3D-bioprinted anisotropic bicellular living hydrogels boost osteochondral regeneration via reconstruction of cartilage-bone interface.

Reconstruction of osteochondral (OC) defects represents an immense challenge due to the need for synchronous regeneration of special stratified tissues. The revolutionary innovation of bioprinting provides a robust method for precise fabrication of tissue-engineered OCs with hierarchical structure; however, their spatial living cues for simultaneous fulfilment of osteogenesis and chondrogenesis to reconstruct the cartilage-bone interface of OC are underappreciated. Here, inspired by natural OC bilayer features, anisotropic bicellular living hydrogels (ABLHs) simultaneously embedding articular cartilage progenitor cells (ACPCs) and bone mesenchymal stem cells (BMSCs) in stratified layers were precisely fabricated via two-channel extrusion bioprinting. The optimum formulation of the 7% GelMA/3% AlgMA hydrogel bioink was demonstrated, with excellent printability at room temperature and maintained high cell viability. Moreover, the chondrogenic ability of ACPCs and the osteogenic ability of BMSCs were demonstrated in vitro, confirming the inherent differential spatial regulation of ABLHs. In addition, ABLHs exhibited satisfactory synchronous regeneration of cartilage and subchondral bone in vivo. Compared with homogeneous hydrogels, the neo-cartilage and neo-bone in ABLHs were augmented by 23.5% and 20.8%, respectively, and more important, a more harmonious cartilage-bone interface was achieved by ABLHs due to their well-tuned cartilage-bone-vessel crosstalk. We anticipate that such a strategy of tissue-mimetic ABLH by means of bioprinting is capable of spatiotemporal cell-driven regeneration, offering insights into the fabrication of anisotropic living materials for the reconstruction of complex organ defects.

Release Kinetics and In Vitro Characterization of Sodium Percarbonate and Calcium Peroxide to Oxygenate Bioprinted Tissue Models.

Oxygen-generating materials have been used in several tissue engineering applications; however, their application as in situ oxygen supply within bioprinted constructs has not been deeply studied. In this study, two oxygen-generating materials, sodium percarbonate (SPO) and calcium peroxide (CPO), were studied for their oxygen release kinetics under a 0.1% O2 condition. In addition, a novel cell-culture-insert setup was used to evaluate the effects of SPO and CPO on the viability of skeletal muscle cells under the same hypoxic condition. Results showed that SPO had a burst oxygen release, while CPO had a more stable oxygen release than SPO. Both SPO and CPO reduced cell viability when used alone. The addition of catalase in SPO and CPO increased the oxygen release rate, as well as improving the viability of skeletal muscle cells; however, CPO still showed cytotoxicity with catalase. Additionally, the utilization of 1 mg/mL SPO and 20 U catalase in a hydrogel for bioprinting significantly enhanced the cell viability under the hypoxic condition. Moreover, bioprinted muscle constructs could further differentiate into elongated myotubes when transferring back to the normoxic condition. This work provides an excellent in vitro model to test oxygen-generating materials and further discover their applications in bioprinting, where they represent promising avenues to overcome the challenge of oxygen shortage in bioprinted constructs before their complete vascularization.

Fabrication of SA/Gel/C scaffold with 3D bioprinting to generate micro-nano porosity structure for skin wound healing: a detailed animal in vivo study.

Bioprinting has exhibited remarkable promises for the fabrication of functional skin substitutes. However, there are some significant challenges for the treatment of full-thickness skin defects in clinical practice. It is necessary to determine bioinks with suitable mechanical properties and desirable biocompatibilities. Additionally, the key for printing skin is to design the skin structure optimally, enabling the function of the skin. In this study, the full-thickness skin scaffolds were prepared with a gradient pore structure constructing the dense layer, epidermis, and dermis by different ratios of bioinks. We hypothesized that the dense layer protects the wound surface and maintains a moist environment on the wound surface. By developing a suitable hydrogel bioink formulation (sodium alginate/gelatin/collagen), to simulate the physiological structure of the skin via 3D printing, the proportion of hydrogels was optimized corresponding to each layer. These results reveal that the scaffold has interconnected macroscopic channels, and sodium alginate/gelatin/collagen scaffolds accelerated wound healing, reduced skin wound contraction, and re-epithelialization in vivo. It is expected to provide a rapid and economical production method of skin scaffolds for future clinical applications.

Bioprinting small diameter blood vessel constructs with an endothelial and smooth muscle cell bilayer in a single step.

