3D-Printed Multifunctional Ag/CeO2/ZnO Reinforced Hydroxyapatite-Based Scaffolds with Effective Antibacterial and Mechanical Properties.

Conventional three-dimensional (3D)-printed hydroxyapatite (HA)-based constructs have limited utility in bone tissue engineering due to their poor mechanical properties, elevated risk of microbial infection, and limited pore interconnectivity. 3D printing of complex multiple components to fabricate fully interconnected scaffolds is a challenging task; here, in this work, we have developed a procedure for fabrication of printable ink for complex systems containing multinanomaterials, i.e., HAACZ (containing 1 wt % Ag, 4 wt % CeO2, and 6 wt % ZnO) with better shear thinning and shape retention properties. Moreover, 3D-printed HAACZ scaffolds showed a modulus of 143.8 GPa, a hardness of 10.8 GPa, a porosity of 59.6%, effective antibacterial properties, and a fully interconnected pore network to be an ideal construct for bone healing. Macropores with an average size of ∼469 and ∼433 µm within the scaffolds of HA and HAACZ and micropores with an average size of ∼0.6 and ∼0.5 µm within the strut of HA and HAACZ were developed. The distribution of fully interconnected micropores was confirmed using computerized tomography, whereas the distribution of micropores within the strut was visualized using Voronoi tessellation. The water contact angle studies revealed the most suitable hydrophilic range of water contact angles of ∼71.7 and ∼76.6° for HA and HAACZ, respectively. HAACZ scaffolds showed comparable apatite formation and cytocompatibility as that of HA. Antibacterial studies revealed effective antibacterial properties for the HAACZ scaffold as compared to HA. There was a decrease in bacterial cell density for HAACZ from 1 × 105 to 1.2 × 103 cells/mm2 against Gram-negative (Escherichia coli) and from 1.9 × 105 to 5.6 × 103 bacterial cells/mm2 against Gram-positive (Staphylococcus aureus). Overall, the 3D-printed HAACZ scaffold resulted in mechanical properties, comparable to those of the cancellous bone, interconnected macro- and microporosities, and excellent antibacterial properties, which could be utilized for bone healing.

Closed-loop vasculature network design for bioprinting large, solid tissue scaffolds.

Vascularization is an indispensable requirement for fabricating large solid tissues and organs. The natural vasculature derived from medical imaging modalities for large tissues and organs are highly complex and convoluted. However, the present bioprinting capabilities limit the fabrication of such complex natural vascular networks. Simplified bioprinted vascular networks, on the other hand, lack the capability to sustain large solid tissues. This work proposes a generalized and adaptable numerical model to design the vasculature by utilizing the tissue/organ anatomy. Starting with processing the patient's medical images, organ structure, tissue-specific cues, and key vasculature tethers are determined. An open-source abdomen magnetic resonance image dataset was used in this work. The extracted properties and cues are then used in a mathematical model for guiding the vascular network formation comprising arterial and venous networks. Next, the generated three-dimensional networks are used to simulate the nutrient transport and consumption within the organ over time and the regions deprived of the nutrients are identified. These regions provide cues to evolve and optimize the vasculature in an iterative manner to ensure the availability of the nutrient transport throughout the bioprinted scaffolds. The mass transport of six components of cell culture media-glucose, glycine, glutamine, riboflavin, human serum albumin, and oxygen was studied within the organ with designed vasculature. As the vascular structure underwent iterations, the organ regions deprived of these key components decreased significantly highlighting the increase in structural complexity and efficacy of the designed vasculature. The numerical method presented in this work offers a valuable tool for designing vascular scaffolds to guide the cell growth and maturation of the bioprinted tissues for faster regeneration post bioprinting.

Polymer-Coated and Nanofiber-Reinforced Functionally Graded Bioactive Glass Scaffolds Fabricated Using Additive Manufacturing.

