Bone Regeneration Based on Tissue Engineering Conceptions - A 21st Century Perspective

Collagen-Alginate Composite Hydrogel: Application in Tissue Engineering and Biomedical Sciences

Alginate (ALG), a polysaccharide derived from brown seaweed, has been extensively investigated as a biomaterial not only in tissue engineering but also for numerous biomedical sciences owing to its wide availability, good compatibility, weak cytotoxicity, low cost, and ease of gelation. Nevertheless, alginate lacks cell-binding sites, limiting long-term cell survival and viability in 3D culture. Collagen (Col), a major component protein found in the extracellular matrix (ECM), exhibits excellent biocompatibility and weak immunogenicity. Furthermore, collagen contains cell-binding motifs, which facilitate cell attachment, interaction, and spreading, consequently maintaining cell viability and promoting cell proliferation. Recently, there has been a growing body of investigations into collagen-based hydrogel trying to overcome the poor mechanical properties of collagen. In particular, collagen-alginate composite (CAC) hydrogel has attracted much attention due to its excellent biocompatibility, gelling under mild conditions, low cytotoxicity, controllable mechanic properties, wider availability as well as ease of incorporation of other biomaterials and bioactive agents. This review aims to provide an overview of the properties of alginate and collagen. Moreover, the application of CAC hydrogel in tissue engineering and biomedical sciences is also discussed.

Simultaneous incorporation of PTH(1-34) and nano-hydroxyapatite into Chitosan/Alginate Hydrogels for efficient bone regeneration

Tissue regeneration based on the utilization of artificial soft materials is considered a promising treatment for bone-related diseases. Here, we report cranial bone regeneration promoted by hydrogels that contain parathyroid hormone (PTH) peptide PTH(1-34) and nano-hydroxyapatite (nHAP). A combination of the positively charged natural polymer chitosan (CS) and negatively charged sodium alginate led to the formation of hydrogels with porous structures, as shown by scanning electron microscopy. Rheological characterizations revealed that the mechanical properties of the hydrogels were almost maintained upon the addition of nHAP and PTH(1-34). In vitro experiments showed that the hydrogel containing nHAP and PTH(1-34) exhibited strong biocompatibility and facilitated osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) via the Notch signaling pathway, as shown by the upregulated expression of osteogenic-related proteins. We found that increasing the content of PTH(1-34) in the hydrogels resulted in enhanced osteogenic differentiation of BMSCs. Implantation of the complex hydrogel into a rat cranial defect model led to efficient bone regeneration compared to the rats treated with the hydrogel alone or with nHAP, indicating the simultaneous therapeutic effect of nHAP and PTH during the treatment process. Both the in vitro and in vivo results demonstrated that simultaneously incorporating nHAP and PTH into hydrogels shows promise for bone regeneration, suggesting a new strategy for tissue engineering and regeneration in the future.

Applications of nanomaterials in tissue engineering

Recent advancement in nanotechnology has brought prominent benefits in tissue engineering, which has been used to repair or reconstruct damaged tissues or organs and design smart drug delivery systems. With numerous applications of nanomaterials in tissue engineering, it is vital to choose appropriate nanomaterials for different tissue engineering applications because of the tissue heterogeneity. Indeed, the use of nanomaterials in tissue engineering is directly determined by the choice. In this review, we mainly introduced the use of nanomaterials in tissue engineering. First, the basic characteristics, preparation and characterization methods of the types of nanomaterials are introduced briefly, followed by a detailed description of the application and research progress of nanomaterials in tissue engineering and drug delivery. Finally, the existing challenges and prospects for future applications of nanomaterials in tissue engineering are discussed.

Additively manufactured BaTiO3 composite scaffolds: A novel strategy for load bearing bone tissue engineering applications

Piezoelectric ceramics, such as BaTiO₃, have gained considerable attention in bone tissue engineering applications thanks to their biocompatibility, ability to sustain a charged surface as well as improve bone cells' adhesion and proliferation. However, the poor processability and brittleness of these materials hinder the fabrication of three-dimensional scaffolds for load bearing tissue engineering applications. For the first time, this study focused on the fabrication and characterisation of BaTiO₃ composite scaffolds by using a multi-material 3D printing technology. Polycaprolactone (PCL) was selected and used as dispersion phase for its low melting point, easy processability and wide adoption in bone tissue engineering. The proposed single-step extrusion-based strategy enabled a faster and solvent-free process, where raw materials in powder forms were mechanically mixed and subsequently fed into the 3D printing system for further processing. PCL, PCL/hydroxyapatite and PCL/BaTiO₃ composite scaffolds were successfully produced with high level of consistency and an inner architecture made of seamlessly integrated layers. The inclusion of BaTiO₃ ceramic particles (10% wt.) significantly improved the mechanical performance of the scaffolds (54 ± 0.5 MPa) compared to PCL/hydroxyapatite scaffolds (40.4 ± 0.1 MPa); moreover, the presence of BaTiO₃ increased the dielectric permittivity over the entire frequency spectrum and tested temperatures. Human osteoblasts Saos-2 were seeded on scaffolds and cellular adhesion, proliferation, differentiation and deposition of bone-like extracellular matrix were evaluated. All tested scaffolds (PCL, PCL/hydroxyapatite and PCL/BaTiO₃) supported cell growth and viability, preserving the characteristic cellular osteoblastic phenotype morphology, with PCL/BaTiO₃ composite scaffolds exhibiting higher mineralisation (ALP activity) and deposited bone-like extracellular matrix (osteocalcin and collagen I). The single-step multi-material additive manufacturing technology used for the fabrication of electroactive PCL/BaTiO₃ composite scaffolds holds great promise for sustainability (reduced material waste and manufacturing costs) and it importantly suggests PCL/BaTiO₃ scaffolds as promising candidates for load bearing bone tissue engineering applications to solve unmet clinical needs.

Hard Dental Tissues Regeneration-Approaches and Challenges

With the development of the modern concept of tissue engineering approach and the discovery of the potential of stem cells in dentistry, the regeneration of hard dental tissues has become a reality and a priority of modern dentistry. The present review reports the recent advances on stem-cell based regeneration strategies for hard dental tissues and analyze the feasibility of stem cells and of growth factors in scaffolds-based or scaffold-free approaches in inducing the regeneration of either the whole tooth or only of its component structures.

Bone tissue regeneration: The role of finely tuned pore architecture of bioactive scaffolds before clinical translation

Spatial dimension of pores and interconnection in macroporous scaffolds is of particular importance in facilitating endogenous cell migration and bone tissue ingrowth. However, it is still a challenge to widely tune structure parameters of scaffolds by conventional methods because of inevitable pore geometrical deformation and poor pore interconnectivity. Here, the long-term in vivo biological performances of nonstoichiometric bioceramic scaffolds with different pore dimensions were assessed in critical-size femoral bone defect model. The 6% Mg-substituted wollastonite (CSi-Mg6) powders were prepared via wet-chemical precipitation and the scaffolds elaborately printed by ceramic stereolithography, displaying designed constant pore strut and tailorable pore height (200, 320, 450, 600 μm), were investigated thoroughly in the bone regeneration process. Together with detailed structural stability and mechanical properties were collaboratively outlined. Both μCT and histological analyses indicated that bone tissue ingrowth was retarded in 200 μm scaffolds in the whole stage (2-16 weeks) but the 320 μm scaffolds showed appreciable bone tissue in the center of porous constructs at 6-10 weeks and matured bone tissue were uniformly invaded in the whole pore networks at 16 weeks. Interestingly, the neo-tissue ingrowth was facilitated in the 450 μm and 600 μm scaffolds after 2 weeks and higher extent of bone regeneration and remodeling at the later stage. These new findings provide critical information on how engineered porous architecture impact bone regeneration in vivo. Simultaneously, this study shows important implications for optimizing the porous scaffolds design by advanced additive manufacture technique to match the clinical translation with high performance.