Bioengineered artificial blood vessels have been a major area of interest over the last decade. Of particular interest are small diameter vessels, as surgical options are currently limited. This study aimed to fabricate a small diameter, heterogeneous bilayer blood vessel-like construct in a single step with gelatin methacryloyl (GelMA) bioink using a 3D micro-extrusion bioprinter on a solid platform. GelMA was supplemented with Hyaluronic acid (HA), glycerol and gelatin to form a GelMA bioink with good printability, mechanical strength, and biocompatibility. Two separate concentrations of GelMA bioink with unique pore sizes were selected to fabricate a heterogeneous bilayer. A higher concentration of GelMA bioink (6% w/v GelMA, 2% gelatin, 0.3% w/v HA, 10% v/v glycerol) was used to load human umbilical vein endothelial cells (HUVECs) and form an inner, endothelial tissue layer. A lower concentration of GelMA bioink (4% w/v GelMA, 4% gelatin, 0.3% w/v HA, 10% v/v glycerol) was used to load smooth muscle cells (SMCs) and form an outer, muscular tissue layer. Bioprinted blood vessel-like grafts were then assessed for mechanical properties with Instron mechanical testing, and suture-ability, and for biological properties including viability, proliferation, and histological analysis. The resulting 20 mm long, 4.0 mm diameter lumen heterogeneous bilayer blood vessel-like construct closely mimics a native blood vessel and maintains high cell viability and proliferation. Our results represent a novel strategy for small diameter blood vessel biofabrication.

Thermal Oxide Layer Enhances Crystallinity and Mechanical Properties for Plasma-Sprayed Hydroxyapatite Biomedical Coatings.

The stability of plasma-sprayed hydroxyapatite (HA) coatings on metallic implants in vivo remains a significant challenge for load-bearing orthopedic implants despite their excellent mechanical and osteoconductive properties. This study focuses on oxide layer formation on the surface of Ti6Al4V samples through furnace heating at 600, 700, and 800 °C for 10 min for optimization of the most effective oxide layer to increase plasma coating crystallinity and improve plasma coating bond strength with the metal surface. The 800 °C heat treatment shows an effective oxide layer which increases coating crystallinity from 64 to 75% and coating adhesive bond strength from 25.9 ± 2.3 to 30.7 ± 1.1 MPa, while simultaneously reducing the dissolution rate of HA coatings. The addition of biologically relevant dopants, MgO and SiO2, show negligible effects on crystallinity and adhesive bond strength on plasma-sprayed HA coatings and additionally show an enhancement effect on osteoblast proliferation and differentiation. Moreover, the inclusion of these additivess shows an increase in osteogenesis in a rat distal femur model after 6 and 10 weeks of implantation. Overall, this study provides a direct solution to improve the crystallinity, adhesive bond strength, and osteogenic properties of plasma-sprayed HA coatings on orthopedic implants that is more manufacturable and translational from research to an industrial scale.

Extrusion-Based Bioprinting: Current Standards and Relevancy for Human-Sized Tissue Fabrication.

The field of bioengineering has long pursued the goal of fabricating large-scale tissue constructs for use both in vitro and in vivo. Recent technological advances have indicated that bioprinting will be a key technique in manufacturing these specimens. This chapter aims to provide an overview of what has been achieved to date through the use of microextrusion bioprinters and what major challenges still impede progress. Microextrusion printer configurations will be addressed along with critical design characteristics including nozzle specifications and bioink modifications. Significant challenges within the field with regard to achieving long-term cell viability and vascularization, and current research that shows promise in mitigating these challenges in the near future are discussed. While microextrusion is a broad field with many applications, this chapter aims to provide an overview of the field with a focus on its applications toward human-sized tissue constructs.

Bioprinted trachea constructs with patient-matched design, mechanical and biological properties.

Tracheal stenosis is a rare but life-threatening disease. Primary clinical procedures for treating this disease are limited if the region requiring repair is long or complex. This study is the first of its kind to fabricate bioprinted tracheal constructs with separate cartilage and smooth muscle regions using polycaprolactone (PCL) and human mesenchymal stem cell (hMSC)-laden hydrogels. Our final bioprinted trachea showed comparable elastic modulus and yield stress compared to native tracheal tissue. In addition, both cartilage and smooth muscle formation were observed in the desired regions of our bioprinted trachea through immunohistochemistry and western blot after two weeks of in vitro culture. This study demonstrates a novel approach to manufacture tissue engineered trachea with mechanical and biological properties similar to native trachea, which represents a step closer to overcoming the clinical challenges of treating tracheal stenosis.

