Biomimetic Nanosilica-Collagen Scaffolds for In Situ Bone Regeneration: Toward a Cell-Free, One-Step Surgery

Collagen as the extracellular matrix biomaterials in the arena of medical sciences

Collagen is a multipurpose material that has several applications in the health care, dental care, and pharmaceutical industries. Crosslinked compacted solids or lattice-like gels can be made from collagen. Biocompatibility, biodegradability, and wound-healing properties make collagen a popular scaffold material for cardiovascular, dentistry, and bone tissue engineering. Due to its essential role in the control of several of these processes, collagen has been employed as a wound-healing adjunct. It forms a major component of the extracellular matrix and regulates wound healing in its fibrillar or soluble forms. Collagen supports cardiovascular and other soft tissues. Oral wounds have been dressed with resorbable forms of collagen for closure of graft and extraction sites, and to aid healing. This present review is concentrated on the use of collagen in bone regeneration, wound healing, cardiovascular tissue engineering, and dentistry.

Natural Affinity Driven Modification by Silicene to Construct a "Thermal Switch" for Tumorous Bone Loss

Tumorous bone defects present significant challenges for surgical bio-reconstruction due to the dual pathological conditions of residual tumor presence and extensive bone loss following excision surgery. To address this challenge, a "thermal switch" smart bone scaffold based on the silicene nanosheet-modified decalcified bone matrix (SNS@DBM) is developed by leveraging the natural affinity between collagen and silicene, which is elucidated by molecular dynamics simulations. Benefitting from its exceptional photothermal ability, biodegradability, and bioactivity, the SNS@DBM "thermal switch" provides an integrated postoperative sequential thermotherapy for tumorous bone loss by exerting three levels of photothermal stimulation (i.e., strong, moderate, and nonstimulation). During the different phases of postoperative bioconstruction, the SNS@DBM scaffold realizes simultaneous residual tumor ablation, tumor recurrence prevention, and bone tissue regeneration. These biological effects are verified in the tumor-bearing nude mice of patient-derived tissue xenografts and critical cranium defect rats. Mechanism research prompts moderate heat stimulus generated by and coordinating with SNSs can upregulate osteogenic genes, promote macrophages M2 polarization, and intensify angiogenesis of H-type vessels. This study introduces a versatile approach to the management of tumorous bone defects.

Preparation and Characterization of Silica-Coated Sodium Alginate Hydrogel Beads and the Delivery of Curcumin

In this study, to address the defects of sodium alginate (SA), such as its susceptibility to disintegration, silica was coated on the outer layer of sodium alginate hydrogel beads in order to improve its swelling and slow-release properties. Tetraethyl orthosilicate (TEOS) was used as the hydrolyzed precursor, and the solution of silica precursor was prepared by sol-gel reaction under acidic conditions. Then SA-silica hydrogel beads prepared by ionic crosslinking method were immersed into the SiO2 precursor solution to prepare SA-silica hydrogel beads. The chemical structure and morphology of the hydrogel beads were characterized by XRD, FTIR, and SEM, and the results showed that the surface of SA-silica beads was successfully encapsulated with the outer layer of SiO2, and the surface was smooth and dense. The swelling experiments showed that the swelling performance effectively decreased with the increase of TEOS molar concentration, and the maximum swelling ratio of the hydrogel beads decreased from 41.07 to 14.3, and the time to reach the maximum swelling ratio was prolonged from 4 h to 8 h. The sustained-release experiments showed that the SA-silica hydrogel beads possessed a good pH sensitivity, and the time of sustained-release was significantly prolonged in vitro. Hemolysis and cytotoxicity experiments showed that the SA-silica hydrogel beads were biocompatible when the TEOS molar concentration was lower than 0.375 M. The SA-silica-2 hydrogel beads had good biocompatibility, swelling properties, and slow-release properties at the same time.

Nanobioactive Blood-Derived Shear-Thinning Biomaterial for Tissue Engineering Applications

The conventional technique for successful bone grafts, involving the use of a patienťs own tissue (autografts), is challenged by limited availability and donor site morbidity. While allografts and xenografts offer alternatives, they come with the risk of rejection. This underscores the pressing need for tailor-made artificial bone graft materials. In this context, injectable hydrogels are emerging as a promising solution for bone regeneration, especially in complex maxillofacial reconstruction cases. These hydrogels can seamlessly adapt to irregular shapes and conservatively fill defects. Our study introduces a shear-thinning biomaterial by blending silicate nanoplatelets (SNs) enriched with human blood-derived plasma rich in growth factors (PRGF) for personalized applications. Notably, our investigations unveil that injectable hydrogel formulations comprising 7.5% PRGF yield sustained protein and growth factor release, affording precise control over critical growth factors essential for tissue regeneration. Moreover, our hydrogel exhibits exceptional biocompatibility in vitro and in vivo and demonstrates hemostatic properties. The hydrogel also presents a robust angiogenic potential and an inherent capacity to promote bone differentiation, proven through Alizarin Red staining, gene expression, and immunostaining assessments of bone-related biomarkers. Given these impressive attributes, our hydrogel stands out as a leading candidate for maxillofacial bone regeneration application. Beyond this, our findings hold immense potential in revolutionizing the field of regenerative medicine, offering an influential platform for crafting precise and effective therapeutic strategies.

Mild Thermotherapy-Assisted GelMA/HA/MPDA@Roxadustat 3D-Printed Scaffolds with Combined Angiogenesis-Osteogenesis Functions for Bone Regeneration

Early reconstruction of the vascular network is a prerequisite to the effective treatment of substantial bone defects. Traditional 3D printed tissue engineering scaffolds designed to repair large bone defects do not effectively regenerate the vascular network, and rely only on the porous structure within the scaffold for nutrient transfer and metabolic waste removal. This leads to delayed bone restoration and hence functional recovery. Therefore, strategies for generation scaffolds with the capacity to efficiently regenerate vascularization should be developed. This study loads roxarestat (RD), which can stabilize HIF-1α expression in a normoxic environment, onto the mesopore polydopamine nanoparticles (MPDA@RD) to enhance the reconstruction of vascular network in large bone defects. Subsequently, MPDA@RD is mixed with GelMA/HA hydrogel bioink to fabricate a multifunctional hydrogel scaffold (GHM@RD) through 3D printing. In vitro results show that the GHM@RD scaffolds achieve good angiogenic-osteogenic coupling by activating the PI3K/AKT/HSP90 pathway in BMSCs and the PI3K/AKT/HIF-1α pathway in HUVECs under mild thermotherapy. In vivo experiments reveal that RD and mild hyperthermia synergistically induce early vascularization and bone regeneration of critical bone defects. In conclusion, the designed GHM@RD drug delivery scaffold with mild hyperthermia holds great therapeutic value for future treatment of large bone defects.

Biomimetic Mineralized 3D-Printed Polycaprolactone Scaffold Induced by Self-Adaptive Nanotopology to Accelerate Bone Regeneration

Three-dimensional (3D)-printed biodegradable polymer scaffolds are at the forefront of personalized constructs for bone tissue engineering. However, it remains challenging to create a biological microenvironment for bone growth. Herein, we developed a novel yet feasible approach to facilitate biomimetic mineralization via self-adaptive nanotopography, which overcomes difficulties in the surface biofunctionalization of 3D-printed polycaprolactone (PCL) scaffolds. The building blocks of self-adaptive nanotopography were PCL lamellae that formed on the 3D-printed PCL scaffold via surface-directed epitaxial crystallization and acted as a linker to nucleate and generate hydroxyapatite crystals. Accordingly, a uniform and robust mineralized layer was immobilized throughout the scaffolds, which strongly bound to the strands and had no effect on the mechanical properties of the scaffolds. In vitro cell culture experiments revealed that the resulting scaffold was biocompatible and enhanced the proliferation and osteogenic differentiation of mouse embryolous osteoblast cells. Furthermore, we demonstrated that the resulting scaffold showed a strong capability to accelerate in vivo bone regeneration using a rabbit bone defect model. This study provides valuable opportunities to enhance the application of 3D-printed scaffolds in bone repair, paving the way for translation to other orthopedic implants.

