A modular design strategy to integrate mechanotransduction concepts in scaffold-based bone tissue engineering

Unraveling the influence of channel size and shape in 3D printed ceramic scaffolds on osteogenesis

Bone has the capacity to regenerate itself for relatively small defects; however, this regenerative capacity is diminished in critical-size bone defects. The development of synthetic materials has risen as a distinct strategy to address this challenge. Effective synthetic materials to have emerged in recent years are bioceramic implants, which are biocompatible and highly bioactive. Yet nothing suitable for the repair of large bone defects has made the transition from laboratory to clinic. The clinical success of bioceramics has been shown to depend not only on the scaffold's intrinsic material properties but also on its internal porous geometry. This study aimed to systematically explore the implications of varying channel size, shape, and curvature in tissue scaffolds on in vivo bone regeneration outcomes. 3D printed bioceramic scaffolds with varying channel sizes (0.3 mm to 1.5 mm), shapes (circular vs rectangular), and curvatures (concave vs convex) were implanted in rabbit femoral defects for 8 weeks, followed by histological evaluation. We demonstrated that circular channel sizes of around 0.9 mm diameter significantly enhanced bone formation, compared to channel with diameters of 0.3 mm and 1.5 mm. Interestingly, varying channel shapes (rectangular vs circular) had no significant effect on the volume of newly formed bone. Furthermore, the present study systematically demonstrated the beneficial effect of concave surfaces on bone tissue growth in vivo, reinforcing previous in silico and in vitro findings. This study demonstrates that optimizing architectural configurations within ceramic scaffolds is crucial in enhancing bone regeneration outcomes. STATEMENT OF SIGNIFICANCE: Despite the explosion of work on developing synthetic scaffolds to repair bone defects, the amount of new bone formed by scaffolds in vivo remains suboptimal. Recent studies have illuminated the pivotal role of scaffolds' internal architecture in osteogenesis. However, these investigations have mostly remained confined to in silico and in vitro experiments. Among the in vivo studies conducted, there has been a lack of systematic analysis of individual architectural features. Herein, we utilized bioceramic 3D printing to conduct a systematic exploration of the effects of channel size, shape, and curvature on bone formation in vivo. Our results demonstrate the significant influence of channel size and curvature on in vivo outcomes. These findings provide invaluable insights into the design of more effective bone scaffolds.

A well plate-based GelMA photo-crosslinking system with tunable hydrogel mechanical properties to regulate the PTH-mediated osteogenic fate

Versatile and efficient regulation of the mechanical properties of the extracellular matrix is crucial not only for understanding the dynamic changes in biological systems, but also for obtaining precise and effective cellular responses in drug testing. In this study, we developed a well plate-based hydrogel photo-crosslinking system to effectively control the mechanical properties of hydrogels and perform high-throughput assays. We improved cell biocompatibility by using gelatin methacryloyl (GelMA) with a visible light photo-crosslinking method. Multiple cell-laden GelMA hydrogels were simultaneously and uniformly created using multi-arrayed 520 nm light-emitting diodes in a well plate format. The elastic modulus of the hydrogels can be widely adjusted (0.5-30 kPa) using a photo-crosslinking system capable of independently controlling the light intensity or exposure time for multiple samples. We demonstrate the feasibility of our system by observing enhanced bone differentiation of human mesenchymal stem cells (hMSCs) cultured on stiffer hydrogels. Additionally, we observed that the osteogenic fate of hMSCs, affected by the different mechanical properties of the gel, was regulated by parathyroid hormone (PTH). Notably, in response to PTH, hMSCs in a high-stiffness microenvironment upregulate osteogenic differentiation while exhibiting increased proliferation in a low-stiffness microenvironment. Overall, the developed system enables the generation of multiple cell-laden three-dimensional cell culture models with diverse mechanical properties and holds significant potential for expansion into drug testing.

Three-Dimensional Modeling with Osteoblast-like Cells under External Magnetic Field Conditions Using Magnetic Nano-Ferrite Particles for the Development of Cell-Derived Artificial Bone

The progress in artificial bone research is crucial for addressing fractures and bone defects in the aging population. However, challenges persist in terms of biocompatibility and structural complexity. Nanotechnology provides a promising avenue by which to overcome these challenges, with nano-ferrite particles (NFPs) exhibiting superparamagnetic properties. The ability to control cell positioning using a magnetic field opens up new possibilities for customizing artificial bones with specific shapes. This study explores the biological effects of NFPs on osteoblast-like cell lines (MC3T3-E1), including key analyses, such as cell viability, cellular uptake of NFPs, calcification processes, cell migration under external magnetic field conditions, and three-dimensional modeling. The results indicate that the impact of NFPs on cell proliferation is negligible. Fluorescence and transmission electron microscopy validated the cellular uptake of NFPs, demonstrating the potential for precise cell positioning through an external magnetic field. Under calcification-inducing conditions, the cells exhibited sustained calcification ability even in the presence of NFPs. The cell movement analysis observed the controlled movement of NFP-absorbing cells under an external magnetic field. Applying a magnetic field along the z-axis induced the three-dimensional shaping of cells incorporating NFPs, resulting in well-arranged z-axis directional patterns. In this study, NFPs demonstrated excellent biocompatibility and controllability under an external magnetic field, laying the foundation for innovative treatment strategies for customizing artificial bones.