Mechanical and biological properties of ZnO, SiO2, and Ag2O doped plasma sprayed hydroxyapatite coating for orthopaedic and dental applications.

In this study, we explored a ternary dopant system utilizing 0.25 wt% ZnO to induce osteogenesis, 0.5 wt% SiO2 to induce angiogenesis, and 2.0 wt% Ag2O to provide secondary infection control within a plasma assisted hydroxyapatite coating for orthopaedic or dental applications. The objective of this study was to understand the effects of ZnO, SiO2, and Ag2O dopants on the mechanical and biological properties of hydroxyapatite (HA) coatings on titanium (Ti). Coatings were deposited using a 30 kW plasma spray system equipped with a supersonic nozzle to produce above standard coating bond strengths of 24 ±â€¯2 MPa on Ti6Al4V and 22 ±â€¯1 MPa on commercially pure Ti substrates. Antibacterial properties were revealed in vitro against E. coli and S. aureus. The ternary dopant system was implanted in 18 male Sprague-Dawley rats with timepoints of 5 and 10 weeks. By week 5, ZnSiAg-HA produced 32% bone mineralization of 68% total bone formation compared to only 11% bone mineralization of 55% total bone formation in the undoped coating. This system can be employed for replacement surgeries and revision surgeries to reduce healing time and enhance osseointegration. STATEMENT OF SIGNIFICANCE: Total hip replacements increased 124% from 2000 to 2010 with an ever-increasing rate due to the rise in average life span and an escalation in surgeries for young patients. Replacement surgeries come with the risk of rejection, poor integration, and infection. This study incorporates biologically relevant metallic oxides of ZnO, SiO2, and Ag2O within a hydroxyapatite coating on titanium deposited using a radio frequency induction plasma spray. A ternary dopant system has not been explored in the current literature and little is known about these particular dopants in vivo. This proposed system can be employed for replacement surgeries to lower healing time and enhance osseointegration between implant and host tissue.

Effects of MgO, ZnO, SrO, and SiO2 in tricalcium phosphate scaffolds on in vitro gene expression and in vivo osteogenesis.

߭tricalcium phosphate (߭TCP) is a versatile bioceramic for its use in many orthopedic and dental applications due to its excellent biocompatibility and biodegradability. Recently, the addition of additives to ߭TCP has been proven to improve bone repair and regeneration, however, the underlying mechanism of enhanced bone regeneration is still unknown. In this study, strontium oxide (SrO), silica (SiO2), magnesia (MgO), and zinc oxide (ZnO) were added to ߭TCP for dense discs fabrication followed by in vitro evaluation using a preosteoblast cell line. Cell viability and gene expression were analyzed at day 3 and day 9 during the cell culture. MgO and SiO2 were found to significantly enhance and expedite osteoblastic differentiation. A potential mechanism was introduced to explain the additive induced osteoblastic differentiation. In addition, in vivo characterizations showed that porous 3D printed MgO-SiO2-TCP scaffolds significantly improved new bone formation after 16 weeks of implantation. This study shows beneficial effects of additives on osteoblastic viability and differentiation in vitro as well as osteogenesis in vivo, which is crucial towards the development of bone tissue engineering scaffolds.

Current Challenges of Bioprinted Tissues Toward Clinical Translation.

IMPACT STATEMENT: This review has a broad overview of the current challenges of bioprinted tissues towards clinical translations and future directions to overcome those challenges. The development of this field has a huge impact on the situation of an insufficient number of organ donors for life-saving organ transplantations.

Compositionally graded doped hydroxyapatite coating on titanium using laser and plasma spray deposition for bone implants.

Plasma sprayed hydroxyapatite (HA) coating is known to improve the osteoconductivity of metallic implants. However, the adhesive bond strength of the coating is affected due to a mismatch in coefficients of thermal expansion (CTE) between the metal and HA ceramic. In this study, a gradient HA coating was prepared on Ti6Al4V by laser engineered net shaping (LENS™) followed by plasma spray deposition. In addition, 1 wt% MgO and 2 wt% Ag2O were mixed with HA to improve the biological and antibacterial properties of the coated implant. Results showed that the presence of an interfacial layer by LENS™ enhanced adhesive bond strength from 26 ±â€¯2 MPa for just plasma spray coating to 39 ±â€¯4 MPa for LENS™ and plasma spray coatings. Presence of MgO and Ag2O did not influence the adhesive bond strength. Also, Ag+ ions release dropped by 70% less with a gradient HA LENS™ layer due to enhanced crystallization of the HA layer. In vitro human osteoblast cell culture revealed presence of Ag2O had no deleterious effect on proliferation and differentiation when compared to pure HA as control and provided antibacterial properties against E. coli and S. aureus bacterial strands. This study presents an innovative way to improve interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic as well as dental implants. STATEMENT OF SIGNIFICANCE: Implants are commonly composed of metals that lack osteoconductivity. Osteoconductivity is a property where bone grows on the surface meaning the material is compatible with the surrounding bone tissue. Plasma sprayed hydroxyapatite (HA) coating improves the osteoconductivity of metallic implants, however, the adhesive bond strength can be weak. This study incorporates a gradient HA coating by using an additive manufacturing technique, laser engineered net shaping (LENS™), followed by plasma spray deposition to enhance the adhesive bond strength by incorporating a thermal barrier. The proposed system has not been well studied in the current literature and the results presented bring forth an innovative way to improve the interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic implants.