Alginate microgels as delivery vehicles for cell-based therapies in tissue engineering and regenerative medicine

Conventional stem cell delivery typically utilize administration of directly injection of allogenic cells or domesticated autogenic cells. It may lead to immune clearance of these cells by the host immune systems. Alginate microgels have been demonstrated to improve the survival of encapsulated cells and overcome rapid immune clearance after transplantation. Moreover, alginate microgels can serve as three-dimensional extracellular matrix to support cell growth and protect allogenic cells from rapid immune clearance, with functions as delivery vehicles to achieve sustained release of therapeutic proteins and growth factors from the encapsulated cells. Besides, cell-loaded alginate microgels can potentially be applied in regenerative medicine by serving as injectable engineered scaffolds to support tissue regrowth. In this review, the properties of alginate and different methods to produce alginate microgels are introduced firstly. Then, we focus on diverse applications of alginate microgels for cell delivery in tissue engineering and regenerative medicine.

Fabrication of Polycaprolactone/Nano Hydroxyapatite (PCL/nHA) 3D Scaffold with Enhanced In Vitro Cell Response via Design for Additive Manufacturing (DfAM)

In this study, we investigated the dual-pore kagome-structure design of a 3D-printed scaffold with enhanced in vitro cell response and compared the mechanical properties with 3D-printed scaffolds with conventional or offset patterns. The compressive modulus of the 3D-printed scaffold with the proposed design was found to resemble that of the 3D-printed scaffold with a conventional pattern at similar pore sizes despite higher porosity. Furthermore, the compressive modulus of the proposed scaffold surpassed that of the 3D-printed scaffold with conventional and offset patterns at similar porosities owing to the structural characteristics of the kagome structure. Regarding the in vitro cell response, cell adhesion, cell growth, and ALP concentration of the proposed scaffold for 14 days was superior to those of the control group scaffolds. Consequently, we found that the mechanical properties and in vitro cell response of the 3D-printed scaffold could be improved by kagome and dual-pore structures through DfAM. Moreover, we revealed that the dual-pore structure is effective for the in vitro cell response compared to the structures possessing conventional and offset patterns.

Bone physiological microenvironment and healing mechanism: Basis for future bone-tissue engineering scaffolds

Bone-tissue defects affect millions of people worldwide. Despite being common treatment approaches, autologous and allogeneic bone grafting have not achieved the ideal therapeutic effect. This has prompted researchers to explore novel bone-regeneration methods. In recent decades, the development of bone tissue engineering (BTE) scaffolds has been leading the forefront of this field. As researchers have provided deep insights into bone physiology and the bone-healing mechanism, various biomimicking and bioinspired BTE scaffolds have been reported. Now it is necessary to review the progress of natural bone physiology and bone healing mechanism, which will provide more valuable enlightenments for researchers in this field. This work details the physiological microenvironment of the natural bone tissue, bone-healing process, and various biomolecules involved therein. Next, according to the bone physiological microenvironment and the delivery of bioactive factors based on the bone-healing mechanism, it elaborates the biomimetic design of a scaffold, highlighting the designing of BTE scaffolds according to bone biology and providing the rationale for designing next-generation BTE scaffolds that conform to natural bone healing and regeneration.

Synthesis and characterization of magnesium diboride nanosheets in alginate/polyvinyl alcohol scaffolds for bone tissue engineering

Boride, which belongs to the distinct category of ceramic materials, has attracted significant attention in tissue engineering applications. Magnesium diboride (MgB2) consists of a plane of magnesium atoms sandwiched between the layers of boron. Even though MgB2 showed its role in various applications, its effect on osteogenesis has not yet been investigated. In this study, we synthesized MgB2 nanosheets (MgB2NS), a new class of 2D-nanoscale structures, by the ultrasonication exfoliation method and incorporated them into a polymeric mixture of alginate (Alg) and polyvinyl alcohol (PVA) by the freeze-drying procedure. The synthesized scaffolds (Alg/PVA/MgB2NS) were characterized by SEM, XRD, FT-IR, protein adsorption, swelling, degradation, and biomineralization studies. These scaffolds were non-toxic to mouse mesenchymal stem cells (mMSCs). MgB2NS in the scaffolds enhanced osteoblast differentiation of mMSCs at the molecular level by the expression of Runx2 and osteoblast differentiation marker genes and at the cellular level by alkaline phosphatase, alizarin Red and von Kossa staining. Overall, our results showed that MgB2NS in Alg/PVA scaffolds have osteogenic potential, suggesting their possible use in bone tissue engineering applications.

Glycyrrhizic Acid Promotes Osteogenic Differentiation of Human Bone Marrow Stromal Cells by Activating the Wnt/β-Catenin Signaling Pathway

Glycyrrhizic acid (GA) is a major triterpene glycoside isolated from liquorice root that has been shown to inhibit osteoclastogenesis. However, there have been no reports regarding the effect of GA on osteogenic differentiation. Therefore, this study was performed to explore the effects and mechanism of action of GA on osteogenesis. A CCK-8 array was used to assess cell viability. The osteogenic capability was investigated by real-time quantitative PCR, western blotting and immunofluorescence analyses. ALP staining and ARS were used to evaluate ALP activity and mineralization, respectively. GA-GelMA hydrogels were designed to verify the therapeutic effects of GA in vivo by radiographic analysis and histological evaluation. Our results show that GA had no significant influence on the viability or proliferation of human bone marrow stromal cells (hBMSCs). GA promoted osteogenic differentiation and enhanced calcium deposition. Furthermore, ratio of active β-catenin and total β-catenin protein increased after treatment with GA. Wnt/catenin signaling inhibitor partially attenuated the effects of GA on osteogenic differentiation. In a mouse femoral fracture model, GA-GelMA hydrogels accelerated bone healing. Our results show that GA promotes the osteogenic differentiation of hBMSCs by modulating the Wnt/β-catenin signaling pathway. GA-GelMA hydrogels promoted bone fracture healing. GA has potential as a cost-effective treatment of bone defects.

Cryptic ligand on collagen matrix unveiled by MMP13 accelerates bone tissue regeneration via MMP13/Integrin α3/RUNX2 feedback loop

Extracellular matrix (ECM) remodeling is necessary for the development and self-healing of tissue, and the process is tissue specific. Matrix metalloproteinases (MMPs) play a role in ECM remodeling by unwinding and cleaving ECM. We hypothesized that ECM remodeling by MMPs is involved in the differentiation of stem cells into specific lineages during self-healing. To prove the hypothesis, we investigated which MMPs are involved in the osteogenic differentiation of human mesenchymal stem cells (hMSCs) grown on a type I collagen (Col I) matrix, and we found that specifically high expression of MMP13 in hMSCs grown on a Col I matirx during osteogenic differentiation. Moreover, knocking down of MMP13 decreased the osteogenic differentiation of hMSCs grown on a Col I matrix. In addition, pre-treatment of recombinant human MMP13 lead to remodeling of Col I matrix and increased the osteogenic differentiation of hMSCs and in vivo bone formation following the upregulation of the expression of runt-related transcription factor 2 (RUNX2), integrin α3 (ITGA3), and focal adhesion kinase. Furthermore, the transcription factor RUNX2 bound to the MMP13 promoter. These results suggest that growth on a remodeled Col I matrix by MMP13 stimulates osteogenic differentiation of hMSCs and self-healing of bone tissue via an MMP13/ITGA3/RUNX2 positive feedback loop. STATEMENT OF SIGNIFICANCE: Self-healing of tissue could be the key to treating diseases that cannot be overcome by present technology. We investigated the mechanism underlying the self-healing of tissue and we found that the osteogenic differentiation was increased in hMSCs grown on a remodeled Col I matrix by the optimized concentration of MMP13 not in hMSCs grown on a Col I fragments cleaved by a high concentration of MMP13. In addition, we found the remodeled Col I matrix by MMP13 increased the osteogenic capacity through a MMP13/integrin α3/RUNX2 positive feedback loop. This result would be able to not only provide a strategy for bone tissue-specific functional materials following strong evidence about the self-healing mechanism of bone through the interaction between stem cells and the ECM matrix. As such, we strongly believe our finding will be of interest to researchers studying biomaterials, stem cell biology and matrix interaction for regenerative medicine and therapy.

