Fabrication of micro/nanoporous collagen/dECM/silk-fibroin biocomposite scaffolds using a low temperature 3D printing process for bone tissue regeneration

Hydrogel-Based 3D Bioprinting Technology for Articular Cartilage Regenerative Engineering

Articular cartilage is an avascular tissue with very limited capacity of self-regeneration. Trauma or injury-related defects, inflammation, or aging in articular cartilage can induce progressive degenerative joint diseases such as osteoarthritis. There are significant clinical demands for the development of effective therapeutic approaches to promote articular cartilage repair or regeneration. The current treatment modalities used for the repair of cartilage lesions mainly include cell-based therapy, small molecules, surgical approaches, and tissue engineering. However, these approaches remain unsatisfactory. With the advent of three-dimensional (3D) bioprinting technology, tissue engineering provides an opportunity to repair articular cartilage defects or degeneration through the construction of organized, living structures composed of biomaterials, chondrogenic cells, and bioactive factors. The bioprinted cartilage-like structures can mimic native articular cartilage, as opposed to traditional approaches, by allowing excellent control of chondrogenic cell distribution and the modulation of biomechanical and biochemical properties with high precision. This review focuses on various hydrogels, including natural and synthetic hydrogels, and their current developments as bioinks in 3D bioprinting for cartilage tissue engineering. In addition, the challenges and prospects of these hydrogels in cartilage tissue engineering applications are also discussed.

3D-printed near-infrared-light-responsive on-demand drug-delivery scaffold for bone regeneration

Although several bioactive 3D-printed bone scaffolds loaded with multiple kinds of biomolecules for enhanced bone regeneration have been recently developed, the manipulation of on-demand release profiles of different biomolecules during bone regeneration remains challenging. Herein, a 3D-printed dual-drug-loaded biomimetic scaffold to regulate the host stem cell recruitment and osteogenic differentiation in a two-stage process for bone regeneration was successfully fabricated. First, a chemotactic small-molecule drug, namely, simvastatin (SIM) was directly incorporated into the hydroxyapatite/collagen bioink for printing and could be rapidly released during the early stage of bone regeneration. Further, near-infrared (NIR)-light-responsive polydopamine-coated hydroxyapatite nanoparticles were designed to deliver the osteogenic drug, i.e., pargyline (PGL) in a controllable manner. Together, our scaffold displayed an on-demand sequential release of those two drugs and could optimize their therapeutic effects to align with the stem cell recruitment and osteoblastic differentiation, thereby promoting bone regeneration. The results confirmed the suitable mechanical strength, high photothermal conversion efficiency, good biocompatibility of our scaffold. The scaffold loaded with SIM could efficiently accelerate the migration of stem cells. In addition, the scaffold with on-demand sequential release promoted alkaline phosphatase (ALP) activity, significantly upregulated gene expression levels of osteogenesis-related markers, and enhanced new-bone-formation capabilities in rabbit cranial defect models. Altogether, this scaffold not only offers a promising strategy to control the behavior of stem cells during bone regeneration but also provides an efficient strategy for controllable sequential release of different biomolecule in bone tissue engineering.

Silk fibroin-based scaffolds for tissue engineering

Silk fibroin is an important natural fibrous protein with excellent prospects for tissue engineering applications. With profound studies in recent years, its potential in tissue repair has been developed. A growing body of literature has investigated various fabricating methods of silk fibroin and their application in tissue repair. The purpose of this paper is to trace the latest developments of SF-based scaffolds for tissue engineering. In this review, we first presented the primary and secondary structures of silk fibroin. The processing methods of SF scaffolds were then summarized. Lastly, we examined the contribution of new studies applying SF as scaffolds in tissue regeneration applications. Overall, this review showed the latest progress in the fabrication and utilization of silk fibroin-based scaffolds.

Design of bone scaffolds with calcium phosphate and its derivatives by 3D printing: A review

Tissue engineering is a fascinating field that combines biology, engineering, and medicine to create artificial tissues and organs. It involves using living cells, biomaterials, and bioengineering techniques to develop functional tissues that can be used to replace or repair damaged or diseased organs in the human body. The process typically starts by obtaining cells from the patient or a donor. These cells are then cultured and grown in a laboratory under controlled conditions. Scaffold materials, such as biodegradable polymers or natural extracellular matrices, are used to provide support and structure for the growing cells. 3D bone scaffolds are a fascinating application within the field of tissue engineering. These scaffolds are designed to mimic the structure and properties of natural bone tissue and serve as a temporary framework for new bone growth. The main purpose of a 3D bone scaffold is to provide mechanical support to the surrounding cells and guide their growth in a specific direction. It acts as a template, encouraging the formation of new bone tissue by providing a framework for cells to attach, proliferate, and differentiate. These scaffolds are typically fabricated using biocompatible materials like ceramics, polymers, or a combination of both. The choice of material depends on factors such as strength, biodegradability, and the ability to facilitate cell adhesion and growth. Advanced techniques like 3D printing have revolutionized the fabrication process of these scaffolds. Using precise layer-by-layer deposition, it allows for the creation of complex, patient-specific geometries, mimicking the intricacies of natural bone structure. This article offers a brief overview of the latest developments in the research and development of 3D printing techniques for creating scaffolds used in bone tissue engineering.

A long-term storable gel-laden chip composite built in a multi-well plate enablingin situcell encapsulation for high-throughput liver model

Hydrogels are widely used as scaffold materials for constructingin vitrothree-dimensional microphysiological systems. However, their high sensitivity to various external cues hinders the development of hydrogel-laden, microscale, and high-throughput chips. Here, we have developed a long-term storable gel-laden chip composite built in a multi-well plate, which enablesin situcell encapsulation and facilitates high-throughput analysis. Through optimized chemical crosslinking and freeze-drying method (C/FD), we have achieved a high-quality of gel-laden chip composite with excellent transparency, uniform porosity, and appropriate swelling and mechanical characteristics. Besides collagen, decellularized extracellular matrix with tissue-specific biochemical compound has been applied as chip composite. As a ready-to-use platform,in situcell encapsulation within the gel has been achieved through capillary force generated during gel reswelling. The liver-mimetic chip composite, comprising HepG2 cells or primary hepatocytes, has demonstrated favorable hepatic functionality and high sensitivity in drug testing. The developed fabrication process with improved stability of gels and storability allows chip composites to be stored at a wide range of temperatures for up to 28 d without any deformation, demonstrating off-the-shelf products. Consequently, this provides an exceptionally simple and long-term storable platform that can be utilized for an efficient tissue-specific modeling and various biomedical applications.

