Biomimetic Design and Bioengineering of Artificial Blood Substitutes: Recent Advances in Nanotechnology, Microfluidics, and Smart Materials for Next-Generation Synthetic Oxygen Carriers

The development of artificial blood substitutes has garnered significant attention in recent decades due to the pressing global demand for safe and efficient alternatives to donor-derived blood. Natural blood transfusions remain the cornerstone of managing blood loss in trauma, surgeries, and chronic conditions like anemia. However, the heavy reliance on human donors introduces multiple limitations, including fluctuating blood supply, the risk of infectious disease transmission, and the need for blood type compatibility (Alayash, 2014; Natanson et al., 2008). Additionally, blood products often require strict storage conditions and have limited shelf lives, making them less viable in emergency or resource-limited settings (Gould & Kramer, 2007). Conventional approaches to blood transfusion are also challenged by increasing global crises such as natural disasters, pandemics, and warfare, where immediate access to safe and compatible blood is often unattainable. This urgent need has accelerated research into artificial blood substitutes, particularly those that mimic the oxygen-carrying function of red blood cells (RBCs), offering the promise of universal compatibility, long shelf life, and on-demand availability (Spahn & Kocian, 2005). The objective of this review is to explore the latest innovations in biomimetic design and bioengineering strategies aimed at developing next-generation synthetic oxygen carriers. By focusing on the integration of nanotechnology, microfluidics, and smart materials, we aim to highlight how these technologies are converging to overcome traditional challenges in artificial blood development. This paper provides an interdisciplinary overview of current progress, from fundamental design requirements to clinical translation. A key theme throughout this review is the importance of biomimicry in the design of artificial blood. Nature has evolved highly efficient and adaptable mechanisms in erythrocytes for oxygen transport, delivery, and regulation. Emulating these mechanisms through engineered systems allows for the creation of synthetic substitutes that can function more effectively and safely in human physiology (Chang, 2006). Innovations such as hemoglobin encapsulation, oxygen-responsive materials, and microfluidic blood vessel mimetics reflect how deeply biomimicry informs and guides the development of functional artificial blood products.

2. Physiological Requirements and Challenges in Designing Synthetic Oxygen Carriers

2.1 Key Functions of Natural Red Blood Cells (RBCs)

Red blood cells (RBCs) serve as the primary oxygen transporters in the human body. They deliver oxygen from the lungs to peripheral tissues and assist in the removal of carbon dioxide through the buffering action of hemoglobin (Hb) (Finch & Lenfant, 1972). The biconcave shape of RBCs provides a high surface-area-to-volume ratio, enabling efficient gas exchange and flexibility to traverse narrow capillaries (Mohandas & Evans, 1994). Mimicking these structural and functional properties is central to the design of effective synthetic oxygen carriers.

2.2 Hemoglobin-Based Oxygen Transport and Its Complexity

Hemoglobin, a tetrameric protein consisting of two alpha and two beta chains, binds oxygen reversibly at its heme groups. This binding is cooperative and regulated by several factors such as pH (Bohr effect), carbon dioxide concentration, and 2,3-bisphosphoglycerate levels (Bunn & Forget, 1986). Maintaining this delicate regulation is challenging in synthetic systems. In natural RBCs, hemoglobin is compartmentalized, preventing direct exposure to plasma, where it could scavenge nitric oxide (NO), increase blood pressure, and induce vasoconstriction (Alayash, 2014).

2.3 Design Criteria for Synthetic Oxygen Carriers

The development of synthetic blood substitutes must satisfy a stringent set of physiological parameters to effectively emulate the functionality of RBCs. Table 1 summarizes the core design criteria for artificial oxygen carriers.

Table 1: Key Design Criteria for Synthetic Oxygen Carriers

(Sakai, 2004; Spahn & Kocian, 2005)

2.4 Major Challenges in Synthetic Oxygen Carrier Design

Despite advancements in formulation and engineering, synthetic oxygen carriers face several biological and physicochemical hurdles:

2.4.1 Toxicity and Oxidative Stress

Cell-free hemoglobin and its derivatives are prone to auto-oxidation, producing methemoglobin, which is incapable of carrying oxygen (Alayash, 2014). Reactive oxygen species (ROS) generated during this process can damage endothelial cells and induce systemic oxidative stress.