Nanocellulose-Based Hybrid Scaffolds for Skin and Bone Tissue Engineering: A 10-Year Overview

Cellulose, the most abundant polymer on Earth, has been widely utilized in its nanoform due to its excellent properties, finding applications across various scientific fields. As the demand for nanocellulose continues to rise and its ease of use becomes apparent, there has been a significant increase in research publications centered on this biomaterial. Nanocellulose, in its different forms, has shown tremendous promise as a tissue engineered scaffold for regeneration and repair. Particularly, nanocellulose-based composites and scaffolds have emerged as highly demanding materials for both soft and hard tissue engineering. Medical practitioners have traditionally relied on collagen and its analogue, gelatin, for treating tissue damage. However, the limited mechanical strength of these biopolymers restricts their direct use in various applications. This issue can be overcome by making hybrids of these biopolymers with nanocellulose. This review presents a comprehensive analysis of the recent and most relevant publications focusing on hybrid composites of collagen and gelatin with a specific emphasis on their combination with nanocellulose. While bone and skin tissue engineering represents two areas where a majority of researchers are concentrating their efforts, this review highlights the use of nanocellulose-based hybrids in these contexts.

3D-printed PCL framework assembling ECM-inspired multi-layer mineralized GO-Col-HAp microscaffold for in situ mandibular bone regeneration

BACKGROUND

In recent years, natural bone extracellular matrix (ECM)-inspired materials have found widespread application as scaffolds for bone tissue engineering. However, the challenge of creating scaffolds that mimic natural bone ECM's mechanical strength and hierarchical nano-micro-macro structures remains. The purposes of this study were to introduce an innovative bone ECM-inspired scaffold that integrates a 3D-printed framework with hydroxyapatite (HAp) mineralized graphene oxide-collagen (GO-Col) microscaffolds and find its application in the repair of mandibular bone defects.

METHODS

Initially, a 3D-printed polycaprolactone (PCL) scaffold was designed with cubic disks and square pores to mimic the macrostructure of bone ECM. Subsequently, we developed multi-layer mineralized GO-Col-HAp microscaffolds (MLM GCH) to simulate natural bone ECM's nano- and microstructural features. Systematic in vitro and in vivo experiments were introduced to evaluate the ECM-inspired structure of the scaffold and to explore its effect on cell proliferation and its ability to repair rat bone defects.

RESULTS

The resultant MLM GCH/PCL composite scaffolds exhibited robust mechanical strength and ample assembly space. Moreover, the ECM-inspired MLM GCH microscaffolds displayed favorable attributes such as water absorption and retention and demonstrated promising cell adsorption, proliferation, and osteogenic differentiation in vitro. The MLM GCH/PCL composite scaffolds exhibited successful bone regeneration within mandibular bone defects in vivo.

CONCLUSIONS

This study presents a well-conceived strategy for fabricating ECM-inspired scaffolds by integrating 3D-printed PCL frameworks with multilayer mineralized porous microscaffolds, enhancing cell proliferation, osteogenic differentiation, and bone regeneration. This construction approach holds the potential for extension to various other biomaterial types.

Spatiotemporal Modulated Scaffold for Endogenous Bone Regeneration via Harnessing Sequentially Released Guiding Signals

The design of a scaffold that can regulate the sequential differentiation of bone marrow mesenchymal stromal cells (BMSCs) according to the endochondral ossification (ECO) mechanism is highly desirable for effective bone regeneration. In this study, we successfully fabricated a dual-networked composite hydrogel composed of gelatin and hyaluronic acid (termed GCDH-M), which can sequentially release chondroitin sulfate (CS) and magnesium/silicon (Mg/Si) ions to provide spatiotemporal guidance for chondrogenesis, angiogenesis, and osteogenesis. The fast release of CS is from the GCDH hydrogel, and the sustained releases of Mg/Si ions are from poly(lactide-co-glycolide) microspheres embedded in the hydrogel. There is a difference in the release rates between CS and ions, resulting in the ability for the fast release of CS and sustained release of ions. The dual networks between the modified gelatin and hyaluronic acid via covalent bonding and host-guest interactions render the hydrogel with some dynamic feature to meet the differentiation development of BMSCs laden inside the hydrogel, i.e., transforming into a chondrogenic phenotype, further to a hypertrophic phenotype and eventually to an osteogenic phenotype. As evidenced by the results of in vitro and in vivo evaluations, this GCDH-M composite hydrogel was proved to be able to create an optimal microenvironment for embedded BMSCs responding to the sequential guiding signals, which aligns with the rhythm of the ECO process and ultimately boosts bone regeneration. The promising outcome achieved with this innovative hydrogel system sheds light on novel scaffold design targeting bone tissue engineering.

Elastic 3D-Printed Nanofibers Composite Scaffold for Bone Tissue Engineering

Loading nanoparticles into hydrogels has been a conventional approach to augment the printability of ink and the physicochemical characteristics of scaffolds in three-dimensional (3D) printing. However, the efficacy of this enhancement has often proven to be limited. We amalgamate electrospun nanofibers with 3D printing techniques to fabricate a composite scaffold reminiscent of a "reinforced concrete" structure, aimed at addressing bone defects. These supple silica nanofibers are synthesized through a dual-step process involving high-speed homogenization and low-temperature ball milling technology. The nanofibers are homogeneously blended with sodium alginate to create the printing ink. The resultant ink was extruded seamlessly, displaying commendable molding properties, thereby yielding scaffolds with favorable macroscopic morphology. In contrast to nanoparticle-reinforced scaffolds, composite scaffolds containing nanofibers exhibit superior mechanical attributes and bioactivity. These nanofiber composite scaffolds demonstrate enhanced osteoinductive properties in both in vitro and in vivo evaluations. To conclude, this research introduces a novel 3D printing approach where the fabricated nanofiber-infused 3D-printed scaffolds hold the potential to revolutionize the realm of 3D printing in the domain of bone tissue engineering.

Multifunctional mesoporous silica nanoparticles for biomedical applications

Mesoporous silica nanoparticles (MSNs) are recognized as a prime example of nanotechnology applied in the biomedical field, due to their easily tunable structure and composition, diverse surface functionalization properties, and excellent biocompatibility. Over the past two decades, researchers have developed a wide variety of MSNs-based nanoplatforms through careful design and controlled preparation techniques, demonstrating their adaptability to various biomedical application scenarios. With the continuous breakthroughs of MSNs in the fields of biosensing, disease diagnosis and treatment, tissue engineering, etc., MSNs are gradually moving from basic research to clinical trials. In this review, we provide a detailed summary of MSNs in the biomedical field, beginning with a comprehensive overview of their development history. We then discuss the types of MSNs-based nanostructured architectures, as well as the classification of MSNs-based nanocomposites according to the elements existed in various inorganic functional components. Subsequently, we summarize the primary purposes of surface-functionalized modifications of MSNs. In the following, we discuss the biomedical applications of MSNs, and highlight the MSNs-based targeted therapeutic modalities currently developed. Given the importance of clinical translation, we also summarize the progress of MSNs in clinical trials. Finally, we take a perspective on the future direction and remaining challenges of MSNs in the biomedical field.

