Oxygen delivery using engineered microparticles

Copper-Based Metal-Organic Framework as a Potential Therapeutic Gas Carrier: Optimization, Synthesis, Characterization, and Computational Studies

The broad spectrum of health conditions and the global pandemic, leading to inadequate medical oxygen supply and management, has driven interest in developing porous nanocarriers for effective oxygenation strategies. We aim to develop an injectable oxygen carrier with regard to biocompatibility, safety, prehospital availability, and universal applicability. In this study, we have tried to identify important functional sites on metal-organic frameworks (MOFs) for gas binding with the help of Grand canonical Monte Carlo simulation. We have synthesized a copper-based MOF (Cu-BTC) with a 1,3,5-benzenetricarboxylic acid linker through a solvothermal approach as a competent porous adsorbent for oxygen storage and delivery. To optimize process variables, we performed statistical analysis using response surface methodology. A quadratic model was developed to study the interaction between independent variables and the response (i.e., maximizing surface area), whose adequacy is validated by the correlation between experimental and predicted values using the ANOVA method. The synthesized Cu-BTC, before and after oxygen loading, was characterized using X-ray diffraction, surface area, along with pore distribution measurement, particle size analysis, scanning electron microscopy, transmission electron microscopy, and gas adsorption studies. The Cu-BTC MOF exhibited an oxygen uptake of 4.6 mmol g-1, the highest among all the oxygen carriers reported in the literature under the same operating conditions. Overall, our findings suggest that this synthesized Cu-BTC with high surface area (1389 m2 g-1), high porosity, optimum oxygen uptake, and good biocompatibility would show potential toward efficient storage and delivery (direct to the targeted site) of medical oxygen to raise the blood oxygen saturation level.

Flowable Oxygen-Release Hydrogel Inhibits Bacteria and Treats Periodontitis

Periodontitis, the chronic inflammation of the periodontal tissues caused by bacteria in plaque, is the leading cause of tooth loss in adults in the world. Currently, periodontitis is effectively treated with mechanical cleaning and the use of antibiotics. However, these treatments only temporarily remove plaque, which can rapidly proliferate and multiply in periodontal pockets over time. Although antibiotics have positive antimicrobial effects, their long-term use increases the risk of the emergence of drug-resistant strains. The emergence of resistant strains reduces the effectiveness of periodontitis treatment and makes the disease more difficult to control. Herein, this paper reports the development of an injectable self-oxygenating composite hydrogel for periodontal therapy, which was produced by loading CaO2 nanoparticles and ascorbic acid into an injectable alginate hydrogel. CaO2 can improve the periodontal pocket microenvironment by reacting with water to generate oxygen, calcium ions can be used as a bone regeneration material, and ascorbic acid protects cells. The authors further showed that the composite hydrogel inhibited growth and colonization of anaerobic bacteria, reduced the degree of inflammation, and promoted alveolar bone regeneration. In conclusion, these findings suggest that the composite hydrogel can be used as a biocompatible, convenient, and effective method for periodontitis treatment.

Systemically injected oxygen within rapidly dissolving microbubbles improves the outcomes of severe hypoxaemia in swine

Acute respiratory failure can cause profound hypoxaemia that leads to organ injury or death within minutes. When conventional interventions are ineffective, the intravenous administration of oxygen can rescue patients from severe hypoxaemia, but at the risk of microvascular obstruction and of toxicity of the carrier material. Here we describe polymeric microbubbles as carriers of high volumes of oxygen (350-500 ml of oxygen per litre of foam) that are stable in storage yet quickly dissolve following intravenous injection, reverting to their soluble and excretable molecular constituents. In swine with profound hypoxaemia owing to acute and temporary (12 min) upper-airway obstruction, the microbubble-mediated delivery of oxygen led to: the maintenance of critical oxygenation, lowered burdens of cardiac arrest, improved survival, and substantially improved neurologic and kidney function in surviving animals. Our findings underscore the importance of maintaining a critical threshold of oxygenation and the promise of injectable oxygen as a viable therapy in acute and temporary hypoxaemic crises.

Alleviating hypoxia and oxidative stress for treatment of cardiovascular diseases: a biomaterials perspective

A state of hypoxia (lack of oxygen) persists in the initial and later phases of healing in cardiovascular diseases, which can alter the tissue's repair or regeneration, ultimately affecting the structure and functionality of the related organ. Consequently, this results in a cascade of events, leading to metabolic stress and the production of reactive oxygen species (ROS) and autophagy. This unwanted situation not only limits the oxygen supply to the needy tissues but also creates an inflammatory state, limiting the exchange of nutrients and other supplements. Consequently, biomaterials have gained considerable attention to alleviate hypoxia and oxidative stress in cardiovascular diseases. Numerous oxygen releasing and antioxidant biomaterials have been developed and proven to alleviate hypoxia and oxidative stress. This review article summarizes the mechanisms involved in cardiovascular pathologies due to hypoxia and oxidative stress, as well as the treatment modalities currently in practice. The applications, benefits and possible shortcomings of these approaches have been discussed. Additionally, the review explores the role of novel biomaterials in combating the limitations of existing approaches, primarily focusing on the development of oxygen-releasing and antioxidant biomaterials for cardiac repair and regeneration. It also directs attention to various other potential applications with critical insights for further advancement in this area.

