Core-Shell Structure of Photopolymer-Grafted Polyurethane as a Controlled Drug Delivery Vehicle for Biomedical Application

Functionalized ultraviolet photocurable bisphenol A-glycerolate dimethacrylates with tailorable size have been synthesized as the core, which have further been grafted using the diisocyanate chain end of polyurethane (PU) as the shell to create a core-shell structure of tunable size for a controlled drug delivery vehicle. The core-shell structure has been elucidated through spectroscopic techniques like 1H NMR, FTIR, and UV-vis and their relative shape and size through TEM and AFM morphology. The greater cross-link density of the core is reflected in the higher glass transition temperature, and the improved thermal stability of the graft copolymer is proven from its thermogravimetric analyses. The flow behavior and enhanced strength of the graft copolymers have been revealed from rheological measurements. The graft copolymer exhibits sustained release of the drug, as compared to pure polyurethane and photopolymer, arising from its core-shell structure and strong interaction between the copolymer and drug, as observed through a significant shifting of absorption peaks in FTIR and UV-vis measurements. Biocompatibility has been tested for the real application of the novel graft copolymer in medical fields, as revealed from MTT assay, cell imaging, and cell adhesion studies. The efficacy of controlled release from a graft copolymer has been verified from the gradual cell killing and ∼70% killing in 3 days vs meager cell killing of ∼25% very quickly in 1 day, followed by the increased cell viability of the system treated with the pure drug. The mechanism of slow and controlled drug release from the core-shell structure has been explored. The fluorescence images support the higher cell-killing efficiency as opposed to a pure drug or a drug embedded in polyurethane. Cells seeded on 3D scaffolds have been developed by embedding a graft copolymer, and fluorescence imaging confirms the successful growth of cells within the scaffold, realizing the potential of the core-shell graft copolymer in the biomedical arena.

Unravelling microRNA regulation and miRNA-mRNA regulatory networks in osteogenesis driven by 3D nanotopographical cues

Three-dimensional (3D) culturing of cells is being adopted for developing tissues for various applications such as mechanistic studies, drug testing, tissue regeneration, and animal-free meat. These approaches often involve cost-effective differentiation of stem or progenitor cells. One approach is to exploit architectural cues on a 3D substrate to drive cellular differentiation, which has been shown to be effective in various studies. Although extensive gene expression data from such studies have shown that gene expression patterns might differ, the gene regulatory networks controlling the expression of genes are rarely studied. In this study, we profiled genes and microRNAs (miRNAs) via next-generation sequencing (NGS) in human mesenchymal stem cells (hMSCs) driven toward osteogenesis via architectural cues in 3D matrices (3D conditions) and compared with cells in two-dimensional (2D) culture driven toward osteogenesis via soluble osteoinductive factors (OF conditions). The total number of differentially expressed genes was smaller in 3D compared to OF conditions. A distinct set of genes was observed under these conditions that have been shown to control osteogenic differentiation via different pathways. Small RNA sequencing revealed a core set of miRNAs to be differentially expressed under these conditions, similar to those that have been previously implicated in osteogenesis. We also observed a distinct regulation of miRNAs in these samples that can modulate gene expression, suggesting supplementary gene regulatory networks operative under different stimuli. This study provides insights into studying gene regulatory networks for identifying critical nodes to target for enhanced cellular differentiation and reveal the differences in physical and biochemical cues to drive cell fates.

Surface nanocrystallization enhances the biomedical performance of additively manufactured stainless steel

Additive manufacturing enables the fabrication of patient-specific implants of complex geometries. Although selective laser melting (SLM) of 316L stainless steel (SS) is well established, post-processing is essential to preparing high-performance biomedical implants. The goal of this study was to investigate surface mechanical attrition treatment (SMAT) as a means to enhance the electrochemical, biomechanical, and biological performances of 316L SS fabricated by SLM in devices for the repair of bone tissues. The SMAT conditions were optimized to induce surface nanocrystallization on the additively manufactured samples. SMAT resulted in a thicker oxide layer, which provided corrosion resistance by forming a passive layer. The fretting wear results showed that the rate of wear decreased after SMAT owing to the formation of a harder nanostructured layer. Surface modification of the alloy by SMAT enhanced its ability to support the attachment and proliferation of pre-osteoblasts in vitro. The study of the response in vivo to the additively manufactured alloy in a critical-sized cranial defect murine model revealed enhanced interactions with the cellular components after the alloy was subjected to SMAT without inducing any adverse immune response. Taken together, the results of this work establish SMAT of additively manufactured metallic implants as an effective strategy for engineering next-generation, high-performance medical devices for orthopedics and craniomaxillofacial applications.