Biomimetic Polyphenolic Scaffolds with Antioxidative Abilities for Improved Bone Regeneration

Bone defects have a severe impact on the health and lives of patients due to their long-lasting and difficult-to-treat features. Recent studies have shown that there are complex microenvironments, including excessive production of reactive oxygen species. Herein, a surface functionalization strategy using metal-polyphenolic networks was used, which was found to be beneficial in restoring oxidative balance and enhancing osseointegration. The surface properties, biocompatibility, intracellular ROS scavenging, and osseointegration capacity were evaluated, and the therapeutic effects were confirmed using a skull defect model. This approach has great potential to improve complex microenvironments and enhance the efficiency of bone tissue regeneration.

Calcium sulfate-Cu2+ delivery system improves 3D-Printed calcium silicate artificial bone to repair large bone defects

There are still limitations in artificial bone materials used in clinical practice, such as difficulty in repairing large bone defects, the mismatch between the degradation rate and tissue growth, difficulty in vascularization, an inability to address bone defects of various shapes, and risk of infection. To solve these problems, our group designed stereolithography (SLA) 3D-printed calcium silicate artificial bone improved by a calcium sulfate-Cu2+ delivery system. SLA technology endows the scaffold with a three-dimensional tunnel structure to induce cell migration to the center of the bone defect. The calcium sulfate-Cu2+ delivery system was introduced to enhance the osteogenic activity of calcium silicate. Rapid degradation of calcium sulfate (CS) induces early osteogenesis in the three-dimensional tunnel structure. Calcium silicate (CSi) which degrades slowly provides mechanical support and promotes bone formation in bone defect sites for a long time. The gradient degradation of these two components is perfectly matched to the rate of repair in large bone defects. On the other hand, the calcium sulfate delivery system can regularly release Cu2+ in the temporal and spatial dimensions, exerting a long-lasting antimicrobial effect and promoting vascular growth. This powerful 3D-printed calcium silicate artificial bone which has rich osteogenic activity is a promising material for treating large bone defects and has excellent potential for clinical application.

Alkaline shear-thinning micro-nanocomposite hydrogels initiate endogenous TGFβ signaling for in situ bone regeneration

Recruiting endogenous stem cells to bone defects without stem cell transplantation and exogenous factor delivery represents a promising strategy for bone regeneration. Herein, we develop an alkaline shear-thinning micro-nanocomposite hydrogel (10-MmN), aiming to alkaline-activate endogenous TGFβ1 and achieve in situ bone regeneration. It contains polyethyleneimine (PEI)-modified gelatin, laponite nanoplatelets (LAP), a bicarbonate buffer with a pH of 10, and gelatin microspheres (MSs). PEI-modified gelatin plays a pivotal role in hydrogel fabrication. It endows the system with sufficient positive charges, and forms a shear-thinning nanocomposite matrix in the pH 10 buffer (10-mN) with negatively charged LAP via electrostatic gelation. For biological functions, the pH 10 buffer dominates alkaline activation of endogenous serum TGFβ1 to recruit rat bone marrow stem cells through the Smad pathway, followed by improved osteogenic differentiation. In addition, MSs are incorporated into 10-mN to form 10-MmN, and function as substrates to provide good attachment sites for the recruited stem cells and facilitate further their osteogenic differentiation. In a rat critical-sized calvarial defect model, 10-MmN exhibits excellent biocompatibility, biodegradability, hydrogel infusion and retention in bone defects with flexible shapes and active bleeding. Importantly, it repairs ~95% of the defect areas in 3 months by recruiting TGFβR2+ and CD90+CD146+ stem cells, and promoting cell proliferation, osteogenic differentiation and bone formation. The present study provides a biomaterial-based strategy to regulate alkalinity in bone defects for the initiation of endogenous TGFβ signaling, which can be extended to treat other diseases.

Flexible Fabrication and Hybridization of Bioactive Hydrogels with Robust Osteogenic Potency

Osteogenic scaffolds reproducing the natural bone composition, structures, and properties have represented the possible frontier of artificially orthopedic implants with the great potential to revolutionize surgical strategies against the bone-related diseases. However, it is difficult to achieve an all-in-one formula with the simultaneous requirement of favorable biocompatibility, flexible adhesion, high mechanical strength, and osteogenic effects. Here in this work, an osteogenic hydrogel scaffold fabricated by inorganic-in-organic integration between amine-modified bioactive glass (ABG) nanoparticles and poly(ethylene glycol) succinimidyl glutarate-polyethyleneimine (TSG-PEI) network was introduced as an all-in-one tool to flexibly adhere onto the defective tissue and subsequently accelerate the bone formation. Since the N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG polymer could quickly react with the NH2-abundant polyethyleneimine (PEI) polymer and ABG moieties, the TSG-PEI@ABG hydrogel was rapidly formed with tailorable structures and properties. Relying on the dense integration between the TSG-PEI network and ABG moieties on a nano-scale level, this hydrogel expressed powerful adhesion to tissue as well as durable stability for the engineered scaffolds. Therefore, its self-endowed biocompatibility, high adhesive strength, compressive modulus, and osteogenic potency enabled the prominent capacities on modulation of bone marrow mesenchymal stem cell (BMSCs) proliferation and differentiation, which may propose a potential strategy on the simultaneous scaffold fixation and bone regeneration promotion for the tissue engineering fields.

Cell unit-inspired natural nano-based biomaterials as versatile building blocks for bone/cartilage regeneration

The regeneration of weight-bearing bone defects and critical-sized cartilage defects remains a significant challenge. A wide range of nano-biomaterials are available for the treatment of bone/cartilage defects. However, their poor compatibility and biodegradability pose challenges to the practical applications of these nano-based biomaterials. Natural biomaterials inspired by the cell units (e.g., nucleic acids and proteins), have gained increasing attention in recent decades due to their versatile functionality, compatibility, biodegradability, and great potential for modification, combination, and hybridization. In the field of bone/cartilage regeneration, natural nano-based biomaterials have presented an unparalleled role in providing optimal cues and microenvironments for cell growth and differentiation. In this review, we systematically summarize the versatile building blocks inspired by the cell unit used as natural nano-based biomaterials in bone/cartilage regeneration, including nucleic acids, proteins, carbohydrates, lipids, and membranes. In addition, the opportunities and challenges of natural nano-based biomaterials for the future use of bone/cartilage regeneration are discussed.

Advances and Prospects in Materials for Craniofacial Bone Reconstruction

The craniofacial region is composed of 23 bones, which provide crucial function in keeping the normal position of brain and eyeballs, aesthetics of the craniofacial complex, facial movements, and visual function. Given the complex geometry and architecture, craniofacial bone defects not only affect the normal craniofacial structure but also may result in severe craniofacial dysfunction. Therefore, the exploration of rapid, precise, and effective reconstruction of craniofacial bone defects is urgent. Recently, developments in advanced bone tissue engineering bring new hope for the ideal reconstruction of the craniofacial bone defects. This report, presenting a first-time comprehensive review of recent advances of biomaterials in craniofacial bone tissue engineering, overviews the modification of traditional biomaterials and development of advanced biomaterials applying to craniofacial reconstruction. Challenges and perspectives of biomaterial development in craniofacial fields are discussed in the end.

Hydrogenated silicene nanosheet functionalized scaffold enables immuno-bone remodeling

An ideal implant needs to have the ability to coordinate the foreign body response and tissue regeneration. Here, Hydrogenated-silicon nanosheets (H-Si NSs) with favorable biodegradability are integrated and functionalized into a β-tricalcium phosphate scaffold (H-Si TCP) for bone defect healing. H-Si TCP can greatly improve bone regeneration through osteoimmunomodulation-guided biodegradation in vivo. The spatiotemporal regulation of degradation products replenishes sufficient nutrients step by step for the entire process of bone repair. Extracellular and intracellular reactive oxygen species (ROS) are first downregulated by reaction with H-Si NSs, followed by marked M2 polarization, remodeling the micro-environment timely for immune-bone regeneration. The release of primary reaction products awakened bone marrow mesenchymal stem cells (BMSCs), which are converted into osteoblasts anchored on scaffolds. Subsequently, biomineralization is promoted by the final degradation products. The intrinsic ROS-responsive, immunoregulatory, and osteo-promotive capability of 2D H-Si NSs makes such composite H-Si TCP scaffold a highly potential alternative for the treatment of critical bone defect.