Gas Delivery Relevant to Human Health using Porous Materials

Gases are essential for various applications relevant to human health, including in medicine, biomedical imaging, and pharmaceutical synthesis. However, gases are significantly more challenging to safely handle than liquids and solids. Herein, we review the use of porous materials, such as metal-organic frameworks (MOFs), zeolites, and silicas, to adsorb medicinally relevant gases and facilitate their handling as solids. Specific topics include the use of MOFs and zeolites to deliver H2S for therapeutic applications, 129Xe for magnetic resonance imaging, O2 for the treatment of cancer and hypoxia, and various gases for use in organic synthesis. This Perspective aims to bring together the organic, inorganic, medicinal, and materials chemistry communities to inspire the design of next-generation porous materials for the storage and delivery of medicinally relevant gases.

Gas Therapy: Generating, Delivery, and Biomedical Applications

Oxygen (O2), nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S), and hydrogen (H2) with direct effects, and carbon dioxide (CO2) with complementary effects on the condition of various diseases are known as therapeutic gases. The targeted delivery and in situ generation of these therapeutic gases with controllable release at the site of disease has attracted attention to avoid the risk of gas poisoning and improve their performance in treating various diseases such as cancer therapy, cardiovascular therapy, bone tissue engineering, and wound healing. Stimuli-responsive gas-generating sources and delivery systems based on biomaterials that enable on-demand and controllable release are promising approaches for precise gas therapy. This work highlights current advances in the design and development of new approaches and systems to generate and deliver therapeutic gases at the site of disease with on-demand release behavior. The performance of the delivered gases in various biomedical applications is then discussed.

SOX71, A Biocompatible Succinyl Derivative of the Triarylmethyl Radical OX071 for In Vivo Quantitative Oxygen Mapping Using Electron Paramagnetic Resonance

PURPOSE

This study aimed to develop a biocompatible oximetric electron paramagnetic resonance (EPR) spin probe with reduced self-relaxation, and sensitivity to oxygen for a higher signal-to-noise ratio and longer relaxation times at high oxygen concentration, compared to the reference spin probe OX071.

PROCEDURES

SOX71 was synthesized by succinylation of the twelve alcohol groups of OX071 spin probe and characterized by EPR at X-Band (9.5 GHz) and at low field (720 MHz). The biocompatibility of SOX71 was tested in vitro and in vivo in mice. A pharmacokinetic study was performed to determine the best time frame for EPR imaging. Finally, a proof-of-concept EPR oxygen imaging was performed on a mouse model of a fibrosarcoma tumor.

RESULTS

SOX71 was synthesized in one step from OX071. SOX71 exhibits a narrow line EPR spectrum with a peak-to-peak linewidth of 66 mG, similar to OX071. SOX71 does not bind to albumin nor show cell toxicity for the concentrations tested up to 5 mM. No toxicity was observed after systemic delivery via intraperitoneal injection in mice at twice the dose required for EPR imaging. After the injection, the probe is readily absorbed into the bloodstream, with a peak blood concentration half an hour, post-injection. Then, the probe is quickly cleared by the kidney with a half-life of ~ 45 min. SOX71 shows long relaxation times under anoxic condition (T1e = 9.5 µs and T2e = 5.1 µs; [SOX71] = 1 mM in PBS at 37 °C, pO2 = 0 mmHg, 720 MHz). Both the relaxation rates R1e and R2e show a decreased sensitivity to pO2, leading to twice longer relaxation times under room air conditions (pO2 = 159 mmHg) compared to OX071. This is ideal for oxygen imaging in samples with a wide range of pO2. Both the relaxation rates R1e and R2e show a decreased sensitivity to self-relaxation compared to OX071, with a negligible effect of the probe concentration on R1e. SOX71 was successfully applied to image oxygen in a tumor.

CONCLUSION

SOX71, a succinylated derivative of OX071 was synthesized, characterized, and applied for in vivo EPR tumor oxygen imaging. SOX71 is highly biocompatible, and shows decreased sensitivity to oxygen and self-relaxation. This first report suggests that SOX71 is superior to OX071 for absolute oxygen mapping under a broad range of pO2 values.

Unveiling the potentials of hydrophilic and hydrophobic polymers in microparticle systems: Opportunities and challenges in processing techniques

Conventional drug delivery systems are associated with various shortcomings, including low bioavailability and limited control over release. Biodegradable polymeric microparticles have emerged as versatile carriers in drug delivery systems addressing all these challenges. This comprehensive review explores the dynamic landscape of microparticles, considering the role of hydrophilic and hydrophobic materials. Within the continuously evolving domain of microparticle preparation methods, this review offers valuable insights into the latest advancements and addresses the factors influencing microencapsulation, which is pivotal for harnessing the full potential of microparticles. Exploration of the latest research in this dynamic field unlocks the possibilities of optimizing microencapsulation techniques to produce microparticles of desired characteristics and properties for different applications, which can help contribute to the ongoing evolution in the field of pharmaceutical science.

Normothermic Ex Situ Machine Perfusion of Vascularized Composite Allografts with Oxygen Microcarriers for 12 Hours Using Real-Time Mitochondrial Redox Quantification

BACKGROUND

Normothermic ex situ perfusion of vascularized composite allografts (VCAs) necessitates high oxygen demand and, thus, increased metabolic activity, which, in turn, requires the use of blood-based perfusion solutions. However, blood-derived perfusates, in turn, constitute an antigenic load. To circumvent this immunogenic problem, we used a perfusate enriched with acellular dextrane oxygen microcarriers to perfuse rat hindlimbs.

