Ultra-low binder content 3D printed calcium phosphate graphene scaffolds as resorbable, osteoinductive matrices that support bone formation in vivo.

Bone regenerative engineering could replace autografts; however, no synthetic material fulfills all design criteria. Nanocarbons incorporated into three-dimensional printed (3DP) matrices can improve properties, but incorporation is constrained to low wt%. Further, unmodified nanocarbons have limited osteogenic potential. Functionalization to calcium phosphate graphene (CaPG) imparts osteoinductivity and osteoconductivity, but loading into matrices remained limited. This work presents ultra-high content (90%), 3DP-CaPG matrices. 3DP-CaPG matrices are highly porous (95%), moderately stiff (3 MPa), and mechanically robust. In vitro, they are cytocompatible and induce osteogenic differentiation of human mesenchymal stem cells (hMSCs), indicated by alkaline phosphatase, mineralization, and COL1α1 expression. In vivo, bone regeneration was studied using a transgenic fluorescent-reporter mouse non-union calvarial defect model. 3DP-CaPG stimulates cellular ingrowth, retains donor cells, and induces osteogenic differentiation. Histology shows TRAP staining around struts, suggesting potential osteoclast activity. Apparent resorption of 3DP-CaPG was observed and presented no toxicity. 3DP-CaPG represents an advancement towards a synthetic bone regeneration matrix.

Graphene-Based Biomaterials for Bone Regenerative Engineering: A Comprehensive Review of the Field and Considerations Regarding Biocompatibility and Biodegradation.

Graphene and its derivatives have continued to garner worldwide interest due to their unique characteristics. Having expanded into biomedical applications, there have been efforts to employ their exceptional properties for the regeneration of different tissues, particularly bone. This article presents a comprehensive review on the usage of graphene-based materials for bone regenerative engineering. The graphene family of materials (GFMs) are used either alone or in combination with other biomaterials in the form of fillers in composites, coatings for both scaffolds and implants, or vehicles for the delivery of various signaling and therapeutic agents. The applications of the GFMs in each of these diverse areas are discussed and emphasis is placed on the characteristics of the GFMs that have implications in this regard. In tandem and of importance, this article evaluates the safety and biocompatibility of the GFMs and carefully elucidates how various factors influence the biocompatibility and biodegradability of this new class of nanomaterials. In conclusion, the challenges and opportunities regarding the use of the GFMs in regenerative engineering applications are discussed, and future perspectives for the developments in this field are proposed.

Fabrication and characterization of mechanically competent 3D printed polycaprolactone-reduced graphene oxide scaffolds.

The ability to produce constructs with a high control over the bulk geometry and internal architecture has situated 3D printing as an attractive fabrication technique for scaffolds. Various designs and inks are actively investigated to prepare scaffolds for different tissues. In this work, we prepared 3D printed composite scaffolds comprising polycaprolactone (PCL) and various amounts of reduced graphene oxide (rGO) at 0.5, 1, and 3 wt.%. We employed a two-step fabrication process to ensure an even mixture and distribution of the rGO sheets within the PCL matrix. The inks were prepared by creating composite PCL-rGO films through solvent evaporation casting that were subsequently fed into the 3D printer for extrusion. The resultant scaffolds were seamlessly integrated, and 3D printed with high fidelity and consistency across all groups. This, together with the homogeneous dispersion of the rGO sheets within the polymer matrix, significantly improved the compressive strength and stiffness by 185% and 150%, respectively, at 0.5 wt.% rGO inclusion. The in vitro response of the scaffolds was assessed using human adipose-derived stem cells. All scaffolds were cytocompatible and supported cell growth and viability. These mechanically reinforced and biologically compatible 3D printed PCL-rGO scaffolds are a promising platform for regenerative engineering applications.

Emergence of the Stem Cell Secretome in Regenerative Engineering.

The secretome is defined as the set of molecules and biological factors that are secreted by cells into the extracellular space. In the past decade, secretome-based therapies have emerged as a promising approach to overcome the limitations associated with cell-based therapies for tissue and organ regeneration. Considering the growing number of recent publications related to secretome-based therapies, this review takes a step-by-step engineering approach to evaluate the role of the stem cell secretome in regenerative engineering. We discuss the functional benefits of the secretome, the techniques used to engineer the secretome and tailor its therapeutic effects, and the delivery systems and strategies that have been developed to use the secretome for tissue regeneration.

Regenerative engineered vascularized bone mediated by calcium peroxide.