2.4.2 Nitric Oxide (NO) Scavenging

Unlike RBC-encapsulated hemoglobin, free or loosely bound hemoglobin in synthetic carriers readily reacts with NO, a critical vasodilator. This interaction depletes NO bioavailability, leading to hypertension and vascular dysfunction (Rohlfs et al., 1998).

2.4.3 Renal Clearance and Accumulation

Unmodified or low-molecular-weight carriers are rapidly filtered through the kidneys, leading to nephrotoxicity and short circulation times (Chang, 2006). Strategies such as PEGylation, polymerization, or encapsulation are employed to increase molecular size and avoid renal clearance.

Table 2: Major Biological and Engineering Challenges in Synthetic Oxygen Carrier Development

(Chang, 2006; Alayash, 2014; Sakai, 2004)

Overall, overcoming these multifactorial challenges requires a multidisciplinary approach that integrates bioengineering, material science, and molecular biology to develop systems that closely replicate the dynamic performance of natural RBCs.

3. Hemoglobin-Based Oxygen Carriers (HBOCs) and Perfluorocarbon-Based Carriers (PFCs)

The development of artificial oxygen carriers has primarily followed two distinct approaches: hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbon-based carriers (PFCs). Both aim to mimic the oxygen transport function of red blood cells (RBCs), albeit through fundamentally different mechanisms. HBOCs leverage modified hemoglobin molecules to carry oxygen, while PFCs utilize chemically inert compounds capable of dissolving and releasing oxygen physically.

3.1 Overview and Types of Hemoglobin-Based Oxygen Carriers (HBOCs)

HBOCs are derived from human, bovine, or recombinant hemoglobin, modified to function outside the RBC membrane. Native hemoglobin is unsuitable for direct infusion due to its rapid dissociation into dimers, renal toxicity, and interaction with nitric oxide (NO), leading to vasoconstriction and oxidative damage (Alayash, 2014). To mitigate these issues, various engineering strategies have been employed, leading to the development of several HBOC types:

Table 3: Major Types of Hemoglobin-Based Oxygen Carriers

(Spahn & Kocian, 2005; Chang, 2006)

Notable HBOC products include Hemopure® (polymerized bovine Hb), PolyHeme® (polymerized human Hb), and MP4OX (PEGylated Hb), all of which have undergone varying levels of clinical testing.

3.2 Advantages and Limitations of Perfluorocarbon-Based Carriers (PFCs)

PFCs are synthetic, fluorinated hydrocarbons capable of physically dissolving large amounts of oxygen and carbon dioxide. Unlike HBOCs, they do not rely on chemical binding but rather on passive gas solubility, governed by Henry’s Law (Riess, 2005). PFCs are typically emulsified with surfactants to ensure biocompatibility and dispersion in blood.

Advantages of PFCs:

50. Chemically inert and stable under physiological conditions
50. Not derived from biological sources, eliminating infection risk
50. High oxygen-carrying capacity under hyperoxic conditions
50. Small particle size allows penetration into ischemic tissues

Limitations of PFCs:

50. Require supplemental oxygen administration to be effective
50. Rapid clearance from circulation
50. Surfactant-related toxicity and flu-like symptoms in some patients

Well-known PFC formulations include Fluosol-DA, the first FDA-approved PFC, and Oxygent, which advanced through clinical trials but was discontinued due to safety concerns (Spahn & Kocian, 2005).

3.3 FDA-Approved and Investigational Products

To date, no artificial oxygen carrier has achieved widespread clinical approval in the United States. However, several products have made significant progress:

Table 4: Selected HBOC and PFC Products and Their Regulatory Status

(Sloan, 2005; Chang, 2006; Riess, 2005)

3.4 Comparative Analysis of HBOCs vs. PFCs

A direct comparison of HBOCs and PFCs reveals distinct strengths and weaknesses, making them suitable for different clinical scenarios. HBOCs are more physiologically analogous to natural hemoglobin and function effectively under normoxic conditions. In contrast, PFCs, though limited by the need for hyperoxia, excel in microcirculatory perfusion due to their small size.