METHODS

Rat hindlimbs (n = 11) were perfused with either (non-), oxygenated dextrane-enriched Phoxilium, or Phoxilium enriched with dextrane oxygen microcarriers (MO2) for 12 h at 37 °C or stored on ice. Oxygenation of the skeletal muscle was assessed with Raman spectroscopy, tissue pO2-probes, and analysis of the perfusate. Transmission electronic microscopy was utilized to assess the ultrastructure of mitochondria of the skeletal muscle.

RESULTS

For all evaluated conditions, ischemia time until perfusion was comparable (22.91 ± 1.64 min; p = 0.1559). After 12 h, limb weight increased significantly by at least 81%, up to 124% in the perfusion groups, and by 27% in the static cold storage (SCS) group. Raman spectroscopy signals of skeletal muscle did not differ substantially among the groups during either perfusion or static cold storage across the duration of the experiment. While the total number of skeletal muscle mitochondria decreased significantly compared to baseline, mitochondrial diameter increased in the perfusion groups and the static cold storage group.

CONCLUSION

The use of oxygen microcarriers in ex situ perfusion of VCA with acellular perfusates under normothermic conditions for 12 h facilitates the maintenance of mitochondrial structure, as well as a subsequent recovery of mitochondrial redox status over time, while markers of muscle injury were lower compared to conventional oxygenated acellular perfusates.

EFFECTS OF M101-AN EXTRACELLULAR HEMOGLOBIN-APPLIED DURING CARDIOPULMONARY RESUSCITATION: AN EXPERIMENTAL RODENT STUDY

ABSTRACT

During and immediately after cardiac arrest, cerebral oxygen delivery is impaired mainly by microthrombi and cerebral vasoconstriction. This may narrow capillaries so much that it might impede the flow of red blood cells and thus oxygen transport. The aim of this proof-of-concept study was to evaluate the effect of M101, an extracellular hemoglobin-based oxygen carrier (Hemarina SA, Morlaix, France) derived from Arenicola marina , applied during cardiac arrest in a rodent model, on markers of brain inflammation, brain damage, and regional cerebral oxygen saturation. Twenty-seven Wistar rats subjected to 6 min of asystolic cardiac arrest were infused M101 (300 mg/kg) or placebo (NaCl 0.9%) concomitantly with start of cardiopulmonary resuscitation. Brain oxygenation and five biomarkers of inflammation and brain damage (from blood, cerebrospinal fluid, and homogenates from four brain regions) were measured 8 h after return of spontaneous circulation. In these 21 different measurements, M101-treated animals were not significantly different from controls except for phospho-tau only in single cerebellum regions ( P = 0.048; ANOVA of all brain regions: P = 0.004). Arterial blood pressure increased significantly only at 4 to 8 min after return of spontaneous circulation ( P < 0.001) and acidosis decreased ( P = 0.009). While M101 applied during cardiac arrest did not significantly change inflammation or brain oxygenation, the data suggest cerebral damage reduction due to hypoxic brain injury, measured by phospho-tau. Global burden of ischemia appeared reduced because acidosis was less severe. Whether postcardiac arrest infusion of M101 improves brain oxygenation is unknown and needs to be investigated.

Fabrication and Characterization of Oxygen-Generating Polylactic Acid/Calcium Peroxide Composite Filaments for Bone Scaffolds

The latest advancements in bone scaffold technology have introduced novel biomaterials that have the ability to generate oxygen when implanted, improving cell viability and tissue maturation. In this paper, we present a new oxygen-generating polylactic acid (PLA)/calcium peroxide (CPO) composite filament that can be used in 3D printing scaffolds. The composite material was prepared using a wet solution mixing method, followed by drying and hot melting extrusion. The concentration of calcium peroxide in the composite varied from 0% to 9%. The prepared filaments were characterized in terms of the presence of calcium peroxide, the generated oxygen release, porosity, and antibacterial activities. Data obtained from scanning electron microscopy and X-ray diffraction showed that the calcium peroxide remained stable in the composite. The maximum calcium and oxygen release was observed in filaments with a 6% calcium peroxide content. In addition, bacterial inhibition was achieved in samples with a calcium peroxide content of 6% or higher. These results indicate that an optimized PLA filament with a 6% calcium peroxide content holds great promise for improving bone generation through bone cell oxygenation and resistance to bacterial infections.

Oxygen therapy alternatives in COVID-19: From classical to nanomedicine

Around 10-15% of COVID-19 patients affected by the Delta and the Omicron variants exhibit acute respiratory insufficiency and require intensive care unit admission to receive advanced respiratory support. However, the current ventilation methods display several limitations, including lung injury, dysphagia, respiratory muscle atrophy, and hemorrhage. Furthermore, most of the ventilatory techniques currently offered require highly trained professionals and oxygen cylinders, which may attain short supply owing to the high demand and misuse. Therefore, the search for new alternatives for oxygen therapeutics has become extremely important for maintaining gas exchange in patients affected by COVID-19. This review highlights and suggest new alternatives based on micro and nanostructures capable of supplying oxygen and/or enabling hematosis during moderate or acute COVID-19 cases.

