Bioresorbable Metals for Biomedical Applications: From Mechanical Components to Electronic Devices

Tin Silver Alloy as a Biomaterial: Corrosion Characteristics and Cellular Behavior

Tin-silver (Sn-Ag) has been used as a permanently implanted biomaterial within the Essure female sterilization device and in dental amalgams; however, little data exist for Sn-Ag's corrosion characteristics and/or cellular interactions. In this study, to assess its suitability as a degradable metallic biomaterial, 95-5 wt% Sn-Ag solder was subjected to corrosion testing including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and anodic potentiodynamic polarization in phosphate-buffered saline (PBS) and cell culture media (with serum proteins) at room temperature (25°C) and body temperature (37°C). Cell culture studies were also performed. Mouse pre-osteoblast cells (MC3T3-E1) were cultured in media on Sn-Ag discs and monitored over 24 h at potentials below, around, or above Sn-Ag's breakdown potential, fixed, and then viewed using SEM. Separately, cells on tissue culture plastic were subjected to increasing concentrations of SnCl2 in media for 24 h before a live-dead imaging at each concentration to determine cell viability and area fraction covered when compared with a control well. The results show both passive (in PBS), with a breakdown potential of -250 mV versus Ag/AgCl and active polarization behavior (in AMEM with proteins). EIS results showed polarization resistance (R p ) in the 105 Ωcm2 range but decreased generally with increasing temperature (p < 0.05). Cells were well attached on Sn-Ag surfaces at OCP and below the breakdown potential, but when anodically polarized, cells reduced their spread area and became more spherical, indicating less viability. SnCl2 exhibited a dose-dependent killing effect on MC3T3 cells with a lethal dose for 50% of about 0.5 mM. The results of these experiments show that Sn-Ag alloys can be considered as degradable metallic biomaterials.

A Review of Additive Manufacturing of Biodegradable Fe and Zn Alloys for Medical Implants Using Laser Powder Bed Fusion (LPBF)

This review explores the advancements in additive manufacturing (AM) of biodegradable iron (Fe) and zinc (Zn) alloys, focusing on their potential for medical implants, particularly in vascular and bone applications. Fe alloys are noted for their superior mechanical properties and biocompatibility but exhibit a slow corrosion rate, limiting their biodegradability. Strategies such as alloying with manganese (Mn) and optimizing microstructure via laser powder bed fusion (LPBF) have been employed to increase Fe's corrosion rate and mechanical performance. Zn alloys, characterized by moderate biodegradation rates and biocompatible corrosion products, address the limitations of Fe, though their mechanical properties require improvement through alloying and microstructural refinement. LPBF has enabled the fabrication of dense and porous structures for both materials, with energy density optimization playing a critical role in achieving defect-free parts. Fe alloys exhibit higher strength and hardness, while Zn alloys offer better corrosion control and biocompatibility. In vitro and in vivo studies demonstrate promising outcomes for both materials, with Fe alloys excelling in load-bearing applications and Zn alloys in controlled degradation and vascular applications. Despite these advancements, challenges such as localized corrosion, cytotoxicity, and long-term performance require further investigation to fully harness the potential of AM-fabricated Fe and Zn biodegradable implants.

Untethered Microgrippers for Biopsy in the Upper Urinary Tract

Untethered microrobots offer the possibility to perform medical interventions in anatomically complex and small regions in the body. Presently, it is necessary to access the upper urinary tract to diagnose and treat Upper Tract Urothelial Carcinoma (UTUC). Diagnostic and treatment challenges include ensuring adequate tissue sampling, accurately grading the disease, achieving completeness in endoscopic treatment, and consistently delivering medications to targeted sites. This work introduces microgrippers (µ-grippers) that are autonomously triggered by physiological temperature for biopsy in the upper urinary tract. The experiments demonstrated that µ-grippers can be deployed using standard ureteral catheters and maneuvered using an external magnetic field. The μ-grippers successfully biopsied tissue samples from ex vivo pig ureters, indicating that the thin-film bilayer springs' autonomous, physiologically triggered actuation exerts enough force to retrieve urinary tract tissue. The quality of these biopsy samples is sufficient for histopathological examination, including hematoxylin and eosin (H&E) and GATA3 immunohistochemical staining. Beyond biopsy applications, the µ-grippers' small size, wafer-scale fabrication, and multifunctionality suggest their potential for statistical sampling in the urinary tract. Experimental data and clinical reports underscore this potential through statistical simulations that compare the efficacy of µ-grippers with conventional tools, such as ureteroscopic forceps and baskets.

