3D printing of Mo-containing scaffolds with activated anabolic responses and bi-lineage bioactivities

Enhanced osteochondral regeneration with a 3D-Printed biomimetic scaffold featuring a calcified interfacial layer

The integrative regeneration of both articular cartilage and subchondral bone remains an unmet clinical need due to the difficulties of mimicking spatial complexity in native osteochondral tissues for artificial implants. Layer-by-layer fabrication strategies, such as 3D printing, have emerged as a promising technology replicating the stratified zonal architecture and varying microstructures and mechanical properties. However, the dynamic and circulating physiological environments, such as mass transportation or cell migration, usually distort the pre-confined biological properties in the layered implants, leading to undistinguished spatial variations and subsequently inefficient regenerations. This study introduced a biomimetic calcified interfacial layer into the scaffold as a compact barrier between a cartilage layer and a subchondral bone layer to facilitate osteogenic-chondrogenic repair. The calcified interfacial layer consisting of compact polycaprolactone (PCL), nano-hydroxyapatite, and tasquinimod (TA) can physically and biologically separate the cartilage layer (TA-mixed, chondrocytes-load gelatin methacrylate) from the subchondral bond layer (porous PCL). This introduction preserved the as-designed independent biological environment in each layer for both cartilage and bone regeneration, successfully inhibiting vascular invasion into the cartilage layer and preventing hyaluronic cartilage calcification owing to devascularization of TA. The improved integrative regeneration of cartilage and subchondral bone was validated through gross examination, micro-computed tomography (micro-CT), and histological and immunohistochemical analyses based on an in vivo rat model. Moreover, gene and protein expression studies identified a key role of Caveolin (CAV-1) in promoting angiogenesis through the Wnt/β-catenin pathway and indicated that TA in the calcified layer blocked angiogenesis by inhibiting CAV-1.

The effect of Si species released from bioactive glasses on cell behaviour: A quantitative review

Despite over 50 years of silicate bioactive glass (SBG) research, commercial success, and 6000+ published articles, there remains a lack of understanding of how soluble silicate (Si) species released from SBGs influences cellular responses. Using a systematic approach, this article quantitatively compares the in vitro responses of cells to SBG dissolution products reported in the literature and determines if there is a Si concentration ([Si]) dependent effect on cell behaviour. Cell behavioural responses to SBGs [Si] in dissolution products included metabolic activity (reported in 52 % of articles), cell number (24 %), protein production (22 %), gene expression (22 %) and biomineralization (24 %). There was a difference in the [Si] reported to cause increased (desirable) cellular responses (median = 30.2 ppm) compared to the [Si] reported to cause decreased (undesirable) cellular responses (median = 52.0 ppm) (P ≤ 0.001). The frequency of undesirable outcomes increased with increasing [Si], with ∼3 times more negative outcomes reported above 52 ppm. We also investigated the effect of [Si] on specific cellular outcomes (e.g., metabolic activity, angiogenesis, osteogenesis), if cell type/species influenced these responses and the impact of other ions (Ca, P, Na) within the SBG dissolution media on cell behaviour. This review has, for the first time, quantitatively compared the cellular responses to SBGs from the literature, providing a quantitative overview of SBG in vitro practices and presents evidence of a range of [Si] where desirable cellular responses may be more likely (30-52 ppm). This review also demonstrates the need for greater standardisation of in vitro methodological approaches and recommends some minimum reporting standards. STATEMENT OF SIGNIFICANCE: This systematic review investigates the relationship between the concentration of Si released from Si-bioactive glasses (SBG) and in vitro cellular responses. Si releasing materials continue to be of considerable scientific, commercial, and medical interest (with 1500+ articles published in the last 3 years) but there is considerable variation in the reported biologically effective Si concentrations and on the importance of Si on cell behaviour. Despite the variation in methodological approaches, this article demonstrated statistical commonalities in the Si concentrations that cause desirable and undesirable cellular behaviours, suggesting a window where positive cellular outcomes are more likely. This review also provides a quantitative analysis of in vitro practices within the bioactive glass field and highlights the need for greater standardisation.