Oxygen-generating microparticles downregulate HIF-1α expression, increase cardiac contractility, and mitigate ischemic injury

Myocardial hypoxia is the low oxygen tension in the heart tissue implicated in many diseases, including ischemia, cardiac dysfunction, or after heart procurement for transplantation. Oxygen-generating microparticles have recently emerged as a potential strategy for supplying oxygen to sustain cell survival, growth, and tissue functionality in hypoxia. Here, we prepared oxygen-generating microparticles with poly D,L-lactic-co-glycolic acid, and calcium peroxide (CPO), which yielded a continuous morphology capable of sustained oxygen release for up to 24 h. We demonstrated that CPO microparticles increased primary rat cardiomyocyte metabolic activity while not affecting cell viability during hypoxia. Moreover, hypoxia-inducible factor (HIF)-1α, which is upregulated during hypoxia, can be downregulated by delivering oxygen using CPO microparticles. Single-cell traction force microscopy data demonstrated that the reduced energy generated by hypoxic cells could be restored using CPO microparticles. We engineered cardiac tissues that showed higher contractility in the presence of CPO microparticles compared to hypoxic cells. Finally, we observed reduced myocardial injuries in ex vivo rabbit hearts treated with CPO microparticles. In contrast, an acute early myocardial injury was observed for the hearts treated with control saline solution in hypoxia. In conclusion, CPO microparticles improved cell and tissue contractility and gene expression while reducing hypoxia-induced myocardial injuries in the heart. STATEMENT OF SIGNIFICANCE: Oxygen-releasing microparticles can reduce myocardial ischemia, allograft rejection, or irregular heartbeats after heart transplantation. Here we present biodegradable oxygen-releasing microparticles that are capable of sustained oxygen release for more than 24 hrs. We then studied the impact of sustained oxygen release from microparticles on gene expresseion and cardiac cell and tissue function. Previous studies have not measured cardiac tissue or cell mechanics during hypoxia, which is important for understanding proper cardiac function and beating. Using traction force microscopy and an engineered tissue-on-a-chip, we demonstrated that our oxygen-releasing microparticles improve cell and tissue contractility during hypoxia while downregulating the HIF-1α expression level. Finally, using the microparticles, we showed reduced myocardial injuries in rabbit heart tissue, confirming the potential of the particles to be used for organ transplantation or tissue engineering.

A new era in oxygen therapeutics? From perfluorocarbon systems to haemoglobin-based oxygen carriers

Blood transfusion is the key to life in case of traumatic emergencies, surgeries and in several pathological conditions. An important goal of whole blood or red blood cell transfusion is the fast delivery of oxygen to vital organs and restoration of circulation volume. Whole blood or red blood cell transfusion has several limitations. Free haemoglobin not only loses its tetrameric configuration and extracts via the kidney leading to nephrotoxicity but also scavenges nitric oxide (NO), leading to vasoconstriction and hypertension. PFC based formulations transport oxygen in vivo, the contribution in terms of clinical outcome is challenging. The oxygen-carrying capacity is not the only criterion for the successful development of haemoglobin-based oxygen carriers (HBOCs). This review is a bird's eye view on the present state of the PFCs and HBOCs in which we analyzed the current modifications made or which are underway in development, their promises, and hurdles in clinical implementation.

A microfluidic device for real-time on-demand intravenous oxygen delivery

SignificanceThe treatment of hypoxemia that is refractory to the current standard of care is time-sensitive and requires skilled caregivers and use of specialized equipment (e.g., extracorporeal membrane oxygenation). Most patients experiencing refractory hypoxemia will suffer organ dysfunction, and death is common in this cohort. Here, we describe a new strategy to stabilize and support patients using a microfluidic device that administers oxygen gas directly to the bloodstream in real time and on demand using a process that we call sequential shear-induced bubble breakup. If successful, the described technology may help to avoid or decrease the incidence of ventilator-related lung injury from refractory hypoxemia.

Oxygen-Releasing Biomaterials: Current Challenges and Future Applications

Oxygen is essential for the survival, function, and fate of mammalian cells. Oxygen tension controls cellular behaviour via metabolic programming, which in turn controls tissue regeneration, stem cell differentiation, drug metabolism, and numerous pathologies. Thus, oxygen-releasing biomaterials represent a novel and unique strategy to gain control over a variety of in vivo processes. Consequently, numerous oxygen-generating or carrying materials have been developed in recent years, which offer innovative solutions in the field of drug efficiency, regenerative medicine, and engineered living systems. In this review, we discuss the latest trends, highlight current challenges and solutions, and provide a future perspective on the field of oxygen-releasing materials.

Self-Oxygenation of Tissues Orchestrates Full-Thickness Vascularization of Living Implants

Bioengineering of tissues and organs has the potential to generate functional replacement organs. However, achieving the full-thickness vascularization that is required for long-term survival of living implants has remained a grand challenge, especially for clinically sized implants. During the pre-vascular phase, implanted engineered tissues are forced to metabolically rely on the diffusion of nutrients from adjacent host-tissue, which for larger living implants results in anoxia, cell death, and ultimately implant failure. Here it is reported that this challenge can be addressed by engineering self-oxygenating tissues, which is achieved via the incorporation of hydrophobic oxygen-generating micromaterials into engineered tissues. Self-oxygenation of tissues transforms anoxic stresses into hypoxic stimulation in a homogenous and tissue size-independent manner. The in situ elevation of oxygen tension enables the sustained production of high quantities of angiogenic factors by implanted cells, which are offered a metabolically protected pro-angiogenic microenvironment. Numerical simulations predict that self-oxygenation of living tissues will effectively orchestrate rapid full-thickness vascularization of implanted tissues, which is empirically confirmed via in vivo experimentation. Self-oxygenation of tissues thus represents a novel, effective, and widely applicable strategy to enable the vascularization living implants, which is expected to advance organ transplantation and regenerative medicine applications.