Maglev-fabricated long and biodegradable stent for interventional treatment of peripheral vessels

While chronic limb-threatening ischemia is a serious peripheral artery disease, the lack of an appropriate stent significantly limits the potential of interventional treatment. In spite of much progress in coronary stents, little is towards peripheral stents, which are expected to be both long and biodegradable and thus require a breakthrough in core techniques. Herein, we develop a long and biodegradable stent with a length of up to 118 mm based on a metal-polymer composite material. To achieve a well-prepared homogeneous coating on a long stent during ultrasonic spraying, a magnetic levitation is employed. In vivo degradation of the stent is investigated in rabbit abdominal aorta/iliac arteries, and its preclinical safety is evaluated in canine infrapopliteal arteries. First-in-man implantation of the stent is carried out in the below-the-knee artery. The 13 months' follow-ups demonstrate the feasibility of the long and biodegradable stent in clinical applications.

Design and Development of Transient Sensing Devices for Healthcare Applications

With the ever-growing requirements in the healthcare sector aimed at personalized diagnostics and treatment, continuous and real-time monitoring of relevant parameters is gaining significant traction. In many applications, health status monitoring may be carried out by dedicated wearable or implantable sensing devices only within a defined period and followed by sensor removal without additional risks for the patient. At the same time, disposal of the increasing number of conventional portable electronic devices with short life cycles raises serious environmental concerns due to the dangerous accumulation of electronic and chemical waste. An attractive solution to address these complex and contradictory demands is offered by biodegradable sensing devices. Such devices may be able to perform required tests within a programmed period and then disappear by safe resorption in the body or harmless degradation in the environment. This work critically assesses the design and development concepts related to biodegradable and bioresorbable sensors for healthcare applications. Different aspects are comprehensively addressed, from fundamental material properties and sensing principles to application-tailored designs, fabrication techniques, and device implementations. The emerging approaches spanning the last 5 years are emphasized and a broad insight into the most important challenges and future perspectives of biodegradable sensors in healthcare are provided.

Fully bioresorbable hybrid opto-electronic neural implant system for simultaneous electrophysiological recording and optogenetic stimulation

Bioresorbable neural implants based on emerging classes of biodegradable materials offer a promising solution to the challenges of secondary surgeries for removal of implanted devices required for existing neural implants. In this study, we introduce a fully bioresorbable flexible hybrid opto-electronic system for simultaneous electrophysiological recording and optogenetic stimulation. The flexible and soft device, composed of biodegradable materials, has a direct optical and electrical interface with the curved cerebral cortex surface while exhibiting excellent biocompatibility. Optimized to minimize light transmission losses and photoelectric artifact interference, the device was chronically implanted in the brain of transgenic mice and performed to photo-stimulate the somatosensory area while recording local field potentials. Thus, the presented hybrid neural implant system, comprising biodegradable materials, promises to provide monitoring and therapy modalities for versatile applications in biomedicine.

Soft, Long-Lived, Bioresorbable Electronic Surgical Mesh with Wireless Pressure Monitor and On-Demand Drug Delivery

Current research in the area of surgical mesh implants is somewhat limited to traditional designs and synthesis of various mesh materials, whereas meshes with multiple functions may be an effective approach to address long-standing challenges including postoperative complications. Herein, a bioresorbable electronic surgical mesh is presented that offers high mechanical strength over extended timeframes, wireless post-operative pressure monitoring, and on-demand drug delivery for the restoration of tissue structure and function. The study of materials and mesh layouts provides a wide range of tunability of mechanical and biochemical properties. Dissolvable dielectric composite with porous structure in a pyramidal shape enhances sensitivity of a wireless capacitive pressure sensor, and resistive microheaters integrated with inductive coils provide thermo-responsive drug delivery system for an antibacterial agent. In vivo evaluations demonstrate reliable, long-lived operation, and effective treatment for abdominal hernia defects, by clear evidence of suppressed complications such as adhesion formation and infections.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

Materials and Device Designs for Wireless Monitoring of Temperature and Thermal Transport Properties of Wound Beds during Healing