Polymeric Based Hydrogel Membranes for Biomedical Applications

The development of biomedical applications is a transdisciplinary field that in recent years has involved researchers from chemistry, pharmacy, medicine, biology, biophysics, and biomechanical engineering. The fabrication of biomedical devices requires the use of biocompatible materials that do not damage living tissues and have some biomechanical characteristics. The use of polymeric membranes, as materials meeting the above-mentioned requirements, has become increasingly popular in recent years, with outstanding results in tissue engineering, for regeneration and replenishment of tissues constituting internal organs, in wound healing dressings, and in the realization of systems for diagnosis and therapy, through the controlled release of active substances. The biomedical application of hydrogel membranes has had little uptake in the past due to the toxicity of cross-linking agents and to the existing limitations regarding gelation under physiological conditions, but now it is proving to be a very promising field This review presents the important technological innovations that the use of membrane hydrogels has promoted, enabling the resolution of recurrent clinical problems, such as post-transplant rejection crises, haemorrhagic crises due to the adhesion of proteins, bacteria, and platelets on biomedical devices in contact with blood, and poor compliance of patients undergoing long-term drug therapies.

Multicellular Bioprinting of Biomimetic Inks for Tendon-to-Bone Regeneration

Tendon-to-bone interface has a hierarchical structure and gradient component that are conducive to distributing the stresses to achieve movement. Conventional biomaterials lack the capacity to induce synchronous repair of multiple tissues, resulting in the failure of the interface repair. Biomimetic strategies have attracted enormous attention in the field of complex structure regeneration because they can meet the different physiological requirements of multiple tissues. Herein, a biomimetic ink mimicking tendon/bone tissues is developed by combining tendon/bone-related cells and Mo-containing silicate (MS) bioceramics. Subsequently, biomimetic multicellular scaffolds are fabricated to achieve the simulation of the hierarchical structure and cellular composition of tendon-to-bone interfaces by the spatial distribution of the biomimetic inks via 3D bioprinting, which is of great significance for inducing the regeneration of complex structures in the interface region. In addition, attributed to the desirable ionic microenvironment created by MS bioceramics, the biomimetic scaffolds possess the dual function of inducing tendon/bone-related cells tenogenic and osteogenic differentiation in vitro, and promote the integrated regeneration of tendon-to-bone interfaces in vivo. The study offers a feasible strategy to construct biomimetic multicellular scaffolds with bifunction for inducing multi-lineage tissue regeneration, especially for regenerating soft-to-hard tissue interfaces.

Design and bioprinting for tissue interfaces

Tissue interfaces include complex gradient structures formed by transitioning of biochemical and mechanical properties in micro-scale. This characteristic allows the communication and synchronistic functioning of two adjacent but distinct tissues. It is particularly challenging to restore the function of these complex structures by transplantation of scaffolds exclusively produced by conventional tissue engineering methods. Three-dimensional (3D) bioprinting technology has opened an unprecedented approach for precise and graded patterning of chemical, biological and mechanical cues in a single construct mimicking natural tissue interfaces. This paper reviews and highlights biochemical and biomechanical design for 3D bioprinting of various tissue interfaces, including cartilage-bone, muscle-tendon, tendon/ligament-bone, skin, and neuro-vascular/muscular interfaces. Future directions and translational challenges are also provided at the end of the paper.

Regeneration of articular cartilage defects: Therapeutic strategies and perspectives

Articular cartilage (AC), a bone-to-bone protective device made of up to 80% water and populated by only one cell type (i.e. chondrocyte), has limited capacity for regeneration and self-repair after being damaged because of its low cell density, alymphatic and avascular nature. Resulting repair of cartilage defects, such as osteoarthritis (OA), is highly challenging in clinical treatment. Fortunately, the development of tissue engineering provides a promising method for growing cells in cartilage regeneration and repair by using hydrogels or the porous scaffolds. In this paper, we review the therapeutic strategies for AC defects, including current treatment methods, engineering/regenerative strategies, recent advances in biomaterials, and present emphasize on the perspectives of gene regulation and therapy of noncoding RNAs (ncRNAs), such as circular RNA (circRNA) and microRNA (miRNA).

