Nanosponges In Drug Delivery: Recent Advances, Applications, Challenges, And Future Perspectives

Figure 1. General Representation of Nanosponge Structure

2.1 Definition and Structure

Nanosponges are hyper-crosslinked polymeric nanoparticles composed of a three-dimensional network of polymers interconnected through cross-linking agents. The resulting structure forms nanoscale cavities capable of encapsulating drug molecules and protecting them from environmental degradation (9).

Cyclodextrin-based nanosponges are the most extensively studied systems. In these systems, cyclodextrin molecules are cross-linked using agents such as diphenyl carbonate, carbonyldiimidazole, or pyromellitic dianhydride to form a porous network (10).

The structure consists of:

• Polymer backbone

• Cross-linking bridges

• Nanocavities for drug entrapment

• Surface functional groups

The drug may be physically trapped inside pores or chemically associated with the polymer matrix depending on its physicochemical properties.

Table 1. Structural Components of Nanosponges

2.2 Properties and Advantages

Nanosponges possess several unique physicochemical and biological properties that distinguish them from conventional drug delivery systems.

Table 2. Important Properties of Nanosponges

Table 3. Advantages of Nanosponges Compared with Conventional Systems

3. Materials Used in Nanosponge Preparation

The selection of suitable polymers and cross-linking agents is crucial in the fabrication of nanosponges, as these materials determine the structural integrity, drug-loading capacity, release characteristics, and biocompatibility of the final formulation. Various natural and synthetic polymers have been utilized to develop nanosponges with tailored properties for specific pharmaceutical applications (15).

3.1 Polymers Used in Nanosponge Preparation

Polymers form the backbone of the nanosponge structure and provide the porous network required for drug encapsulation. Cyclodextrins are the most widely used polymers because of their ability to form inclusion complexes with drug molecules. Other polymers such as ethyl cellulose, polymethyl methacrylate, polycaprolactone, and biodegradable copolymers have also been investigated for nanosponge synthesis (16,17).

Table 4. Common Polymers Used in Nanosponge Preparation

3.2 Cross-Linking Agents

Cross-linking agents connect polymer chains and generate the porous three-dimensional architecture of nanosponges. The degree of cross-linking significantly influences pore size, drug loading, and release kinetics (18).

Table 5. Common Cross-Linking Agent

3.3 Solvents Used During Preparation

Various solvents are employed during nanosponge synthesis depending on the polymer and cross-linker selected. Solvents facilitate polymer dissolution and improve reaction efficiency (19).

Table 6. Solvents Used in Nanosponge Synthesis

3.4 Factors Affecting Material Selection

The choice of materials depends on:

• Drug physicochemical properties
• Desired release profile
• Route of administration
• Biocompatibility requirements
• Stability considerations
• Regulatory acceptance

Proper selection of polymers and cross-linkers enables the development of nanosponges with high entrapment efficiency, improved stability, and controlled drug release characteristics (20).

4. METHODS OF PREPARATION

Several techniques have been developed for nanosponge synthesis. The preparation method significantly affects particle size, morphology, drug loading capacity, and release behavior. Selection of a suitable method depends on the nature of the polymer, cross-linking agent, and intended application (21).

4.1 Solvent Method

The solvent method is one of the most commonly employed techniques for preparing cyclodextrin-based nanosponges. In this method, the polymer is dissolved in a suitable solvent and reacted with a cross-linking agent under controlled temperature conditions. After completion of the reaction, the product is purified and dried to obtain nanosponges (22).

Advantages

• Simple process
• High product yield
• Suitable for large-scale production

Limitations

• Use of organic solvents
• Additional purification steps required

4.2 Ultrasound-Assisted Method

In this technique, polymer and cross-linking agent mixtures are subjected to ultrasonic energy without using solvents. Ultrasonic waves promote efficient cross-linking and formation of porous nanostructures (23).