Table 5: Comparative Characteristics of HBOCs and PFCs

(Spahn & Kocian, 2005; Alayash, 2014)

In conclusion, both HBOCs and PFCs offer unique pathways for developing synthetic oxygen carriers. While HBOCs more closely replicate the biological function of natural RBCs, PFCs present novel opportunities for oxygen delivery in niche clinical contexts. Ongoing research and optimization are crucial for overcoming current limitations and realizing their full therapeutic potential.

4. Advances in Nanotechnology for Blood Substitute Engineering

Nanotechnology has revolutionized the field of artificial blood substitute development by enabling precise engineering of hemoglobin-based carriers with improved functionality, biocompatibility, and targeting capabilities. The ability to manipulate materials at the nanoscale has led to the creation of novel systems that mimic red blood cells (RBCs) more closely than traditional formulations. This section outlines the key advances in nanoparticle-based hemoglobin carriers, core–shell nanostructures for controlled oxygen release, surface modification strategies, and addresses toxicity and biocompatibility concerns.

4.1 Nanoparticle-Based Hemoglobin Carriers

Nanocarriers offer a platform for encapsulating or conjugating hemoglobin (Hb) to improve circulation time, reduce immunogenicity, and enhance oxygen delivery. Several types of nanostructures have been investigated:

4.1.1 Liposomes and Polymersomes

Liposomes—spherical vesicles with phospholipid bilayers—have been widely explored to encapsulate hemoglobin, forming artificial red blood cells or “hemosomes.” These carriers mimic the RBC membrane and offer biocompatibility and oxygen transport capabilities (Chang, 2006). Polymersomes, composed of amphiphilic block copolymers, provide better mechanical strength and longer circulation times than liposomes. They can be engineered to encapsulate not only Hb but also enzymes like catalase and superoxide dismutase, enhancing resistance to oxidative stress (Sharma et al., 2016).

4.1.2 Dendrimers and Other Nanostructures

Dendrimers are highly branched synthetic macromolecules with tunable surface functionalities. Hb can be covalently linked to dendrimer surfaces, producing uniform nanoparticles with controllable oxygen-binding capacity and prolonged systemic retention (Huang et al., 2011). Nanoparticle-based hemoglobin (Hb) carriers are being extensively explored as alternatives to red blood cells for oxygen delivery, each offering unique structural features and functional advantages. Liposomes, composed of phospholipid bilayer vesicles, closely mimic the natural red blood cell membrane, offering excellent biocompatibility; however, they suffer from limited mechanical stability, which can hinder their circulation time and functionality under stress. Polymersomes, formed from block copolymers, provide enhanced robustness, prolonged circulation, and resistance to oxidative degradation, but their complex synthesis can pose challenges for large-scale production and clinical translation. Dendrimers, highly branched synthetic macromolecules, are monodisperse with a modifiable surface, enabling functionalization for targeted delivery, yet they can exhibit cytotoxicity at higher concentrations, necessitating careful dose optimization. Albumin-based carriers, in which hemoglobin is conjugated to albumin nanoparticles, leverage the natural carrier properties of albumin to extend the half-life of Hb in circulation, although they may demonstrate reduced oxygen-binding efficiency compared to native hemoglobin. Together, these systems exemplify the trade-offs between biocompatibility, stability, oxygen-carrying capacity, and manufacturability in the development of synthetic oxygen carriersn(Chang, 2006; Sharma et al., 2016; Huang et al., 2011).