One of the main challenges hindering the clinical translation of bone tissue engineering scaffolds is the lack of establishment of functional vasculature. Insufficient vascularization and poor oxygen supply limit cell survival within the constructs resulting in poor osseointegration with the host tissue and eventually leading to inadequate bone regeneration. Inspired by cues from developmental biology, we regenerative engineered a composite matrix by incorporating calcium peroxide (CaO2 ) into poly(lactide-co-glycolide) (PLGA) microsphere-based matrices and sought to assess whether the delivery of the byproducts of CaO2 decomposition, namely O2 , Ca2+ , and H2 O2 could enhance the regeneration of vascularized bone tissue. The composite microspheres were successfully fabricated via the oil-in-water emulsion method. The presence and encapsulation of CaO2 was confirmed using scanning electron microscopy, energy dispersive x-ray spectroscopy, thermogravimetric analysis, and X-ray powder diffraction. The microspheres were further heat sintered into three-dimensional porous scaffolds and characterized for their degradation and release of byproducts. The in vitro cytocompatibility of the matrices and their ability to support osteogenic differentiation was confirmed using human adipose-derived stem cells. Lastly, an in vivo study was performed in a mouse critical-sized calvarial defect model to evaluate the capacity of these matrices in supporting vascularized bone regeneration. Results demonstrated that the presence of CaO2 increased cellularization and biological activity throughout the matrices. There was greater migration of host cells to the interior of the matrices and greater survival and persistence of donor cells after 8 weeks, which in synergy with the composite matrices led to enhanced vascularized bone regeneration.

Phosphate graphene as an intrinsically osteoinductive scaffold for stem cell-driven bone regeneration.

Synthetic, resorbable scaffolds for bone regeneration have potential to transform the clinical standard of care. Here, we demonstrate that functional graphenic materials (FGMs) could serve as an osteoinductive scaffold: recruiting native cells to the site of injury and promoting differentiation into bone cells. By invoking a Lewis acid-catalyzed Arbuzov reaction, we are able to functionalize graphene oxide (GO) to produce phosphate graphenes (PGs) with unprecedented control of functional group density, mechanical properties, and counterion identity. In aqueous environments, PGs release inducerons, including Ca2+ and PO43- Calcium phosphate graphene (CaPG) intrinsically induces osteogenesis in vitro and in the presence of bone marrow stromal cells (BMSCs), can induce ectopic bone formation in vivo. Additionally, an FGM can be made by noncovalently loading GO with the growth factor recombinant human bone morphogenetic protein 2 (rhBMP-2), producing a scaffold that induces ectopic bone formation with or without BMSCs. The FGMs reported here are intrinsically inductive scaffolds with significant potential to revolutionize the regeneration of bone.

Skeletal Muscle Regenerative Engineering.

Skeletal muscles have the intrinsic ability to regenerate after minor injury, but under certain circumstances such as severe trauma from accidents, chronic diseases or battlefield injuries the regeneration process is limited. Skeletal muscle regenerative engineering has emerged as a promising approach to address this clinical issue. The regenerative engineering approach involves the convergence of advanced materials science, stem cell science, physical forces, insights from developmental biology, and clinical translation. This article reviews recent studies showing the potential of the convergences of technologies involving biomaterials, stem cells and bioactive factors in concert with clinical translation, in promoting skeletal muscle regeneration. Several types of biomaterials such as electrospun nanofibers, hydrogels, patterned scaffolds, decellularized tissues, and conductive matrices are being investigated. Detailed discussions are given on how these biomaterials can interact with cells and modulate their behavior through physical, chemical and mechanical cues. In addition, the application of physical forces such as mechanical and electrical stimulation are reviewed as strategies that can further enhance muscle contractility and functionality. The review also discusses established animal models to evaluate regeneration in two clinically relevant muscle injuries; volumetric muscle loss (VML) and muscle atrophy upon rotator cuff injury. Regenerative engineering approaches using advanced biomaterials, cells, and physical forces, developmental cues along with insights from immunology, genetics and other aspects of clinical translation hold significant potential to develop promising strategies to support skeletal muscle regeneration.

The roles of ions on bone regeneration.

Bone scientists are actively investigating a range of methods to promote skeletal tissue regeneration. A review of recent literature has revealed that several ions are uniquely capable of inducing stem cell differentiation down desired lineages. There exists enormous promise for these ions to be used in bone regenerative medicine. Given that these ions can be released from biodegradable polymeric materials, their long-term delivery can be achieved through a variety of controlled-release strategies compared with the relatively few options available for expensive and fragile polypeptide-based growth factors. In this review, we highlight the developments in using ions in conjunction with biomaterials for bone regeneration.

Enhanced osteogenic differentiation of stem cells via microfluidics synthesized nanoparticles.

Advancement of bone tissue engineering as an alternative for bone regeneration has attracted significant interest due to its potential in reducing the costs and surgical trauma affiliated with the effective treatment of bone defects. We have improved the conventional approach of producing polymeric nanoparticles, as one of the most promising choices for drug delivery systems, using a microfluidics platform, thus further improving our control over osteogenic differentiation of mesenchymal stem cells. Molecular dynamics simulations were carried out for theoretical understanding of our experiments in order to get a more detailed molecular-scale insight into the drug-carrier interactions. In this work, with the sustained intracellular delivery of dexamethasone from microfluidics-synthesized nanoparticles, we explored the effects of particle design on controlling stem cell fates. We believe that the insights learned from this work will lead to the discovery of new strategies to tune differentiation for in situ differentiation or stem cell therapeutics. FROM THE CLINICAL EDITOR: The use of mesenchymal stem cells has been described by many researchers as a novel therapy for bone regeneration. One major hurdle in this approach is the control of osteogenic differentiation. In this article, the authors described elegantly their microfluidic system in which dexamethasone loaded nanoparticles were produced. This system would allow precise fabrication of nanoparticles and consequently higher efficiency in cellular differentiation.