Polysaccharide-based hydrogel with photothermal effect for accelerating wound healing

Polysaccharide-based hydrogel has excellent biochemical function, abundant sources, good biocompatibility and other advantages, and has a broad application prospect in biomedical fields, especially in the field of wound healing. With its inherent high specificity and low invasive burden, photothermal therapy has shown great application prospect in preventing wound infection and promoting wound healing. Combining polysaccharide-based hydrogel with photothermal therapy (PTT), multifunctional hydrogel with photothermal, bactericidal, anti-inflammatory and tissue regeneration functions can be designed, so as to achieve better therapeutic effect. This review first focuses on the basic principles of hydrogel and PTT, and the types of polysaccharides that can be used to design hydrogels. In addition, according to the different materials that produce photothermal effects, the design considerations of several representative polysaccharide-based hydrogels are emphatically introduced. Finally, the challenges faced by polysaccharide-based hydrogels with photothermal properties are discussed, and the future prospects of this field are put forward.

Functional engineering strategies of 3D printed implants for hard tissue replacement

Three-dimensional printing technology with the rapid development of printing materials are widely recognized as a promising way to fabricate bioartificial bone tissues. In consideration of the disadvantages of bone substitutes, including poor mechanical properties, lack of vascularization and insufficient osteointegration, functional modification strategies can provide multiple functions and desired characteristics of printing materials, enhance their physicochemical and biological properties in bone tissue engineering. Thus, this review focuses on the advances of functional engineering strategies for 3D printed biomaterials in hard tissue replacement. It is structured as introducing 3D printing technologies, properties of printing materials (metals, ceramics and polymers) and typical functional engineering strategies utilized in the application of bone, cartilage and joint regeneration.

A 3D-printed molybdenum-containing scaffold exerts dual pro-osteogenic and anti-osteoclastogenic effects to facilitate alveolar bone repair

The positive regulation of bone-forming osteoblast activity and the negative feedback regulation of osteoclastic activity are equally important in strategies to achieve successful alveolar bone regeneration. Here, a molybdenum (Mo)-containing bioactive glass ceramic scaffold with solid-strut-packed structures (Mo-scaffold) was printed, and its ability to regulate pro-osteogenic and anti-osteoclastogenic cellular responses was evaluated in vitro and in vivo. We found that extracts derived from Mo-scaffold (Mo-extracts) strongly stimulated osteogenic differentiation of bone marrow mesenchymal stem cells and inhibited differentiation of osteoclast progenitors. The identified comodulatory effect was further demonstrated to arise from Mo ions in the Mo-extract, wherein Mo ions suppressed osteoclastic differentiation by scavenging reactive oxygen species (ROS) and inhibiting mitochondrial biogenesis in osteoclasts. Consistent with the in vitro findings, the Mo-scaffold was found to significantly promote osteoblast-mediated bone formation and inhibit osteoclast-mediated bone resorption throughout the bone healing process, leading to enhanced bone regeneration. In combination with our previous finding that Mo ions participate in material-mediated immunomodulation, this study offers the new insight that Mo ions facilitate bone repair by comodulating the balance between bone formation and resorption. Our findings suggest that Mo ions are multifunctional cellular modulators that can potentially be used in biomaterial design and bone tissue engineering.

Biodegradable Poly(D-L-lactide-co-glycolide) (PLGA)-Infiltrated Bioactive Glass (CAR12N) Scaffolds Maintain Mesenchymal Stem Cell Chondrogenesis for Cartilage Tissue Engineering

Regeneration of articular cartilage remains challenging. The aim of this study was to increase the stability of pure bioactive glass (BG) scaffolds by means of solvent phase polymer infiltration and to maintain cell adherence on the glass struts. Therefore, BG scaffolds either pure or enhanced with three different amounts of poly(D-L-lactide-co-glycolide) (PLGA) were characterized in detail. Scaffolds were seeded with primary porcine articular chondrocytes (pACs) and human mesenchymal stem cells (hMSCs) in a dynamic long-term culture (35 days). Light microscopy evaluations showed that PLGA was detectable in every region of the scaffold. Porosity was greater than 70%. The biomechanical stability was increased by polymer infiltration. PLGA infiltration did not result in a decrease in viability of both cell types, but increased DNA and sulfated glycosaminoglycan (sGAG) contents of hMSCs-colonized scaffolds. Successful chondrogenesis of hMSC-colonized scaffolds was demonstrated by immunocytochemical staining of collagen type II, cartilage proteoglycans and the transcription factor SOX9. PLGA-infiltrated scaffolds showed a higher relative expression of cartilage related genes not only of pAC-, but also of hMSC-colonized scaffolds in comparison to the pure BG. Based on the novel data, our recommendation is BG scaffolds with single infiltrated PLGA for cartilage tissue engineering.