4.2 Core–Shell Nanostructures for Controlled Oxygen Release

Core–shell nanoparticles represent a breakthrough in mimicking the natural oxygen release kinetics of RBCs. Typically, the core contains hemoglobin or oxygen reservoirs, while the shell regulates the rate of oxygen diffusion. For example, polymer-coated iron oxide nanoparticles or silica shells with controlled porosity can release oxygen gradually, preventing bursts of oxygen that may cause oxidative tissue damage (Li et al., 2017). Thermo-responsive or pH-responsive materials in the shell can further tailor oxygen release to the local physiological environment, such as hypoxic tissues or tumors. Core–shell nanostructures have emerged as promising platforms for targeted oxygen delivery in various pathological conditions. These systems typically consist of a functional core enclosed by a responsive shell that modulates the release of oxygen. For instance, nanostructures with hemoglobin (Hb) as the core and PEG-polylactic acid as the shell utilize pH-sensitive release mechanisms, making them particularly effective for tumor-targeted oxygen delivery, where the acidic microenvironment facilitates oxygen release. Another design incorporates perfluorocarbons encapsulated within silica nanoparticles, allowing diffusion-controlled oxygen release, suitable for hypoxia therapy by gradually supplying oxygen to oxygen-deprived tissues. Additionally, a hybrid system combining Hb and catalase within a poly(N-isopropylacrylamide) shell offers a temperature-responsive release profile, which is especially beneficial for oxygen delivery in ischemic conditions, where localized temperature changes can trigger oxygen liberation. These core–shell constructs provide a strategic advantage in achieving controlled and site-specific oxygen supplementation (Li et al., 2017; Wang et al., 2019).

4.3 Surface Modification for Immune Evasion and Targeting

To enhance systemic circulation and reduce clearance by the reticuloendothelial system (RES), nanocarriers are often surface-modified with “stealth” materials. Polyethylene glycol (PEG) is the most widely used, forming a hydration layer that inhibits protein adsorption and immune recognition (Alayash, 2014). Other strategies include:

50. Zwitterionic coatings: Provide anti-fouling properties superior to PEG.
50. Targeting ligands: Peptides, antibodies, or small molecules (e.g., folic acid) allow specific binding to hypoxic tissues or tumor cells (Zhao et al., 2020).
50. Cell membrane camouflaging: Coating nanoparticles with natural membranes (e.g., RBC membrane) to evade immune detection and prolong circulation (Hu et al., 2013).

These modifications significantly improve the pharmacokinetics and targeting efficiency of synthetic oxygen carriers.

4.4 Toxicity Concerns and Biocompatibility Assessment

Despite advances in nanotechnology, potential toxicity remains a major barrier to clinical translation. Nanoparticles may:

50. Accumulate in organs like liver and spleen
50. Induce inflammatory or immune responses
50. Generate reactive oxygen species (ROS) and oxidative stress

Biocompatibility testing involves in vitro assays (e.g., hemolysis, cytotoxicity, ROS generation) and in vivo models assessing biodistribution, organ histology, and immune responses (Dobrovolskaia & McNeil, 2007). Biocompatibility is a critical consideration in the evaluation of nanocarriers for therapeutic applications. One of the primary parameters assessed is hemolysis, typically measured using a spectrophotometric assay. An acceptable threshold for hemolysis is less than 5%, indicating minimal red blood cell membrane disruption. Cytotoxicity is another essential factor, commonly evaluated through MTT or LDH release assays, where a cell viability of 80% or higher is considered ideal. The generation of reactive oxygen species (ROS) is assessed using DCFDA fluorescence assays, and biocompatible nanocarriers should exhibit ROS levels comparable to untreated controls, ensuring that they do not induce oxidative stress. Immunogenicity is evaluated by measuring cytokine levels, particularly IL-6 and TNF-α, through ELISA. A minimal cytokine response indicates a low potential for immune system activation. Finally, in vivo biodistribution, often tracked via fluorescence or radiolabel techniques, should demonstrate low accumulation in reticuloendothelial system (RES) organs such as the liver and spleen, which helps to reduce potential off-target effects and enhance therapeutic efficacy (Dobrovolskaia & McNeil, 2007; Alayash, 2014). Nanotechnology-based approaches have significantly expanded the potential of artificial oxygen carriers by offering precise control over structure, oxygen release, circulation time, and immune evasion. However, the balance between performance and safety must be carefully optimized through rigorous design and preclinical testing. Continued innovation in materials science and biocompatibility assessment will pave the way for clinically viable synthetic blood substitutes.