In this study, carbon nanotube (CNT) reinforced functionally graded bioactive glass scaffolds have been fabricated using additive manufacturing technique. Sol-gel method was used for the synthesis of the bioactive glass. For ink preparation, Pluronic F-127 was used as an ink carrier. The CNT-reinforced scaffolds were coated with the polymer polycaprolactone (PCL) using dip-coating method to improve their properties further by sealing the micro-cracks. The CNT- reinforcement and polymer coating resulted in an improvement in the compressive strength of the additively manufactured scaffolds by 98% in comparison to pure bioactive glass scaffolds. Further, the morphological analysis revealed interconnected pores and their size appropriate for osteogenesis and angiogenesis. Evaluation of the in vitro bioactivity of the scaffolds after immersion in simulated body fluid (SBF) confirmed the formation of hydroxyapatite (HA). Further, the cellular studies showed good cell viability and initiation of osteogensis. These results demonstrate the potential of these scaffolds for bone tissue engineering applications.

Effects of Boron Oxide Concentration and Carbon Nanotubes Reinforcement on Bioactive Glass Scaffolds for Bone Tissue Engineering.

In this work, the effect of varying content of B2O3 with respect to SiO2 on mechanical and bioactivity properties have been evaluated for borosilicate bioactive glasses containing SiO2, B2O3, CaO and P2O5. The bioactive glasses have been synthesized using the sol-gel technique. The synthesized glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Field Emission Scanning electron microscopy (FESEM). These bioactive glasses were fabricated as scaffolds by using polymer foam replication method. Subsequently, in vitro bioactivity evaluation of borosilicate bioactive glass was done. Based on the XRD and energy-dispersive X-ray spectroscopy (EDS) results showing good apatite-formation ability when soaked in simulated body fluid (SBF), one of the bioactive glass (BG-B30 containing 30 mol% B2O3) was selected for further study. The compressive strength of the bioactive glass scaffolds was within the range of trabecular bone. However, it was found near the lower limit of the trabecular bone (0.2-12 MPa). Therefore, BG-B30 scaffold was reinforced with carbon nanotubes (CNTs) to allow for mechanical manipulation during tissue engineering applications. The compressive strength increased from 1.05 MPa to 7.42 MPa (a 606% increase) after reinforcement, while the fracture toughness rose from 0.12 MPa √ m to 0.45 MPa √ m (a 275% increase). Additionally, connectivity of the pores in the CNT reinforced BG-B30 scaffolds were evaluated and the pores were found to be well connected. The evaluated properties of the fabricated scaffolds demonstrate their potential as a synthetic graft for possible application in bone tissue engineering.

Compressive Strength Enhancement of Carbon Nanotube Reinforced 13-93B1 Bioactive Glass Scaffolds.

45S5 Bioglass® has been used quite extensively in the form of particulate as synthetic bone graft. However, 45S5 glass has certain limitations such as difficulty in sintering and slow and partial conversion to hydroxy carbonated apatite. In pursuit of overcoming these limitations, bioactive glasses (13-93B1) containing increased amount of B2O3 by partial replacement of SiO2 have been prepared using sol-gel technique in this study. Since bioactive glasses are brittle in nature, therefore, they are unsuitable for load bearing sites. Consequently, 3D porous scaffolds by reinforcement with varying weight percent of carbon nanotubes (CNTs) have been fabricated in this work by physical mixing and polymer foam replication technique. Compared with pure 13-93B1 bioactive glasses, addition of 0.2 weight percent of CNT resulted in maximum increase in compressive strength from 1.80 MPa to 5.84 MPa (a 224% increase) and elastic modulus from 102 MPa to 269.4 MPa (a 164% increase), respectively. Bioactivity of these scaffolds was confirmed in vitro using simulated body fluid test for 28 days. The compressive strength post-SBF studies were within the range of compressive strength of trabecular bone. These results show potential of fabricating a 3D porous scaffold with sufficient strength and biocompatibility using CNT-1393B1 bioactive glasses.