Metal Material, Properties and Design Methods of Porous Biomedical Scaffolds for Additive Manufacturing: A Review

Design an implant similar to the human bone is one of the critical problems in bone tissue engineering. Metal porous scaffolds have good prospects in bone tissue replacement due to their matching elastic modulus, better strength, and biocompatibility. However, traditional processing methods are challenging to fabricate scaffolds with a porous structure, limiting the development of porous scaffolds. With the advancement of additive manufacturing (AM) and computer-aided technologies, the development of porous metal scaffolds also ushers in unprecedented opportunities. In recent years, many new metal materials and innovative design methods are used to fabricate porous scaffolds with excellent mechanical properties and biocompatibility. This article reviews the research progress of porous metal scaffolds, and introduces the AM technologies used in porous metal scaffolds. Then the applications of different metal materials in bone scaffolds are summarized, and the advantages and limitations of various scaffold design methods are discussed. Finally, we look forward to the development prospects of AM in porous metal scaffolds.

Specifiable biomimetic microsponges for timed release of crystal entrapped biomolecules useful in bone repair

Most marine materials, by nature, contain crystals of inorganic matter with specific structures that allow the loading, release, and delivery of biomolecules that can be utilized in clinical applications. These structures can be biomimetically synthesized. Aggregates of inorganic particles generated by biomimetic microsponges may provide surfaces and structures for cell attachment, organization, and promotion of matrix synthesis. Biomimetic microsponges have been developed with tunable release profiles differing by the rate (speed over distance), velocity (rate of change in direction), and the quantity discharged over time, according to biomolecular species. Specifically, the types of proteins involved guide and regulate cells in physical contact with the microsponges, for instance, reprogramming somatic cells, the switching phenotypes, or specifying stem cell differentiation. Applications for these microsponges include gene transfection of localized cells and promotion of bone matrix synthesis by the externalized display of RGD cell adhesive peptides and the release of crystal entrapped, occluded, adsorbed and infused rhBMP-2 and plasmid. A requirement for de novo bone formation is a solid structure to enable osteocytes to lay new bone tissue. In this study, biomimetic microsponges highlight tremendous potential as osteoconductive packing material in bone repair with parallel influence on regeneration. Majorly, microsponges offer pronounced osteoinductivity, unlike many other bone particulates, by solid-state integration of active regenerative biological molecules through the prism of the biomineral crystalline structure.

Assessment of a PCL-3D Printing-Dental Pulp Stem Cells Triplet for Bone Engineering: An In Vitro Study

The search of suitable combinations of stem cells, biomaterials and scaffolds manufacturing methods have become a major focus of research for bone engineering. The aim of this study was to test the potential of dental pulp stem cells to attach, proliferate, mineralize and differentiate on 3D printed polycaprolactone (PCL) scaffolds. A 100% pure M_w: 84,500 ± 1000 PCL was selected. 5 × 10 × 5 mm³ parallelepiped scaffolds were designed as a wood-pilled structure composed of 20 layers of 250 μm in height, in a non-alternate order ([0,0,0,90,90,90°]). 3D printing was made at 170 °C. Swine dental pulp stem cells (DPSCs) were extracted from lower lateral incisors of swine and cultivated until the cells reached 80% confluence. The third passage was used for seeding on the scaffolds. Phenotype of cells was determined by flow Cytometry. Live and dead, Alamar blue™, von Kossa and alizarin red staining assays were performed. Scaffolds with 290 + 30 μm strand diameter, 938 ± 80 μm pores in the axial direction and 689 ± 13 μm pores in the lateral direction were manufactured. Together, cell viability tests, von Kossa and Alizarin red staining indicate the ability of the printed scaffolds to support DPSCs attachment, proliferation and enable differentiation followed by mineralization. The selected material-processing technique-cell line (PCL-3D printing-DPSCs) triplet can be though to be used for further modelling and preclinical experiments in bone engineering studies.

A novel 3D indirect co-culture system based on a collagen hydrogel scaffold for enhancing the osteogenesis of stem cells

In this study, the paracrine effect between adipose-derived mesenchymal stem cells (ADSCs) and osteoblasts was investigated in collagen-based three-dimensional (3D) scaffolds. 3D encapsulation of mesenchymal stem cells in hydrogel scaffolds was conducted for bone tissue regeneration. Osteoblasts were encapsulated in alginate microbeads with uniform size, which could be controlled by varying the supply voltage using electrostatic droplet extrusion. Osteoblast-encapsulated microbeads were embedded with ADSCs in collagen bulk hydrogel scaffolds with a high survival rate. The separated space between the two types of cells made it possible to confirm ADSC differentiation into osteogenic lineages in the 3D collagen hydrogel scaffold by the paracrine effect in vitro. Furthermore, co-cultured ADSC and osteoblasts showed enhanced bone formation compared with the ADSC monoculture group in the rat calvarial defect model. The system developed in this study provides a novel in vitro tissue model for bone regeneration without exogenous factors, and it has the potential to be used to study the paracrine effect in various co-culture systems in the near future.

Surface modification of the simvastatin factor-loaded silk fibroin promotes the healing of rotator cuff injury through β-catenin signaling

Rupture of the rotator cuff is a common injury of the shoulder joint in sports professionals. In addition, research on repair of the rotator cuff has gained popularity over the recent years. Given the high rate of re-tear after surgery, it is necessary to design and prepare biodegradable materials with good mechanical properties, for the management of the condition. Consequently, the present study conducted surface modification of the simvastatin factor-loaded silk fibroin for the repair of chronic rotator cuff injury in SD rats. The in vitro experiments were analyzed through scanning electron microscopy and the water contact angle. Additionally, the CCK-8 assay was used to observe the effect of the intervention on the proliferation of BMSCs. Moreover, the osteogenic differentiation of BMSCs was detected through the ALP and ARS assays while the expression of osteogenic genes was examined using qRT-PCR and Western blot analysis. Furthermore, a model for repairing chronic rotator cuff tears in SD rats was established in vivo. Thereafter, rotator cuff repair and healing were evaluated through HE staining while Masson and Sirius staining was used to detect the collagen formation ratio. Additionally, the study analyzed the mechanism underlying the effect of simvastatin-loaded silk fibroin. The results showed that the simvastatin-loaded silk fibroin membrane had better biocompatibility and the in vitro experiments confirmed that it could promote the proliferation and osteogenic differentiation of BMSCs. In addition, the in vivo HE staining experiments similarly confirmed that it could enhance tendon bone healing and alleviate inflammation in chronic rotator cuff injuries. On the other hand, Masson and Sirius staining showed that the simvastatin-loaded silk fibroin could promote the formation of collagen. Further analysis also revealed that it could promote the osteogenic differentiation of BMSCs by activating the β-catenin signaling pathway. In general, these findings suggested that surface modification of the simvastatin factor-loaded silk fibroin was a potential means of improving the healing of rotator cuff injuries and can be implemented in clinical practice in future.

Mechanical and Degradation Properties of Hybrid Scaffolds for Tissue Engineered Heart Valve (TEHV)

In addition to biocompatibility, an ideal scaffold for the regeneration of valvular tissue should also replicate the natural heart valve extracellular matrix (ECM) in terms of biomechanical properties and structural stability. In our previous paper, we demonstrated the development of collagen type I and hyaluronic acid (HA)-based scaffolds with interlaced microstructure. Such hybrid scaffolds were found to be compatible with cardiosphere-derived cells (CDCs) to potentially regenerate the diseased aortic heart valve. This paper focused on the quantification of the effect of crosslinking density on the mechanical properties under dry and wet conditions as well as degradation resistance. Elastic moduli increased with increasing crosslinking densities, in the dry and wet state, for parent networks, whereas those of interlaced scaffolds were higher than either network alone. Compressive and storage moduli ranged from 35 ± 5 to 95 ± 5 kPa and 16 ± 2 kPa to 113 ± 6 kPa, respectively, in the dry state. Storage moduli, in the dry state, matched and exceeded those of human aortic valve leaflets (HAVL). Similarly, degradation resistance increased with increasing the crosslinking densities for collagen-only and HA-only scaffolds. Interlaced scaffolds showed partial degradation in the presence of either collagenase or hyaluronidase as compared to when exposed to both enzymes together. These results agree with our previous findings that interlaced scaffolds were composed of independent collagen and HA networks without crosslinking between them. Thus, collagen/HA interlaced scaffolds have the potential to fill in the niche for designing an ideal tissue engineered heart valve (TEHV).