Development of hybrid 3D printing approach for fabrication of high-strength hydroxyapatite bioscaffold using FDM and DLP techniques

This study develops a hybrid 3D printing approach that combines fused deposition modeling (FDM) and digital light processing (DLP) techniques for fabricating bioscaffolds, enabling rapid mass production. The FDM technique fabricates outer molds, while DLP prints struts for creating penetrating channels. By combining these components, hydroxyapatite (HA) bioscaffolds with different channel sizes (600, 800, and 1000μm) and designed porosities (10%, 12.5%, and 15%) are fabricated using the slurry casting method with centrifugal vacuum defoaming for significant densification. This innovative method produces high-strength bioscaffolds with an overall porosity of 32%-37%, featuring tightly bound HA grains and a layered surface structure, resulting in remarkable cell viability and adhesion, along with minimal degradation rates and superior calcium phosphate deposition. The HA scaffolds show hardness ranging from 1.43 to 1.87 GPa, with increasing compressive strength as the designed porosity and channel size decrease. Compared to human cancellous bone at a similar porosity range of 30%-40%, exhibiting compressive strengths of 13-70 MPa and moduli of 0.8-8 GPa, the HA scaffolds demonstrate robust strengths ranging from 40 to 73 MPa, paired with lower moduli of 0.7-1.23 GPa. These attributes make them well-suited for cancellous bone repair, effectively mitigating issues like stress shielding and bone atrophy.

Pulmonary decellularized extracellular matrix (dECM) modified polyethylene terephthalate three-dimensional cell carriers regulate the proliferation and paracrine activity of mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) possess a high degree of self-renewal capacity and in vitro multi-lineage differentiation potential. Decellularized materials have garnered considerable attention due to their elevated biocompatibility, reduced immunogenicity, excellent biodegradability, and the ability to partially mimic the in vivo microenvironment conducive to cell growth. To address the issue of mesenchymal stem cells losing their stem cell characteristics during two-dimensional (2D) cultivation, this study established three-dimensional cell carriers modified with lung decellularized extracellular matrix and assessed its impact on the life activities of mesenchymal stem cells. Methods: This study employed PET as a substrate material, grafting with polydopamine (PDA), and constructing a decellularized extracellular matrix (dECM) coating on its surface, thus creating the PET/PDA/dECM three-dimensional (3D) composite carrier. Subsequently, material characterization of the cellular carriers was conducted, followed by co-culturing with human umbilical cord mesenchymal stem cells in vitro, aiming to investigate the material's impact on the proliferation and paracrine activity of mesenchymal stem cells. Results and Discussion: Material characterization demonstrated successful grafting of PDA and dECM materials, and it had complete hydrophilicity, high porosity, and excellent mechanical properties. The material was rich in various ECM proteins (collagen I, collagen IV , laminin, fibronectin, elastin), indicating good biocompatibility. In long-term in vitro cultivation (14 days) experiments, the PET/PDA/dECM three-dimensional composite carrier significantly enhanced adhesion and proliferation of human umbilical cord-derived mesenchymal stem cells (HUCMSCs), with a proliferation rate 1.9 times higher than that of cells cultured on tissue culture polystyrene (TCPS) at day 14. Furthermore, it effectively maintained the stem cell characteristics, expressing specific antigens for HUCMSCs. Through qPCR, Western blot, and ELISA experiments, the composite carrier markedly promoted the expression and secretion of key cell factors in HUCMSCs. These results demonstrate that the PET/PDA/dECM composite carrier holds great potential for scaling up MSCs' long-term in vitro cultivation and the production of paracrine factors.

Decellularized extracellular matrix and silk fibroin-based hybrid biomaterials: A comprehensive review on fabrication techniques and tissue-specific applications

Biomaterials play a fundamental role in tissue engineering by providing biochemical and physical cues that influence cellular fate and matrix development. Decellularized extracellular matrix (dECM) as a biomaterial is distinguished by its abundant composition of matrix proteins, such as collagen, elastin, fibronectin, and laminin, as well as glycosaminoglycans and proteoglycans. However, the mechanical properties of only dECM-based constructs may not always meet tissue-specific requirements. Recent advancements address this challenge by utilizing hybrid biomaterials that harness the strengths of silk fibroin (SF), which contributes the necessary mechanical properties, while dECM provides essential cellular cues for in vitro studies and tissue regeneration. This review discusses emerging trends in developing such biopolymer blends, aiming to synergistically combine the advantages of SF and dECM through optimal concentrations and desired cross-linking density. We focus on different fabrication techniques and cross-linking methods that have been utilized to fabricate various tissue-engineered hybrid constructs. Furthermore, we survey recent applications of such biomaterials for the regeneration of various tissues, including bone, cartilage, trachea, bladder, vascular graft, heart, skin, liver, and other soft tissues. Finally, the trajectory and prospects of the constructs derived from this blend in the tissue engineering field have been summarized, highlighting their potential for clinical translation.

Advances in 3D Bioprinting of Biomimetic and Engineered Meniscal Grafts

The meniscus plays a crucial role in loads distribution and protection of articular cartilage. Meniscal injury can result in cartilage degeneration, loss of mechanical stability in the knee joint and ultimately lead to arthritis. Surgical interventions provide only short-term pain relief but fail to repair or regenerate the injured meniscus. Emerging tissue engineering approaches based on 3D bioprinting provide alternatives to current surgical methods for meniscus repair. In this review, the current bioprinting techniques employed in developing engineered meniscus grafts are summarized and discuss the latest strategies for mimicking the gradient structure, composition, and viscoelastic properties of native meniscus. Recent progress is highlighted in gene-activated matrices for meniscus regeneration as well. Finally, a perspective is provided on the future development of 3D bioprinting for meniscus repair, emphasizing the potential of this technology to revolutionize meniscus regeneration and improve patient outcomes.

Towards resorbable 3D-printed scaffolds for craniofacial bone regeneration

This review will briefly examine the development of 3D-printed scaffolds for craniofacial bone regeneration. We will, in particular, highlight our work using Poly(L-lactic acid) (PLLA) and collagen-based bio-inks. This paper is a narrative review of the materials used for scaffold fabrication by 3D printing. We have also reviewed two types of scaffolds that we designed and fabricated. Poly(L-lactic acid) (PLLA) scaffolds were printed using fused deposition modelling technology. Collagen-based scaffolds were printed using a bioprinting technique. These scaffolds were tested for their physical properties and biocompatibility. Work in the emerging field of 3D-printed scaffolds for bone repair is briefly reviewed. Our work provides an example of PLLA scaffolds that were successfully 3D-printed with optimal porosity, pore size and fibre thickness. The compressive modulus was similar to, or better than, the trabecular bone of the mandible. PLLA scaffolds generated an electric potential upon cyclic/repeated loading. The crystallinity was reduced during the 3D printing. The hydrolytic degradation was relatively slow. Osteoblast-like cells did not attach to uncoated scaffolds but attached well and proliferated after coating the scaffold with fibrinogen. Collagen-based bio-ink scaffolds were also printed successfully. Osteoclast-like cells adhered, differentiated, and survived well on the scaffold. Efforts are underway to identify means to improve the structural stability of the collagen-based scaffolds, perhaps through mineralization by the polymer-induced liquid precursor process. 3D-printing technology is promising for constructing next-generation bone regeneration scaffolds. We describe our efforts to test PLLA and collagen scaffolds produced by 3D printing. The 3D-printed PLLA scaffolds showed promising properties akin to natural bone. Collagen scaffolds need further work to improve structural integrity. Ideally, such biological scaffolds will be mineralized to produce true bone biomimetics. These scaffolds warrant further investigation for bone regeneration.