In Vitro Characterizations of Si4+ and Zn2+ Doped Plasma Sprayed Hydroxyapatite Coatings Using Osteoblast and Osteoclast Coculture.

Osteoporosis is one of the most commonly identified bone disorders, which leads to an enhanced risk of bone fracture, especially for the older population. Hydroxyapatite (HA) coated titanium (Ti) alloys have been used widespread for load bearing applications like hip or knee replacements owing to their compositional similarity to natural bone; however, incorporation of osteoinductivity is still a challenge. The objective of this study is to evaluate the effects of SiO2 and ZnO as dopants in HA coated Ti alloys on cellular osteoporotic conditions mimicked by an in vitro osteoblast and osteoclast coculture model. HA, Si-HA, and Zn-HA coatings showed adhesive bond strengths of 25.7 ± 1.9 MPa, 23.8 ± 2.3 MPa, and 22.9 ± 3.5 MPa, respectively. To study the effects of doped HA coatings on the simulated osteoporotic cellular condition, human mesenchymal stem cells (hMSCs) and monocytes (THP-1) were seeded simultaneously in a ratio of 1:4, respectively. Gene expressions studies were carried out with marker genes showing that the presence of the dopants in the HA coating enhanced osteoblast proliferation along with diminishing cell growth of osteoclasts. This study demonstrates the promising effects of SiO2 and ZnO in plasma sprayed HA coatings on alleviating osteoporosis cellular conditions, which can potentially be used for load-bearing implants in aging patients whose bone resorption is more dominant than bone formation.

Additive manufacturing of biomaterials.

Biomaterials are used to engineer functional restoration of different tissues to improve human health and the quality of life. Biomaterials can be natural or synthetic. Additive manufacturing (AM) is a novel materials processing approach to create parts or prototypes layer-by-layer directly from a computer aided design (CAD) file. The combination of additive manufacturing and biomaterials is very promising, especially towards patient specific clinical applications. Challenges of AM technology along with related materials issues need to be realized to make this approach feasible for broader clinical needs. This approach is already making a significant gain towards numerous commercial biomedical devices. In this review, key additive manufacturing methods are first introduced followed by AM of different materials, and finally applications of AM in various treatment options. Realization of critical challenges and technical issues for different AM methods and biomaterial selections based on clinical needs are vital. Multidisciplinary research will be necessary to face those challenges and fully realize the potential of AM in the coming days.

A smartphone colorimetric reader integrated with an ambient light sensor and a 3D printed attachment for on-site detection of zearalenone.

Smartphone biosensors could be cost-effective, portable instruments to be used for the readout of liquid colorimetric assays. However, current reported smartphone colorimetric readers have relied on photos of liquid assays captured using a camera, and then analyzed using software programs. This approach results in a relatively low accuracy and low generality. In this work, we reported a novel smartphone colorimetric reader that has been integrated with an ambient light sensor and a 3D printed attachment for the readout of liquid colorimetric assays. The portable and low-cost ($0.15) reader utilized a simplified electronic and light path design. Furthermore, our reported smartphone colorimetric reader can be compatible with different smartphones. As a proof of principle, the utility of this device was demonstrated using it in conjunction with an enzyme-linked immunosorbent assay to detect zearalenone. Results were consistent with those obtained using a professional microplate reader. The developed smartphone colorimetric reader was capable of providing scalable, cost-effective, and accurate results for liquid colorimetric assays that related to clinical diagnoses, environment pollution, and food testing. Graphical abstract A novel smartphone colorimetric reader that has been integrated with an ambient light sensor and a 3D printed attachment for the readout of liquid colorimetric assays.