Sequential Dual-Biofactor Release from the Scaffold of Mesoporous HA Microspheres and PLGA Matrix for Boosting Endogenous Bone Regeneration

The combined design of scaffold structure and multi-biological factors is a prominent strategy to promote bone regeneration. Herein, a composite scaffold of mesoporous hydroxyapatite (HA) microspheres loaded with the bone morphogenetic protein-2 (BMP-2) and a poly(DL-lactic-co-glycolic acid) (PLGA) matrix is constructed by 3D printing. Furthermore, the chemokine stromal cell-derived factor-1α (SDF-1α) is adsorbed on a scaffold surface to achieve the sequential release of the dual-biofactors. The results indicate that the rapid release of SDF-1α chemokine on the scaffold surface effectively recruits bone marrow-derived mesenchymal stem cells (BMSCs) to the target defect area, whereas the long-term sustained release of BMP-2 from the HA microspheres in the degradable PLGA matrix successfully triggers the osteogenic differentiation in the recruited BMSCs, significantly promoting bone regeneration and reconstruction. In addition, these structures/biofactors specially combining scaffold exhibit significantly better biological performance than that of other combined scaffolds, including the bare HA/PLGA scaffold, the scaffold loaded with SDF-1α or BMP-2 biofactor alone, and the scaffold with surface SDF-1α and BMP-2 dual-biofactors. The utilization of mesoporous HA, the assembly method, and sequential release of the two biofactors in the 3D printed composite scaffold present a new method for future design of high-performance bone repairing scaffolds.

Fabrication of Injectable Kartogenin-Conjugated Composite Hydrogel with a Sustained Drug Release for Cartilage Repair

Cartilage tissue engineering has attracted great attention in defect repair and regeneration. The utilization of bioactive scaffolds to effectively regulate the phenotype and proliferation of chondrocytes has become an elemental means for cartilage tissue regeneration. On account of the simultaneous requirement of mechanical and biological performances for tissue-engineered scaffolds, in this work we prepared a naturally derived hydrogel composed of a bioactive kartogenin (KGN)-linked chitosan (CS-KGN) and an aldehyde-modified oxidized alginate (OSA) via the highly efficient Schiff base reaction and multifarious physical interactions in mild conditions. On the basis of the rigid backbones and excellent biocompatibility of these two natural polysaccharides, the composite hydrogel demonstrated favorable morphology, easy injectability, good mechanical strength and tissue adhesiveness, low swelling ratio, long-term sustainable KGN release, and facilitated bone marrow mesenchymal stem cell activity, which could simultaneously provide the mechanical and biological supports to promote chondrogenic differentiation and repair the articular cartilage defects. Therefore, we believe this work can offer a designable consideration and potential alternative candidate for cartilage and other soft tissue implants.

Enhancement of Scaffold In Vivo Biodegradability for Bone Regeneration Using P28 Peptide Formulations

The field of bone tissue engineering has shown a great variety of bone graft substitute materials under development to date, with the aim to reconstruct new bone tissue while maintaining characteristics close to the native bone. Currently, insufficient scaffold degradation remains the critical limitation for the success of tailoring the bone formation turnover rate. This study examines novel scaffold formulations to improve the degradation rate in vivo, utilising chitosan (CS), hydroxyapatite (HAp) and fluorapatite (FAp) at different ratios. Previously, the P28 peptide was reported to present similar, if not better performance in new bone production to its native protein, bone morphogenetic protein-2 (BMP-2), in promoting osteogenesis in vivo. Therefore, various P28 concentrations were incorporated into the CS/HAp/FAp scaffolds for implantation in vivo. H&E staining shows minimal scaffold traces in most of the defects induced after eight weeks, showing the enhanced biodegradability of the scaffolds in vivo. The HE stain highlighted the thickened periosteum indicating a new bone formation in the scaffolds, where CS/HAp/FAp/P28 75 µg and CS/HAp/FAp/P28 150 µg showed the cortical and trabecular thickening. CS/HAp/FAp 1:1 P28 150 µg scaffolds showed a higher intensity of calcein green label with the absence of xylenol orange label, which indicates that mineralisation and remodelling was not ongoing four days prior to sacrifice. Conversely, double labelling was observed in the CS/HAp/FAp 1:1 P28 25 µg and CS/HAp/FAp/P28 75 µg, which indicates continued mineralisation at days ten and four prior to sacrifice. Based on the HE and fluorochrome label, CS/HAp/FAp 1:1 with P28 peptides presented a consistent positive osteoinduction following the implantation in the femoral condyle defects. These results show the ability of this tailored formulation to improve the scaffold degradation for bone regeneration and present a cost-effective alternative to BMP-2.

Three Dimensional Printing and Its Applications Focusing on Microneedles for Drug Delivery

Microneedles (MNs) are considered to be a novel smart injection system that causes significantly low skin invasion upon puncturing, due to the micron-sized dimensions that pierce into the skin painlessly. This allows transdermal delivery of numerous therapeutic molecules, such as insulin and vaccines. The fabrication of MNs is carried out through conventional old methods such as molding, as well as through newer and more sophisticated technologies, such as three-dimensional (3D) printing, which is considered to be a superior, more accurate, and more time- and production-efficient method than conventional methods. Three-dimensional printing is becoming an innovative method that is used in education through building intricate models, as well as being employed in the synthesis of fabrics, medical devices, medical implants, and orthoses/prostheses. Moreover, it has revolutionary applications in the pharmaceutical, cosmeceutical, and medical fields. Having the capacity to design patient-tailored devices according to their dimensions, along with specified dosage forms, has allowed 3D printing to stand out in the medical field. The different techniques of 3D printing allow for the production of many types of needles with different materials, such as hollow MNs and solid MNs. This review covers the benefits and drawbacks of 3D printing, methods used in 3D printing, types of 3D-printed MNs, characterization of 3D-printed MNs, general applications of 3D printing, and transdermal delivery using 3D-printed MNs.

Fabrication of Poly(ε-caprolactone)-embedded Lignin-Chitosan Nanocomposite Porous Scaffolds from Pickering Emulsions

Poly(ε-caprolactone) (PCL)-incorporated lignin-chitosan biomass-based nanocomposite porous scaffolds have been effectively prepared by templating oil-in-water Pickering high internal phase emulsions (HIPEs). PCL is dissolved in oil and chitosan and lignin nanoparticles originate in water. The continuous phase of the emulsions is gelled by cross-linking of chitosan with genipin and then freeze-dried to obtain porous scaffolds. The resulting scaffolds display interconnected and tunable pore structures. An increase in PCL content increases the mechanical strength and greatly reduces the water absorption capacity of the scaffolds. Scaffolds loaded with the anti-bacterial drug enrofloxacin show a slow drug release profile, adjustable release rate, and favorable long-term anti-bacterial activity. Moreover, Pickering emulsion templates with suitable viscosity are used as 3D printing inks to construct porous scaffolds with personalized geometry. The results imply that the simplicity and versatility of the technique of combining freeze-drying with Pickering HIPE templates is a promising approach to fabricate hydrophobic biopolymer-incorporated biomass-based nanocomposite porous scaffolds for biomedical applications.