Mechano-driven regeneration predicts response variations in large animal model based on scaffold implantation site and individual mechano-sensitivity

It is well founded that the mechanical environment may regulate bone regeneration in orthopedic applications. The purpose of this study is to investigate the mechanical contributions of the scaffold and the host to bone regeneration, in terms of subject specificity, implantation site and sensitivity to the mechanical environment. Using a computational approach to model mechano-driven regeneration, bone ingrowth in porous titanium scaffolds was simulated in the distal femur and proximal tibia of three goats and compared to experimental results. The results showed that bone ingrowth shifted from a homogeneous distribution pattern, when scaffolds were in contact with trabecular bone (max local ingrowth 12.47%), to a localized bone ingrowth when scaffolds were implanted in a diaphyseal location (max local ingrowth 20.64%). The bone formation dynamics revealed an apposition rate of 0.37±0.28%/day in the first three weeks after implantation, followed by limited increase in bone ingrowth until the end of the experiment (12 weeks). According to in vivo data, we identified one animal whose sensitivity to mechanical stimulation was higher than the other two. Moreover, we found that the stimulus initiating bone formation was consistently higher in the femur than in the tibia for all the individuals. Overall, the dependence of the osteogenic response on the host biomechanics means that, from a mechanical perspective, the regenerative potential depends on both the scaffold and the host environment. Therefore, this work provides insights on how the mechanical conditions of both the recipient and the scaffold contribute to meet patient and location-specific characteristics.

Increased Osteogenic Potential of Pre-Osteoblasts on Three-Dimensional Printed Scaffolds Compared to Porous Scaffolds for Bone Regeneration

Background

One of the main challenges with conventional scaffold fabrication methods is the inability to control scaffold architecture. Recently, scaffolds with controlled shape and architecture have been fabricated using three-dimensional printing (3DP). Herein, we aimed to determine whether the much tighter control of microstructure of 3DP poly(lactic-co-glycolic) acid/β-tricalcium phosphate (PLGA/β-TCP) scaffolds is more effective in promoting osteogenesis than porous scaffolds produced by solvent casting/porogen leaching.

Methods

Physical and mechanical properties of porous and 3DP scaffolds were studied. The response of pre-osteoblasts to the scaffolds was analyzed after 14 days.

Results

TThe 3DP scaffolds had a smoother surface (Ra: 22 ± 3 µm) relative to the highly rough surface of porous scaffolds (Ra: 110 ± 15 µm). Water contact angle was 112 ± 4° on porous and 76 ± 6° on 3DP scaffolds. Porous and 3DP scaffolds had the pore size of 408 ± 90 and 315 ± 17 µm and porosity of 85 ± 5% and 39 ± 7%, respectively. Compressive strength of 3DP scaffolds (4.0 ± 0.3 MPa) was higher than porous scaffolds (1.7 ± 0.2 MPa). Collagenous matrix deposition was similar on both scaffolds. Cells proliferated from day 1 to day 14 by fourfold in porous and by 3.8-fold in 3DP scaffolds. Alkaline phosphatase (ALP) activity was 21-fold higher in 3DP scaffolds than porous scaffolds.

Conclusion

The 3DP scaffolds show enhanced mechanical properties and ALP activity compared to porous scaffolds in vitro, suggesting that 3DP PLGA/β-TCP scaffolds are possibly more favorable for bone formation.

Biomaterial Properties Modulating Bone Regeneration

Biomaterial scaffolds have been gaining momentum in the past several decades for their potential applications in the area of tissue engineering. They function as three-dimensional porous constructs to temporarily support the attachment of cells, subsequently influencing cell behaviors such as proliferation and differentiation to repair or regenerate defective tissues. In addition, scaffolds can also serve as delivery vehicles to achieve sustained release of encapsulated growth factors or therapeutic agents to further modulate the regeneration process. Given the limitations of current bone grafts used clinically in bone repair, alternatives such as biomaterial scaffolds have emerged as potential bone graft substitutes. This review summarizes how physicochemical properties of biomaterial scaffolds can influence cell behavior and its downstream effect, particularly in its application to bone regeneration.

Graphene Oxide Quantum Dots Promote Osteogenic Differentiation of Stem Cells from Human Exfoliated Deciduous Teeth via the Wnt/β-Catenin Signaling Pathway

Graphene oxide quantum dots (GOQDs) are a carbon nanomaterial with broad potential for application in the field of nanomaterial biomedicine. Stem cells from human exfoliated deciduous teeth (SHEDs) play an important role in tissue engineering and regenerative medicine. This study investigated the effects of GOQDs on SHED osteogenic differentiation. GOQDs were synthesized; then, the proliferation of SHEDs incubated in GOQDs at different concentrations was evaluated; and the live cells were observed. We observed that live SHEDs incubated in GOQDs emitted green fluorescence in the absence of chemical dyes, and 1, 10, and 50 μg/mL GOQDs significantly promoted SHED proliferation. Culture with the osteogenic induction medium containing 10 μg/mL GOQDs induced calcium nodule formation, increased alkaline phosphatase (ALP) activity, and upregulated SHED mRNA and protein levels of OCN, RUNX2, COL I, and β-catenin. With the addition of Dickkopf 1 (DKK-1) or β-catenin knockdown, expression levels of the above mRNAs and proteins were decreased in GOQD-treated SHEDs. In summary, at a concentration of 10 μg/mL, GOQDs promote SHED proliferation and osteogenic differentiation via the Wnt/β-catenin signaling pathway. This work provides new ideas and fundamental information on interactions between GOQDs and SHEDs that are relevant for the biomedical engineering field.

Role of bone 1stem cell-seeded 3D polylactic acid/polycaprolactone/hydroxyapatite scaffold on a critical-sized radial bone defect in rat

Osteoconductive biomaterials were used to find the most reliable materials in bone healing. Our focus was on the bone healing capacity of the stem cell-loaded and unloaded PLA/PCL/HA scaffolds. The 3D scaffold of PLA/PCL/HA was characterized by scanning electron microscopy (SEM), rheology, X-ray diffraction (XRD), and Fourier transform-infrared (FT-IR) spectroscopy. Bone marrow stem cells (BMSCs) have multipotential differentiation into osteoblasts. Forty Wistar male rats were used to organize four experimental groups: control, autograft, scaffold, and BMSCs-loaded scaffold groups. qRT-PCR showed that the BMSCs-loaded scaffold had a higher expression level of CD31 and osteogenic markers compared with the control group (P < 0.05). Radiology and computed tomography (CT) scan evaluations showed significant improvement in the BMSCs-loaded scaffold compared with the control group (P < 0.001). Biomechanical estimation demonstrated significantly higher stress (P < 0.01), stiffness (P < 0.001), and ultimate load (P < 0.01) in the autograft and BMSCs-loaded scaffold groups compared with the untreated group and higher strain was seen in the control group than the other groups (P < 0.01). Histomorphometric and immunohistochemical (IHC) investigations showed significantly improved regeneration scores in the autograft and BMSCs-loaded scaffold groups compared with the control group (P < 0.05). Also, there was a significant difference between the scaffold and control groups in all tests (P < 0.05). The results depicted that our novel approach will allow to develop PLA/PCL/HA 3D scaffold in bone healing via BMSC loading.