3D Printing for Bone-Cartilage Interface Regeneration

Due to the vasculature defects and/or the avascular nature of cartilage, as well as the complex gradients for bone-cartilage interface regeneration and the layered zonal architecture, self-repair of cartilage and subchondral bone is challenging. Currently, the primary osteochondral defect treatment strategies, including artificial joint replacement and autologous and allogeneic bone graft, are limited by their ability to simply repair, rather than induce regeneration of tissues. Meanwhile, over the past two decades, three-dimension (3D) printing technology has achieved admirable advancements in bone and cartilage reconstruction, providing a new strategy for restoring joint function. The advantages of 3D printing hybrid materials include rapid and accurate molding, as well as personalized therapy. However, certain challenges also exist. For instance, 3D printing technology for osteochondral reconstruction must simulate the histological structure of cartilage and subchondral bone, thus, it is necessary to determine the optimal bioink concentrations to maintain mechanical strength and cell viability, while also identifying biomaterials with dual bioactivities capable of simultaneously regenerating cartilage. The study showed that the regeneration of bone-cartilage interface is crucial for the repair of osteochondral defect. In this review, we focus on the significant progress and application of 3D printing technology for bone-cartilage interface regeneration, while also expounding the potential prospects for 3D printing technology and highlighting some of the most significant challenges currently facing this field.

Bioactive glasses incorporating less-common ions to improve biological and physical properties

Bioactive glasses (BGs) have been a focus of research for over five decades for several biomedical applications. Although their use in bone substitution and bone tissue regeneration has gained important attention, recent developments have also seen the expansion of BG applications to the field of soft tissue engineering. Hard and soft tissue repair therapies can benefit from the biological activity of metallic ions released from BGs. These metallic ions are incorporated in the BG network not only for their biological therapeutic effects but also in many cases for influencing the structure and processability of the glass and to impart extra functional properties. The "classical" elements in silicate BG compositions are silicon (Si), phosphorous (P), calcium (Ca), sodium (Na), and potassium (K). In addition, other well-recognized biologically active ions have been incorporated in BGs to provide osteogenic, angiogenic, anti-inflammatory, and antibacterial effects such as zinc (Zn), magnesium (Mg), silver (Ag), strontium (Sr), gallium (Ga), fluorine (F), iron (Fe), cobalt (Co), boron (B), lithium (Li), titanium (Ti), and copper (Cu). More recently, rare earth and other elements considered less common or, some of them, even "exotic" for biomedical applications, have found room as doping elements in BGs to enhance their biological and physical properties. For example, barium (Ba), bismuth (Bi), chlorine (Cl), chromium (Cr), dysprosium (Dy), europium (Eu), gadolinium (Gd), ytterbium (Yb), thulium (Tm), germanium (Ge), gold (Au), holmium (Ho), iodine (I), lanthanum (La), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), nitrogen (N), palladium (Pd), rubidium (Rb), samarium (Sm), selenium (Se), tantalum (Ta), tellurium (Te), terbium (Tb), erbium (Er), tin (Sn), tungsten (W), vanadium (V), yttrium (Y) as well as zirconium (Zr) have been included in BGs. These ions have been found to be particularly interesting for enhancing the biological performance of doped BGs in novel compositions for tissue repair (both hard and soft tissue) and for providing, in some cases, extra functionalities to the BG, for example fluorescence, luminescence, radiation shielding, anti-inflammatory, and antibacterial properties. This review summarizes the influence of incorporating such less-common elements in BGs with focus on tissue engineering applications, usually exploiting the bioactivity of the BG in combination with other functional properties imparted by the presence of the added elements.