Methods for fabricating oxygen releasing biomaterials

Sustained external supply of oxygen (O₂) to engineered tissue constructs is important for their survival in the body while angiogenesis is taking place. In the recent years, the trend towards the fabrication of various O₂-generating materials that can provide prolonged and controlled O₂ source to the large volume tissue constructs resulted in preventing necrosis associated with the lack of O₂ supply. In this review, we explain different methods employed in the fabrication of O₂-generating materials such as emulsion, microfluidics, solvent casting, freeze drying, electrospraying, gelation, microfluidic and three-dimensional (3D) bioprinting methods. After discussing pros and cons of each method, we review physical, chemical, and biological characterisation techniques used to analyse the resulting product. Finally, the challenges and future directions in the field are discussed.

A Robust Oxygen Microbubble Radiosensitizer for Iodine-125 Brachytherapy

Iodine-125 (125I) brachytherapy, a promising form of radiotherapy, is increasingly applied in the clinical treatment of a wide range of solid tumors. However, the extremely hypoxic microenvironment in solid tumors can cause hypoxia-induced radioresistance to 125I brachytherapy, resulting in therapeutic inefficacy. In this study, the aim is to sensitize hypoxic areas in solid tumors using ultrasound-activated oxygen microbubbles for 125I brachytherapy. A modified emulsion freeze-drying method is developed to prepare microbubbles that can be lyophilized for storage and easily reconstituted in situ before administration. The filling gas of the microbubbles is modified by the addition of sulfur hexafluoride to oxygen such that the obtained O2/SF6 microbubbles (OS MBs) achieve a much longer half-life (>3×) than that of oxygen microbubbles. The OS MBs are tested in nasopharyngeal carcinoma (CNE2) tumor-bearing mice and oxygen delivery by the OS MBs induced by ultrasound irradiation relieve hypoxia instantly. The post-treatment results of brachytherapy combined with the ultrasound-triggered OS MBs show a greatly improved therapeutic efficacy compared with brachytherapy alone, illustrating ultrasound-mediated oxygen delivery with the developed OS MBs as a promising strategy to improve the therapeutic outcome of 125I brachytherapy in hypoxic tumors.

Oxygen-Carrying Polymer Nanoconstructs for Radiodynamic Therapy of Deep Hypoxic Malignant Tumors

Radiodynamic therapy (RDT) is an emerging non-invasive anti-cancer treatment based on the generation of the reactive oxygen species (ROS) at the lesion site following the interaction between X-rays and a photosensitizer drug (PS). The broader application of RDT is impeded by the tumor-associated hypoxia that results in low availability of oxygen for the generation of sufficient amounts of ROS. Herein, a novel nanoparticle drug formulation for RDT, which addresses the problem of low oxygen availability, is reported. It consists of poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) co-loaded with a PS drug verteporfin (VP), and the clinically approved oxygen-carrying molecule, perfluorooctylbromide (PFOB). When triggered by X-rays (4 Gy), under both normoxic and hypoxic conditions, PLGA-VP-PFOB nanoconstructs (NCs) induced a significant increase of the ROS production compared with matching PLGA-VP nanoparticles. The RDT with NCs effectively killed ~60% of human pancreatic cancer cells in monolayer cultures, and almost completely suppressed the outgrowth of tumor cells in 2-weeks clonogenic assay. In a 3D engineered model of pancreatic cancer metastasis to the liver, RDT with NCs destroyed ~35% of tumor cells, demonstrating an exceptional efficiency at a tissue level. These results show that PLGA-VP-PFOB is a promising agent for RDT of deep-seated hypoxic tumors.

Oxygen releasing materials: Towards addressing the hypoxia-related issues in tissue engineering

Manufacturing macroscale cell-laden architectures is one of the biggest challenges faced nowadays in the domain of tissue engineering. Such living constructs, in fact, pose strict requirements for nutrients and oxygen supply that can hardly be addressed through simple diffusion in vitro or without a functional vasculature in vivo. In this context, in the last two decades, a substantial amount of work has been carried out to develop smart materials that could actively provide oxygen-release to contrast local hypoxia in large-size constructs. This review provides an overview of the currently available oxygen-releasing materials and their synthesis and mechanism of action, highlighting their capacities under in vitro tissue cultures and in vivo contexts. Additionally, we also showcase an emerging concept, herein termed as "living materials as releasing systems", which relies on the combination of biomaterials with photosynthetic microorganisms, namely algae, in an "unconventional" attempt to supply the damaged or re-growing tissue with the necessary supply of oxygen. We envision that future advances focusing on tissue microenvironment regulated oxygen-supplying materials would unlock an untapped potential for generating a repertoire of anatomic scale, living constructs with improved cell survival, guided differentiation, and tissue-specific biofunctionality.

Hyperbaric polymer microcapsules for tunable oxygen delivery

Over the past decade, there have been many attempts to engineer systems capable of delivering oxygen to overcome the effects of both systemic and local hypoxia that occurs as a result of traumatic injury, cell transplantation, or tumor growth, among many others. Despite progress in this field, which has led to a new class of oxygen-generating biomaterials, most reported techniques lack the tunability necessary for independent control over the oxygen flux (volume per unit time) and the duration of delivery, both of which are key parameters for overcoming tissue hypoxia of varying etiologies. Here, we show that these critical parameters can be effectively manipulated using hyperbarically-loaded polymeric microcapsules (PMC). PMCs are micron-sized particles with hollow cores and polymeric shells. We show that oxygen delivery through PMCs is dependent on its permeability through the polymeric shell, the shell thickness, and the pressure gradient across the shell. We also demonstrate that incorporating an intermediate oil layer between the polymeric shell and the gas core prevents rapid outgassing by effectively lowering the resultant pressure gradient across the polymeric membrane following depressurization.