Chronic wounds represent a major health risk for diabetic patients. Regeneration of such wounds requires regular medical treatments over periods that can extend for several months or more. Schemes for monitoring the healing process can provide important feedback to the patient and caregiver. Although qualitative indicators such as malodor or fever can provide some indirect information, quantitative measurements of the wound bed have the potential to yield important insights. The work presented here introduces materials and engineering designs for a wireless system that captures spatio-temporal temperature and thermal transport information across the wound continuously throughout the healing process. Systematic experimental and computational studies establish the materials aspects and basic capabilities of this technology. In vivo studies reveal that both the temperature and the changes in this quantity offer information on wound status, with indications of initial exothermic reactions and mechanisms of scar tissue formation. Bioresorbable materials serve as the foundations for versions of this device that create possibilities for monitoring on and within the wound site, in a way that bypasses the risks of physical removal.

Full-thickness osteochondral defect repair using a biodegradable bilayered scaffold of porous zinc and chondroitin sulfate hydrogel

The regeneration of osteochondral tissue necessitates the re-establishment of a gradient owing to the unique characteristics and healing potential of the chondral and osseous phases. As the self-healing capacity of hyaline cartilage is limited, timely mechanical support during neo-cartilage formation is crucial to achieving optimal repair efficacy. In this study, we devised a biodegradable bilayered scaffold, comprising chondroitin sulfate (CS) hydrogel to regenerate chondral tissue and a porous pure zinc (Zn) scaffold for regeneration of the underlying bone as mechanical support for the cartilage layer. The photocured CS hydrogel possessed a compressive strength of 82 kPa, while the porous pure Zn scaffold exhibited a yield strength of 11 MPa and a stiffness of 0.8 GPa. Such mechanical properties are similar to values reported for cancellous bone. In vitro biological experiments demonstrated that the bilayered scaffold displayed favorable cytocompatibility and promoted chondrogenic and osteogenic differentiation of bone marrow stem cells. Upon implantation, the scaffold facilitated the simultaneous regeneration of bone and cartilage tissue in a porcine model, resulting in (i) a smoother cartilage surface, (ii) more hyaline-like cartilage, and (iii) a superior integration into the adjacent host tissue. Our bilayered scaffold exhibits significant potential for clinical application in osteochondral regeneration.

Bioabsorbable Composites Based on Polymeric Matrix (PLA and PCL) Reinforced with Magnesium (Mg) for Use in Bone Regeneration Therapy: Physicochemical Properties and Biological Evaluation

Improvements in Tissue Engineering and Regenerative Medicine (TERM)-type technologies have allowed the development of specific materials that, together with a better understanding of bone tissue structure, have provided new pathways to obtain biomaterials for bone tissue regeneration. In this manuscript, bioabsorbable materials are presented as emerging materials in tissue engineering therapies related to bone lesions because of their ability to degrade in physiological environments while the regeneration process is completed. This comprehensive review aims to explore the studies, published since its inception (2010s) to the present, on bioabsorbable composite materials based on PLA and PCL polymeric matrix reinforced with Mg, which is also bioabsorbable and has recognized osteoinductive capacity. The research collected in the literature reveals studies based on different manufacturing and dispersion processes of the reinforcement as well as the physicochemical analysis and corresponding biological evaluation to know the osteoinductive capacity of the proposed PLA/Mg and PCL/Mg composites. In short, this review shows the potential of these composite materials and serves as a guide for those interested in bioabsorbable materials applied in bone tissue engineering.

A Sewing Approach to the Fabrication of Eco/bioresorbable Electronics

Eco/bioresorbable electronics represent an emerging class of technology defined by an ability to dissolve or otherwise harmlessly disappear in environmental or biological surroundings after a period of stable operation. The resulting devices provide unique capabilities as temporary biomedical implants, environmental sensors, and related systems. Recent publications report schemes to overcome challenges in fabrication that follow from the low thermostability and/or high chemical reactivity of the eco/bioresorbable constituent materials. Here, this work reports the use of high-speed sewing machines, as the basis for a high-throughput manufacturing technique that addresses many requirements for these applications, without the need for high temperatures or reactive solvents. Results demonstrate that a range of eco/bioresorbable metal wires and polymer threads can be embroidered into complex, user-defined conductive patterns on eco/bioresorbable substrates. Functional electronic components, such as stretchable interconnects and antennas are possible, along with fully integrated systems. Examples of the latter include wirelessly powered light-emitting diodes, radiofrequency identification tags, and temporary cardiac pacemakers. These advances add to a growing range of options in high-throughput, automated fabrication of eco/bioresorbable electronics.