Surgical Advances in Osteosarcoma

Simple Summary

Osteosarcoma (OS) is the most common bone cancer in children. OS most commonly arises in the legs, but can arise in any bone, including the spine, head or neck. Along with chemotherapy, surgery is a mainstay of OS treatment and in the 1990s, surgeons began to shift from amputation to limb-preserving surgery. Since then, improvements in imaging, surgical techniques and implant design have led to improvements in functional outcomes without compromising on the cancer outcomes for these patients. This paper summarises these advances, along with a brief discussion of future technologies currently in development.

Abstract

Osteosarcoma (OS) is the most common primary bone cancer in children and, unfortunately, is associated with poor survival rates. OS most commonly arises around the knee joint, and was traditionally treated with amputation until surgeons began to favour limb-preserving surgery in the 1990s. Whilst improving functional outcomes, this was not without problems, such as implant failure and limb length discrepancies. OS can also arise in areas such as the pelvis, spine, head, and neck, which creates additional technical difficulty given the anatomical complexity of the areas. We reviewed the literature and summarised the recent advances in OS surgery. Improvements have been made in many areas; developments in pre-operative imaging technology have allowed improved planning, whilst the ongoing development of intraoperative imaging techniques, such as fluorescent dyes, offer the possibility of improved surgical margins. Technological developments, such as computer navigation, patient specific instruments, and improved implant design similarly provide the opportunity to improve patient outcomes. Going forward, there are a number of promising avenues currently being pursued, such as targeted fluorescent dyes, robotics, and augmented reality, which bring the prospect of improving these outcomes further.

Characterization of Polycaprolactone Nanohydroxyapatite Composites with Tunable Degradability Suitable for Indirect Printing

Degradable bone implants are designed to foster the complete regeneration of natural tissue after large-scale loss trauma. Polycaprolactone (PCL) and hydroxyapatite (HA) composites are promising scaffold materials with superior mechanical and osteoinductive properties compared to the single materials. However, producing three-dimensional (3D) structures with high HA content as well as tuneable degradability remains a challenge. To address this issue and create homogeneously distributed PCL-nanoHA (nHA) scaffolds with tuneable degradation rates through both PCL molecular weight and nHA concentration, we conducted a detailed characterisation and comparison of a range of PCL-nHA composites across three molecular weight PCLs (14, 45, and 80 kDa) and with nHA content up to 30% w/w. In general, the addition of nHA results in an increase of viscosity for the PCL-nHA composites but has little effect on their compressive modulus. Importantly, we observe that the addition of nHA increases the rate of degradation compared to PCL alone. We show that the 45 and 80 kDa PCL-nHA groups can be fabricated via indirect 3D printing and have homogenously distributed nHA even after fabrication. Finally, the cytocompatibility of the composite materials is evaluated for the 45 and 80 kDa groups, with the results showing no significant change in cell number compared to the control. In conclusion, our analyses unveil several features that are crucial for processing the composite material into a tissue engineered implant.

Trabecular architecture during the healing process of a tibial diaphysis defect

The adaptation of trabecular bone microstructure to mechanical loads has been intensively investigated. However, loading-unrelated aspects of trabecular architecture remain unclear. We used synchrotron radiation-based X-ray microtomography to study the 3D microarchitecture of newly formed trabecular tissue in a defect produced in the cortical region of the rat tibia diaphysis, in the absence (7, 14, and 21 days) or the presence (21 days) of carbonated hydroxyapatite/alginate (cHA) microspheres. This work provides the first evidence that the woven bone trabecular network, formed during the healing process, displays a well-organized 3D microarchitecture consisting of nodes with 3 (3-N), 4 (4-N) and 5 (5-N) connecting trabeculae, with a mean relative abundance of (3-N)/(4-N)/(5-N) = 66/24/7, for the analyzed periods. The measured inter-trabecular angles (ITA) distribution presented a Gaussian profile, with mean value at 115° for 3-N nodes, and 105° for 4-N nodes, close to the angles of idealized 3D regular structures (120° and 109.5°, respectively). Changes in the dispersion of ITA distribution suggested that a highly symmetric trabecular fabric organized under tensegrity principles is formed early during the bone healing process. Post-implantation, cHA disaggregated into multiple fragments (~20-400 μm), stimulating osteoconduction and bone growth toward the interior of the medullary cavity. The presence of biomaterials in bone defects affected the trabecular dimensions; however, it did not interfere with the formation of geometrical motifs with topological parameters similar to those found in the sham-defects. STATEMENT OF SIGNIFICANCE: The trabecular bone microstructure enables the tissue to meet the necessary mechanical and functional demands. However, the process of trabecular microarchitecture formation during healing, in the absence or presence of a bone graft, is not yet well understood. This work demonstrated that, from the beginning of its formation in cortical bone defects, the woven-bone trabecular network is spatially organized according to the principle of tensegrity. This microarchitecture is comprised of highly symmetric geometric motifs and is an intrinsic characteristic of trabecular growth, regardless of hierarchical scale or mechanical stimulation. The addition of a biodegradable nanostructured calcium phosphate graft did not disrupt trabecular microarchitecture; however, graft biodegradation should be controlled to optimize the reproduction of intrinsic trabecular motifs throughout the defect.

Boosting osteogenic potential and bone regeneration by co-cultured cell derived extracellular matrix incorporated porous electrospun scaffold

Implants for bone regeneration to remedy segmental bone defects, osteomyelitis, necrotic bone tissue and non-union fractures have worldwide appeal. Although biomaterials offer most of the advantages by improving tissue growth but developments are more commonly achieved via biologically derived molecules. To aid site specific bone tissue regeneration by synthetic scaffold, cell derived extracellular matrix (ECM) can be a crucial component. In this study, co-cultured bone marrow mesenchymal stem cell and osteoblastic cells derived ECM incorporated electrospun polycaprolactone (PCL) membranes were assessed for bone tissue engineering application. The preliminary experimental details indicated that, co-culture of cells supported enhanced in vitro ECM synthesis followed by successful deposition of osteoblastic ECM into electrospun membranes. The acellular samples revealed retention of ECM related biomacromolecules (collagen, glycosaminoglycan) and partial recovery of pores after decellularization. In vitro biocompatibility tests ensured improvement of proliferation and osteoblastic differentiation of MC3T3-E1 cells in decellularized ECM containing membrane (PCL-ECM) compared to bare membrane (PCL-B) which was further confirmed by osteogenic marker proteins expression analysis. The decellularized PCL-ECM membrane allowed great improvement of bone regeneration over the bare membrane (PCL-B) in 8 mm size critical sized rat skull defects at 2 months of post implantation. In short, the outcome of this study could be impactful in development and application of cell derived ECM based synthetic electrospun templates for bone tissue engineering application.[Formula: see text].

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

In vivo bone regeneration using a bioactive nanocomposite scaffold and human mesenchymal stem cells

Due to the osteoconductive role of bioceramics, use of these bioactive nanocomposite scaffolds that can maintain their structural integrity during bone tissue repair is one of the major goals of tissue engineering. Herein, a nanofibrous poly-L-lactic acid (PLLA) scaffold was fabricated by electrospinning and then gelatin and hydroxyapatite nanoparticles (nHA) were coated over the surface of the scaffold. Osteoconductivity of the fabricated nano-composite scaffolds was then studied while grafted on the rat calvarial defects. Our results indicated that the coating of PLLA scaffold with nHA and gelatin increased the adhesion and growth of the human bone marrow derived mesenchymal stem cells (BM-MSCs) and also significantly increased the level of mineralization over a week culture period. The results of radiographic and histological studies showed that the newly created bone tissue at the defect site was significantly higher in animals treated with nanocomposite scaffolds than the empty scaffolds and control groups. This increase in the defect reconstruction was significantly increased after culturing BM-MSCs on the scaffolds, especially nanocomposite scaffolds. It can be concluded that the combination of nanocomposite scaffolds and BM-MSCs could be a very good candidate for treatment of bone lesions and could be considered as a bony bioimplant.