Multi-leveled Nanosilicate Implants Can Facilitate Near-Perfect Bone Healing

Several studies have shown that nanosilicate-reinforced scaffolds are suitable for bone regeneration. However, hydrogels are inherently too soft for load-bearing bone defects of critical sizes, and hard scaffolds typically do not provide a suitable three-dimensional (3D) microenvironment for cells to thrive, grow, and differentiate naturally. In this study, we bypass these long-standing challenges by fabricating a cell-free multi-level implant consisting of a porous and hard bone-like framework capable of providing load-bearing support and a softer native-like phase that has been reinforced with nanosilicates. The system was tested with rat bone marrow mesenchymal stem cells in vitro and as a cell-free system in a critical-sized rat bone defect. Overall, our combinatorial and multi-level implant design displayed remarkable osteoconductivity in vitro without differentiation factors, expressing significant levels of osteogenic markers compared to unmodified groups. Moreover, after 8 weeks of implantation, histological and immunohistochemical assays indicated that the cell-free scaffolds enhanced bone repair up to approximately 84% following a near-complete defect healing. Overall, our results suggest that the proposed nanosilicate bioceramic implant could herald a new age in the field of orthopedics.

Covalent binding modes between BMP-2-derived peptides and graphene in 3D scaffolds determine their osteoinductivity and capacity for calvarial defect repair in vivo

Covalent introduction of bioactive molecules is one of main strategies to significantly enhance the biological activities of bone repair materials. In this study, three most-commonly used chemical groups were respectively introduced on graphene (GP), followed by covalent binding with bone morphogenetic protein-2 (BMP-2) -derived peptides, ensuring that the same molar mass of peptides was bound to different functionalized GP (f-GP). Then the same amount of composites composed of different f-GP and peptides were respectively compounded with poly (lactic-co-glycolic acid) to fabricate 3D scaffolds. In vivo study demonstrated that the scaffolds containing ammonized GP covalently bound with the peptides through amide binding could reach best efficiency of promoting ectopic bone regeneration and repairing calvarial defect probably because the most positive charges on the peptide chain and surface of the ammonized GP could absorb more specific proteins in vivo and have better interactions with them, thereby differentiating most inducible cells into osteogenic cells. Our results indicate that the performances of scaffolds containing covalently bound bioactive molecules can be controlled by the covalent binding mode, and that our prepared scaffold containing ammonized GP covalently bound with the BMP-2-derived peptides through amide binding possess inspiring potential applicable prospects for bone tissue regeneration and engineering.

Bioinspired Piezoelectric Periosteum to Augment Bone Regeneration via Synergistic Immunomodulation and Osteogenesis

Ideal periosteum materials are required to participate in a sequence of bone repair-related physiological events, including the initial immune response, endogenous stem cell recruitment, angiogenesis, and osteogenesis. However, conventional tissue-engineered periosteal materials have difficulty achieving these functions by simply mimicking the periosteum via structural design or by loading exogenous stem cells, cytokines, or growth factors. Herein, we present a novel biomimetic periosteum preparation strategy to comprehensively enhance the bone regeneration effect using functionalized piezoelectric materials. The resulting biomimetic periosteum possessing an excellent piezoelectric effect and improved physicochemical properties was prepared using a biocompatible and biodegradable poly(3-hydroxybutyric acid-co-3-hydrovaleric acid) (PHBV) polymer matrix, antioxidized polydopamine-modified hydroxyapatite (PHA), and barium titanate (PBT), which were further incorporated into the polymer matrix to fabricate a multifunctional piezoelectric periosteum by a simple one-step spin-coating method. The addition of PHA and PBT dramatically enhanced the physicochemical properties and biological functions of the piezoelectric periosteum, resulting in improved surface hydrophilicity and roughness, enhanced mechanical performance, tunable degradation behavior, and stable and desired endogenous electrical stimulations, which is conducive to accelerating bone regeneration. Benefiting from endogenous piezoelectric stimulation and bioactive components, the as-fabricated biomimetic periosteum demonstrated favorable biocompatibility, osteogenic activity, and immunomodulatory functions in vitro, which not only promoted adhesion, proliferation, and spreading as well as osteogenesis of mesenchymal stem cells (MSCs) but also effectively induced M2 macrophage polarization, thereby suppressing reactive oxygen species (ROS)-induced inflammatory reactions. Through in vivo experiments, the biomimetic periosteum with endogenous piezoelectric stimulation synergistically accelerated the formation of new bone in a rat critical-sized cranial defect model. The whole defect was almost completely covered by new bone at 8 weeks post treatment, with a thickness close to that of the host bone. Collectively, with its favorable immunomodulatory and osteogenic properties, the biomimetic periosteum developed here represents a novel method to rapidly regenerate bone tissue using piezoelectric stimulation.

Remote control of the recruitment and capture of endogenous stem cells by ultrasound for in situ repair of bone defects

Stem cell-based tissue engineering has provided a promising platform for repairing of bone defects. However, the use of exogenous bone marrow mesenchymal stem cells (BMSCs) still faces many challenges such as limited sources and potential risks. It is important to develop new approach to effectively recruit endogenous BMSCs and capture them for in situ bone regeneration. Here, we designed an acoustically responsive scaffold (ARS) and embedded it into SDF-1/BMP-2 loaded hydrogel to obtain biomimetic hydrogel scaffold complexes (BSC). The SDF-1/BMP-2 cytokines can be released on demand from the BSC implanted into the defected bone via pulsed ultrasound (p-US) irradiation at optimized acoustic parameters, recruiting the endogenous BMSCs to the bone defected or BSC site. Accompanied by the daily p-US irradiation for 14 days, the alginate hydrogel was degraded, resulting in the exposure of ARS to these recruited host stem cells. Then another set of sinusoidal continuous wave ultrasound (s-US) irradiation was applied to excite the ARS intrinsic resonance, forming highly localized acoustic field around its surface and generating enhanced acoustic trapping force, by which these recruited endogenous stem cells would be captured on the scaffold, greatly promoting them to adhesively grow for in situ bone tissue regeneration. Our study provides a novel and effective strategy for in situ bone defect repairing through acoustically manipulating endogenous BMSCs.

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We designed ARS and embedded it into SDF-1/BMP-2 loaded hydrogel to form BSC.

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The BSC can release SDF-1/BMP-2 by p-US irradiation for recruitment of endogenous BMSCs and capture them by s-US irradiation.

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The in situ repair of bone defects were successfully realized by US-mediated control of the recruitment and capture of BMSCs.

Alkaline "Nanoswords" Coordinate Ferroptosis-like Bacterial Death for Antibiosis and Osseointegration

Ferroptosis is an iron-dependent cell death and is associated with cancer therapy. Can it play a role in resistance of postoperative infection of implants, especially with an extracellular supplement of Fe ions in a non-cytotoxic dose? To answer this, "nanoswords" of Fe-doped titanite are fabricated on a Ti implant surface to resist bacterial invasion by a synergistic action of ferroptosis-like bacteria killing, proton disturbance, and physical puncture. The related antibiosis mechanism is explored by atomic force microscopy and genome sequencing. The nanoswords induce an increased local pH value, which not only weakens the proton motive force, reducing adenosine triphosphate synthesis of Staphylococcus aureus, but also decreases the membrane modulus, making the nanoswords distort and even puncture a bacterial membrane easily. Simultaneously, more Fe ions are taken by bacteria due to increased bacterial membrane permeability, resulting in ferroptosis-like death of bacteria, and this is demonstrated by intracellular iron enrichment, lipid peroxidation, and glutathione depletion. Interestingly, a microenvironment constructed by these nanoswords improves osteoblast behavior in vitro and bone regeneration in vivo. Overall, the nanoswords can induce ferroptosis-like bacterial death without cytotoxicity and have great promise in applications with clinical implants for outstanding antibiosis and biointegration performance.