Recent Advances in Biodegradable Green Electronic Materials and Sensor Applications

As environmental issues have become the dominant agenda worldwide, the necessity for more environmentally friendly electronics has recently emerged. Accordingly, biodegradable or nature-derived materials for green electronics have attracted increased interest. Initially, metal-green hybrid electronics are extensively studied. Although these materials are partially biodegradable, they have high utility owing to their metallic components. Subsequently, carbon-framed materials (such as graphite, cylindrical carbon nanomaterials, graphene, graphene oxide, laser-induced graphene) have been investigated. This has led to the adoption of various strategies for carbon-based materials, such as blending them with biodegradable materials. Moreover, various conductive polymers have been developed and researchers have studied their potential use in green electronics. Researchers have attempted to fabricate conductive polymer composites with high biodegradability by shortening the polymer chains. Furthermore, various physical, chemical, and biological sensors that are essential to modern society have been studied using biodegradable compounds. These recent advances in green electronics have paved the way toward their application in real life, providing a brighter future for society.

Advances in Bioresorbable Triboelectric Nanogenerators

With the growing demand for next-generation health care, the integration of electronic components into implantable medical devices (IMDs) has become a vital factor in achieving sophisticated healthcare functionalities such as electrophysiological monitoring and electroceuticals worldwide. However, these devices confront technological challenges concerning a noninvasive power supply and biosafe device removal. Addressing these challenges is crucial to ensure continuous operation and patient comfort and minimize the physical and economic burden on the patient and the healthcare system. This Review highlights the promising capabilities of bioresorbable triboelectric nanogenerators (B-TENGs) as temporary self-clearing power sources and self-powered IMDs. First, we present an overview of and progress in bioresorbable triboelectric energy harvesting devices, focusing on their working principles, materials development, and biodegradation mechanisms. Next, we examine the current state of on-demand transient implants and their biomedical applications. Finally, we address the current challenges and future perspectives of B-TENGs, aimed at expanding their technological scope and developing innovative solutions. This Review discusses advancements in materials science, chemistry, and microfabrication that can advance the scope of energy solutions available for IMDs. These innovations can potentially change the current health paradigm, contribute to enhanced longevity, and reshape the healthcare landscape soon.

Advances in Bioresorbable Materials and Electronics

Transient electronic systems represent an emerging class of technology that is defined by an ability to fully or partially dissolve, disintegrate, or otherwise disappear at controlled rates or triggered times through engineered chemical or physical processes after a required period of operation. This review highlights recent advances in materials chemistry that serve as the foundations for a subclass of transient electronics, bioresorbable electronics, that is characterized by an ability to resorb (or, equivalently, to absorb) in a biological environment. The primary use cases are in systems designed to insert into the human body, to provide sensing and/or therapeutic functions for timeframes aligned with natural biological processes. Mechanisms of bioresorption then harmlessly eliminate the devices, and their associated load on and risk to the patient, without the need of secondary removal surgeries. The core content focuses on the chemistry of the enabling electronic materials, spanning organic and inorganic compounds to hybrids and composites, along with their mechanisms of chemical reaction in biological environments. Following discussions highlight the use of these materials in bioresorbable electronic components, sensors, power supplies, and in integrated diagnostic and therapeutic systems formed using specialized methods for fabrication and assembly. A concluding section summarizes opportunities for future research.

Regenerative bioelectronics: A strategic roadmap for precision medicine

In the past few decades, stem cell-based regenerative engineering has demonstrated its significant potential to repair damaged tissues and to restore their functionalities. Despite such advancement in regenerative engineering, the clinical translation remains a major challenge. In the stance of personalized treatment, the recent progress in bioelectronic medicine likewise evolved as another important research domain of larger significance for human healthcare. Over the last several years, our research group has adopted biomaterials-based regenerative engineering strategies using innovative bioelectronic stimulation protocols based on either electric or magnetic stimuli to direct cellular differentiation on engineered biomaterials with a range of elastic stiffness or functional properties (electroactivity/magnetoactivity). In this article, the role of bioelectronics in stem cell-based regenerative engineering has been critically analyzed to stimulate futuristic research in the treatment of degenerative diseases as well as to address some fundamental questions in stem cell biology. Built on the concepts from two independent biomedical research domains (regenerative engineering and bioelectronic medicine), we propose a converging research theme, 'Regenerative Bioelectronics'. Further, a series of recommendations have been put forward to address the current challenges in bridging the gap in stem cell therapy and bioelectronic medicine. Enacting the strategic blueprint of bioelectronic-based regenerative engineering can potentially deliver the unmet clinical needs for treating incurable degenerative diseases.