Advantages

• Solvent-free process
• Environmentally friendly
• Uniform particle size distribution

Limitations

• Specialized equipment required

4.3 Emulsion Solvent Diffusion Method

This method is widely used for preparing polymeric nanosponges. The polymer and drug are dissolved in an organic phase and emulsified into an aqueous phase containing stabilizers. Solvent diffusion and evaporation lead to nanosponge formation (24).

Advantages

• Suitable for hydrophobic drugs
• High drug entrapment efficiency

Limitations

• Residual solvent concerns

4.4 Melt Method

In the melt method, polymers and cross-linkers are heated above their melting points without the use of solvents. Cross-linking occurs during heating, resulting in nanosponge formation (25).

Advantages

• Solvent-free
• Economical

Limitations

• Not suitable for thermolabile drugs

4.5 Microwave-Assisted Synthesis

Microwave irradiation accelerates the cross-linking reaction and significantly reduces preparation time. Uniform heating improves nanosponge formation and reproducibility (26).

Advantages

• Rapid synthesis
• Reduced reaction time
• Energy efficient

Limitations

• Requires microwave reactor

4.6 Green Synthesis Approaches

Recent studies focus on eco-friendly preparation methods utilizing biodegradable polymers, aqueous media, and natural cross-linkers. Green synthesis minimizes environmental impact while maintaining formulation performance (27).

Table 7. Comparison of Nanosponge Preparation Methods

Figure 2: Preparation and Characterization of Nanosponges

5. CHARACTERIZATION OF NANOSPONGES

Characterization of nanosponges is essential to evaluate their physicochemical properties, drug-loading efficiency, stability, and drug-release behavior. Various analytical techniques are employed to ensure the quality and performance of nanosponge formulations. Proper characterization helps establish a correlation between structural properties and therapeutic efficacy (28).

5.1 Particle Size Analysis

Particle size is a critical parameter influencing drug loading, release kinetics, biodistribution, and cellular uptake. Nanosponge particle size is commonly measured using Dynamic Light Scattering (DLS), laser diffraction, or nanoparticle tracking analysis (29).

Significance

• Influences drug release rate
• Affects stability and dispersibility
• Determines tissue penetration and bioavailability

Table 8. Importance of Particle Size in Nanosponges

5.2 Zeta Potential

Zeta potential measures the surface charge of nanoparticles and predicts colloidal stability. Higher absolute zeta potential values indicate greater repulsive forces between particles, preventing aggregation (30).

Interpretation

5.3 Surface Morphology

The morphology and surface characteristics of nanosponges are evaluated using:

• Scanning Electron Microscopy (SEM)
• Transmission Electron Microscopy (TEM)
• Atomic Force Microscopy (AFM)

These techniques provide information regarding particle shape, pore structure, and surface texture (31).

5.4 Fourier Transform Infrared Spectroscopy (FTIR)

FTIR spectroscopy is used to identify functional groups and investigate drug-polymer interactions. Shifts in characteristic absorption peaks indicate successful encapsulation and compatibility between the drug and nanosponge matrix (32).

Applications

• Compatibility studies
• Confirmation of cross-linking
• Identification of chemical interactions

5.5 Differential Scanning Calorimetry (DSC)

DSC evaluates thermal behavior and physical state changes in nanosponge formulations. It is useful for determining melting points, crystallinity, and drug-polymer interactions (33).

Significance

• Detects encapsulation of drug
• Determines thermal stability
• Evaluates crystallinity changes

5.6 X-Ray Diffraction (XRD)

XRD analysis determines the crystalline or amorphous nature of the drug and nanosponge system. Drug encapsulation often results in reduced crystallinity, enhancing drug solubility and dissolution (34).

Table 9. Characterization Techniques and Their Applications

5.7 Entrapment Efficiency

Entrapment efficiency represents the percentage of drug successfully incorporated into the nanosponge matrix relative to the total drug used during formulation (35).

Factors Affecting Entrapment Efficiency

• Polymer concentration
• Cross-linking density
• Drug solubility
• Preparation method

5.8 In Vitro Drug Release Studies

Drug release studies evaluate the release profile of encapsulated drugs under simulated physiological conditions. Commonly used dissolution media include phosphate buffer, simulated gastric fluid, and simulated intestinal fluid (36).