DLP fabrication of customized porous bioceramics with osteoinduction ability for remote isolation bone regeneration

Currently, various bioceramics have been widely used in bone regeneration. However, it remains a huge challenge to remote isolation bone regeneration, such as severed finger regeneration. The remote isolation bone tissue has a poor regenerative microenvironment that lacks enough blood and nutrition supply. It is very difficult to repair and regenerate. In this study, well-controlled multi-level porous 3D-printed calcium phosphate (CaP) bioceramic scaffolds with precision customized structures were fabricated by high-resolution digital light projection (DLP) printing technology for remote isolation bone regeneration. In vitro results demonstrated that optimizing material processing procedures could achieve multi-level control of 3D-printed CaP bioceramic scaffolds and enhance the osteoinduction ability of bioceramics effectively. In vivo results indicated that 3D-printed CaP bioceramic scaffolds constructed by optimized processing procedure exhibited a promising ability of bone regeneration and osteoinduction in ectopic osteogenesis and in situ caudal vertebrae regeneration in beagles. This study provided a promising strategy based on 3D-printed CaP bioceramic scaffolds constructed by optimized processing procedures for remote isolation bone regeneration, such as severed finger regeneration.

Nanosilica-Anchored Polycaprolactone/Chitosan Nanofibrous Bioscaffold to Boost Osteogenesis for Bone Tissue Engineering

The strategy of incorporating bioactive inorganic nanomaterials without side effects as osteoinductive supplements is promising for bone regeneration. In this work, a novel biomass nanofibrous scaffold synthesized by electrospinning silica (SiO₂) nanoparticles into polycaprolactone/chitosan (PCL/CS) nanofibers was reported for bone tissue engineering. The nanosilica-anchored PCL/CS nanofibrous bioscaffold (PCL/CS/SiO₂) exhibited an interlinked continuous fibers framework with SiO₂ nanoparticles embedded in the fibers. Compact bone-derived cells (CBDCs), the stem cells derived from the bone cortex of the mouse, were seeded to the nanofibrous bioscaffolds. Scanning electron microscopy and cell counting were used to observe the cell adhesion. The Counting Kit-8 (CCK-8) assay was used. Alkaline phosphatase (ALP), Alizarin red staining, real-time Polymerase Chain Reaction and Western blot tests were performed to confirm the osteogenesis of the CBDCs on the bioscaffolds. The research results demonstrated that the mechanical property of the PCL together with the antibacterial and hydrophilic properties of the CS are conducive to promoting cell adhesion, growth, migration, proliferation and differentiation. SiO₂ nanoparticles, serving as bone induction factors, effectively promote the osteoblast differentiation and bone regeneration. This novel SiO₂-anchored nanofibrous bioscaffold with superior bone induction activity provides a better way for bone tissue regeneration.

Mesoporous Silica Promotes Osteogenesis of Human Adipose-Derived Stem Cells Identified by a High-Throughput Microfluidic Chip Assay

Silicon-derived biomaterials are conducive to regulating the fate of osteo-related stem cells, while their effects on the osteogenic differentiation of human adipose-derived stem cells (hADSCs) remain inconclusive. Mesoporous silica (mSiO₂) is synthesized in a facile route that exhibited the capability of promoting osteogenic differentiation of hADSCs. The metabolism of SiO₂ in cells is proposed according to the colocalization fluorescence analysis between lysosomes and nanoparticles. The released silicon elements promote osteogenic differentiation. The detection of secretory proteins through numerous parallel experiments performed via a microfluidic chip confirms the positive effect of SiO₂ on the osteogenic differentiation of hADSCs. Moreover, constructed with superparamagnetic iron oxide (Fe₃O₄), the magnetic nanoparticles (MNPs) of Fe₃O₄@mSiO₂ endow the cells with magnetic resonance imaging (MRI) properties. The MNP-regulated osteogenic differentiation of autologous adipose-derived stem cells provides considerable clinical application prospects for stem cell therapy of bone tissue repair with an effective reduction in immune rejection.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.

Surface Functionalization of Hydroxyapatite Scaffolds with MgAlEu-LDH Nanosheets for High-Performance Bone Regeneration

Although artificial bone repair scaffolds, such as titanium alloy, bioactive glass, and hydroxyapatite (HAp), have been widely used for treatment of large-size bone defects or serious bone destruction, they normally exhibit unsatisfied bone repair efficiency because of their weak osteogenic and angiogenesis performance as well as poor cell crawling and adhesion properties. Herein, the surface functionalization of MgAlEu-layered double hydroxide (MAE-LDH) nanosheets on porous HAp scaffolds is reported as a simple and effective strategy to prepare HAp/MAE-LDH scaffolds for enhanced bone regeneration. The surface functionalization of MAE-LDHs on the porous HAp scaffold can significantly improve its surface roughness, specific surface, and hydrophilicity, thus effectively boosting the cells adhesion and osteogenic differentiation. Importantly, the MAE-LDHs grown on HAp scaffolds enable the sustained release of Mg2+ and Eu3+ ions for efficient bone repair and vascular regeneration. In vitro experiments suggest that the HAp/MAE-LDH scaffold presents much enhanced osteogenesis and angiogenesis properties in comparison with the pristine HAp scaffold. In vivo assays further reveal that the new bone mass and mineral density of HAp/MAE-LDH scaffold increased by 3.18- and 2.21-fold, respectively, than that of pristine HAp scaffold. The transcriptome sequencing analysis reveals that the HAp/MAE-LDH scaffold can activate the Wnt/β-catenin signaling pathway to promote the osteogenic and angiogenic abilities.

Facile Construction of Hybrid Hydrogels with High Strength and Biocompatibility for Cranial Bone Regeneration

The significant efforts being made towards the utilization of artificial soft materials holds considerable promise for developing tissue engineering scaffolds for bone-related diseases in clinics. However, most of these biomaterials cannot simultaneously satisfy the multiple requirements of high mechanics, good compatibility, and biological osteogenesis. In this study, an osteogenic hybrid hydrogel between the amine-functionalized bioactive glass (ABG) and 4-armed poly(ethylene glycol) succinimidyl glutarate-gelatin network (SGgel) is introduced to flexibly adhere onto the defective tissue and to subsequently guide bone regeneration. Relying on the rapid ammonolysis reaction between amine groups (-NH₂) of gelatin and ABG components and N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG polymer, the hydrogel networks were formed within seconds, offering a multifunctional performance, including easy injection, favorable biocompatibility, biological and mechanical properties (compressive strength: 4.2 MPa; storage modulus: 10⁴ kPa; adhesive strength: 56 kPa), which could facilitate the stem cell viability, proliferation, migration and differentiation into osteocytes. In addition, the integration between the SGgel network and ABG moieties within a nano-scale level enabled the hybrid hydrogel to form adhesion to tissue, maintain the durable osteogenesis and accelerate bone regeneration. Therefore, a robust approach to the simultaneously satisfying tough adhesion onto the tissue defects and high efficiency for bone regeneration on a mouse skull was achieved, which may represent a promising strategy to design therapeutic scaffolds for tissue engineering in clinical applications.

Exosome-Functionalized Ti6Al4V Scaffolds Promoting Osseointegration by Modulating Endogenous Osteogenesis and Osteoimmunity

Periprosthetic bone defects are the most serious problem of revision total hip arthroplasty, which can easily lead to insufficient osteointegration between the prosthesis and host bone. Bone marrow mesenchymal stem cells (BMSCs) and a moderate inflammatory response at the prosthesis-bone interface play an important role in osteointegration. Here, we developed microarc oxide titanium implant loaded engineered exosomes (S-Exos) to promote osseointegration at the prosthesis-bone interface. First, Smurf1-shRNA was transferred into the BMSCs using a viral vector to prepare S-Exos, which were subsequently immobilized to the microarc oxide titanium implant surface with positively charged polyethyleneimine. The immobilized S-Exos could be slowly and uniformly released and subsequently phagocytosed by BMSCs and macrophages. Once the S-Exos were phagocytosed, they could simultaneously activate the BMP/Smad signaling pathway in the BMSCs and promote macrophage M2 polarization, both of which enhance osseointegration. Specifically, this S-Exos coating exhibits a dual effect of promoting osseointegration, including the osseointegration of BMSCs by activating the BMP/Smad signaling pathway and the macrophage M2 polarization promoting osseointegration. In summary, the construction of S-Exos modified microarc oxide titanium implants could provide a new method for promoting osteointegration between the prosthesis and host bone in revision total hip arthroplasty.