Absorption Dominated Directional Electromagnetic Interference Shielding through Asymmetry in a Multilayered Construct with an Exceptionally High Green Index

Fabricating green electromagnetic interference (EMI) shields is the need of the hour because strong secondary reflections in the vicinity of the shield adversely affect the environment and the reliability of the neighboring devices. To this end, the present work aims to maximize the absorption-based EMI shielding through a multilayered construct comprising a porous structure (pore size less than λ/5), a highly conducting entity, and a layer to match the impedance. The elements of this construct were positioned so that the incoming electromagnetic (EM) radiation interacts with the other layers of the construct before the conducting entity. This positioning of the layers in the construct offers a high green shielding index (g_s) and low reflection coefficient (R ∼ 0.1) with an exceptionally high percent absorption (up to 99%). Polyurethane (PU) foams were fabricated using the salt-leaching technique and strategically positioned with carbon nanotube (CNT) papers and polycarbonate (PC)-based films to obtain symmetric and asymmetric constructs. These structures were then employed to gain mechanistic insight into the directional dependency of shielding performance, g_s, and heat dissipation ability. Interestingly, maximum total shielding effectiveness (SE_T) of -52 dB (88% absorption @8.2 GHz) and specific shielding effectiveness/thickness (SSE_t) of -373 dB/cm²g were achieved for a symmetric construct whereas, for the asymmetric construct, the SE_T and SSE_t were -37 dB and -280 dB/cm²g, respectively, with an exceptionally high g_s of 8.6, the highest reported so far. The asymmetricity in the construct led to directional dependence of the absorption component (% SE_A, shielding effectiveness due to absorption) and heat dissipation, primarily governed by the electrical and thermal conductivity gradient, respectively. This study opens new avenues in this field and reports constructs with an exceptionally high green index.

Anisotropy of Additively Manufactured Co-28Cr-6Mo Influences Mechanical Properties and Biomedical Performance

Additive manufacturing (AM) of biomedical alloys such as Co-Cr-Mo alloys holds immense potential for fabricating implants with complex geometry and tailored to meet patient-specific needs. However, layer-by-layer fabrication in AM processes results in undesired anisotropy due to the solidification texture and grain morphology. The present study aimed to investigate the effect of build orientation on the mechanical properties and functional performance, including tribocorrosion behavior and cytocompatibility of an orthopedic Co-28Cr-6Mo alloy manufactured by selective laser melting. Although the fabricated alloy showed weak crystallographic texture due to the rotational scanning strategy, significant anisotropy was found in the tensile properties due to the grain size and morphology. The presence of larger, elongated grains along the build direction as compared to smaller, equiaxed grains perpendicular to the build direction imparted the observed tensile anisotropy. Quantitative analysis based on current models for strengthening mechanisms is insufficient to explain the observed anisotropy, which is ascribed to the possible role of the cellular dendrites and stacking fault strengthening in Co-Cr alloys. Unlike the electrochemical behavior, which was largely independent of the build orientation, the bio-tribocorrosion studies revealed an anisotropic wear rate under fretting conditions. Osteoblast attachment and proliferation were found to be higher on the plane perpendicular to the build direction, owing to the differences in grain size. This work provides novel insights into the role of the manufacturing parameters in a selective-laser-melted Co-Cr alloy and its potential application in engineering load-bearing orthopedic implants.

Surface Decoration of Redox-Modulating Nanoceria on 3D-Printed Tissue Scaffolds Promotes Stem Cell Osteogenesis and Attenuates Bacterial Colonization

Oxidative stress at the bone defect site delays the bone regeneration process. Increased level of reactive oxygen species (ROS) is the primary cause of oxidative stress at the damaged site. Bone tissue scaffolds that scavenge ROS offer a potential and yet unexplored route for faster bone healing. Cerium oxide (ceria) is known for its redox-modulating behavior. Three-dimensional (3D)-printed porous scaffolds fabricated from degradable polymers provide a physical microenvironment but lack the bioactivity for tissue regeneration. In this work, porous poly(lactic acid) (PLA) scaffolds were prepared by 3D printing and modified with poly(ethylene imine) and citric acid to decorate with ceria nanoparticles. Scanning electron micrographs revealed a macroporous architecture decorated with ceria particles. The compressive modulus of 27 MPa makes them suitable for trabecular bone. The scaffolds supported human mesenchymal stem cell growth, confirming cytocompatibility. The ability to scavenge ROS confirmed that surface functionalization with ceria could reduce oxidative stress levels in the cells. Stem cell osteogenesis was enhanced after ceria decoration of the PLA scaffolds. Transcriptional profiling studied by sequencing revealed changes in the expression of genes associated with inflammation and cell-material interactions. The ceria-functionalized scaffolds show enhanced antibacterial activity against both Gram-negative and Gram-positive bacterial strains. These results demonstrate that surface decoration with nanoceria offers a viable route for enhancing the bioactivity of 3D-printed PLA scaffolds for bone tissue regeneration with ROS scavenging and antibacterial capability.