Objectives

• Determine release kinetics
• Predict in vivo behavior
• Optimize formulation performance

6. DRUG LOADING AND RELEASE MECHANISM

Drug loading and release are the fundamental functions of nanosponge-based drug delivery systems. The porous structure of nanosponges provides numerous cavities capable of entrapping active pharmaceutical ingredients and releasing them in a controlled manner (37).

6.1 Drug Loading Mechanism

Drug loading involves incorporation of drug molecules into nanosponge cavities through physical adsorption, inclusion complexation, diffusion, or molecular entrapment (38).

Steps in Drug Loading

Drug Solution

↓

Mixing with Nanosponges

↓

Drug Diffusion into Cavities

↓

Encapsulation

↓

Loaded Nanosponges

Factors Affecting Drug Loading

• Molecular size of drug
• Drug solubility
• Pore size of nanosponges
• Degree of cross-linking
• Drug-polymer affinity

6.2 Drug Release Mechanism

Drug release from nanosponges occurs through diffusion, desorption, erosion, swelling, or environmental stimuli. The release profile depends on the nature of the polymer, cross-linking density, and physicochemical properties of the drug (39).

Drug Release from Nanosponges

Drug Loaded

Nanosponges

↓

Penetration of Medium

↓

Drug Diffusion

↓

Controlled Release

↓

Therapeutic Action

6.3 Diffusion-Controlled Release

The majority of nanosponge systems release drugs by diffusion. After exposure to biological fluids, drug molecules gradually diffuse through nanosponge pores into the surrounding medium (40).

Advantages

• Sustained drug release
• Reduced dosing frequency
• Improved patient compliance

6.4 Stimuli-Responsive Release

Advanced nanosponges can release drugs in response to specific stimuli such as:

• pH changes
• Temperature
• Enzymes
• Redox conditions
• Light exposure

These systems provide site-specific and on-demand drug delivery (41,42)

7. Recent Advances in Nanosponge Technology

Nanosponges have emerged as one of the most promising nanocarrier systems due to their unique porous architecture, high drug-loading capacity, and ability to provide controlled and targeted drug delivery. Recent advances in nanosponge technology have focused on improving therapeutic efficacy, biocompatibility, targeting capability, and responsiveness to physiological stimuli. These developments have expanded the application of nanosponges beyond conventional drug delivery systems (43).

7.1 Stimuli-Responsive Nanosponges

Stimuli-responsive or "smart" nanosponges are designed to release drugs in response to specific environmental triggers such as pH, temperature, enzymes, redox potential, or light. These systems improve site-specific drug delivery and minimize adverse effects on healthy tissues (44).

Advantages

• Controlled drug release
• Improved therapeutic efficacy
• Reduced systemic toxicity
• Enhanced targeting efficiency

Table 10:. Types of Stimuli-Responsive Nanosponges

7.2 Targeted Nanosponge Systems

Surface-functionalized nanosponges have been developed for active targeting of specific tissues and cells. Ligands such as antibodies, peptides, folic acid, and aptamers are attached to the nanosponge surface to enhance cellular uptake and target specificity (45).

Benefits

• Increased drug accumulation at target site
• Reduced off-target effects
• Improved therapeutic outcomes

7.3 Hybrid Nanosponges

Hybrid nanosponges combine nanosponges with other nanocarriers such as liposomes, metallic nanoparticles, hydrogels, and polymeric nanoparticles. These hybrid systems integrate the advantages of multiple delivery platforms (46).

Applications

• Combination drug therapy
• Controlled release formulations
• Theranostic systems

7.4 Biodegradable Nanosponges

Recent research emphasizes biodegradable nanosponges prepared from natural and synthetic biodegradable polymers. These systems undergo degradation after drug release, minimizing long-term toxicity and environmental concerns (47).