3D Printed Multiphasic Scaffolds for Osteochondral Repair: Challenges and Opportunities

Osteochondral (OC) defects are debilitating joint injuries characterized by the loss of full thickness articular cartilage along with the underlying calcified cartilage through to the subchondral bone. While current surgical treatments can provide some relief from pain, none can fully repair all the components of the OC unit and restore its native function. Engineering OC tissue is challenging due to the presence of the three distinct tissue regions. Recent advances in additive manufacturing provide unprecedented control over the internal microstructure of bioscaffolds, the patterning of growth factors and the encapsulation of potentially regenerative cells. These developments are ushering in a new paradigm of 'multiphasic' scaffold designs in which the optimal micro-environment for each tissue region is individually crafted. Although the adoption of these techniques provides new opportunities in OC research, it also introduces challenges, such as creating tissue interfaces, integrating multiple fabrication techniques and co-culturing different cells within the same construct. This review captures the considerations and capabilities in developing 3D printed OC scaffolds, including materials, fabrication techniques, mechanical function, biological components and design.

Osteochondral Tissue Engineering: The Potential of Electrospinning and Additive Manufacturing

The socioeconomic impact of osteochondral (OC) damage has been increasing steadily over time in the global population, and the promise of tissue engineering in generating biomimetic tissues replicating the physiological OC environment and architecture has been falling short of its projected potential. The most recent advances in OC tissue engineering are summarised in this work, with a focus on electrospun and 3D printed biomaterials combined with stem cells and biochemical stimuli, to identify what is causing this pitfall between the bench and the patients' bedside. Even though significant progress has been achieved in electrospinning, 3D-(bio)printing, and induced pluripotent stem cell (iPSC) technologies, it is still challenging to artificially emulate the OC interface and achieve complete regeneration of bone and cartilage tissues. Their intricate architecture and the need for tight spatiotemporal control of cellular and biochemical cues hinder the attainment of long-term functional integration of tissue-engineered constructs. Moreover, this complexity and the high variability in experimental conditions used in different studies undermine the scalability and reproducibility of prospective regenerative medicine solutions. It is clear that further development of standardised, integrative, and economically viable methods regarding scaffold production, cell selection, and additional biochemical and biomechanical stimulation is likely to be the key to accelerate the clinical translation and fill the gap in OC treatment.

3D printed intelligent scaffold prevents recurrence and distal metastasis of breast cancer

Rationale: Tumors are commonly treated by resection, which usually leads to massive hemorrhage and tumor cell residues, thereby increasing the risk of local recurrence and distant metastasis.

Methods: Herein, an intelligent 3D-printed poly(lactic-co-glycolic acid), gelatin, and chitosan scaffold loaded with anti-cancer drugs was prepared that showed hemostatic function and good pH sensitivity.

Results: Following in situ implantation in wounds, the scaffolds absorbed hemorrhage and cell residues after surgery, and promoted wound healing. In an in vivo environment, the scaffold responded to the slightly acidic environment of the tumor to undergo sustained drug release to significantly inhibit the recurrence and growth of the tumor, and reduced drug toxicity, all without causing damage to healthy tissues and with good biocompatibility.

Conclusions: The multifunctional intelligent scaffold represents an excellent treatment modality for breast cancer following resection, and provides great potential for efficient cancer therapy.

3D printing of metal-organic framework nanosheets-structured scaffolds with tumor therapy and bone construction