An interference screw made using a silk fibroin-based bulk material with high content of hydroxyapatite for anterior cruciate ligament reconstruction in a rabbit model

Upgradation is still in need for the clinically applied interference screws in anterior cruciate ligament reconstruction for more reliable fixation. Silk fibroin bulk materials offer a promising opportunity for this application except lacking osteoinductivity to some extent. Here we report a novel silk-based bulk material with high content of hydroxyapatite-silk fibroin (HA-SF) hybrid particles, which is prepared via a dual-network hydrogel. This composite bulk material possesses a compression modulus of 3.2 GPa, comparable to that of the natural compact bone, and presents satisfactory cytocompatibility and osteoinductivity in vitro when combined with the HA-SF nanoparticles particularly. This composite bulk material shaped into interference screws exhibits remarkable biomechanical properties and significant new-bone ingrowth in the host bone tunnel in a rabbit anterior cruciate ligament reconstruction (ACLR) model at 4 weeks and 12 weeks post-operatively. Moreover, considering that this "hydrogel method" allows the material to be formed in a mold, avoiding complicated post fabrication, it is a potential candidate for clinical translation.

Surface-treated 3D printed Ti-6Al-4V scaffolds with enhanced bone regeneration performance: an in vivo study

Background

Given their highly adjustable and predictable properties, three-dimensional(3D) printed geometrically ordered porous biomaterials offer unique opportunities as orthopedic implants. The performance of such biomaterials is, however, as much a result of the surface properties of the struts as it is of the 3D porous structure. In our previous study, we have investigated the in vitro performances of selective laser melted (SLM) Ti-6Al-4V scaffolds which are surface modified by the bioactive glass (BG) and mesoporous bioactive glass (MBG), respectively. The results demonstrated that such modification enhanced the attachment, proliferation, and differentiation of human bone marrow stromal cells (hBMSC). Here, we take the next step by assessing the therapeutic potential of 3D printed Ti-6Al-4V scaffolds with BG and MBG surface modifications for bone regeneration in a rabbit bone defect model.

Methods

3D printed Ti-6Al-4V scaffolds with BG and MBG surface modifications were implanted into the femoral condyle of the rabbits, the Ti-6Al-4V scaffolds without surface modification were used as the control. At week 3, 6, and 9 after the implantation, micro-computed tomography (micro-CT) imaging, fluorescence double-labeling to determine the mineral apposition rate (MAR), and histological analysis of non-decalcified sections were performed.

Results

We found significantly higher volumes of regenerated bone, significantly higher values of the relevant bone morphometric parameters, clear signs of bone matrix apposition and maturation, and the evidence of progressed angiogenesis and blood vessel formation in the groups where the bioactive glass was added as a coating, particularly the MGB group.

Conclusions

The MBG coating resulted in enhanced osteoconduction and vascularization in bone defect healing, which was attributed to the release of silicon and calcium ions and the presence of a nano-mesoporous structure on the surface of the MBG specimens.

Comprehensive assessment of bioactive glass and glass-ceramic scaffold permeability: experimental measurements by pressure wave drop, modelling and computed tomography-based analysis

Proper microstructural and transport properties are fundamental requirements for a suitable scaffold design and realization in tissue engineering applications. Scaffold microstructure (i.e. pore size, shape and distribution) and transport properties (i.e. intrinsic permeability), are commonly recognized as the key parameters related to the biological performance, such as cell attachment, penetration depth and tissue vascularization. While pore characteristics are relatively easy to asses, accurate and reliable evaluation of permeability still remains a challenge. In the present study, the microstructural properties of foam-replicated bioactive glass-derived scaffolds (basic composition 47.5SiO₂-2.5P₂O₅-20CaO-10MgO-10Na₂O-10K₂O mol.%) were determined as function of the sintering temperature within the range 600-850°C, identified on the basis of thermal analyses that were previously performed on the material. Scaffolds with total porosity between 55 and 84 vol.% and trabecular-like architecture were obtained, with pore morphological features varying according to the sintering temperature. Mathematical modelling, supported by micro-computed tomography (μ-CT) imaging, was implemented to selectively investigate the effect of different pore features on intrinsic permeability, which was determined by laminar airflow alternating pressure wave drop measurements and found to be within 0.051-2.811·10^-10 m². The calculated effective porosity of the scaffolds was in the range of 46 to 66 vol.%, while the average pore diameter assessed by μ-CT varied between 220 and 780 μm, where the values in the lower range were observed for higher sintering temperatures (750-850°C). Experimental results were critically discussed by means of a robust statistical analysis. Finally, the complete microstructural characterization of the scaffolds was achieved by applying the general constitutive equation based on Forchheimer's theory.

Clinical observation of mineralized collagen bone grafting after curettage of benign bone tumors

Curettage of benign bone tumor is a common cause for bone defect. For such bone defect repair, autogenous bone, allogeneic bone and traditional artificial bone graft substitutes have many disadvantages. In recent years, a biomimetic mineralized collagen (MC) with similar composition and microstructures to the natural bone matrix was developed and used for treating various bone defects. In this work, a retrospective study analyzed clinical outcomes of patients treated with curettage of benign bone tumors and bone grafting with MC, in comparison to another group treated with the same surgical method and autogenous bone. Lane–Sandhu X-ray score of the autogenous bone group was superior to the MC group at 1 month after the operation, but the two groups had no statistical difference at 6 and 12 months. The MC group was better in Musculoskeletal Tumor Society scoring at 1 and 6 months after the operation, and the two groups had no statistical difference at 12 month. Therefore, the MC performed not as good as autogenous bone in early stage of bone healing but achieved comparable outcomes in long-term follow-ups. Moreover, the MC has advantages in function recovery and avoided potential complications induced by harvesting autogenous bone.

Convergence of scaffold-guided bone regeneration and RIA bone grafting for the treatment of a critical-sized bone defect of the femoral shaft

BACKGROUND

Critical-sized bone defects, mainly from trauma, infection or tumor resection are a challenging condition, often resulting in prolonged, complicated course of treatment. Autografts are considered as the gold standard to replace lost bone. However, limited amount of bone graft volume and donor-site morbidity have established the need for the development of alternative methods such as scaffold-based tissue engineering (TE). The emerging market of additive manufacturing (3D-printing) has markedly influenced the manufacturing of scaffolds out of a variety of biodegradable materials. Particularly medical-grade polycaprolactone and tricalcium phosphate (mPCL-TCP) scaffolds show appropriate biocompatibility and osteoconduction with good biomechanical strength in large preclinical animal models. This case report aims to show first evidence of the feasibility, safety, and efficacy of mPCL-TCP scaffolds applied in a patient with a long bone segmental defect.

CASE PRESENTATION

The presented case comprises a 29-year-old patient who has suffered a left-sided II° open femoral shaft fracture. After initial external fixation and subsequent conversion to reamed antegrade femoral nailing, the patient presented with an infection in the area of the formerly open fracture. Multiple revision surgeries followed to eradicate microbial colonization and attempt to achieve bone healing. However, 18 months after the index event, still insufficient diaphyseal bone formation was observed with circumferential bony defect measuring 6 cm at the medial and 11 cm at the lateral aspect of the femur. Therefore, the patient received a patient-specific mPCL-TCP scaffold, fitting the exact anatomical defect and the inserted nail, combined with autologous bone graft (ABG) harvested with the Reamer-Irrigator-Aspirator system (RIA-Synthes®) as well as bone morphogenetic protein-2 (BMP-2). Radiographic follow-up 12 months after implantation of the TE scaffold shows advanced bony fusion and bone formation inside and outside the fully interconnected scaffold architecture.

CONCLUSION

This case report shows a promising translation of scaffold-based TE from bench to bedside. Preliminary evidence indicates that the use of medical-grade scaffolds is safe and has the potential to improve bone healing. Further, its synergistic effects when combined with ABG and BMP-2 show the potential of mPCL-TCP scaffolds to support new bone formation in segmental long bone defects.