4. Advances in Nanotechnology for Blood Substitute Engineering

Nanotechnology has revolutionized the field of artificial blood substitute development by enabling precise engineering of hemoglobin-based carriers with improved functionality, biocompatibility, and targeting capabilities. The ability to manipulate materials at the nanoscale has led to the creation of novel systems that mimic red blood cells (RBCs) more closely than traditional formulations. This section outlines the key advances in nanoparticle-based hemoglobin carriers, core–shell nanostructures for controlled oxygen release, surface modification strategies, and addresses toxicity and biocompatibility concerns.

4.1 Nanoparticle-Based Hemoglobin Carriers

Nanocarriers offer a platform for encapsulating or conjugating hemoglobin (Hb) to improve circulation time, reduce immunogenicity, and enhance oxygen delivery. Several types of nanostructures have been investigated:

4.1.1 Liposomes and Polymersomes

Liposomes—spherical vesicles with phospholipid bilayers—have been widely explored to encapsulate hemoglobin, forming artificial red blood cells or “hemosomes.” These carriers mimic the RBC membrane and offer biocompatibility and oxygen transport capabilities (Chang, 2006). Polymersomes, composed of amphiphilic block copolymers, provide better mechanical strength and longer circulation times than liposomes. They can be engineered to encapsulate not only Hb but also enzymes like catalase and superoxide dismutase, enhancing resistance to oxidative stress (Sharma et al., 2016).

4.1.2 Dendrimers and Other Nanostructures

Dendrimers are highly branched synthetic macromolecules with tunable surface functionalities. Hb can be covalently linked to dendrimer surfaces, producing uniform nanoparticles with controllable oxygen-binding capacity and prolonged systemic retention (Huang et al., 2011).

Table 6: Examples of Nanoparticle-Based Hemoglobin Carriers

(Chang, 2006; Sharma et al., 2016; Huang et al., 2011)

4.2 Core–Shell Nanostructures for Controlled Oxygen Release

Core–shell nanoparticles represent a breakthrough in mimicking the natural oxygen release kinetics of RBCs. Typically, the core contains hemoglobin or oxygen reservoirs, while the shell regulates the rate of oxygen diffusion.

For example, polymer-coated iron oxide nanoparticles or silica shells with controlled porosity can release oxygen gradually, preventing bursts of oxygen that may cause oxidative tissue damage (Li et al., 2017). Thermo-responsive or pH-responsive materials in the shell can further tailor oxygen release to the local physiological environment, such as hypoxic tissues or tumors.

Table 7: Core–Shell Nanostructures for Oxygen Delivery

(Li et al., 2017; Wang et al., 2019)

4.3 Surface Modification for Immune Evasion and Targeting

To enhance systemic circulation and reduce clearance by the reticuloendothelial system (RES), nanocarriers are often surface-modified with “stealth” materials. Polyethylene glycol (PEG) is the most widely used, forming a hydration layer that inhibits protein adsorption and immune recognition (Alayash, 2014). Other strategies include:

50. Zwitterionic coatings: Provide anti-fouling properties superior to PEG.
50. Targeting ligands: Peptides, antibodies, or small molecules (e.g., folic acid) allow specific binding to hypoxic tissues or tumor cells (Zhao et al., 2020).
50. Cell membrane camouflaging: Coating nanoparticles with natural membranes (e.g., RBC membrane) to evade immune detection and prolong circulation (Hu et al., 2013).

These modifications significantly improve the pharmacokinetics and targeting efficiency of synthetic oxygen carriers.

4.4 Toxicity Concerns and Biocompatibility Assessment

Despite advances in nanotechnology, potential toxicity remains a major barrier to clinical translation. Nanoparticles may:

50. Accumulate in organs like liver and spleen
50. Induce inflammatory or immune responses
50. Generate reactive oxygen species (ROS) and oxidative stress

Biocompatibility testing involves in vitro assays (e.g., hemolysis, cytotoxicity, ROS generation) and in vivo models assessing biodistribution, organ histology, and immune responses (Dobrovolskaia & McNeil, 2007).