Decellularized extracellular matrix-based composite scaffolds for tissue engineering and regenerative medicine

Despite the considerable advancements in fabricating polymeric-based scaffolds for tissue engineering, the clinical transformation of these scaffolds remained a big challenge because of the difficulty of simulating native organs/tissues' microenvironment. As a kind of natural tissue-derived biomaterials, decellularized extracellular matrix (dECM)-based scaffolds have gained attention due to their unique biomimetic properties, providing a specific microenvironment suitable for promoting cell proliferation, migration, attachment and regulating differentiation. The medical applications of dECM-based scaffolds have addressed critical challenges, including poor mechanical strength and insufficient stability. For promoting the reconstruction of damaged tissues or organs, different types of dECM-based composite platforms have been designed to mimic tissue microenvironment, including by integrating with natural polymer or/and syntenic polymer or adding bioactive factors. In this review, we summarized the research progress of dECM-based composite scaffolds in regenerative medicine, highlighting the critical challenges and future perspectives related to the medical application of these composite materials.

A comprehensive review of silk-fibroin hydrogels for cell and drug delivery applications in tissue engineering and regenerative medicine

Hydrogel scaffolds hold great promise for developing novel treatment strategies in the field of regenerative medicine. Within this context, silk fibroin (SF) has proven to be a versatile material for a wide range of tissue engineering applications owing to its structural and functional properties. In the present review, we report on the design and fabrication of different forms of SF-based scaffolds for tissue regeneration applications, particularly for skin, bone, and neural tissues. In particular, SF hydrogels have emerged as delivery systems for a wide range of bio-actives. Given the growing interest in the field, this review has a primary focus on the fabrication, characterization, and properties of SF hydrogels. We also discuss their potential for the delivery of drugs, stem cells, genes, peptides, and growth factors, including future directions in the field of SF hydrogel scaffolds.

Development of Silk Fibroin-Based Non-Crosslinking Thermosensitive Bioinks for 3D Bioprinting

Three-dimensional (3D) bioprinting holds great promise for tissue engineering, allowing cells to thrive in a 3D environment. However, the applicability of natural polymers such as silk fibroin (SF) in 3D bioprinting faces hurdles due to limited mechanical strength and printability. SF, derived from the silkworm Bombyx mori, is emerging as a potential bioink due to its inherent physical gelling properties. However, research on inducing thermosensitive behavior in SF-based bioinks and tailoring their mechanical properties to specific tissue requirements is notably lacking. This study addresses these gaps through the development of silk fibroin-based thermosensitive bioinks (SF-TPBs). Precise modulation of gelation time and mechanical robustness is achieved by manipulating glycerol content without recourse to cross-linkers. Chemical analysis confirms β-sheet conformation in SF-TPBs independent of glycerol concentration. Increased glycerol content improves gelation kinetics and results in rheological properties suitable for 3D printing. Overall, SF-TPBs offer promising prospects for realizing the potential of 3D bioprinting using natural polymers.

Construction of 3D bioprinting of HAP/collagen scaffold in gelation bath for bone tissue engineering

Reconstruction of bone defects remains a clinical challenge, and 3D bioprinting is a fabrication technology to treat it via tissue engineering. Collagen is currently the most popular cell scaffold for tissue engineering; however, a shortage of printability and low mechanical strength limited its application via 3D bioprinting. In the study, aiding with a gelatin support bath, a collagen-based scaffold was fabricated via 3D printing, where hydroxyapatite (HAP) and bone marrow mesenchymal stem cells (BMSCs) were added to mimic the composition of bone. The results showed that the blend of HAP and collagen showed suitable rheological performance for 3D extrusion printing and enhanced the composite scaffold's strength. The gelatin support bath could effectively support the HAP/collagen scaffold's dimension with designed patterns at room temperature. BMSCs in/on the scaffold kept living and proliferating, and there was a high alkaline phosphate expression. The printed collagen-based scaffold with biocompatibility, mechanical properties and bioactivity provides a new way for bone tissue engineering via 3D bioprinting.

Low-temperature deposition manufacturing technology: a novel 3D printing method for bone scaffolds

The application of three-dimensional printing technology in the medical field has great potential for bone defect repair, especially personalized and biological repair. As a green manufacturing process that does not involve liquefication through heating, low-temperature deposition manufacturing (LDM) is a promising type of rapid prototyping manufacturing and has been widely used to fabricate scaffolds in bone tissue engineering. The scaffolds fabricated by LDM have a multi-scale controllable pore structure and interconnected micropores, which are beneficial for the repair of bone defects. At the same time, different types of cells or bioactive factor can be integrated into three-dimensional structural scaffolds through LDM. Herein, we introduced LDM technology and summarize its applications in bone tissue engineering. We divide the scaffolds into four categories according to the skeleton materials and discuss the performance and limitations of the scaffolds. The ideas presented in this review have prospects in the development and application of LDM scaffolds.

Biofunctionalization of 3D printed collagen with bevacizumab-loaded microparticles targeting pathological angiogenesis

Pathological angiogenesis is a crucial attribute of several chronic diseases such as cancer, age-related macular degeneration, and osteoarthritis (OA). In the case of OA, pathological angiogenesis mediated by the vascular endothelial growth factor (VEGF), among other factors, contributes to cartilage degeneration and to implants rejection. In line with this, the use of the anti-VEGF bevacizumab (BVZ) has been shown to prevent OA progression and support cartilage regeneration. The aim of this work was to functionalize a medical grade collagen with poly (lactic-co-glycolic acid) (PLGA) microparticles containing BVZ via three-dimensional (3D) printing to target pathological angiogenesis. First, the effect of several formulation parameters on the encapsulation and release of BVZ from PLGA microparticles was studied. Then, the anti-angiogenic activity of released BVZ was tested in a 3D cell model. The 3D printability of the microparticle-loaded collagen ink was tested by evaluating the shape fidelity of 3D printed structures. Results showed that the release and the encapsulation efficiency of BVZ could be tuned as a function of several formulation parameters. In addition, the released BVZ was observed to reduce vascularization by human umbilical vein endothelial cells. Finally, the collagen ink with embedded BVZ microparticles was successfully printed, leading to shape-stable meniscus-, nose- and auricle-like structures. Taken altogether, we defined the conditions for the successful combination of BVZ-loaded microparticles with the 3D printing of a medical grade collagen to target pathological angiogenesis.

