cell viability and improved adhesion in the experimental group. Furthermore, the experimental group exhibited more calcium nodules and higher expression levels of osteogenic genes, including COL-I, OCN, and RUNX2. HE staining and micro-CT scans revealed enhanced bone tissue regeneration in the defective area of the PDB group. Through extensive experimentation, we evaluated the scaffold's effectiveness in augmenting osteoblast proliferation and differentiation. This study emphasized the potential of piezoelectric PVDF-b-PTFE nanofibrous membranes with controlled BMP-2 release as a promising approach for bone tissue engineering, providing a viable solution for addressing bone defects.

3D printing technology and its combination with nanotechnology in bone tissue engineering

With the graying of the world's population, the morbidity of age-related chronic degenerative bone diseases, such as osteoporosis and osteoarthritis, is increasing yearly, leading to an increased risk of bone defects, while current treatment methods face many problems, such as shortage of grafts and an incomplete repair. Therefore, bone tissue engineering offers an alternative solution for regenerating and repairing bone tissues by constructing bioactive scaffolds with porous structures that provide mechanical support to damaged bone tissue while promoting angiogenesis and cell adhesion, proliferation, and activity. 3D printing technology has become the primary scaffold manufacturing method due to its ability to precisely control the internal pore structure and complex spatial shape of bone scaffolds. In contrast, the fast development of nanotechnology has provided more possibilities for the internal structure and biological function of scaffolds. This review focuses on the application of 3D printing technology in bone tissue engineering and nanotechnology in the field of bone tissue regeneration and repair, and explores the prospects for the integration of the two technologies.

Stimulus-Responsive Hydrogels as Drug Delivery Systems for Inflammation Targeted Therapy

Deregulated inflammations induced by various factors are one of the most common diseases in people's daily life, while severe inflammation can even lead to death. Thus, the efficient treatment of inflammation has always been the hot topic in the research of medicine. In the past decades, as a potential biomaterial, stimuli-responsive hydrogels have been a focus of attention for the inflammation treatment due to their excellent biocompatibility and design flexibility. Recently, thanks to the rapid development of nanotechnology and material science, more and more efforts have been made to develop safer, more personal and more effective hydrogels for the therapy of some frequent but tough inflammations such as sepsis, rheumatoid arthritis, osteoarthritis, periodontitis, and ulcerative colitis. Herein, from recent studies and articles, the conventional and emerging hydrogels in the delivery of anti-inflammatory drugs and the therapy for various inflammations are summarized. And their prospects of clinical translation and future development are also discussed in further detail.

Exploiting Benefits of Vaterite Metastability to Design Degradable Systems for Biomedical Applications

The widespread application of calcium carbonate is determined by its high availability in nature and simplicity of synthesis in laboratory conditions. Moreover, calcium carbonate possesses highly attractive physicochemical properties that make it suitable for a wide range of biomedical applications. This review provides a conclusive analysis of the results on using the tunable vaterite metastability in the development of biodegradable drug delivery systems and therapeutic vehicles with a controlled and sustained release of the incorporated cargo. This manuscript highlights the nuances of vaterite recrystallization to non-porous calcite, dissolution at acidic pH, biodegradation at in vivo conditions and control over these processes. This review outlines the main benefits of vaterite instability for the controlled liberation of the encapsulated molecules for the development of biodegradable natural and synthetic polymeric materials for biomedical purposes.

Cytocompatibility Evaluation of PEG-Methylsulfone Hydrogels

Methylsulfone derivatized poly(ethylene) glycol (PEG) macromers can be biofunctionalized with thiolated ligands and cross-linked with thiol-based cross-linkers to obtain bioactive PEG hydrogels for in situ cell encapsulation. Methylsulfonyl-thiol (MS-SH) reactions present several advantages for this purpose when compared to other thiol-based cross-linking systems. They proceed with adequate and tunable kinetics for encapsulation, they reach a high conversion degree with good selectivity, and they generate stable reaction products. Our previous work demonstrated the cytocompatibility of cross-linked PEG-MS/thiol hydrogels in contact with fibroblasts. However, the cytocompatibility of the in situ MS-SH cross-linking reaction itself, which generates methylsulfinic acid as byproduct at the cross-linked site, remains to be evaluated. These studies are necessary to evaluate the potential of these systems for in vivo applications. Here we perform an extensive cytocompatibility study of PEG hydrogels during in situ cross-linking by the methylsulfonyl-thiol reaction. We compare these results with maleimide-thiol cross-linked PEGs which are well established for cell culture and in vivo experiments and do not involve the release of a byproduct. We show that fibroblasts and endothelial cells remain viable after in situ polymerization of methylsulfonyl-thiol gels on the top of the cell layers. Cell viability seems better than after in situ cross-linking hydrogels with maleimide-thiol chemistry. The endothelial cell proinflammatory phenotype is low and similar to the one obtained by the maleimide-thiol reaction. Finally, no activation of monocytes is observed. All in all, these results demonstrate that the methylsulfonyl-thiol chemistry is cytocompatible and does not trigger high pro-inflammatory responses in endothelial cells and monocytes. These results make methylsulfonyl-thiol chemistries eligible for in vivo testing and eventually clinical application in the future.