Table 8: Biocompatibility Parameters in Nanocarrier Evaluation

(Dobrovolskaia & McNeil, 2007; Alayash, 2014)

Nanotechnology-based approaches have significantly expanded the potential of artificial oxygen carriers by offering precise control over structure, oxygen release, circulation time, and immune evasion. However, the balance between performance and safety must be carefully optimized through rigorous design and preclinical testing. Continued innovation in materials science and biocompatibility assessment will pave the way for clinically viable synthetic blood substitutes.

5. Role of Microfluidics in Synthetic Blood Design and Testing

Microfluidic technology—often described as “lab-on-a-chip”—has become indispensable for evaluating and optimizing next-generation synthetic oxygen carriers. By miniaturizing physiological environments, these platforms enable precise control of flow, shear stress, and mass-transfer processes that govern red blood cell (RBC) behavior and blood substitute performance (Whitesides, 2006).

5.1 Microfluidic Platforms That Simulate Microvascular Flow and RBC Behavior

Microchannels fabricated in polydimethylsiloxane (PDMS), glass, or thermoplastics can be patterned with cross-sections as small as 5 µm—comparable to human capillaries. These devices reproduce key hemodynamic parameters such as Fahraeus-Lindqvist viscosity reduction and plasma skimming, allowing direct visualization of hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbon-based carriers (PFCs) under physiologic shear (Lee et al., 2019).

Table 9. Microfluidic Models for Simulating Microvascular Flow

5.2 High-Throughput Screening for Oxygen-Delivery Performance

Droplet-based microfluidics and multiplexed channel grids allow thousands of parallel tests while consuming nanoliter volumes (Bhise et al., 2020). By integrating optical oxygen sensors or phosphorescent dyes into each droplet/segment, researchers can rapidly rank carrier formulations by oxygen-loading capacity, release kinetics, and oxidative stability. This approach accelerates lead selection prior to animal studies, cutting material use by >90 % (Ren et al., 2023).

5.3 Organ-on-Chip Models for Hemocompatibility and Vascular Reactivity Testing

Endothelium-lined microfluidic chips emulate arterial or venous segments, enabling evaluation of nitric-oxide scavenging, vasomotor signaling, and inflammatory responses to synthetic carriers (Huh et al., 2013). More complex “heart-on-chip” and “lung-on-chip” systems reproduce pulsatile pressures and gas-exchange barriers, offering insights unattainable in static cell culture.

Table 10. Representative Organ-on-Chip Platforms for Blood Substitute Testing

5.4 Integration with Biosensors for Real-Time Monitoring

Embedding optical fiber probes, electrochemical electrodes, or field-effect transistors within microfluidic channels permits continuous measurement of dissolved O?, pH, oxidative species, and cytokine release (Wu et al., 2018). Real-time feedback guides flow-rate adjustments and reveals transient phenomena such as methemoglobin formation.

Table 11. Biosensor Modalities Integrated into Microfluidic Blood-Testing Chips

Microfluidic systems bridge the gap between benchtop chemistry and in vivo testing by providing physiologically relevant, high-resolution, and scalable evaluation tools. Their ability to couple organ-level functions with integrated sensing positions microfluidics as a core component of the synthetic blood R & D pipeline moving forward.

6. Smart and Stimuli-Responsive Materials in Artificial Blood Systems

The integration of smart and stimuli-responsive materials into synthetic oxygen carriers marks a significant advancement in the biomimetic design of artificial blood. These materials respond dynamically to environmental cues—such as pH, temperature, or oxygen levels—allowing for controlled, context-specific release of oxygen and other functionalities. Inspired by biological feedback systems, these “intelligent” carriers improve oxygen delivery efficiency, reduce side effects, and hold potential for theranostic (therapeutic + diagnostic) applications.