Nanosized zeolites as a gas delivery platform in a glioblastoma model

Approaches able to counteract, at least temporarily, hypoxia, a well-known factor of resistance to treatment in solid tumors are highly desirable. Herein, we report the use of nanosized zeolite crystals as hyperoxic/hypercapnic gas carriers for glioblastoma. First, the non-toxic profile of nanosized zeolite crystals in living animals (mice, rats and non-human primates) and in various cell types is presented. Second, the ability of the nanosized zeolites to act as a vasoactive agent for a targeted re-oxygenation of the tumor after intravenous injection is shown. As attested by an MRI protocol, the zeolites were able to increase oxygenation and blood volume specifically within the brain tumor whilst no changes in the healthy-non tumoral brain-were observed. The first proof of concept for the use of metal-containing nanosized zeolites as a tool for vectorization of hyperoxic/hypercapnic gases in glioblastoma is revealed.

Oxygen-generating smart hydrogels supporting chondrocytes survival in oxygen-free environments

Cartilage is one of our body's tissues which are not repaired automatically by itself. Problems associated with cartilage are very common worldwide and are considered the leading cause of pain and disability. Smart biomaterial or "Four dimensional" (4D) biomaterials has started emerging as a suitable candidate, which are principally three dimensional (3D) materials that change their morphology or generate a response measured at space and time to physiologic stimuli. In this context, the release of oxygen through hydrogels in contact with water is considered as 4D biomaterials. The objective of this study is to develop strategies to release oxygen in a sustainable and prolonged manner through hydrogels systems to promote chondrocytes survival in oxygen-free environment. The 4D biomaterials are engineered from gelatin methacryloyl (GelMA) loaded with calcium peroxide (CPO), which have the ability to generate oxygen in a controlled and sustained manner for up to 6 days. The incorporation of CPO into the hydrogel system provided materials with enhanced mechanical and porosity properties. Furthermore, the hydrogels promoted chondrocyte survival and reduced cell death under oxygen-free conditions.

Enhanced Tumor Synergistic Therapy by Injectable Magnetic Hydrogel Mediated Generation of Hyperthermia and Highly Toxic Reactive Oxygen Species

Nanoparticle-mediated tumor magnetic induction hyperthermia has received tremendous attention. However, it has been a challenge to improve the efficacy at 42 °C therapeutic temperatures without resistance to induced thermal stress. Therefore, we designed a magnetic hydrogel nanozyme (MHZ) utilizing inclusion complexation between PEGylated nanoparticles and α-cyclodextrin, which can enhance tumor oxidative stress levels by generating reactive oxygen species through nanozyme-catalyzed reactions based on tumor magnetic hyperthermia. MHZ can be injected and diffused into the tumor tissue due to shear thinning as well as magnetocaloric phase transition properties, and magnetic heat generated by the Fe₃O₄ first gives 42 °C of hyperthermia to the tumor. Fe₃O₄ nanozyme exerts peroxidase-like properties in the acidic environment of tumor to generate hydroxyl radicals (^•OH) by the Fenton reaction. The hyperthermia promotes the enzymatic activity of Fe₃O₄ nanozyme to produce more ^•OH. Simultaneously, ^•OH further damages the protective heat shock protein 70, which is highly expressed in hyperthermia to enhance the therapeutic effect of hyperthermia. This single magnetic nanoparticle exerts dual functions of hyperthermia and catalytic therapy to synergistically treat tumors, overcoming the resistance of tumor cells to induced thermal stress without causing severe side effects to normal tissues at 42 °C hyperthermia.

Anti-Tumor Drug-Loaded Oxygen Nanobubbles for the Degradation of HIF-1α and the Upregulation of Reactive Oxygen Species in Tumor Cells

Hypoxia is a key concern during the treatment of tumors, and hypoxia-inducible factor 1 alpha (HIF-1α) has been associated with increased tumor resistance to therapeutic modalities. In this study, doxorubicin-loaded oxygen nanobubbles (Dox/ONBs) were synthesized, and the effectiveness of drug delivery to MDA-MB-231 breast cancer and HeLa cells was evaluated. Dox/ONBs were characterized using optical and fluorescence microscopy, and size measurements were performed through nanoparticle tracking analysis (NTA). The working mechanism of Dox was evaluated using reactive oxygen species (ROS) assays, and cellular penetration was assessed with confocal microscopy. Hypoxic conditions were established to assess the effect of Dox/ONBs under hypoxic conditions compared with normoxic conditions. Our results indicate that Dox/ONBs are effective for drug delivery, enhancing oxygen levels, and ROS generation in tumor-derived cell lines.