Bioinspired sandwich-like hybrid surface functionalized scaffold capable of regulating osteogenesis, angiogenesis, and osteoclastogenesis for robust bone regeneration

Recently, strategies that focus on biofunctionalized implant surfaces to enhance bone defect healing through the synergistic regulation of osteogenesis, angiogenesis, and osteoclastogenesis have attracted increasing attention in the bone tissue engineering field. Studies have shown that the Wnt/β-catenin signaling pathway has an imperative effect of promoting osteogenesis and angiogenesis while reducing osteoclastogenesis. However, how to prepare biofunctionalized bone implants with balanced osteogenesis, angiogenesis, and osteoclastogenesis by activating the Wnt/β-catenin pathway has seldom been investigated. Herein, through a bioinspired dopamine chemistry and self-assembly method, BML-284 (BML), a potent and highly selective Wnt signaling activator, was loaded on a mussel-inspired polydopamine (PDA) layer that had been immobilized on the porous beta-tricalcium calcium phosphate (β-TCP) scaffold surface and subsequently modified by a biocompatible carboxymethyl chitosan hydrogel to form a sandwich-like hybrid surface. β-TCP provides a biomimetic three-dimensional porous microenvironment similar to that of natural cancellous bone, and the BML-loaded sandwich-like hybrid surface endows the scaffold with multifunctional properties for potential application in bone regeneration. The results show that the sustained release of BML from the sandwich-like hybrid surface significantly facilitates the adhesion, migration, proliferation, spreading, and osteogenic differentiation of MC3T3-E1 cells as well as the angiogenic activity of human umbilical vein endothelial cells. In addition to osteogenesis and angiogenesis, the hybrid surface also exerts critical roles in suppressing osteoclastic activity. Remarkably, in a critical-sized cranial defect model, the biofunctionalized β-TCP scaffold could potentially trigger a chain of biological events: stimulating the polarization of M2 macrophages, recruiting endogenous stem cells and endothelial cells at the injury site to enable a favorable microenvironment for greatly accelerating bone ingrowth and angiogenesis while compromising osteoclastogenesis, thereby promoting bone healing. Therefore, these surface-biofunctionalized β-TCP implants, which regulate the synergies of osteogenesis, angiogenesis, and anti-osteoclastogenesis, indicate strong potential for clinical application as advanced orthopedic implants.

A unique biomimetic modification endows polyetherketoneketone scaffold with osteoinductivity by activating cAMP/PKA signaling pathway

Osteoinductivity of a biomaterial scaffold can notably enhance the bone healing performance. In this study, we developed a biomimetic and hierarchically porous polyetherketoneketone (PEKK) scaffold with unique osteoinductivity using a combined surface treatment strategy of a sulfonated process and a nano bone-like apatite deposition. In a beagle intramuscular model, the scaffold induced bone formation ectopically after 12-week implantation. The better bone healing ability of the scaffold than the original PEKK was also confirmed in orthotopic sites. After culturing with bone marrow-derived mesenchymal stem cells (BMSCs), the scaffold induced osteogenic differentiation of BMSCs, and the new bone formation could be mainly depending on cell signaling through adenylate cyclase 9, which activates the cyclic adenosine monophosphate/protein kinase A signaling cascade pathways. The current work reports a new osteoinductive synthetic polymeric scaffold with its detailed molecular mechanism of action for bone repair and regeneration.

Precisely Tuning the Pore-Wall Surface Composition of Bioceramic Scaffolds Facilitates Angiogenesis and Orbital Bone Defect Repair

Orbital bone damage (OBD) may result in severe post-traumatic enophthalmos, craniomaxillofacial deformities, vision loss, and intracranial infections. However, it is still a challenge to fabricate advanced biomaterials that can match the individual anatomical structure and enhance OBD repair in situ. Herein, we aimed to develop a selective surface modification strategy on bioceramic scaffolds and evaluated the effects of inorganic or organic functional coating on angiogenesis and osteogenesis, ectopically and orthotopically in OBD models. It was shown that the low thermal bioactive glass (BG) modification or layer-by-layer assembly of a biomimetic hydrogel (Biogel) could readily integrate into the pore wall of the bioceramic scaffolds. The BG and Biogel modification showed appreciable enhancement in the initial compressive strength (∼30-75%) or structural stability in vivo, respectively. BG modification could enhance by nearly 2-fold the vessel ingrowth, and the osteogenic capacity was also accelerated, accompanied with a mild scaffold biodegradation after 3 months. Meanwhile, the Biogel-modified scaffolds showed enhanced osteogenic differentiation and mineralization through calcium and phosphorus retention. The potential mechanism of the enhanced bone repair was elucidated via vascular and osteogenic cell responses in vitro, and the cell tests indicated that the Biogel and BG functional layers were both beneficial for in vitro osteoblastic differentiation and mineralization on bioceramics. Totally, these findings demonstrated that the bioactive ions or biomolecules could significantly improve the angiogenic and osteogenic capabilities of conventional bioceramics, and the integration of inorganic or organic functional coating in the pore wall is a highly flexible material toolbox that can be tailored directly to improve orbital bone defect repair.

A sustained release of alendronate from an injectable tetra-PEG hydrogel for efficient bone repair

Significant efforts on construction of smart drug delivery for developing minimally invasive gelling system to prolong local delivery of bisphosphonates are considered as promising perspectives for the bone-related diseases, which provide the hydrogels with unique bioactivities for bone repair in clinic. Herein, we have constructed an alendronate (ALN)-conjoined injectable tetra-PEG hydrogel with excellent biocompatibility, uniform network, and favorable mechanical properties in one-pot strategy. In views of the quick ammonolysis reaction between N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG and amine groups of tetra-PEG-NH₂ polymer and ALN molecules, the uniform networks were formed within seconds along with the easy injection, favorable biocompatibility and mechanical properties for hydrogel scaffolds. On account of the simultaneous physical encapsulation and chemical linkage of the ALN within the hydrogels, the ALN-conjoined tetra-PEG hydrogel exhibited a sustained drug release delivery that could persistently and effectively facilitate viability, growth, proliferation, and osteogenesis differentiation of stem cells, thereby allowing the consequent adaptation of hydrogels into the bone defects with irregular shapes, which endowed the ALN-conjoined tetra-PEG hydrogel with depot formulation capacity for governing the on-demand release of ALN drugs. Consequently, the findings imply that these drug-based tetra-PEG hydrogels mediate optimal release of therapeutic cargoes and effective promotion of in situ bone regeneration, which will be broadly utilized as therapeutic scaffolds in tissue engineering and regenerative medicine.