Recent Advances in the Production of Pharmaceuticals Using Selective Laser Sintering

Selective laser sintering (SLS) is an additive manufacturing process that has shown promise in the production of medical devices, including hip cups, knee trays, dental crowns, and hearing aids. SLS-based 3D-printed dosage forms have the potential to revolutionise the production of personalised drugs. The ability to manipulate the porosity of printed materials is a particularly exciting aspect of SLS. Porous tablet formulations produced by SLS can disintegrate orally within seconds, which is challenging to achieve with traditional methods. SLS also enables the creation of amorphous solid dispersions in a single step, rather than the multi-step process required with conventional methods. This review provides an overview of 3D printing, describes the operating mechanism and necessary materials for SLS, and highlights recent advances in SLS for biomedical and pharmaceutical applications. Furthermore, an in-depth comparison and contrast of various 3D printing technologies for their effectiveness in tissue engineering applications is also presented in this review.

3D bioprinting of tissue constructs employing dual crosslinking of decellularized extracellular matrix hydrogel

Bioprinted tissues are currently being utilized for drug and cosmetic screening mostly, but the long-term goal is to achieve human scale functional tissues and organs for transplantation. Hence, recapitulating the multiscale architecture, 3D structures, and complexity of native tissues is the key to produce bioengineered tissues/organs. Decellularized extracellular matrix (dECM)-based biomaterials are widely being used as bioinks for 3D bioprinting for tissue engineering applications. Their potential to provide excellent biocompatibility for the cells drove researchers to use them extensively. However, the decellularization process involves many detergents and enzymes which may contribute to their loss of mechanical properties. Moreover, thermal gelation of dECM-based hydrogels is typically slow which affects the shape fidelity, printability, and physical properties while printing complex structures with 3D printing. But, thermally gelled dECM hydrogels provide excellent cell viability and functionality. To overcome this, a novel dual crosslinking of unmodified dECM has been proposed in this study to render shape fidelity and enhance cell viability and functionality. The dECM-based bioink can be initially polymerized superficially on exposure to light to achieve immediate stability and can attain further stability upon thermal gelation. This dual crosslinking mechanism can maintain the microenvironment of the structure, hence allowing the printing of stable flexible structures. Optimized concentrations of novel photo crosslinkers have been determined and printing of a few complex-shaped anatomical structures has been demonstrated. This approach of fabricating complex scaffolds employing dual crosslinking can be used for the bioprinting of different complex tissue structures with tissue-specific dECM based bioinks.

Recent Advances in Decellularized Matrix-Derived Materials for Bioink and 3D Bioprinting

As an emerging 3D printing technology, 3D bioprinting has shown great potential in tissue engineering and regenerative medicine. Decellularized extracellular matrices (dECM) have recently made significant research strides and have been used to create unique tissue-specific bioink that can mimic biomimetic microenvironments. Combining dECMs with 3D bioprinting may provide a new strategy to prepare biomimetic hydrogels for bioinks and hold the potential to construct tissue analogs in vitro, similar to native tissues. Currently, the dECM has been proven to be one of the fastest growing bioactive printing materials and plays an essential role in cell-based 3D bioprinting. This review introduces the methods of preparing and identifying dECMs and the characteristic requirements of bioink for use in 3D bioprinting. The most recent advances in dECM-derived bioactive printing materials are then thoroughly reviewed by examining their application in the bioprinting of different tissues, such as bone, cartilage, muscle, the heart, the nervous system, and other tissues. Finally, the potential of bioactive printing materials generated from dECM is discussed.

A novel decellularized matrix of Wnt signaling-activated osteocytes accelerates the repair of critical-sized parietal bone defects with osteoclastogenesis, angiogenesis, and neurogenesis

Cell source is the key to decellularized matrix (DM) strategy. This study compared 3 cell types, osteocytes with/without dominant active Wnt/β-catenin signaling (daCO and WTO) and bone marrow stromal cells (BMSCs) for their DMs in bone repair. Decellularization removes all organelles and >95% DNA, and retained >74% collagen and >71% GAG, maintains the integrity of cell basement membrane with dense boundaries showing oval and honeycomb structure in osteocytic DM and smooth but irregular shape in the BMSC-DM. DM produced higher cell survival rate (90%) and higher proliferative activity. In vitro, daCO-DM induces more and longer stress fibers in BMSCs, conducive to cell adhesion, spreading, and osteogenic differentiation. 8-wk after implantation of the critical-sized parietal bone defect model, daCO-DM formed tight structures, composed of a large number of densely-arranged type-I collagen under polarized light microscope, which is similar to and integrated with host bone. BV/TV (>54%) was 1.5, 2.9, and 3.5 times of WTO-DM, BMSC-DM, and none-DM groups, and N.Ob/T.Ar (3.2 × 10²/mm²) was 1.7, 2.9, and 3.3 times. At 4-wk, daCO-DM induced osteoclastogenesis, 2.3 times higher than WTO-DM; but BMSC-DM or none-DM didn't. daCO-DM increased the expression of RANKL and MCSF, Vegfa and Angpt1, and Ngf in BMSCs, which contributes to osteoclastogenesis, angiogenesis, and neurogenesis, respectively. daCO-DM promoted H-type vessel formation and nerve markers β3-tubulin and NeuN expression. Conclusion: daCO-DM produces metabolic and neurovascularized organoid bone to accelerate the repair of bone defects. These features are expected to achieve the effect of autologous bone transplantation, suitable for transformation application.

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Decellularized matrix of osteocytes with dominant-active β-catenin (daCO-DM) promotes osteogenesis for regenerative repair.

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daCO-DM induces BMSCs to form stress fibers, conducive to cell adhesion, spreading, and differentiation towards osteoblasts.

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daCO-DM-induced osteoblasts have strong activity secreting dense and orderly-arranged type I collagen as host bone’s.

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daCO-DM induces BMSCs to express pre-osteoclastogenic cytokine RANKL and MCSF for osteoclastogenesis of marrow monocytes.

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daCO-DM enhances BMSCs to express angiogenic Vegfa and Angpt1, and neurogenic Ngf potentially for neurovascularization.

An Overview of Collagen-Based Composite Scaffold for Bone Tissue Engineering

Bone regeneration or restoration is a series of well-ordered physiological activities that occur throughout a person's life, they are continuously being repaired and remodeled. A conventional bone repair procedure, such as autograft and allograft bone transplant, has failed to address bone reconstruction disputes and complexity. On the other hand, Tissue Engineering is a potential therapy option for repairing rather than replacing the damaged tissue. Biomaterials in bone tissue engineering (BTE) help pave the way for damaged tissues as an artificial extracellular matrix, facilitating new tissue growth. Collagen-based biomaterials for repair and replacement have inspired much interest in the hunt for versatile biomaterials compatible with human tissue. It is a major organic component of extracellular matrix in bone and has been employed as scaffolding material in BTE for decades. In this review, we documented the role of collagen in BTE, focusing on collagen type I, its crosslinking capability, collagen-based biomaterials, and fabrication methods. It also considers osteoblast citration a critical process in bone formation, a unique perspective for an old relationship.