Bioinorganics and Wound Healing

Wound dressings and the healing enhancement (increasing healing speed and quality) are two components of wound care that lead to a proper healing. Wound care today consists mostly of providing an optimal environment by removing waste and necrotic tissues from a wound, preventing infections, and keeping the wounds adequately moist. This is however often not enough to re-establish the healing process in chronic wounds; with the local disruption of vascularization, the local environment is lacking oxygen, nutrients, and has a modified ionic and molecular concentration which limits the healing process. This disruption may affect cellular ionic pumps, energy production, chemotaxis, etc., and will affect the healing process. Biomaterials for wound healing range from simple absorbents to sophisticated bioactive delivery vehicles. Often placing a material in or on a wound can change multiple parameters such as pH, ionic concentration, and osmolarity, and it can be challenging to pinpoint key mechanism of action. This article reviews the literature of several inorganic ions and molecules and their potential effects on the different wound healing phases and their use in new wound dressings.

pH-Responsive Oxygen Nanobubbles for Spontaneous Oxygen Delivery in Hypoxic Tumors

Tumor hypoxia is a significant factor leading to the resistance of tumors to treatment, especially for photodynamic therapy and radiotherapy where oxygen is needed to kill cancer cells. Oxygen delivery agents such as oxygen-saturated perfluorocarbon nanoemulsions and lipid oxygen microbubbles have been employed to supply oxygen to hypoxic tumors with ultrasound activation. Such oxygen delivery systems are still associated with several drawbacks, including premature oxygen release and the dependence of external stimuli. To address these limitations, we developed oxygen nanobubbles that were enclosed by the acetalated dextran polymer shells for spontaneous oxygeneration in response to a minor pH drop in the tumor microenvironment. The acetalated dextran polymer shell serves as a robust barrier against gas dissolution in the circulating blood to retain the majority of the oxygen payload, and its pH-responsive property enables an abrupt burst release of oxygen in the mild acidic tumor microenvironment. The acetalated dextran oxygen nanobubbles exhibited excellent stability and biocompatibility. In vitro and in vivo experiments were conducted to investigate the pH-responsive oxygen release. The external stimuli-free supply of oxygen by the acetalated dextran oxygen nanobubbles was evaluated on CNE2 tumor-bearing mice, and the intratumoral oxygen level increased by 6-fold after the administration of the oxygen nanobubbles, manifesting that our pH-responsive oxygen nanobubbles hold great potential as a potent oxygen delivery agent to overcome the hypoxia-induced resistance.

Artificial Oxygen Carriers-Past, Present, and Future-a Review of the Most Innovative and Clinically Relevant Concepts

Blood transfusions are a daily practice in hospitals. Since these products are limited in availability and have various, harmful side effects, researchers have pursued the goal to develop artificial blood components for about 40 years. Development of oxygen therapeutics and stem cells are more recent goals. Medline (https://www.ncbi.nlm.nih.gov/pubmed/?holding=ideudelib), ClinicalTrials.gov (https://clinicaltrials.gov), EU Clinical Trials Register (https://www.clinicaltrialsregister.eu), and Australian New Zealand Clinical Trials Registry (http://www.anzctr.org.au) were searched up to July 2018 using search terms related to artificial blood products in order to identify new and ongoing research over the last 5 years. However, for products that are already well known and important to or relevant in gaining a better understanding of this field of research, the reader is punctually referred to some important articles published over 5 years ago. This review includes not only clinically relevant substances such as heme-oxygenating carriers, perfluorocarbon-based oxygen carriers, stem cells, and organ conservation, but also includes interesting preclinically advanced compounds depicting the pipeline of potential new products. In- depth insights into specific benefits and limitations of each substance, including the biochemical and physiologic background are included. "Fancy" ideas such as iron-based substances, O2 microbubbles, cyclodextranes, or lugworms are also elucidated. To conclude, this systematic up-to-date review includes all actual achievements and ongoing clinical trials in the field of artificial blood products to pursue the dream of artificial oxygen carrier supply. Research is on the right track, but the task is demanding and challenging.

Size-Controlled Preparation of Microsized Perfluorocarbon Emulsions as Oxygen Carriers via the Shirasu Porous Glass Membrane Emulsification Technique

We have developed microsized perfluorocarbon (PFC) emulsions with different sizes as artificial oxygen carriers (OCs) via Shirasu porous glass membrane emulsification. Monodispersed PFC emulsions with narrow size distribution were obtained. By changing the membrane pore size, we were able to precisely control the size of emulsions and fabricate emulsions similar in size to human red blood cells. Behaviors of Pluronics with different physiochemical properties (F127, F68, P85, and P103) as surfactants were also investigated, which evidenced that the type and concentration of Pluronics have a major impact on the size of emulsions and the response to different thermal conditions. The F127-stabilized microsized PFC emulsions were stable even during autoclave sterilization. The emulsions were loaded with Ru(ddp)-an oxygen-sensitive probe-on their surfaces to indicate oxygen concentration. Finally, incubations with HeLa cells that show fluorescence in response to hypoxia cultured in 2D and 3D suggested promising potential of our emulsions for OCs.

Promoting vascularization for tissue engineering constructs: current strategies focusing on HIF-regulating scaffolds

INTRODUCTION

Vascularization remains one of the greatest yet unmet challenges in tissue engineering. When engineered tissues are scaled up to therapeutically relevant dimensions, their demand of oxygen and nutrients can no longer be met by diffusion. Thus, there is a need for perfusable vascular structures. Hypoxia-inducible factors (HIF) act as transcriptional oxygen sensors and regulate a multitude of genes involved in adaptive processes to hypoxia, including angiogenesis. Thus, targeting HIFs is a promising strategy to induce vascularization of engineered tissues.

AREAS COVERED

Here we review current vascularization strategies and summarize the present knowledge regarding activation of HIF signaling by ions, iron chelating agents, α-Ketoglutarate (αKG) analogues, and the lipid-lowering drug simvastatin to induce angiogenesis. Specifically, we focus on the incorporation of HIF-activating agents into biomaterials and scaffolds for controlled release.