Hierarchically Porous Implants Orchestrating a Physiological Viscoelastic and Piezoelectric Microenvironment for Bone Regeneration

The extracellular matrix microenvironment of bone tissue comprises several physiological cues. Thus, artificial bone substitute materials with a single cue are insufficient to meet the demands for bone defect repair. Regeneration of critical-size bone defects remains challenging in orthopedic surgery. Intrinsic viscoelastic and piezoelectric cues from collagen fibers play crucial roles in accelerating bone regeneration, but scaffolds or implants providing integrated cues have seldom been reported. In this study, it is aimed to design and prepare hierarchically porous poly(methylmethacrylate)/polyethyleneimine/poly(vinylidenefluoride) composite implants presenting a similar viscoelastic and piezoelectric microenvironment to bone tissue via anti-solvent vapor-induced phase separation. The viscoelastic and piezoelectric cues of the composite implants for human bone marrow mesenchymal stem cell line stimulate and activate Piezo1 proteins associated with mechanotransduction signaling pathways. Cortical and spongy bone exhibit excellent regeneration and integration in models of critical-size bone defects on the knee joint and femur in vivo. This study demonstrates that implants with integrated physiological cues are promising artificial bone substitute materials for regenerating critical-size bone defects.

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3 MPa, tensile yield strength of 139.7 MPa, elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7 μm/y in Hanks' solution and 11.4 μm/y in DMEM solution, and a degradation rate of 49.5 μm/y in Hanks' solution and 30.3 μm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3 MPa, a yield strength of 139.7 MPa, an elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.

Materials and Design Approaches for a Fully Bioresorbable, Electrically Conductive and Mechanically Compliant Cardiac Patch Technology

Myocardial infarction (MI) is one of the leading causes of death and disability. Recently developed cardiac patches provide mechanical support and additional conductive paths to promote electrical signal propagation in the MI area to synchronize cardiac excitation and contraction. Cardiac patches based on conductive polymers offer attractive features; however, the modest levels of elasticity and high impedance interfaces limit their mechanical and electrical performance. These structures also operate as permanent implants, even in cases where their utility is limited to the healing period of tissue damaged by the MI. The work presented here introduces a highly conductive cardiac patch that combines bioresorbable metals and polymers together in a hybrid material structure configured in a thin serpentine geometry that yields elastic mechanical properties. Finite element analysis guides optimized choices of layouts in these systems. Regular and synchronous contraction of human induced pluripotent stem cell-derived cardiomyocytes on the cardiac patch and ex vivo studies offer insights into the essential properties and the bio-interface. These results provide additional options in the design of cardiac patches to treat MI and other cardiac disorders.

Soft, bioresorbable, transparent microelectrode arrays for multimodal spatiotemporal mapping and modulation of cardiac physiology

Transparent microelectrode arrays (MEAs) that allow multimodal investigation of the spatiotemporal cardiac characteristics are important in studying and treating heart disease. Existing implantable devices, however, are designed to support chronic operational lifetimes and require surgical extraction when they malfunction or are no longer needed. Meanwhile, bioresorbable systems that can self-eliminate after performing temporary functions are increasingly attractive because they avoid the costs/risks of surgical extraction. We report the design, fabrication, characterization, and validation of a soft, fully bioresorbable, and transparent MEA platform for bidirectional cardiac interfacing over a clinically relevant period. The MEA provides multiparametric electrical/optical mapping of cardiac dynamics and on-demand site-specific pacing to investigate and treat cardiac dysfunctions in rat and human heart models. The bioresorption dynamics and biocompatibility are investigated. The device designs serve as the basis for bioresorbable cardiac technologies for potential postsurgical monitoring and treating temporary patient pathological conditions in certain clinical scenarios, such as myocardial infarction, ischemia, and transcatheter aortic valve replacement.