6.1 Smart Polymers and Hydrogels Responsive to pH, Temperature, and Oxygen Tension

Smart polymers and hydrogels undergo physicochemical changes in response to stimuli, making them ideal candidates for the controlled release of oxygen. For example, pH-responsive hydrogels made from poly(N-isopropylacrylamide) (PNIPAAm) or polyacrylic acid (PAA) can swell or collapse based on tissue acidity—an important feature for targeting hypoxic or inflamed tissues (Li et al., 2019).

Temperature-sensitive materials are also being explored. PNIPAAm exhibits a lower critical solution temperature (LCST) near physiological temperature (~32°C), enabling reversible gelation in vivo (Liu et al., 2022). Oxygen-sensitive carriers using perfluorocarbon-hydrogel hybrids or hemoglobin-grafted smart polymers can modulate release based on local O? gradients, mimicking allosteric regulation seen in hemoglobin itself.

Table 12. Stimuli-Responsive Polymers in Blood Substitute Design

6.2 Self-Regulating Oxygen Carriers Mimicking Biological Feedback Loops

Nature uses feedback inhibition to control oxygen delivery—exemplified by hemoglobin's cooperative binding and Bohr effect. To emulate this, researchers are engineering self-regulating systems wherein oxygen release is modulated by local oxygen tension, CO? levels, or pH. One approach uses heme-mimetic moieties embedded in polymer matrices that change conformation upon oxygen binding, thus altering oxygen affinity dynamically (Yu et al., 2021). Another uses boronic acid-functionalized hydrogels to respond to reactive oxygen species (ROS), enabling antioxidant co-delivery with O? carriers in ischemic zones.

6.3 Shape-Shifting and Self-Assembling Biomaterials

Self-assembling peptides, micelles, and block copolymers are used to construct nanostructures that mimic red blood cells’ morphology and function. These shape-adaptive carriers can undergo transitions—from spherical to discoid shapes—under flow conditions, improving margination and microvascular navigation (Deng et al., 2020).

Shape-shifting vesicles also enable staged oxygen delivery: e.g., oxygen is stored in the hydrophobic core, while outer shells respond to pH or enzymatic triggers to expose or activate the core. This not only mimics RBC flexibility but also enhances delivery precision.

Table 13. Self-Assembling and Shape-Adaptive Materials

6.4 Multifunctional (Theranostic) Blood Substitutes

Smart materials also enable theranostic applications by co-delivering therapeutic agents and imaging contrast molecules alongside oxygen. For example, nanocarriers loaded with hemoglobin and MRI contrast agents like Gd-DTPA enable simultaneous monitoring of perfusion and tissue oxygenation (Kwon et al., 2021). Additionally, temperature-sensitive liposomes can release both oxygen and anti-inflammatory drugs in inflamed tissues. Such multifunctionality is critical for managing complex conditions like trauma, stroke, or cancer, where both oxygen support and site-specific therapy are essential. Stimuli-responsive materials empower artificial blood substitutes with the ability to behave like living systems—adjusting their function in real-time to match tissue needs. These innovations enhance safety, specificity, and therapeutic potential, ushering in the era of smart blood technologies.

7. Clinical Translation and Regulatory Landscape

7.1 Current Status of Clinical Trials and Commercial Products

Despite decades of research, only a few synthetic oxygen carriers have progressed to clinical testing. Hemoglobin-based oxygen carriers (HBOCs) like HemAssist (Baxter) and PolyHeme (Northfield Laboratories) reached Phase III trials but were ultimately discontinued due to adverse events, including increased risk of myocardial infarction and mortality (Natanson et al., 2008). Perfluorocarbon-based carriers such as Fluosol-DA and Oxygent were evaluated for temporary oxygenation, particularly in cases of anemia or during surgery, but encountered issues with efficacy and pulmonary side effects (Spahn & Kocian, 2005). Currently, Hemopure (Hb-glutaraldehyde polymer from bovine sources) is authorized for limited clinical use in South Africa and under expanded access in the U.S., especially during blood shortages (Winslow, 2006).

Table 14. Examples of Artificial Oxygen Carriers in Clinical/Preclinical Development