Engineering Stem Cell Recruitment and Osteoinduction via Bioadhesive Molecular Mimics to Improve Osteoporotic Bone-Implant Integration

For patients with osteoporosis, the therapeutic outcomes of osteoimplants are substantially affected by the impaired proliferation, migration, and osteogenic differentiation abilities of bone marrow mesenchymal stem cells (BMSCs). To improve bone-implant integration in osteoporotic condition, here we reported a one-step biomimetic surface strategy to introduce BMSC recruiting and osteoinductive abilities onto metallic osteoimplants. In our design, the bioadhesive molecular peptide mimic inspired by mussel foot proteins (Mfps) was used as molecular bridging for surface functionalization. Specifically, a BMSC-targeting peptide sequence (E7) and an osteogenic growth peptide (Y5) were grafted onto the titanium implant surfaces through a mussel adhesion mechanism. We found that a rational E7/Y5 feeding ratio could lead to an optimal dual functionalization capable of not only significantly improving the biocompatibility of the implant but also enabling it to recruit endogenous BMSCs for colonization, proliferation, and osteogenic differentiation. Mechanistically, the E7-assisted in situ recruitment of endogenous BMSCs as well as the enhanced interfacial osteogenesis and osteointegration was associated with activation of the C-X-C chemokine receptor type 4 (CXCR4) receptor on the cell surface and promotion of stromal cell-derived factor (SDF-1α) autocrine secretion. We anticipated that rational dual-functional surfaces through bioadhesive molecular mimics will provide a simple, effective, nonimmunogenic, and safe means to improve the clinical outcomes of intraosseous implants, especially under osteoporotic conditions.

A rethinking of collagen as tough biomaterials in meat packaging: assembly from native to synthetic

Due to the high moisture-associated typical rheology and the changeable and harsh processing conditions in the production process, packaging materials for meat products have higher requirements including a sufficient mechanical strength and proper ductility. Collagen, a highly conserved structural protein consisting of a triple helix of Gly-X-Y repeats, has been proved to be suitable packaging material for meat products. The treated animal digestive tract (i.e. the casing) is the perfect natural packaging material for wrapping meat into sausage. Its thin walls, strong toughness and impact resistance make it the oldest and best edible meat packaging. Collagen casing is another wisdom of meat packaging, which is made by collagen fibers from hide skin, presenting a rapid growth in casing market. To strengthen mechanical strength and barrier behaviors of collagen-based packaging materials, different physical, chemical, and biological cross-linking methods are springing up exuberantly, as well as a variety of reinforcement approaches including nanotechnology. In addition, the rapid development of biomimetic technology also provides a good research idea and means for the promotion of collagen's assembly and relevant mechanical properties. This review can offer some reference on fundamental theory and practical application of collagenous materials in meat products.

Alendronate-functionalized double network hydrogel scaffolds for effective osteogenesis

Development of artificial bone substitutes mimicking the extracellular matrix is a promising strategy for bone repair and regeneration. In views of the actual requirement of biomechanics, biodegradability, and bioactivity, herein, a double-network (DN) hydrogel was constructed by interspersing a methacrylated gelatin (GelMA) network into alendronate (ALN)-modified oxidized alginate (OSA) network via Schiff base reaction and photo-crosslinking process to promote in situ bone regeneration. This GelMA@OSA-ALN DN hydrogel possessed favorable network and pores, good biocompatibility, and enhanced biomechanics. Notably, the introduction of Schiff base furnished the ND hydrogel scaffold with pH-responsive biodegradation and sustained ALN drug release delivery, which could provide effective bioactivity, upregulate osteogenesis-related genes, and promote the cell viability, growth, proliferation, and osteogenesis differentiation for bone regeneration. Therefore, we provide a new insight to develop functional DN hydrogel scaffold toward governing the on-demand drug release and achieving the stem cell therapy, which will be developed into the minimally invasive gelling system to prolong local delivery of bisphosphonates for the bone-related diseases.

Mineralized Enzyme-Based Biomaterials with Superior Bioactivities for Bone Regeneration

The formation and metabolic balance of bone tissue is a controllable process of biomineralization, which is regulated by various cells, biomolecules, and ions. Enzyme molecules play an important role in this process, and alkaline phosphatase (ALP) is one of the most critical factors. In this study, inspired by the process of bone biomineralization, a biomimetic strategy is achieved for the preparation of mineralized ALP nanoparticles (MALPNs), by taking advantages of the unique reaction between ALP and calcium ions in Dulbecco's modified Eagle's medium. Benefiting from the mild biomineralization reaction, the MALPN system highly maintains the activity of ALP. Furthermore, the in vitro studies show that the MALPN system significantly enhances the proliferation of bone marrow mesenchymal stem cells and upregulates their osteogenic differentiation. When evaluated as synthetic graft materials for bone regeneration, the MALPN-incorporated gelatin methacryloyl graft shows excellent mechanical properties, a sustained release profile of ALP, and high biocompatibility and efficacy in guiding bone regeneration and vascularization for critical-sized rat calvarial defect. Moreover, we also demonstrate that the biomimetic mineralization strategy can be adopted for other proteins such as acid phosphatase, bovine serum albumin, fibrinogen, and gelatin, suggesting its universality for constructing mineralized protein-/enzyme-based bioactive materials for the application of tissue regeneration.

Synergistic effects of nanoattapulgite and hydroxyapatite on vascularization and bone formation in a rabbit tibia bone defect model

Hydroxyapatite (HA) is a promising scaffold material for the treatment of bone defects. However, the lack of angiogenic properties and undesirable mechanical properties (such as fragility) limits the application of HA. Nanoattapulgite (ATP) is a nature-derived clay mineral and has been proven to be a promising bioactive material for bone regeneration due to its ability to induce osteogenesis. In this study, polyvinyl alcohol/collagen/ATP/HA (PVA/COL/ATP/HA) scaffolds were printed. Mouse bone marrow mesenchymal stem/stromal cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were used in vitro to assess the biocompatibility and the osteogenesis and vascularization induction potentials of the scaffolds. Subsequently, in vivo micro-CT and histological staining were carried out to evaluate new bone formation in a rabbit tibial defect model. The in vitro results showed that the incorporation of ATP increased the printing fidelity and mechanical properties, with values of compressive strengths up to 200% over raw PC-H scaffolds. Simultaneously, the expression levels of osteogenic-related genes and vascularization-related genes were significantly increased after the incorporation of ATP. The in vivo results showed that the PVA/COL/ATP/HA scaffolds exhibited synergistic effects on promoting vascularization and bone formation. The combination of ATP and HA provides a promising strategy for vascularized bone tissue engineering.

Silk Fibroin as Adjuvant in the Fabrication of Mechanically Stable Fibrin Biocomposites

Fibrin is a very attractive material for the development of tissue-engineered scaffolds due to its exceptional bioactivity, versatility in the fabrication, affinity to cell mediators; and the possibility to isolate it from blood plasma, making it autologous. However, fibrin application is greatly limited due to its low mechanical properties, fast degradation, and strong contraction in the presence of cells. In this study, we present a new strategy to overcome these drawbacks by combining it with another natural polymer: silk fibroin. Specifically, we fabricated biocomposites of fibrin (5 mg/mL) and silk fibroin (0.1, 0.5 and 1% w/w) by using a dual injection system, followed by ethanol annealing. The shear elastic modulus increased from 23 ± 5 Pa from fibrin alone, to 67 ± 22 Pa for fibrin/silk fibroin 0.1%, 241 ± 67 Pa for fibrin/silk fibroin 0.5% and 456 ± 32 Pa for fibrin/silk fibroin 1%. After culturing for 27 days with strong contractile cells (primary human arterial smooth muscle cells), fibrin/silk fibroin 0.5% and fibrin/silk fibroin 1% featured minimal cell-mediated contraction (ca. 15 and 5% respectively) in contrast with the large surface loss of the pure fibrin scaffolds (ca. 95%). Additionally, the composites enabled the formation of a proper endothelial cell layer after culturing with human primary endothelial cells under standard culture conditions. Overall, the fibrin/silk fibroin composites, manufactured within this study by a simple and scalable biofabrication approach, offer a promising avenue to boost the applicability of fibrin in tissue engineering.