A liquid metal-polydopamine composite for cell culture and electro-stimulation

Gallium (Ga) is a low melting point metal in the liquid state in the biological environment which presents a unique combination of fluidity, softness, and metallic electrical and thermal properties. In this work, liquid Ga is proposed as a biocompatible electrode material for cell culture by electro-stimulation since the cytotoxicity of Ga is generally considered low and some Ga compounds have been reported to exhibit anti-bacterial and anti-inflammatory activities. Complementarily, polydopamine (PDA) was coated on liquid Ga to increase the attachment capability of cells on the liquid Ga electrode and provide enhanced biocompatibility. The liquid Ga layer could be readily painted at room temperature on a solid inert substrate, followed by the formation of a nanoscale PDA coating layer resulting in a conformable and biocompatible composite electrode. The PDA layer was shown to coordinate with Ga³⁺, which is sourced from liquid Ga, providing electrical conductivity in the cell culture medium. The PDA-Ga³⁺ composite acted as a conductive substrate for advanced electro-stimulation for cell culture methods of representative animal fibroblasts. The cell proliferation was observed to increase by ∼143% as compared to a standard glass coverslip at a low potential of 0.1 V of direct coupling stimulation. This novel PDA-Ga³⁺ composite has potential applications in cell culture and regenerative medicine.

Biocompatible Material-Based Flexible Biosensors: From Materials Design to Wearable/Implantable Devices and Integrated Sensing Systems

Human beings have a greater need to pursue life and manage personal or family health in the context of the rapid growth of artificial intelligence, big data, the Internet of Things, and 5G/6G technologies. The application of micro biosensing devices is crucial in connecting technology and personalized medicine. Here, the progress and current status from biocompatible inorganic materials to organic materials and composites are reviewed and the material-to-device processing is described. Next, the operating principles of pressure, chemical, optical, and temperature sensors are dissected and the application of these flexible biosensors in wearable/implantable devices is discussed. Different biosensing systems acting in vivo and in vitro, including signal communication and energy supply are then illustrated. The potential of in-sensor computing for applications in sensing systems is also discussed. Finally, some essential needs for commercial translation are highlighted and future opportunities for flexible biosensors are considered.

Pathway of transient electronics towards connected biomedical applications

Transient electronic devices have shown promising applications in hardware security and medical implants with diagnosing therapeutics capabilities since their inception. Control of the device transience allows the device to "dissolve at will" after its functional operation, leading to the development of on-demand transient electronics. This review discusses the recent developments and advantages of triggering strategies (e.g., electrical, thermal, ultrasound, and optical) for controlling the degradation of on-demand transient electronics. We also summarize bioresorbable sensors for medical diagnoses, including representative applications in electrophysiology and neurochemical sensing. Along with the profound advancements in medical diagnosis, the commencement of therapeutic systems such as electrical stimulation and drug delivery for the biomedical or medical implant community has also been discussed. However, implementing a transient electronic system in real healthcare infrastructure is still in its infancy. Many critical challenges still need to be addressed, including strategies to decouple multimodal sensing signals, dissolution selectivity in the presence of multiple stimuli, and a complete sensing-stimulation closed-loop system. Therefore, the review discusses future opportunities in transient decoupling sensors and robust transient devices, which are selective to a particular stimulus and act as hardware-based passwords. Recent advancements in closed-loop controller-enabled electronics have also been analyzed for future opportunities of using data-driven artificial intelligence-powered controllers in fully closed-loop transient systems.

Actively Triggerable Metals via Liquid Metal Embrittlement for Biomedical Applications

Actively triggerable materials, which break down upon introduction of an exogenous stimulus, enable precise control over the lifetime of biomedical technologies, as well as adaptation to unforeseen circumstances, such as changes to an established treatment plan. Yet, most actively triggerable materials are low-strength polymers and hydrogels with limited long-term durability. By contrast, metals possess advantageous functional properties, including high mechanical strength and conductivity, that are desirable across several applications within biomedicine. To realize actively triggerable metals, a mechanism called liquid metal embrittlement is leveraged, in which certain liquid metals penetrate the grain boundaries of certain solid metals and cause them to dramatically weaken or disintegrate. In this work, it is demonstrated that eutectic gallium indium (EGaIn), a biocompatible alloy of gallium, can be formulated to reproducibly trigger the breakdown of aluminum within different physiologically relevant environments. The breakdown behavior of aluminum after triggering can further be readily controlled by manipulating its grain structure. Finally, three possible use cases of biomedical devices constructed from actively triggerable metals are demonstrated.