Research Progress of Shape Memory Polymer and 4D Printing in Biomedical Application

As a kind of smart material, shape memory polymer (SMP) shows great application potential in the biomedical field. Compared with traditional metal-based medical devices, SMP-based devices have the following characteristics: 1) The adaptive ability allows the biomedical device to better match the surrounding tissue after being implanted into the body by minimally invasive implantation; 2) it has better biocompatibility and adjustable biodegradability; 3) mechanical properties can be regulated in a large range to better match with the surrounding tissue. 4D printing technology is a comprehensive technology based on smart materials and 3D printing, which has great application value in the biomedical field. 4D printing technology breaks through the technical bottleneck of personalized customization and provides a new opportunity for the further development of the biomedical field. This paper summarizes the application of SMP and 4D printing technology in the field of bone tissue scaffolds, tracheal scaffolds, and drug release, etc. Moreover, this paper analyzes the existing problems and prospects, hoping to provide a preliminary discussion and useful reference for the application of SMP in biomedical engineering.

Three-Dimensional Digital Light-Processing Bioprinting Using Silk Fibroin-Based Bio-Ink: Recent Advancements in Biomedical Applications

Three-dimensional (3D) bioprinting has been developed as a viable method for fabricating functional tissues and organs by precisely spatially arranging biomaterials, cells, and biochemical components in a layer-by-layer fashion. Among the various bioprinting strategies, digital light-processing (DLP) printing has gained enormous attention due to its applications in tissue engineering and biomedical fields. It allows for high spatial resolution and the rapid printing of complex structures. Although bio-ink is a critical aspect of 3D bioprinting, only a few bio-inks have been used for DLP bioprinting in contrast to the number of bio-inks employed for other bioprinters. Recently, silk fibroin (SF), as a natural bio-ink material used for DLP 3D bioprinting, has gained extensive attention with respect to biomedical applications due to its biocompatibility and mechanical properties. This review introduces DLP-based 3D bioprinting, its related technology, and the fabrication process of silk fibroin-based bio-ink. Then, we summarize the applications of DLP 3D bioprinting based on SF-based bio-ink in the tissue engineering and biomedical fields. We also discuss the current limitations and future perspectives of DLP 3D bioprinting using SF-based bio-ink.

Engineering Biomimetic Extracellular Matrix with Silica Nanofibers: From 1D Material to 3D Network

Biomaterials at nanoscale is a fast-expanding research field with which extensive studies have been conducted on understanding the interactions between cells and their surrounding microenvironments as well as intracellular communications. Among many kinds of nanoscale biomaterials, mesoporous fibrous structures are especially attractive as a promising approach to mimic the natural extracellular matrix (ECM) for cell and tissue research. Silica is a well-studied biocompatible, natural inorganic material that can be synthesized as morpho-genetically active scaffolds by various methods. This review compares silica nanofibers (SNFs) to other ECM materials such as hydrogel, polymers, and decellularized natural ECM, summarizes fabrication techniques for SNFs, and discusses different strategies of constructing ECM using SNFs. In addition, the latest progress on SNFs synthesis and biomimetic ECM substrates fabrication is summarized and highlighted. Lastly, we look at the wide use of SNF-based ECM scaffolds in biological applications, including stem cell regulation, tissue engineering, drug release, and environmental applications.

Electrospun Silk Fibroin/kappa-Carrageenan Hybrid Nanofibers with Enhanced Osteogenic Properties for Bone Regeneration Applications

In this study, a novel nanofibrous hybrid scaffold based on silk fibroin (SF) and different weight ratios of kappa-carrageenan (k-CG) (1, 3, and 5 mg of k-CG in 1 mL of 12 wt% SF solution) was prepared using electrospinning and genipin (GP) as a crosslinker. The presence of k-CG in SF nanofibers was analyzed and confirmed using Fourier transform infrared spectroscopy (FTIR). In addition, X-ray diffraction (XRD) analysis confirmed that GP could cause SF conformation to shift from random coils or α-helices to β-sheets and thereby facilitate a more crystalline and stable structure. The ultimate tensile strength (UTS) and Young's modulus of the SF mats were enhanced after crosslinking with GP from 3.91 ± 0.2 MPa to 8.50 ± 0.3 MPa and from 9.17 ± 0.3 MPa to 31.2 ± 1.2 MP, respectively. Notably, while the mean fiber diameter, wettability, and biodegradation rate of the SF nanofibers increased with increasing k-CG content, a decreasing effect was determined in terms of UTS and Young's modulus. Additionally, better cell viability and proliferation were observed on hybrid scaffolds with the highest k-CG content. Osteogenic differentiation was determined from alkaline phosphatase (ALP) activity and Alizarin Red staining and expression of osteogenic marker genes. To this end, we noticed that k-CG enhanced ALP activity, calcium deposition, and expression of osteogenic genes on the hybrid scaffolds. Overall, hybridization of SF and k-CG can introduce a promising scaffold for bone regeneration; however, more biological evaluations are required.

Optimizing Chitosan/Collagen Type I/Nanohydroxyapatite Cross-linked Porous Scaffolds for Bone Tissue Engineering

Bio-composite scaffolds mimicking the natural microenvironment of bone tissue offer striking advantages in material-guided bone regeneration. The combination of biodegradable natural polymers and bioactive ceramics that leverage potent bio-mimicking cues has been an active strategy to achieve success in bone tissue engineering. Herein, a competitive approach was followed to point out an optimized bio-composite scaffold in terms of scaffold properties and stimulation of osteoblast differentiation. The scaffolds, composed of chitosan/collagen type I/nanohydroxyapatite (Chi/Coll/nHA) as the most attractive components in bone tissue engineering, were analyzed. The scaffolds were prepared by freeze-drying method and cross-linked using different types of cross-linkers. Based on the physicochemical and mechanical characterization, the scaffolds were eliminated comparatively. All types of scaffolds displayed highly porous structures. The cross-linker type and collagen content had prominent effects on mechanical strength. Glyoxal cross-linked structures displayed optimum mechanical and structural properties. The MC3T3-E1 proliferation, osteogenic-related gene expression, and matrix mineralization were better pronounced in collagen presence and triggered as collagen type I amount was increased. The results highlighted that glyoxal cross-linked scaffolds containing equal amounts of Chi and Coll by mass and 1% (w/v) nHA are the best candidates for osteoblast differentiation and matrix mineralization.