Microfluidic Formulation of Topological Hydrogels for Microtissue Engineering

Microfluidics has recently emerged as a powerful tool in generation of submillimeter-sized cell aggregates capable of performing tissue-specific functions, so-called microtissues, for applications in drug testing, regenerative medicine, and cell therapies. In this work, we review the most recent advances in the field, with particular focus on the formulation of cell-encapsulating microgels of small "dimensionalities": "0D" (particles), "1D" (fibers), "2D" (sheets), etc., and with nontrivial internal topologies, typically consisting of multiple compartments loaded with different types of cells and/or biopolymers. Such structures, which we refer to as topological hydrogels or topological microgels (examples including core-shell or Janus microbeads and microfibers, hollow or porous microstructures, or granular hydrogels) can be precisely tailored with high reproducibility and throughput by using microfluidics and used to provide controlled "initial conditions" for cell proliferation and maturation into functional tissue-like microstructures. Microfluidic methods of formulation of topological biomaterials have enabled significant progress in engineering of miniature tissues and organs, such as pancreas, liver, muscle, bone, heart, neural tissue, or vasculature, as well as in fabrication of tailored microenvironments for stem-cell expansion and differentiation, or in cancer modeling, including generation of vascularized tumors for personalized drug testing. We review the available microfluidic fabrication methods by exploiting various cross-linking mechanisms and various routes toward compartmentalization and critically discuss the available tissue-specific applications. Finally, we list the remaining challenges such as simplification of the microfluidic workflow for its widespread use in biomedical research, bench-to-bedside transition including production upscaling, further in vivo validation, generation of more precise organ-like models, as well as incorporation of induced pluripotent stem cells as a step toward clinical applications.

Multiparametric Material Functionality of Microtissue-Based In Vitro Models as Alternatives to Animal Testing

With the definition of the 3R principle by Russel and Burch in 1959, the search for an adequate substitute for animal testing has become one of the most important tasks and challenges of this time, not only from an ethical, but also from a scientific, economic, and legal point of view. Microtissue-based in vitro model systems offer a valuable approach to address this issue by accounting for the complexity of natural tissues in a simplified manner. To increase the functionality of these model systems and thus make their use as a substitute for animal testing more likely in the future, the fundamentals need to be continuously improved. Corresponding requirements exist in the development of multifunctional, hydrogel-based materials, whose properties are considered in this review under the aspects of processability, adaptivity, biocompatibility, and stability/degradability.

Translating Therapeutic Microgels into Clinical Applications

Microgels are crosslinked, water-swollen networks with a 10 nm to 100 µm diameter and can be modified chemically or biologically to render them biocompatible for advanced clinical applications. Depending on their intended use, microgels require different mechanical and structural properties, which can be engineered on demand by altering the biochemical composition, crosslink density of the polymer network, and the fabrication method. Here, the fundamental aspects of microgel research and development, as well as their specific applications for theranostics and therapy in the clinic, are discussed. A detailed overview of microgel fabrication techniques with regards to their intended clinical application is presented, while focusing on how microgels can be employed as local drug delivery materials, scavengers, and contrast agents. Moreover, microgels can act as scaffolds for tissue engineering and regeneration application. Finally, an overview of microgels is given, which already made it into pre-clinical and clinical trials, while future challenges and chances are discussed. This review presents an instructive guideline for chemists, material scientists, and researchers in the biomedical field to introduce them to the fundamental physicochemical properties of microgels and guide them from fabrication methods via characterization techniques and functionalization of microgels toward specific applications in the clinic.

Recent approaches towards bone tissue engineering

Bone tissue engineering approaches have evolved towards addressing the challenges of tissue mimetic requirements over the years. Different strategies have been combining scaffolds, cells, and biologically active cues using a wide range of fabrication techniques, envisioning the mimicry of bone tissue. On the one hand, biomimetic scaffold-based strategies have been pursuing different biomaterials to produce scaffolds, combining with diverse and innovative fabrication strategies to mimic bone tissue better, surpassing bone grafts. On the other hand, biomimetic scaffold-free approaches mainly foresee replicating endochondral ossification, replacing hyaline cartilage with new bone. Finally, since bone tissue is highly vascularized, new strategies focused on developing pre-vascularized scaffolds or pre-vascularized cellular aggregates have been a motif of study. The recent biomimetic scaffold-based and scaffold-free approaches in bone tissue engineering, focusing on materials and fabrication methods used, are overviewed herein. The biomimetic vascularized approaches are also discussed, namely the development of pre-vascularized scaffolds and pre-vascularized cellular aggregates.