A Review on Manufacturing Processes of Biocomposites Based on Poly(α-Esters) and Bioactive Glass Fillers for Bone Regeneration

The incorporation of bioactive and biocompatible fillers improve the bone cell adhesion, proliferation and differentiation, thus facilitating new bone tissue formation upon implantation. During these last 20 years, those biocomposites have been explored for making complex geometry devices likes screws or 3D porous scaffolds for the repair of bone defects. This review provides an overview of the current development of manufacturing process with synthetic biodegradable poly(α-ester)s reinforced with bioactive fillers for bone tissue engineering applications. Firstly, the properties of poly(α-ester), bioactive fillers, as well as their composites will be defined. Then, the different works based on these biocomposites will be classified according to their manufacturing process. New processing techniques, particularly additive manufacturing processes, open up a new range of possibilities. These techniques have shown the possibility to customize bone implants for each patient and even create scaffolds with a complex structure similar to bone. At the end of this manuscript, a contextualization exercise will be performed to identify the main issues of process/resorbable biocomposites combination identified in the literature and especially for resorbable load-bearing applications.

Wire Arc Additive Manufacturing of Zinc as a Degradable Metallic Biomaterial

Wire arc additive manufacturing (WAAM) offers a high rate of material deposition among various additive manufacturing techniques with wire as feedstock material but has not been established for zinc alloys. Zn alloys can be used as degradable biomaterials, in contrast to conventional permanent metallic biomaterials. In this work, commercially pure Zn was processed by WAAM to obtain near-dense parts, and the properties obtained through WAAM-processed Zn were compared with wrought (WR) Zn samples. The microstructure and hardness values of the WAAM (41 ± 1 HV0.3) components were found to be similar to those of the WR (35 ± 2 HV0.3) components. Bulk X-ray diffraction texture measurements suggested that WAAM builds exhibit a heavily textured microstructure compared to the WR counterparts, with peak intensities around <3 3−6 2> or <0 0 0 2> in the directions parallel to the build direction (BD). The corrosion rates in simulated body fluid (SBF) were similar for WAAM (0.45 mmpy) and WR (0.3 mmpy) samples. The weight loss measurements in SBF were found to be marginally higher in the WAAM samples compared to the WR counterparts for a duration of up to 21 days. MC3T3-E1 preosteoblasts were found to be healthy and proliferating in the culture medium containing the degradation products from WAAM-Zn in a manner similar to WR-Zn. This work establishes the feasibility of processing Zn by WAAM for use in bioresorbable metallic implants.

Effect of Pulse Frequency on the Microstructure and the Degradation of Pulse Electroformed Zinc for Fabricating the Shell of Biodegradable Dosing Pump

In this work, we applied single-pulse electrodeposition method to prepare biodegradable zinc coating for the shell of an implantable dosing pump, and explored the effect of pulse frequency on microstructures and degradation behavior of electroformed zinc. Samples were produced by single-pulse electro-deposition technique with different pulse frequencies (50 Hz, 100 Hz, and 1000 Hz). By controlling the pulse frequency, the thickness of the zinc coating can be adjusted. The 50 Hz produced zinc film possesses strong (11.0) grain orientation, 100 Hz produced zinc film possesses clear ((11.0) and (10.0)) grain orientations, yet 1000 Hz produced zinc film shows more random grain orientations of (10.0), (10.1), and (11.0), which provides a possible way to design a controllable nanometer surface microtopography. Although thermodynamic degradation tendency implied from open current corrosion voltage were similar, the kinetic corrosion rate showed a clear increasing trend as pulse frequency increased from 50 Hz to 1000 Hz, which corresponded with the electrochemical impedance spectroscopy and long-term soaking test in hanks solution. According to ISO 10993-5:2009 and ISO 10993-4:2002, electrodeposited zinc materials produced in this study showed a benign hemolysis ratio and no toxicity for cell growth. Zinc prepared under 50 Hz shows the best blood compatibility. Electrodeposited zinc materials are expected to be used for the shell of a degradable dosing pump.