Foaming of PCL-Based Composites Using scCO2: Structure and Physical Properties

The process of foaming poly(caprolactone)-based composites using supercritical carbon dioxide was analyzed. The impact of the conditions of the solid-foam production process on the process efficiency and properties of porous structures was investigated. The novel application of various types of porogens—hydroxyapatite, nanocellulose, carboxymethylcellulose, and graphene oxide—was tested in order to modify the properties and improve the quality of solid foams, increasing their usefulness in specialized practical applications. The study showed a significant influence of the foaming process conditions on the properties of solid foams. The optimal process parameters were determined to be pressure 18 MPa, temperature 70 °C, and time 1 h in order to obtain structures with appropriate properties for applications in biomedical engineering, and the most promising material for their production was selected: a composite containing 5% hydroxyapatite or 0.2% graphene oxide.

Mineralized collagen as a bioactive ink to support encapsulation of human adipose stem cells: A step towards the future of bone regeneration

Bioprinting - printing with incorporated living cells - has earned special attention on tissue engineering approaches, aiming to closer reproduce the 3D microenvironment of the target tissue. However, it raises extra complexity related to the need to use cell-friendly printing conditions that still comply with material printing fidelity. Inspired by the composite nano structural organization of mineralized tissues, this work reports the efficiency of the chemical approach followed to in situ mineralize blue shark skin collagen, at a nano scale level, to ultimately produce stable inks. The influence of initial cellular density was evaluated by assessing three different concentrations (2.5, 5 and 7.5 × 10⁶ cells·ml^-1) of human adipose stem cells (hASC), with the higher density of encapsulated cells presenting improved viability in a long culture term. Immunodetection of osteogenic-related markers, like RUNX2 and osteopontin, 21 days after cell culture in basal conditions confirmed the potential of the ink to be applied for osteogenic purposes, which may be associated with the success of the cell-to-ink interaction and the Ca²⁺ ions released from the co-precipitated hydroxyapatite. A combination of mineralized shark collagen, alginate and hASC is thus proposed as a bioactive bioink with potential properties for regeneration of bone tissue.

Therapeutic Treatments for Osteoporosis-Which Combination of Pills Is the Best among the Bad?

Osteoporosis is a chronical, systemic skeletal disorder characterized by an increase in bone resorption, which leads to reduced bone density. The reduction in bone mineral density and therefore low bone mass results in an increased risk of fractures. Osteoporosis is caused by an imbalance in the normally strictly regulated bone homeostasis. This imbalance is caused by overactive bone-resorbing osteoclasts, while bone-synthesizing osteoblasts do not compensate for this. In this review, the mechanism is presented, underlined by in vitro and animal models to investigate this imbalance as well as the current status of clinical trials. Furthermore, new therapeutic strategies for osteoporosis are presented, such as anabolic treatments and catabolic treatments and treatments using biomaterials and biomolecules. Another focus is on new combination therapies with multiple drugs which are currently considered more beneficial for the treatment of osteoporosis than monotherapies. Taken together, this review starts with an overview and ends with the newest approaches for osteoporosis therapies and a future perspective not presented so far.

3D bioprinted silk fibroin hydrogels for tissue engineering

The development of biocompatible and precisely printable bioink addresses the growing demand for three-dimensional (3D) bioprinting applications in the field of tissue engineering. We developed a methacrylated photocurable silk fibroin (SF) bioink for digital light processing 3D bioprinting to generate structures with high mechanical stability and biocompatibility for tissue engineering applications. Procedure 1 describes the synthesis of photocurable methacrylated SF bioink, which takes 2 weeks to complete. Digital light processing is used to fabricate 3D hydrogels using the bioink (1.5 h), which are characterized in terms of methacrylation, printability, mechanical and rheological properties, and biocompatibility. The physicochemical properties of the bioink can be modulated by varying photopolymerization conditions such as the degree of methacrylation, light intensity, and concentration of the photoinitiator and bioink. The versatile bioink can be used broadly in a range of applications, including nerve tissue engineering through co-polymerization of the bioink with graphene oxide, and for wound healing as a sealant. Procedure 2 outlines how to apply 3D-printed SF hydrogels embedded with chondrocytes and turbinate-derived mesenchymal stem cells in one specific in vivo application, trachea tissue engineering, which takes 2-9 weeks.

3D Bioprinting of Biomimetic Bilayered Scaffold Consisting of Decellularized Extracellular Matrix and Silk Fibroin for Osteochondral Repair

Recently, three-dimensional (3D) bioprinting technology is becoming an appealing approach for osteochondral repair. However, it is challenging to develop a bilayered scaffold with anisotropic structural properties to mimic a native osteochondral tissue. Herein, we developed a bioink consisting of decellularized extracellular matrix and silk fibroin to print the bilayered scaffold. The bilayered scaffold mimics the natural osteochondral tissue by controlling the composition, mechanical properties, and growth factor release in each layer of the scaffold. The in vitro results show that each layer of scaffolds had a suitable mechanical strength and degradation rate. Furthermore, the scaffolds encapsulating transforming growth factor-beta (TGF-β) and bone morphogenetic protein-2 (BMP-2) can act as a controlled release system and promote directed differentiation of bone marrow-derived mesenchymal stem cells. Furthermore, the in vivo experiments suggested that the scaffolds loaded with growth factors promoted osteochondral regeneration in the rabbit knee joint model. Consequently, the biomimetic bilayered scaffold loaded with TGF-β and BMP-2 would be a promising strategy for osteochondral repair.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Biomaterials in bone and mineralized tissue engineering using 3D printing and bioprinting technologies

This review focuses on recently developed printable biomaterials for bone and mineralized tissue engineering. 3D printing or bioprinting is an advanced technology to design and fabricate complex functional 3D scaffolds, mimicking native tissue forin vivoapplications. We categorized the biomaterials into two main classes: 3D printing and bioprinting. Various biomaterials, including natural, synthetic biopolymers and their composites, have been studied. Biomaterial inks or bioinks used for bone and mineralized tissue regeneration include hydrogels loaded with minerals or bioceramics, cells, and growth factors. In 3D printing, the scaffold is created by acellular biomaterials (biomaterial inks), while in 3D bioprinting, cell-laden hydrogels (bioinks) are used. Two main classes of bioceramics, including bioactive and bioinert ceramics, are reviewed. Bioceramics incorporation provides osteoconductive properties and induces bone formation. Each biopolymer and mineral have its advantages and limitations. Each component of these composite biomaterials provides specific properties, and their combination can ameliorate the mechanical properties, bioactivity, or biological integration of the 3D printed scaffold. Present challenges and future approaches to address them are also discussed.

Multi-Dimensional Printing for Bone Tissue Engineering

The development of 3D printing has significantly advanced the field of bone tissue engineering by enabling the fabrication of scaffolds that faithfully recapitulate desired mechanical properties and architectures. In addition, computer-based manufacturing relying on patient-derived medical images permits the fabrication of customized modules in a patient-specific manner. In addition to conventional 3D fabrication, progress in materials engineering has led to the development of 4D printing, allowing time-sensitive interventions such as programed therapeutics delivery and modulable mechanical features. Therapeutic interventions established via multi-dimensional engineering are expected to enhance the development of personalized treatment in various fields, including bone tissue regeneration. Here, recent studies utilizing 3D printed systems for bone tissue regeneration are summarized and advances in 4D printed systems are highlighted. Challenges and perspectives for the future development of multi-dimensional printed systems toward personalized bone regeneration are also discussed.