Effects of MgO and SiO2 on Plasma-Sprayed Hydroxyapatite Coating: An in Vivo Study in Rat Distal Femoral Defects.

Plasma-sprayed hydroxyapatite (HA)-coated titanium implants have been widely used in orthopedic applications due to their inheritance of an excellent mechanical property from titanium and great osteoconductivity from HA. However, the lack of osteoinductivity limits their further applications. In this study, 1 wt % MgO and 0.5 wt % SiO2 were mixed with HA for making plasma-sprayed coatings on titanium implants. Plasma-sprayed HA- and MgO/SiO2-HA-coated titanium implants showed adhesive bond strengths of 25.73 ± 1.92 and 23.44 ± 2.89 MPa, respectively. The presence of MgO and SiO2 significantly increased the osteogenesis, osseointegration, and bone mineralization of HA-coated titanium implants by the evaluation of their histomorphology after 6, 10, and 14 weeks of implantation in rat distal femoral defects. Implant pushout tests also showed a shear modulus of 149.83 ± 3.69 MPa for MgO/SiO2-HA-coated implants after 14 weeks of implantation, compared to 52.68 ± 10.41 MPa for uncoated implants and 83.92 ± 3.68 MPa for pure HA-coated implants; These are differences in the shear modulus of 96% and 56.4%, respectively. This study assesses for the first time the quality of the bone-implant interface of induction plasma-sprayed MgO and SiO2 binary-doped HA coatings on load-bearing implants compared to bare titanium and pure HA coatings in a quantitative manner. Relating the osseointegration and interface shear modulus to the quality of implant fixation is critical to the advancement and implementation of HA-coated orthopedic implants.

Doped tricalcium phosphate bone tissue engineering scaffolds using sucrose as template and microwave sintering: enhancement of mechanical and biological properties.

ß-tricalcium phosphate (ß-TCP) is a widely used biocompatible ceramic in orthopedic and dental applications. However, its osteoinductivity and mechanical properties still require improvements. In this study, porous ß-TCP and MgO/ZnO-TCP scaffolds were prepared by the thermal decomposition of sucrose. Crack-free cylindrical scaffolds could only be prepared with the addition of MgO and ZnO due to their stabilization effects. Porous MgO/ZnO-TCP scaffolds with a density of 61.39±0.66%, an estimated pore size of 200µm and a compressive strength of 24.96±3.07MPa were prepared by using 25wt% sucrose after conventional sintering at 1250°C. Microwave sintering further increased the compressive strength to 37.94±6.70MPa, but it decreased the open interconnected porosity to 8.74±1.38%. In addition, the incorporation of polycaprolactone (PCL) increased 22.36±3.22% of toughness while maintaining its compressive strength at 25.45±2.21MPa. Human osteoblast cell line was seeded on scaffolds to evaluate the effects of MgO/ZnO and PCL on the biological property of ß-TCP in vitro. Both MgO/ZnO and PCL improved osteoinductivity of ß-TCP. PCL also decreased osteoblastic apoptosis due to its particular surface chemistry. This novel porous MgO/ZnO-TCP scaffold with PCL shows improved mechanical and biological properties, which has great potential in bone tissue engineering applications.

Doped tricalcium phosphate scaffolds by thermal decomposition of naphthalene: Mechanical properties and in vivo osteogenesis in a rabbit femur model.

Tricalcium phosphate (TCP) is a bioceramic that is widely used in orthopedic and dental applications. TCP structures show excellent biocompatibility as well as biodegradability. In this study, porous ß-TCP scaffolds were prepared by thermal decomposition of naphthalene. Scaffolds with 57.64% ± 3.54% density and a maximum pore size around 100 µm were fabricated via removing 30% naphthalene at 1150°C. The compressive strength for these scaffolds was 32.85 ± 1.41 MPa. Furthermore, by mixing 1 wt % SrO and 0.5 wt % SiO2 , pore interconnectivity improved, but the compressive strength decreased to 22.40 ± 2.70 MPa. However, after addition of polycaprolactone coating layers, the compressive strength of doped scaffolds increased to 29.57 ± 3.77 MPa. Porous scaffolds were implanted in rabbit femur defects to evaluate their biological property. The addition of dopants triggered osteoinduction by enhancing osteoid formation, osteocalcin expression, and bone regeneration, especially at the interface of the scaffold and host bone. This study showed processing flexibility to make interconnected porous scaffolds with different pore size and volume fraction porosity, while maintaining high compressive mechanical strength and excellent bioactivity. Results show that SrO/SiO2 -doped porous TCP scaffolds have excellent potential to be used in bone tissue engineering applications.