Biodegradable Molybdenum (Mo) and Tungsten (W) Devices: One Step Closer towards Fully-Transient Biomedical Implants

Close monitoring of vital physiological parameters is often key in following the evolution of certain medical conditions (e.g., diabetes, infections, post-operative status or post-traumatic injury). The allocation of trained medical staff and specialized equipment is, therefore, necessary and often translates into a clinical and economic burden on modern healthcare systems. As a growing field, transient electronics may establish fully bioresorbable medical devices capable of remote real-time monitoring of therapeutically relevant parameters. These devices could alert remote medical personnel in case of any anomaly and fully disintegrate in the body without a trace. Unfortunately, the need for a multitude of biodegradable electronic components (power supplies, wires, circuitry) in addition to the electrochemical biosensing interface has halted the arrival of fully bioresorbable electronically active medical devices. In recent years molybdenum (Mo) and tungsten (W) have drawn increasing attention as promising candidates for the fabrication of both energy-powered active (e.g., transistors and integrated circuits) and passive (e.g., resistors and capacitors) biodegradable electronic components. In this review, we discuss the latest Mo and W-based dissolvable devices for potential biomedical applications and how these soluble metals could pave the way towards next-generation fully transient implantable electronic systems.

Titanium Surface Characteristics Induce the Specific Reprogramming of Toll-like Receptor Signaling in Macrophages

Most of the research on titanium-based dental implants (Ti-discs) is focused on how they are able to stimulate the formation of new tissue and/or cytotoxic studies, with very scarce data on their effects on functional responses by immunocompetent cells. In particular, the link between the rewiring of innate immune responses and surface biomaterials properties is poorly understood. To address this, we characterize the functional response of macrophage cultures to four different dental titanium surfaces (MA: mechanical abrasion; SB + AE: sandblasting plus etching; SB: sandblasting; AE: acid etching). We use different Toll-like receptor (TLR) ligands towards cell surface receptors (bacterial lipopolysaccharide LPS for TLR4; imiquimod for TLR7; synthetic bacterial triacylated lipoprotein for TLR2/TLR1) and endosomal membrane receptor (poly I:C for TLR3) to simulate bacterial (cell wall bacterial components) or viral infections (dsRNA and ssRNA). The extracellular and total LDH levels indicate that exposure to the different Ti-surfaces is not cytotoxic for macrophages under resting or TLR-stimulated conditions, although there is a tendency towards an impairment in macrophage proliferation, viability or adhesion under TLR4, TLR3 and TLR2/1 stimulations in SB discs cultures. The secreted IL-6 and IL-10 levels are not modified upon resting macrophage exposure to the Ti-surfaces studied as well as steady state levels of iNos or ArgI mRNA. However, macrophage exposure to MA Ti-surface do display an enhanced immune response to TLR4, TLR7 or TLR2/1 compared to other Ti-surfaces in terms of soluble immune mediators secreted and M1/M2 gene expression profiling. This change of characteristics in cellular phenotype might be related to changes in cellular morphology. Remarkably, the gene expression of Tlr3 is the only TLR that is differentially affected by distinct Ti-surface exposure. These results highlight the relevance of patterned substrates in dental implants to achieve a smart manipulation of the immune responses in the context of personalized medicine, cell-based therapies, preferential lineage commitment of precursor cells or control of tissue architecture in oral biology.

Mechanical properties, in vitro and in vivo biocompatibility analysis of pure iron porous implant produced by metal injection molding: A new eco-friendly feedstock from natural rubber (Hevea brasiliensis)

Metal injection molding (MIM) has become an important manufacturing technology for biodegradable medical devices. As a biodegradable metal, pure iron is a promising biomaterial due to its mechanical properties and biocompatibility. In light of this, we performed the first study that manufactured and evaluated the in vitro and in vivo biocompatibility of samples of iron porous implants produced by MIM with a new eco-friendly feedstock from natural rubber (Hevea brasiliensis), a promisor binder that provides elastic property in the green parts. The iron samples were submitted to tests to determine density, microhardness, hardness, yield strength, and stretching. The biocompatibility of the samples was studied in vitro with adipose-derived mesenchymal stromal cells (ADSCs) and erythrocytes, and in vivo on a preclinical model with Wistar rats, testing the iron samples after subcutaneous implant. Results showed that the manufactured samples have adequate physical, and mechanical characteristics to biomedical devices and they are cytocompatible with ADSCs, hemocompatible and biocompatible with Wistars rats. Therefore, pure iron produced by MIM can be considered a promising material for biomedical applications.