Bioactive Sr2+/Fe3+co-substituted hydroxyapatite in cryogenically 3D printed porous scaffolds for bone tissue engineering

Developing multi-doped bioceramics that possess biological multifunctionality is becoming increasingly attractive and promising for bone tissue engineering. In this view innovative Sr²⁺/Fe³⁺co-substituted nano-hydroxyapatite with gradient doping concentrations fixed at 10 mol% has been deliberately designed previously. Herein, to evaluate their therapeutic potentials for bone healing, novel gradient SrFeHA/PCL scaffolds are fabricated by extrusion cryogenic 3D printing technology with subsequent lyophilization. The obtained scaffolds exhibit desired 3D interconnected porous structure and rough microsurface, along with appreciable release of bioactive Sr²⁺/Fe³⁺from SrFeHA components. These favorable physicochemical properties render printed scaffolds realizing effective biological applications bothin vitroandin vivo, particularly the moderate co-substituted Sr7.5Fe2.5HA and Sr5Fe5HA groups exhibit remarkably enhanced bioactivity that not only promotes the functions of MC3T3 osteoblasts and HUVECs directly, but also energetically manipulates favorable macrophages activation to concurrently facilitate osteogenesis/angiogenesis. Moreover,in vivosubcutaneous implantation and cranial defects repair outcomes further confirm their superior capacity to dictate immune reaction, implants vascularization andin situbone regeneration, mainly dependent on the synergetic effects of released Sr²⁺/Fe³⁺. Accordingly, for the first time, present study highlights the great potential of Sr7.5Fe2.5HA and Sr5Fe5HA for ameliorating bone regeneration process by coupling of immunomodulation with enhanced angio- and osteogenesis and hence may provide a new promising alternative for future bone tissue engineering.

Recent Advances in 3D Printing with Protein-Based Inks

Three-dimensional (3D) printing is a transformative manufacturing strategy, allowing rapid prototyping, customization, and flexible manipulation of structure-property relationships. Proteins are particularly appealing to formulate inks for 3D printing as they serve as essential structural components of living systems, provide a support presence in and around cells and for tissue functions, and also provide the basis for many essential ex vivo secreted structures in nature. Protein-based inks are beneficial in vivo due to their mechanics, chemical and physical match to the specific tissue, and full degradability, while also to promoting implant-host integration and serving as an interface between technology and biology. Exploiting the biological, chemical, and physical features of protein-based inks can provide key opportunities to meet the needs of tissue engineering and regenerative medicine. Despite these benefits, protein-based inks impose nontrivial challenges to 3D printing such as concentration and rheological features and reconstitution of the structural hierarchy observed in nature that is a source of the robust mechanics and functions of these materials. This review introduces photo-crosslinking mechanisms and rheological principles that underpins a variety of 3D printing techniques. The review also highlights recent advances in the design, development, and biomedical utility of monolithic and composite inks from a range of proteins, including collagen, silk, fibrinogen, and others. One particular focus throughout the review is to introduce unique material characteristics of proteins, including amino acid sequences, molecular assembly, and secondary conformations, which are useful for designing printing inks and for controlling the printed structures. Future perspectives of 3D printing with protein-based inks are also provided to support the promising spectrum of biomedical research accessible to these materials.

Partially Digested Osteoblast Cell Line-Derived Extracellular Matrix Induces Rapid Mineralization and Osteogenesis

An extracellular matrix (ECM) utilized as a biomaterial can be obtained from organs of living organisms. Therefore, it has some limitations in its supply because of insufficient organs. Furthermore, therapeutic efficacy of ECMs varies depending on factors such as donor's health condition and age. For this reason, ECMs obtained from a cell line could be a good alternative because they can be produced under a controlled environment with uniform quality. Thus, the purpose of this study was to investigate the potential of the MC3T3-E1 cell line-derived ECM as bone graft. The optimized decellularization process was developed to separate the ECM from MC3T3-E1, osteoblast cell line, using Trypsin-EDTA and Triton X-100. The decellularized ECM was partially digested using pepsin. Also, human bone marrow-derived mesenchymal stem cells induced faster osteogenesis on the ECM-coated surface than on the collagen-coated surface. Partially digested ECM fragments were embedded on the polyethylene glycol scaffold without additional chemical modification or crosslinking. Micro-computed tomography and histological analysis results showed that the ECM in the scaffold promoted actual bone regeneration after in vivo implantation to a mouse calvarial defect model. This study suggests that the bone-specific ECM derived from the cell line can replace the ECM from organs for application in tissue engineering and regenerative medicine.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Collagen Type I Biomaterials as Scaffolds for Bone Tissue Engineering

Collagen type I is the main organic constituent of the bone extracellular matrix and has been used for decades as scaffolding material in bone tissue engineering approaches when autografts are not feasible. Polymeric collagen can be easily isolated from various animal sources and can be processed in a great number of ways to manufacture biomaterials in the form of sponges, particles, or hydrogels, among others, for different applications. Despite its great biocompatibility and osteoconductivity, collagen type I also has some drawbacks, such as its high biodegradability, low mechanical strength, and lack of osteoinductive activity. Therefore, many attempts have been made to improve the collagen type I-based implants for bone tissue engineering. This review aims to summarize the current status of collagen type I as a biomaterial for bone tissue engineering, as well as to highlight some of the main efforts that have been made recently towards designing and producing collagen implants to improve bone regeneration.

Crosslinking strategies for silk fibroin hydrogels: promising biomedical materials

Due to their strong biomimetic potential, silk fibroin (SF) hydrogels are impressive candidates for tissue engineering, due to their tunable mechanical properties, biocompatibility, low immunotoxicity, controllable biodegradability, and a remarkable capacity for biomaterial modification and the realization of a specific molecular structure. The fundamental chemical and physical structure of SF allows its structure to be altered using various crosslinking strategies. The established crosslinking methods enable the formation of three-dimensional (3D) networks under physiological conditions. There are different chemical and physical crosslinking mechanisms available for the generation of SF hydrogels (SFHs). These methods, either chemical or physical, change the structure of SF and improve its mechanical stability, although each method has its advantages and disadvantages. While chemical crosslinking agents guarantee the mechanical strength of SFH through the generation of covalent bonds, they could cause some toxicity, and their usage is not compatible with a cell-friendly technology. On the other hand, physical crosslinking approaches have been implemented in the absence of chemical solvents by the induction of β-sheet conformation in the SF structure. Unfortunately, it is not easy to control the shape and properties of SFHs when using this method. The current review discusses the different crosslinking mechanisms of SFH in detail, in order to support the development of engineered SFHs for biomedical applications.