Advancements in the pathogenesis of hepatic osteodystrophy and the potential therapeutic of mesenchymal stromal cells

Hepatic osteodystrophy (HOD) is a metabolically associated bone disease mainly manifested as osteoporosis with the characteristic of bone loss induced by chronic liver disease (CLD). Due to its high incidence in CLD patients and increased risk of fracture, the research on HOD has received considerable interest. The specific pathogenesis of HOD has not been fully revealed. While it is widely believed that disturbance of hormone level, abnormal secretion of cytokines and damage of intestinal barrier caused by CLD might jointly affect the bone metabolic balance of bone formation and bone absorption. At present, the treatment of HOD is mainly to alleviate the bone loss by drug treatment, but the efficacy and safety are not satisfactory. Mesenchymal stromal cells (MSCs) are cells with multidirectional differentiation potential, cell transplantation therapy based on MSCs is an emerging therapeutic approach. This review mainly summarized the pathogenesis and treatment of HOD, reviewed the research progress of MSCs therapy and the combination of MSCs and scaffolds in the application of osteoporotic bone defects, and discussed the potential and limitations of MSCs therapy, providing theoretical basis for subsequent studies.

Modeling of the PHEMA-gelatin scaffold enriched with graphene oxide utilizing finite element method for bone tissue engineering

The development of computer-aided facilities has contributed to the optimization of tissue engineering techniques due to the reduction in necessary practical assessments and the removal of animal or human-related ethical issues. Herein, a bone scaffold based on poly (2-hydroxyethyl methacrylate) (PHEMA), gelatin and graphene oxide (GO), was simulated by SOLIDWORKS and ABAQUS under a normal compression force using finite element method (FEM). Concerning the mechanotransduction impact, GO could support the stability of the structure and reduce the possibility of the failure resulting in the integrity and durability of the scaffold efficiency which would be beneficial for osteogenic differentiation.

Nondeterministic multiobjective optimization of 3D printed ceramic tissue scaffolds

Despite significant advances in the design optimization of bone scaffolds for enhancing their biomechanical properties, the functionality of these synthetic constructs remains suboptimal. One of the main challenges in the structural optimization of bone scaffolds is associated with the large uncertainties caused by the manufacturing process, such as variations in scaffolds' geometric features and constitutive material properties after fabrication. Unfortunately, such non-deterministic issues have not been considered in the existing optimization frameworks, thereby limiting their reliability. To address this challenge, a novel multiobjective robust optimization approach is proposed here such that the effects of uncertainties on the optimized design can be minimized. This study first conducted computational analyses of a parameterized ceramic scaffold model to determine its effective modulus, structural strength, and permeability. Then, surrogate models were constructed to formulate explicit mathematical relationships between the geometrical parameters (design variables) and mechanical and fluidic properties. The Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to generate the robust Pareto solutions for an optimal set of trade-offs between the competing objective functions while ensuring the effects of the noise parameters to be minimal. Note that the nondeterministic optimization of tissue scaffold presented here is the first of its kind in open literature, which is expected to shed some light on this significant topic of scaffold design and additive manufacturing in a more realistic way.

Criteria, Challenges, and Opportunities for Acellularized Allogeneic/Xenogeneic Bone Grafts in Bone Repairing

As bone grafts become more commonly needed by patients and as donors become scarcer, acellularized bone grafts (ABGs) are becoming more popular for restorative purposes. While autogeneic grafts are reliable as a gold standard, allogeneic and xenogeneic ABGs have been shown to be of particular interest due to the limited availability of autogeneic resources and reduced patient well-being in long-term surgeries. Because of the complete similarity of their structures with native bone, excellent mechanical properties, high biocompatibility, and similarities of biological behaviors (osteoinductive and osteoconductive) with local bones, successful outcomes of allogeneic and xenogeneic ABGs in both in vitro and in vivo research have raised hopes of repairing patients' bone injuries in clinical applications. However, clinical trials have been delayed due to a lack of standardized protocols pertaining to acellularization, cell seeding, maintenance, and diversity of ABG evaluation criteria. This study sought to uncover these factors by exploring the bone structures, ossification properties of ABGs, sources, benefits, and challenges of acellularization approaches (physical, chemical, and enzymatic), cell loading, and type of cells used and effects of each of the above items on the regenerative technologies. To gain a perspective on the repair and commercialization of products before implementing new research activities, this study describes the differences between ABGs created by various techniques and methods applied to them. With a comprehensive understanding of ABG behavior, future research focused on treating bone defects could provide a better way to combine the treatment approaches needed to treat bone defects.