EXPERT OPINION

Vascularization of tissue constructs through activation of upstream regulators of angiogenesis offers advantages but also suffers from drawbacks. HIFs can induce a complete angiogenic program; however, this program appears to be too slow to vascularize larger constructs before cell death occurs. It is therefore crucial that HIF-activation is combined with cell protective strategies and prevascularization techniques to obtain fully vascularized, vital tissues of therapeutically relevant dimensions.

Lipid-Polymer Bilaminar Oxygen Nanobubbles for Enhanced Photodynamic Therapy of Cancer

Hypoxia in solid tumors may be a hindrance to effective treatments of tumors in achieving their therapeutic potential, especially for photodynamic therapy (PDT) which requires oxygen as the supplement substrate. Oxygen delivery using perfluorocarbon emulsions or lipid oxygen microbubbles has been developed as the agents to supply endogenous oxygen to fuel singlet oxygen generation in PDT. However, such methods suffer from premature oxygen release and storage issues. To address these limitations, we designed lipid-polymer bilaminar oxygen nanobubbles with chlorin e6 (Ce6) conjugated to the polymer shell as a novel oxygen self-supplement agent for PDT. The resultant nanobubbles possessed excellent stability to reduce the risk of premature oxygen release and were stored as freeze-dried powders to avoid shelf storage issues. In vitro and in vivo experimental results demonstrated that the nanobubbles exhibited much higher cellular uptake rates and tumor targeting efficiency compared to free Ce6. Using the oxygen nanobubbles for PDT, a significant enhancement of therapeutic efficacy and survival rates was achieved on a C6 glioma-bearing mice model with no noticeable side effects, owing to the greatly enhanced singlet oxygen generation powered by oxygen encapsulated nanobubbles.

Oxygen-Carrying Micro/Nanobubbles: Composition, Synthesis Techniques and Potential Prospects in Photo-Triggered Theranostics

Microbubbles and nanobubbles (MNBs) can be prepared using various shells, such as phospholipids, polymers, proteins, and surfactants. MNBs contain gas cores due to which they are echogenic and can be used as contrast agents for ultrasonic and photoacoustic imaging. These bubbles can be engineered in various sizes as vehicles for gas and drug delivery applications with novel properties and flexible structures. Hypoxic areas in tumors develop owing to an imbalance of oxygen supply and demand. In tumors, hypoxic regions have shown more resistance to chemotherapy, radiotherapy, and photodynamic therapies. The efficacy of photodynamic therapy depends on the effective accumulation of photosensitizer drug in tumors and the availability of oxygen in the tumor to generate reactive oxygen species. MNBs have been shown to reverse hypoxic conditions, degradation of hypoxia inducible factor 1α protein, and increase tissue oxygen levels. This review summarizes the synthesis methods and shell compositions of micro/nanobubbles and methods deployed for oxygen delivery. Methods of functionalization of MNBs, their ability to deliver oxygen and drugs, incorporation of photosensitizers and potential application of photo-triggered theranostics, have also been discussed.

Tunable Polymer Microcapsules for Controlled Release of Therapeutic Gases

Encapsulation and delivery of oxygen, carbon dioxide, and other therapeutic gases, using polymeric microcapsules (PMCs) is an emerging strategy to deliver gas as an injectable therapeutic. The gas cargo is stored within the PMC core and its release is mediated by the physiochemical properties of the capsule shell. Although use of PMCs for the rapid delivery of gases has been well described, methods which tune the material properties of PMCs for sustained release of gas are lacking. In this work, we describe a simple method for the high-yield production of gas-in-oil-filled PMCs with tunable sizes and core gas content from preformed polymers using the sequential phase separation and self-emulsification of emulsion-based templates. We demonstrate that prolonged gas release occurs from gas-in-oil PMCs loaded with oxygen and carbon dioxide gas, each of which could have significant clinical applications.

A two-step synthesis for preparing metal microcapsules with a biodegradable polymer substrate

Novel method of producing metal microcapsules, using nanoparticles as the stabiliser, allows better control of nanoparticle distribution thus optimisation of metal shells.

Introduction of vasculature in engineered three-dimensional tissue

Background

With recent developments in tissue engineering technology, various three-dimensional tissues can be generated now. However, as the tissue thickness increases due to three-dimensionalization, it is difficult to increase the tissue scale without introduction of blood vessels.

Main text

Many methods for vasculature induction have been reported recently. In this review, we introduced several methods which are adjustable vascularization in three-dimensional tissues according to three steps. First, "selection" provides potents for engineered tissues with vascularization ability. Second, "assembly technology" is used to fabricate tissues as three-dimensional structures and simultaneously inner neo-vasculature. Third, a "perfusion" technique is used for maturation of blood vessels in three-dimensional tissues. In "selection", selection of cells and materials gives the ability to promote angiogenesis in three-dimensional tissues. During the cell assembly step, cell sheet engineering, nanofilm coating technology, and three-dimensional printing technology could be used to produce vascularized three-dimensional tissues. Perfusion techniques to perfuse blood or cell culture medium throughout three-dimensional tissues with a unified inlet and outlet could induce functional blood vessels within retransplantable three-dimensional tissues. Combination of each step technology allows simulation of perivascular microenvironments in target tissues and drive vascularization in three-dimensional tissues.

Conclusion

The biomimetic microenvironment of target tissues will induce adequate cell-cell interaction, distance, cell morphology, and function within tissues. It could be accelerated for vascularization within three-dimensional tissues and give us the functional tissues. Since vascularized three-dimensional tissues are highly functional, they are expected to contribute to the development of regenerative medicine and drug safety tests for drug discovery in the future.