Three-Dimensional Printing of Calcium Carbonate/Hydroxyapatite Scaffolds at Low Temperature for Bone Tissue Engineering

Three-dimensional (3D) printing technology has been applied to fabricate bone tissue engineering scaffolds for a wide range of materials with precisely control over scaffold structures. Coral is a potential bone repair and bone replacement material. Due to the natural source limitation of coral, we developed a fabrication protocol for 3D printing of calcium carbonate (CaCO₃) nanoparticles for coral replacement in the application of bone tissue engineering. Up to 80% of CaCO₃ nanoparticles can be printed with high resolution using poly-l-lactide as a blender. The scaffolds were subjected to a controlled hydrothermal process for incomplete conversion of carbonate to phosphate to produce CaCO₃ scaffold covered by hydroxyapatite (HA) to modify the biocompatibility and degradation of CaCO₃/HA scaffolds. X-ray diffraction and Fourier transform infrared spectroscopy showed that HA was converted and attached to the surface of the scaffold, and the surface morphology and microstructure were studied using a scanning electron microscope. To confirm the bone regeneration performance of the scaffold, cell proliferation and osteogenic differentiation of MC3T3 cells on the scaffold were evaluated. In addition, in vivo experiments showed that CaCO₃/HA scaffolds can promote bone growth and repairing process and has high potential in bone tissue engineering. ClinicalTrials.gov ID: SH9H-2020-A603.

Tissue Engineering in Musculoskeletal Tissue: A Review of the Literature

Tissue engineering refers to the attempt to create functional human tissue from cells in a laboratory. This is a field that uses living cells, biocompatible materials, suitable biochemical and physical factors, and their combinations to create tissue-like structures. To date, no tissue engineered skeletal muscle implants have been developed for clinical use, but they may represent a valid alternative for the treatment of volumetric muscle loss in the near future. Herein, we reviewed the literature and showed different techniques to produce synthetic tissues with the same architectural, structural and functional properties as native tissues.

3D bioprinting of mechanically tuned bioinks derived from cardiac decellularized extracellular matrix

3D bioprinting is a powerful technique for engineering tissues used to study cell behavior and tissue properties in vitro. With the right formulation and printing parameters, bioinks can provide native biological and mechanical cues while allowing for versatile 3D structures that recapitulate tissue-level organization. Bio-based materials that support cellular adhesion, differentiation, and proliferation - including gelatin, collagen, hyaluronic acid, and alginate - have been successfully used as bioinks. In particular, decellularized extracellular matrix (dECM) has become a promising material with the unique ability to maintain both biochemical and topographical micro-environments of native tissues. However, dECM has shown technical limitations for 3D printing (3DP) applications posed by its intrinsically low mechanical stability. Herein, we report hydrogel bioinks composed of partially digested, porcine cardiac decellularized extracellular matrix (cdECM), Laponite-XLG nanoclay, and poly(ethylene glycol)-diacrylate (PEG-DA). The Laponite facilitated extrusion-based 3DP, while PEG-DA enabled photo-polymerization after printing. Improving upon previously reported bioinks derived from dECM, our bioinks combine extrudability, shape fidelity, rapid cross-linking, and cytocompatibility in a single formulation (> 97% viability of encapsulated human cardiac fibroblasts and > 94% viability of human induced pluripotent stem cell derived cardiomyocytes after 7 days). The compressive modulus of the cured hydrogel bioinks was tunable from 13.4-89 kPa by changing the concentration of PEG-DA in the bioink formulation. Importantly, this span of mechanical stiffness encompasses ranges of tissue stiffness from healthy (compressive modulus ~5-15 kPa) to fibrotic (compressive modulus ~30-100 kPa) cardiac tissue states. The printed constructs demonstrated shape fidelity, adaptability to different printing conditions, and high cell viability following extrusion and photo-polymerization, highlighting the potential for applications in modeling both healthy and fibrotic cardiac tissue.

Cryogenic 3D printing of dual-delivery scaffolds for improved bone regeneration with enhanced vascularization

Three-dimensional (3D) printing has been increasingly employed to produce advanced bone tissue engineering scaffolds with biomimetic structures and matched mechanical strengths, in order to induce improved bone regeneration in defects with a critical size. Given that the successful bone regeneration requires both excellent osteogenesis and vascularization, endowing scaffolds with both strong bone forming ability and favorable angiogenic potential would be highly desirable to induce improved bone regeneration with required vascularization. In this investigation, customized bone tissue engineering scaffolds with balanced osteoconductivity/osteoinductivity were produced via cryogenic 3D printing of β-tricalcium phosphate and osteogenic peptide (OP) containing water/poly(lactic-co-glycolic acid)/dichloromethane emulsion inks. The fabricated scaffolds had a hierarchically porous structure and were mechanically comparable to human cancellous bone. Angiogenic peptide (AP) containing collagen I hydrogel was then coated on scaffold surface to further provide scaffolds with angiogenic capability. A sequential release with a quick AP release and a slow but sustained OP release was obtained for the scaffolds. Both rat endothelial cells (ECs) and rat bone marrow derived mesenchymal stem cells (MSCs) showed high viability on scaffolds. Improved in vitro migration and angiogenesis of ECs were obtained for scaffolds delivered with AP while enhanced osteogenic differentiation was observed in scaffolds containing OP. The in vivo results showed that, toward scaffolds containing both AP and OP, the quick release of AP induced obvious angiogenesis in vivo, while the sustained OP release significantly improved the new bone formation. This study provides a facile method to produce dual-delivery scaffolds to achieve multiple functions.

Recent advances in 3D bioprinting of musculoskeletal tissues

The musculoskeletal system is essential for maintaining posture, protecting organs, facilitating locomotion, and regulating various cellular and metabolic functions. Injury to this system due to trauma or wear is common, and severe damage may require surgery to restore function and prevent further harm. Autografts are the current gold standard for the replacement of lost or damaged tissues. However, these grafts are constrained by limited supply and donor site morbidity. Allografts, xenografts, and alloplastic materials represent viable alternatives, but each of these methods also has its own problems and limitations. Technological advances in three-dimensional (3D) printing and its biomedical adaptation, 3D bioprinting, have the potential to provide viable, autologous tissue-like constructs that can be used to repair musculoskeletal defects. Though bioprinting is currently unable to develop mature, implantable tissues, it can pattern cells in 3D constructs with features facilitating maturation and vascularization. Further advances in the field may enable the manufacture of constructs that can mimic native tissues in complexity, spatial heterogeneity, and ultimately, clinical utility. This review studies the use of 3D bioprinting for engineering bone, cartilage, muscle, tendon, ligament, and their interface tissues. Additionally, the current limitations and challenges in the field are discussed and the prospects for future progress are highlighted.