After surgical resection for a bone tumor, the uncleared bone tumor cells can multiply and cause recurrence of the bone tumor. It is worthwhile to design a scaffold that kills the remaining bone tumor cells and repairs bone defects that were given rise to by surgical resection. Additionally, it is extremely important to consider the function of angiogenesis in the process of bone regeneration because the newly formed blood vessels can offer the nutrients for bone regeneration. In this work, a novel metal-organic framework Cu-TCPP nanosheets interface-structured β-tricalcium phosphate (TCP) (Cu-TCPP-TCP) scaffold was successfully prepared through integrating a 3D-printing technique with an in-situ growth method in a solvothermal system. Owing to the excellent photothermal effect of Cu-TCPP nanosheets, Cu-TCPP-TCP scaffolds that were illuminated by near-infrared (NIR) light demonstrated photothermal performance, which was well regulated through varying the contents of Cu-TCPP nanosheets, and the ambient humidity and power density of NIR light. When cultured with osteosarcoma cells, Cu-TCPP-TCP scaffolds killed a significant quantity of osteosarcoma cells through released heat energy after exposure to NIR light with power density 1.0 W cm^-2 and duration 10 min. Similarly, Cu-TCPP-TCP scaffolds ablated subcutaneous bone tumor tissues on the backs of naked mice and suppressed their growth because of the heat energy transformed from NIR light. I n-vitro studies found that Cu-TCPP-TCP scaffolds ably supported the attachments of both human bone marrow stromal cells (HBMSCs) and human umbilical vein endothelial cells (HUVECs), and significantly stimulated expressions of osteogenesis differentiation-related genes in HBMSCs and angiogenesis differentiation-related genes in HUVECs. After implanting Cu-TCPP-TCP scaffolds into the bone defects of rabbits, they effectively promoted bone regeneration. Thus, the integration of the bone-forming bioactivity of TCP scaffolds with the photothermal properties of Cu-TCPP nanosheets and angiogenesis activity of Cu ions makes Cu-TCPP-TCP scaffolds multifunctional, representing a new horizon to develop biomaterials for simultaneously curing bone tumors and repairing bone defects.

An intestinal model with a finger-like villus structure fabricated using a bioprinting process and collagen/SIS-based cell-laden bioink

The surface of the small intestine has a finger-like microscale villus structure, which provides a large surface area to realize efficient digestion and absorption. However, the fabrication of a villus structure using a cell-laden bioink containing a decellularized small intestine submucosa, SIS, which can induce significant cellular activities, has not been attempted owing to the limited mechanical stiffness, which sustains the complex projective finger-like 3D structure. In this work, we developed a human intestinal villi model with an innovative bioprinting process using a collagen/SIS cell-laden bioink. Methods: A Caco-2-laden microscale villus structure (geometry of the villus: height = 831.1 ± 36.2 μm and diameter = 190.9 ± 3.9 μm) using a bioink consisting of collagen type-I and SIS was generated using a vertically moving 3D bioprinting process. By manipulating various compositions of dECM and a crosslinking agent in the bioink and the processing factors (printing speed, printing time, and pneumatic pressure), the villus structure was achieved. Results: The epithelial cell-laden collagen/SIS villi showed significant cell proliferation (1.2-fold) and demonstrated meaningful results for the various cellular activities, such as the expression of tight-junction proteins (ZO-1 and E-cadherin), ALP and ANPEP activities, MUC17 expression, and the permeability coefficient and the glucose uptake ability, compared with the pure 3D collagen villus structure. Conclusion: In vitro cellular activities demonstrated that the proposed cell-laden collagen/dECM villus structure generates a more meaningful epithelium layer mimicking the intestinal structure, compared with the pure cell-laden collagen villus structure having a similar villus geometry. Based on the results, we believe that this dECM-based 3D villus model will be helpful in obtaining a more realistic physiological small-intestine model.

Proteoglycan 4 predicts tribological properties of repaired cartilage tissue

Purpose: One of the essential requirements in maintaining the normal joint motor function is the perfect tribological property of the articular cartilage. Many cartilage regeneration strategies have been developed for treatment in early stages of osteoarthritis, but there is little information on how repaired articular cartilage regains durability. The identification of biomarkers that can predict wear resistant property is critical to advancing the success of cartilage regeneration therapies. Proteoglycan 4 (PRG4) is a macromolecule distributing on the chondrocyte surface that contributes to lubrication. In this study, we investigate if PRG4 expression is associated with tribological properties of regenerated cartilage, and is able to predict its wear resistant status.

Methods: Two different strategies including bone marrow enrichment plus microfracture (B/BME-MFX) and microfracture alone (B-MFX) of cartilage repair in sheep were used. PRG4 expression and a series of tribological parameters on regenerated cartilage were rigorously examined and compared.

Results: Highly and continuously expression of PRG4 in regenerated cartilage surface was negatively correlated with each tribological parameter (P<0.0001, respectively). Multivariate analysis showed that PRG4 expression was the key predictor that contributed to the promotion of cartilage wear resistance.

Conclusion: Higher PRG4 expression in regenerated cartilage is significantly associated with wear resistance improvement. PRG4 may be useful for predicting the wear resistant status of regenerated cartilage and determining the optimal cartilage repair strategy.