In Vitro bioactivity, biocompatibility and corrosion resistance of multi-ionic (Ce/Si) co-doped hydroxyapatite porous coating on Ti-6Al-4 V for bone regeneration applications

Dual-doped hydroxyapatite (Ce⁴⁺/Si⁴⁺ doped HAP) coating with admirable bacterial resistance and enriched bioactivity was fabricated via spin-coating technique. In this study, Ce/Si co-doped hydroxyapatite was coated on Ti-6Al-4 V substrates as a triple layer with extreme centrifugal force (2000 RPM, 3000 RPM and 4000 RPM) to improve the biological performance of the coating in terms of enhanced bone apposition. Further, the coated substrate was characterized by XRD, FTIR and SEM-EDS techniques. The contact angle of the coating was measured through the sessile drop method and in vitro biomineralization was carried out in SBF solution to predict the apatite formation on the surface of the coated implant. Pathogen restriction behaviour of the coating was studied using gram-negative and gram-positive bacteria such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa respectively. Among these, gram-negative bacteria, Escherichia coli revealed greater inhibition than other bacteria. In vitro cell viability assay using MG-63 osteoblast cell was performed for the optimised coating acquired at 4000 RPM and the result showed excellent biocompatibility towards the cell line. Corrosion resistance behaviour of the coating using Polarization and EIS study exhibited excellent corrosion resistance. Therefore, based on the in vitro studies, the designed multifunctional coating can act as a potential biomaterial in the field of biomedical engineering.

Interplay of Hydrogel Composition and Geometry on Human Mesenchymal Stem Cell Osteogenesis

Microgels are emerging as an outstanding platform for tissue regeneration because they overcome issues associated with conventional bulk/macroscopic hydrogels such as limited cell-cell contact and cell communication and low diffusion rates. Owing to the enhanced mass transfer and injectability via a minimally invasive procedure, these microgels are becoming a promising approach for bone regeneration applications. Nevertheless, there still remains a huge gap between the understanding of how the hydrogel matrix composition can influence cell response and overall tissue formation when switching from bulk formats to microgel format, which is often neglected or rarely studied. Here, we fabricated polyethylene glycol-based microgels and bulk hydrogels incorporating gelatin and hyaluronic acid (HA), either individually or together, and assessed the impact of both hydrogel composition and format upon the osteogenic differentiation of encapsulated human bone marrow-derived mesenchymal stem cells (hBMSCs). Osteogenesis was significantly greater in microgels than bulk hydrogels for both gelatin alone (Gel) and gelatin HA composite (Gel:HA) hydrogels, as determined by the expression of Runt-related transcription factor (Runx2) and alkaline phosphatase (ALP) genes and mineral deposition. Interestingly, Gel and Gel:HA hydrogels behaved differently between bulk and microgel format. In bulk format, overall osteogenic outcomes were better in Gel:HA hydrogels, but in microgel format, while the level of osteogenic gene expression was equivalent between both compositions, the degree of mineralization was reduced in Gel:HA microgels. Investigation into the affinity of hydroxyapatite for the different matrix compositions indicated that the decreased mineralization of Gel:HA microgels was likely due to a low affinity of hydroxyapatite to bind to HA and support mineral deposition, which has a greater impact on microgels than bulk hydrogels. Together, these findings suggest that both hydrogel composition and format can determine the success of tissue formation and that there is a complex interplay of these two factors on both cell behavior and matrix deposition. This has important implications for tissue engineering, showing that hydrogel composition and geometry must be evaluated together when optimizing conditions for cell differentiation and tissue formation.

Bone marrow aspirate concentrate and platelet-rich fibrin in fresh extraction sockets: A histomorphometric and immunohistochemical study in humans

The aim of this study was to evaluate the level of mineralized tissue and expression of bone markers in sockets grafted with platelet-rich fibrin and bone marrow aspirate concentrate (BMAC). Patients requiring extraction of one maxillary anterior tooth were randomized into three groups. After tooth extraction, the sockets in the control group (CG) were permitted to fill with blood clot. In the platelet-rich fibrin group (PRFG), after blood processing, the sockets were grafted with PRF plug. In the bone marrow aspirate concentrate combined with platelet-rich fibrin group (BM/PG), after blood and bone marrow processing, the sockets were grafted with a mixture of PRF plug and BMAC. After 6 months, the sites were reopened and bone cores were harvested and prepared for histomorphometric and immunohistochemical evaluation. The following levels were measured: mineralized tissue, expression of RUNX-2, and osteocalcin. Fifteen patients were included in this study. The histomorphometric analysis showed a more pronounced level of mineralized tissue in PRFG and BM/PG (54.20 ± 4.31% and 64.70 ± 6.74%, respectively) when compared with CG (40.60 ± 5.98%) (p = 0.0283 and p = 0.0090, respectively). The expression of RUNX-2 was very low in BM/PG (0.80 ± 0.84%) and absent in CG and PRFG (p = 0.0528). Osteocalcin expression was higher for BM/PG (23.40 ± 1.52%) when compared with CG and PRFG (18.40 ± 2.07% and 16.20 ± 1.92%, respectively) (p = 0.0117 and p = 0.0088, respectively). This preliminary study indicates that clinical use of bone marrow aspirate concentrate, when combined with platelet-rich fibrin as a carrier, might have some potential to increase mineralization in fresh extraction sockets.

Biodegradable Hydrogels Loaded with Magnetically Responsive Microspheres as 2D and 3D Scaffolds

Scaffolds play an essential role in the success of tissue engineering approaches. Their intrinsic properties are known to influence cellular processes such as adhesion, proliferation and differentiation. Hydrogel-based matrices are attractive scaffolds due to their high-water content resembling the native extracellular matrix. In addition, polymer-based magnetoelectric materials have demonstrated suitable bioactivity, allowing to provide magnetically and mechanically activated biophysical electrical stimuli capable of improving cellular processes. The present work reports on a responsive scaffold based on poly (L-lactic acid) (PLLA) microspheres and magnetic microsphere nanocomposites composed of PLLA and magnetostrictive cobalt ferrites (CoFe2O4), combined with a hydrogel matrix, which mimics the tissue's hydrated environment and acts as a support matrix. For cell proliferation evaluation, two different cell culture conditions (2D and 3D matrices) and two different strategies, static and dynamic culture, were applied in order to evaluate the influence of extracellular matrix-like confinement and the magnetoelectric/magneto-mechanical effect on cellular behavior. MC3T3-E1 proliferation rate is increased under dynamic conditions, indicating the potential use of hydrogel matrices with remotely stimulated magnetostrictive biomaterials for bone tissue engineering.

Effectiveness of a biodegradable 3D polylactic acid/poly(ɛ-caprolactone)/hydroxyapatite scaffold loaded by differentiated osteogenic cells in a critical-sized radius bone defect in rat

The effects of a scaffold made of polylactic acid, poly (ɛ-caprolactone) and hydroxyapatite by indirect 3D printing method with and without differentiated bone cells was tested on the regeneration of a critical radial bone defect in rat. The scaffold characterization and mechanical performance were determined by the rheology, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The defects were created in forty Wistar rats which were randomly divided into the untreated, autograft, scaffold cell-free, and differentiated bone cell-seeded scaffold groups (n = 10 in each group). The expression level of angiogenic and osteogenic markers, analyzed by quantitative real time-polymerase chain reaction (in vitro), significantly improved (p < 0.05) in the scaffold group compared to the untreated one. Radiology and computed tomography scan demonstrated a significant improvement in the cell-seeded scaffold group compared to the untreated one (p < 0.001). Biomechanical, histopathological, histomorphometric, and immunohistochemical investigations showed significantly better regeneration scores in the cell-seeded scaffold and autograft groups compared to the untreated group (p < 0.05). The cell-seeded scaffold and autograft groups did show comparable results on the 80^th day post-treatment (p > 0.05), however, most results in the scaffold group were significantly higher than the untreated group (p < 0.05). Differentiated bone cells can enhance bone regeneration potential of the scaffold.