Manufacturing, characterization, and degradation of a poly(lactic acid) warp-knitted spacer fabric scaffold as a candidate for tissue engineering applications

Three-dimensional bioabsorbable textiles represent a novel technology for the manufacturing of tissue engineering scaffolds. In the present study, 3D bioabsorbable poly(lactic acid) (PLA) spacer fabric scaffolds are fabricated by warp-knitting and their potential for tissue engineering is explored in vitro. Changes in physical properties and mechanical performance with different heat setting treatments are assessed. To characterize the microenvironment experienced by cells in the scaffolds, yarn properties are investigated prior to, and during, hydrolytic degradation. The differences in yarn morphology, thermal properties, infrared spectra, and mechanical properties are investigated and monitored during temperature accelerated in vitro degradation tests in phosphate buffered saline (PBS) solution at 58 °C and pH 7.4 for 55 days. Yarn and textile cytocompatibility are tested to assess the effect of materials employed, manufacturing conditions, post processing and sterilization on cell viability, together with the cytocompatibility of the textile degradation products. Results show that the heat setting process can be used to modify scaffold properties, such as thickness, porosity, pore size and stiffness within the range useful for tissue regeneration. Scaffold degradation rate in physiological conditions is estimated by comparing yarn degradation data with PLA degradation data from literature. This will potentially allow the prediction of scaffold mechanical stability in the long term and thus its suitability for the remodelling of different tissues. Mouse calvaria preosteoblast MC3T3-E1 cells attachment and proliferation are observed on the scaffold over 12 days of in vitro culture by 4',6-diamidino-2-phenylindole (DAPI) fluorescent staining and DNA quantification. The present work shows the potential of spacer fabric scaffolds as a versatile and scalable scaffold fabrication technique, having the ability to create a microenvironment with appropriate physical, mechanical, and degradation properties for 3D tissue engineering. The high control and tunability of spacer fabric properties makes it a promising candidate for the regeneration of different tissues in patient-specific applications.

Preparation, properties and application of graphene-based materials in tissue engineering scaffolds

Tissue engineering has great application prospect as an effective treatment for tissue and organ injury, functional reduction or loss. Bioactive tissues are reconstructed and damaged organs are repaired by the three elements including cells, scaffold materials and growth factors. Graphene-based composites can be used as reinforcing auxiliary materials for tissue scaffold preparation because of their large specific surface area, and good mechanical support. Tissue engineering scaffolds with graphene-based composites have been widely studied. Part of research have focused on the application of graphene-based composites in single tissue engineering; The basic principles of graphene materials used in tissue engineering are summarized in some researches. Some studies emphasized the key problems and solutions urgently needed to be solved in the development of tissue engineering, and discussed their application prospect. Some related studies mainly focused on the conductivity of graphene, and discussed the application of electroactive scaffolds in tissue engineering. In this review, the composite materials for preparing tissue engineering scaffolds are briefly described, which emphasizes the preparation methods, biological properties and practical applications of graphene-based composite scaffolds. The synthetic techniques with stressing solvent casting, electrospinning and 3D printing are introduced in detail. The mechanical, cell-oriented and biocompatible properties of graphene-based composite scaffolds in tissue engineering are analyzed and summarized. Their applications in bone tissue engineering, nerve tissue engineering, cardiovascular tissue engineering and other tissue engineering are summarized systematically. In addition, this work also looks forward to the difficulties and challenges in the future research, providing some references for the follow-up research of graphene-based composites in tissue engineering scaffolds.

Cryogenic 3D printing of modified polylactic acid scaffolds with biomimetic nanofibrous architecture for bone tissue engineering

The individualized polylactic acid (PLA) scaffolds fabricated by 3D printing technique have a good application prospect in the bone tissue engineering field. However, 3D printed PLA scaffold mainly manufactured by using a Fused Deposition Modelling fabrication technique (FDM) has some disadvantages, such as having smooth surface, strong hydrophobicity, poor cell adhesion, undesirable bioactivity, the degradation and deterioration at a high temperature triggering an inflammatory response. In this work, the aminated modified polylactic acid nanofibrous scaffold prepared by cryogenic 3D printing technology is designed to provide a feasible countermeasure to solve the key problems existing at present. The prepared scaffolds were fully characterized in terms of physico-chemical and morphological analyses, and the collected results revealed that the using of the cryogenic 3D printing technology can effectively avoid the degradation and deterioration of PLA at a high temperature required by FDM technique and promote the formation of nanofibrous structures. The in vitro tests with MC3T3-E1 cells confirmed that the cell-responsive biomimetic fibrous architecture and improved hydrophilicity due to the introduction of hydrophilic active amino groups provided a bioactive interface for cell adhesion and growth. Meanwhile, the active amino groups introduced by ammonolysis reaction can act as active sites for biomineralization. Thus, the as-prepared scaffolds may hold great potential for bone tissue engineering applications.