Osteogenic Capability of Vaterite-Coated Nonwoven Polycaprolactone Scaffolds for In Vivo Bone Tissue Regeneration

In current orthopedic practice, bone implants used to-date often exhibit poor osteointegration, impaired osteogenesis, and, eventually, implant failure. Actively pursued strategies for tissue engineering could overcome these shortcomings by developing new hybrid materials with bioinspired structure and enhanced regenerative potential. In this study, the osteogenic and therapeutic potential of bioactive vaterite is investigated as a functional component of a fibrous polymeric scaffold for bone regeneration. Hybrid two-layered polycaprolactone scaffolds coated with vaterite (PCL/CaCO₃ ) are studied during their 28-days implantation period in a rat femur defect. After this period, the study of tissue formation in the defected area is performed by the histological study of femur cross-sections. Immobilization of alkaline phosphatase (ALP) into PCL/CaCO₃ scaffolds accelerates new bone tissue formation and defect repair. PCL/CaCO₃ and PCL/CaCO₃ /ALP scaffolds reveal 37.3% and 62.9% areas, respectively, filled with newly formed bone tissue in cross-sections compared to unmineralized PCL scaffold (17.5%). Bone turnover markers are monitored on the 7th and 28th days after implantation and reveal an increase of osteocalcin level for both PCL/CaCO₃ and PCL/CaCO₃ /ALP compared with PCL indicating the activation of osteogenesis. These findings indicate that vaterite, as an osteoconductive component of polymeric scaffolds, promotes osteogenesis, supports angiogenesis, and facilitates bone defect repair.

Rational Design of Thermoresponsive Microgel Templates with Polydopamine Surface Coating for Microtissue Applications

Functional microgels provide a versatile basis for synthetic in vitro platforms as alternatives to animal experiments. The tuning of the physical, chemical, and biological properties of synthetic microgels can be achieved by blending suitable polymers and formulating them such to reflect the heterogenous and complex nature of biological tissues. Based on this premise, this paper introduces the development of volume-switchable core-shell microgels as 3D templates to enable cell growth for microtissue applications, using a systematic approach to tune the microgel properties based on a deep conceptual and practical understanding. Microscopic microgel design, such as the tailoring of the microgel size and spherical shape, is achieved by droplet-based microfluidics, while on a nanoscopic scale, a thermoresponsive polymer basis, poly(N-isopropylacrylamide) (PNIPAAm), is used to provide the microgel volume switchability. Since PNIPAAm has only limited cell-growth promoting properties, the cell adhesion on the microgel is further improved by surface modification with polydopamine, which only slightly affects the microgel properties, thereby simplifying the system. To further tune the microgel thermoresponsiveness, different amounts of N-hydroxyethylacrylamide are incorporated into the PNIPAAm network. In a final step, cell growth on the microgel surface is investigated, both at a single microgel platform and in spheroidal cell structures.

Triply-responsive OEG-based microgels and hydrogels: regulation of swelling ratio, volume phase transition temperatures and mechanical properties

Facile methods to coordinate swelling ratio, volume-phase transition temperatures and mechanical properties for pH-, thermal-, and cationic-responsive microgels and hydrogels.

Effect Of Local Modulation In Enzymatic Homeostasis On Bone Turnover Marker Dynamics In Blood At Substituting Femur Defects With Vaterite Scaffolds

The goal of this research was the investigation of concentration changes in the blood bone turnover markers during local modulation of enzymatic homeostasis by means of targeted delivery of alkaline phosphatase (ALP) with polycaprolactone (PCL) and vaterite (VT) scaffolds implanted into the femur defects in white rats. Material and Methods ― The tests of PCL/VT/ALP scaffold implantations into the bone defects were performed on 30 white rats, and the serum of intact animals was used as the control. ELISA and multiplex assay were used to find inflammatory and bone turnover markers including monocyte chemoattractant-1, sclerostin, fibroblast growth factor-23, connective tissue growth factor (CTGF), osteoprotegerin, osteocalcin, β-сross laps and the activity of tartrate-resistant acid phosphatase-5b in the blood of experimental animals. The activity of serum ALP was tested with the conventional kinetic method. The morphology of the reparative processes was verified by microscopy of specimens taken from the implantation areas and stained with hematoxylin or eosin. Results ― The PCL/VT/ALP scaffold implantations into the bone defects of white rats caused active osteogenesis along with the steady rise in osteocalcin concentration in blood. ALP activity in the blood did not depend on the exogenous enzyme in the scaffold and rose by the 28th day after the implantations. The targeted ALP delivery into the defect area caused the rise in CTGF concentration as well as the decrease in blood sclerostin within a short time after the implantations. Conclusion ― The modulation of the local enzyme homeostasis by means of the targeted ALP delivery with PCL/VT scaffolds stimulated reparative osteogenesis within a short time after the implantations with no changes to the bloodstream or local inflammatory changes suggesting their biocompatibility and the safety in use.