Polyetheretherketone and Its Composites for Bone Replacement and Regeneration

In this article, recent advances in the development, preparation, biocompatibility and mechanical properties of polyetheretherketone (PEEK) and its composites for hard and soft tissue engineering are reviewed. PEEK has been widely employed for fabricating spinal fusions due to its radiolucency, chemical stability and superior sterilization resistance at high temperatures. PEEK can also be tailored into patient-specific implants for treating orbital and craniofacial defects in combination with additive manufacturing process. However, PEEK is bioinert, lacking osseointegration after implantation. Accordingly, several approaches including surface roughening, thin film coating technology, and addition of bioactive hydroxyapatite (HA) micro-/nanofillers have been adopted to improve osseointegration performance. The elastic modulus of PEEK is 3.7-4.0 GPa, being considerably lower than that of human cortical bone ranging from 7-30 GPa. Thus, PEEK is not stiff enough to sustain applied stress in load-bearing orthopedic implants. Therefore, HA micro-/nanofillers, continuous and discontinuous carbon fibers are incorporated into PEEK for enhancing its stiffness for load-bearing applications. Among these, carbon fibers are more effective than HA micro-/nanofillers in providing additional stiffness and load-bearing capabilities. In particular, the tensile properties of PEEK composite with 30wt% short carbon fibers resemble those of cortical bone. Hydrophobic PEEK shows no degradation behavior, thus hampering its use for making porous bone scaffolds. PEEK can be blended with hydrophilic polymers such as polyglycolic acid and polyvinyl alcohol to produce biodegradable scaffolds for bone tissue engineering applications.

Robotic in situ 3D bio-printing technology for repairing large segmental bone defects

Introduction

The traditional clinical treatment of long segmental bone defects usually requires multiple operations and depends on donor availability. The 3D bio-printing technology constitutes a great potential therapeutic tool for such an injury. However, in situ 3D bio-printing remains a major challenge.

Objectives

In this study, we report the repair of long segmental bone defects by in situ 3D bio-printing using a robotic manipulator 3D printer in a swine model.

Methods

We systematically optimized bio-ink gelation under physiological conditions to achieve desirable mechanical properties suitable for bone regeneration, and a D-H kinematic model was used to improve printing accuracy to 0.5 mm.

Results

These technical improvements allowed the repair of long segmental defects generated on the right tibia of pigs using 3D bio-printing within 12 min. The 3D bio-printing group showed improved treatment effects after 3 months.

Conclusion

These findings indicated that robotic in situ 3D bio-printing is promising for direct clinical application.

Bone tissue engineering gelatin-hydroxyapatite/graphene oxide scaffolds with the ability to release vitamin D: fabrication, characterization, and in vitro study

Developing smart scaffolds with drug release capability is one of the main approaches to bone tissue engineering. The current study involves the fabrication of novel gelatin (G)-hydroxyapatite (HA)-/vitamin D (VD)-loaded graphene oxide (GO) scaffolds with different concentrations through solvent-casting method. Characterizations confirmed the successful synthesis of HA and GO, and VD was loaded in GO with 36.87 ± 4.87% encapsulation efficiency. Physicochemical characterizations showed that the scaffold containing 1% VD-loaded GO had the best mechanical properties and its porosity percentage and density was in the range of natural spongy bone. All scaffolds were degraded after 1-month, subjecting to phosphate buffer saline. The release profile of VD did not match any mathematical kinetics model, porosities and the degradation rate of the scaffolds were dominant controlling factors of release behavior. Studies on the bioactivity of scaffolds immersed in simulated body fluid indicated that VD and HA could encourage the formation of secondary apatite crystals in vitro. Buccal fat pad-derived stem cells (BFPSCs) were seeded on the scaffolds, MTT assay, alkaline phosphatase activity as an indicator of osteoconductivity, and cell adhesion were conducted in order to evaluate in vitro biological responses. All scaffolds highly supported cell adhesion, MTT assay indicated better cell viability in 0.5% VD-loaded GO containing scaffold, and the scaffold enriched with 2% VD-loaded GO performed the most ALP activity. The results demonstrated the potential of these scaffolds to induce bone regeneration. Developing smart scaffolds with drug release capability is one of the main approaches to bone tissue engineering. The current study involves the fabrication of novel gelatin (G)-hydroxyapatite (HA)-/vitamin D (VD)-loaded graphene oxide (GO) scaffolds with different concentrations through solvent-casting method. Characterizations confirmed the successful synthesis of HA and GO, and VD was loaded in GO with 36.87 ± 4.87% encapsulation efficiency. Physicochemical characterizations showed that the scaffold containing 1% VD-loaded GO had the best mechanical properties and its porosity percentage and density was in the range of natural spongy bone. All scaffolds were degraded after 1-month, subjecting to phosphate buffer saline. The release profile of VD did not match any mathematical kinetics model, porosities and the degradation rate of the scaffolds were dominant controlling factors of release behavior. Studies on the bioactivity of scaffolds immersed in simulated body fluid indicated that VD and HA could encourage the formation of secondary apatite crystals in vitro. Buccal fat pad-derived stem cells (BFPSCs) were seeded on the scaffolds, MTT assay, alkaline phosphatase activity as an indicator of osteoconductivity, and cell adhesion were conducted in order to evaluate in vitro biological responses. All scaffolds highly supported cell adhesion, MTT assay indicated better cell viability in 0.5% VD-loaded GO containing scaffold, and the scaffold enriched with 2% VD-loaded GO performed the most ALP activity. The results demonstrated the potential of these scaffolds to induce bone regeneration.

The effects of oyster shell/alpha-calcium sulfate hemihydrate/platelet-rich plasma/bone mesenchymal stem cells bioengineering scaffold on rat critical-sized calvarial defects

Engineering scaffolds combining natural biomineral and artificially synthesized material hold promising potential for bone tissue regeneration. We fabricated a bioengineering scaffold, oyster shell (OS) and alpha-calcium sulfate hemihydrate (α-CSH) as scaffold, platelet-rich plasma (PRP) as provider of growth factors and bone mesenchymal stem cells (BMSCs) as seed cells, and determined it could be applied as a new type of bone graft substitutes by rat calvarial defects repairing experiment in vitro and in vivo. SEM showed that the mean diameter of the pores was about 150 μm with a range of 50-200 μm, and scaffold's porosity was ~27.4% by Archimedes' Principle. In vitro, Scaffold + BMSCs + PRP group presented a higher ALP activity compared with other groups by ELISA (P < 0.05). But the expression of OC was not detectable on day 4 or 8. The MTT assay showed that the relative cell number of BMSCs+PRP group increased significantly (P < 0.05). In vivo, the smallest defect area of skull and highest volume of regenerated new bone were observed in Scaffold + PRP + BMSCs group by X-ray and Micro-CT analysis (P < 0.05). And the similar results also were observed in HE and Masson staining. The immunohistochemistry staining for osteogenic marker proteins ALP and OC showed that the most obvious positive staining was observed in Scaffold + PRP + BMSCs group (P < 0.05). The expression of inflammatory markers IL-6 and TNF-α was the lowest in control group (P < 0.05). In conclusion, a bioengineering scaffold based on OS, created by simply combining α-CSH and PRP and implanting with BMSCs, could be clinically useful and has marked advantages as a targeted, off-the-shelf, cell-loaded treatment option for the bone healing of critical-size calvarial defects.

OsteoBLAST: Computational Routine of Global Molecular Analysis Applied to Biomaterials Development

For bone purposes, surface modifications are a common trend in biomaterials research aiming to reduce the time necessary for osteointegration, culminating in faster recovery of patients. In this scenario, analysis of intracellular signaling pathways have emerged as an important and reliable strategy to predict biological responses from in vitro approaches. We have combined global analysis of intracellular protein phosphorylation, systems biology and bioinformatics into an early biomaterial analysis routine called OsteoBLAST. We employed the routine as follows: the PamChip tyrosine kinase assay was applied to mesenchymal stem cells grown on three distinct titanium surfaces: machined, dual acid-etched and nanoHA. Then, OsteoBLAST was able to identify the most reliable spots to further obtain the differential kinome profile and finally to allow a comparison among the different surfaces. Thereafter, NetworKIN, STRING, and Cytoscape were used to build and analyze a supramolecular protein-protein interaction network, and DAVID tools identified biological signatures in the differential kinome for each surface.