Multifunctional modified polylactic acid nanofibrous scaffold incorporating sodium alginate microspheres decorated with strontium and black phosphorus for bone tissue engineering

Polylactic acid (PLA) nanofibrous scaffolds have received extensive attention in the field of tissue engineering due to their excellent degradability, biocompatibility and the biomimetic extracellular matrix (ECM) topographies. However, the cell affinity and osteogenic activity of PLA scaffolds is not satisfactory because of their intrinsic hydrophobicity, the absence of cell recognition sites and the nucleation sites of the in vivo biomineralization. Furthermore, effective anti-inflammatory activity for the in vivo scaffold could not be ignored, so a strategy to develop a multifunctional PLLA (poly-L-lactic acid) nanofibrous scaffold with improved hydrophilicity, osteoinductivity, excellent near-infrared photothermal-responsive drug release capacity and anti-inflammatory activity via incorporating sodium alginate microspheres decorated with strontium and ibuprofen-loaded black phosphorus (BP + IBU@SA microspheres) into aminated modified PLLA nanofiber network is proposed in this study. Scanning electron microscopy (SEM) observation showed that the BP + IBU@SA microspheres were homogeneously dispersed into the modified PLLA matrix with uniform nanofiber structure and the chemical composition of the as-prepared scaffolds was confirmed by X-ray diffraction analysis (XRD) and elemental mapping. The photothermal property of the scaffolds was assessed under near-infrared (NIR) light irradiation, the results manifested that the entrapment of BP nanosheets endowed PLLA nanofibrous scaffold with significantly high photothermal conversion efficiency and optical cycle stability. Meanwhile, the scaffold also displayed an excellent photothermal-responsive intelligent drug release performance toward Sr²⁺ and ibuprofen. Moreover, the in vitro studies revealed that the as-developed scaffolds possessed a good biocompatibility for cell adhesion and proliferation and an improved bioactivity to induce apatite formation. All these results indicated the potential of the fabricated scaffolds in tissue engineering applications.

Molecular Regulators of Cellular Mechanoadaptation at Cell-Material Interfaces

Diverse essential cellular behaviors are determined by extracellular physical cues that are detected by highly orchestrated subcellular interactions with the extracellular microenvironment. To maintain the reciprocity of cellular responses and mechanical properties of the extracellular matrix, cells utilize a variety of signaling pathways that transduce biophysical stimuli to biochemical reactions. Recent advances in the micromanipulation of individual cells have shown that cellular responses to distinct physical and chemical features of the material are fundamental determinants of cellular mechanosensation and mechanotransduction. In the process of outside-in signal transduction, transmembrane protein integrins facilitate the formation of focal adhesion protein clusters that are connected to the cytoskeletal architecture and anchor the cell to the substrate. The linkers of nucleoskeleton and cytoskeleton molecular complexes, collectively termed LINC, are critical signal transducers that relay biophysical signals between the extranuclear cytoplasmic region and intranuclear nucleoplasmic region. Mechanical signals that involve cytoskeletal remodeling ultimately propagate into the nuclear envelope comprising the nuclear lamina in assistance with various nuclear membrane proteins, where nuclear mechanics play a key role in the subsequent alteration of gene expression and epigenetic modification. These intracellular mechanical signaling cues adjust cellular behaviors directly associated with mechanohomeostasis. Diverse strategies to modulate cell-material interfaces, including alteration of surface rigidity, confinement of cell adhesive region, and changes in surface topology, have been proposed to identify cellular signal transduction at the cellular and subcellular levels. In this review, we will discuss how a diversity of alterations in the physical properties of materials induce distinct cellular responses such as adhesion, migration, proliferation, differentiation, and chromosomal organization. Furthermore, the pathological relevance of misregulated cellular mechanosensation and mechanotransduction in the progression of devastating human diseases, including cardiovascular diseases, cancer, and aging, will be extensively reviewed. Understanding cellular responses to various extracellular forces is expected to provide new insights into how cellular mechanoadaptation is modulated by manipulating the mechanics of extracellular matrix and the application of these materials in clinical aspects.