Common Biodegradable Polymers

• Chitosan
• Gelatin
• Polycaprolactone
• Polylactic acid (PLA)
• PLGA

7.5 Nanosponges for Biological Molecules

Modern nanosponge systems are capable of delivering proteins, peptides, nucleic acids, and vaccines. Their porous structure protects sensitive biomolecules from enzymatic degradation and enhances bioavailability (48).

Table 11:. Recent Innovations in Nanosponge Technology

7.6 Nanosponges in Cancer Therapy

Advanced nanosponge formulations have demonstrated significant potential in cancer treatment through controlled release and targeted delivery of chemotherapeutic agents. These systems improve drug accumulation in tumor tissues while reducing systemic toxicity (49).

8. APPLICATIONS OF NANOSPONGES IN DRUG DELIVERY

Nanosponges have attracted considerable attention as versatile drug carriers due to their ability to encapsulate both hydrophilic and hydrophobic drugs. Their porous structure allows controlled release, improved stability, and enhanced bioavailability, making them suitable for various routes of administration (50).

8.1 Oral Drug Delivery

Oral administration is the most widely used route of drug delivery. Nanosponges improve the solubility and dissolution rate of poorly water-soluble drugs, thereby enhancing oral bioavailability (51).

Advantages

• Improved dissolution
• Enhanced gastrointestinal stability
• Sustained drug release
• Better patient compliance

Examples

• Itraconazole
• Curcumin
• Paclitaxel
• Resveratrol

8.2 Topical Drug Delivery

Nanosponges are extensively used in topical formulations such as creams, gels, lotions, and ointments. They provide sustained release of drugs at the skin surface and reduce local irritation (52).

Advantages

• Controlled drug release
• Improved skin retention
• Reduced irritation
• Enhanced patient compliance

Applications

• Acne treatment
• Antifungal therapy
• Anti-inflammatory therapy
• Wound healing

8.3 Ocular Drug Delivery

Ocular drug delivery remains challenging because of rapid tear turnover and limited corneal permeability. Nanosponge systems increase drug residence time on the ocular surface and improve drug penetration (53).

Advantages

• Prolonged precorneal retention
• Enhanced corneal permeation
• Reduced dosing frequency

Applications

• Glaucoma
• Conjunctivitis
• Dry eye syndrome
• Corneal infections

8.4 Pulmonary Drug Delivery

Nanosponges have demonstrated potential for pulmonary administration due to their small particle size and controlled-release characteristics. They enable direct delivery of drugs to the lungs, enhancing therapeutic effectiveness (54).

Advantages

• Rapid onset of action
• Reduced systemic exposure
• Improved lung targeting

Applications

• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Pulmonary infections
• Lung cancer

8.5 Parenteral Drug Delivery

Parenteral administration allows direct delivery of nanosponge formulations into systemic circulation. Nanosponges improve the stability of injectable drugs and facilitate targeted delivery to diseased tissues (55).

Advantages

• Immediate therapeutic effect
• Controlled systemic release
• Enhanced targeting capability

Applications

• Cancer chemotherapy
• Antibiotic delivery
• Peptide delivery
• Protein therapeutics

8.6 Future Direction of Drug Delivery Applications

The integration of nanosponges with advanced targeting strategies, nanotechnology, and personalized medicine is expected to further improve drug delivery efficiency. Future research is focused on multifunctional nanosponges capable of simultaneous diagnosis and therapy, often referred to as theranostic nanosponges (56).

9. THERAPEUTIC APPLICATIONS OF NANOSPONGES

Nanosponges have gained considerable attention in pharmaceutical research due to their ability to enhance drug solubility, stability, bioavailability, and targeted delivery. Their unique porous structure enables encapsulation of a wide range of therapeutic agents, making them suitable for the treatment of various diseases. Recent studies have demonstrated significant applications of nanosponges in cancer therapy, antimicrobial treatment, inflammatory disorders, and neurological diseases (57).

Figure 3: Application of Nanosponges

9.1 Cancer Therapy

Cancer remains one of the leading causes of mortality worldwide. Conventional chemotherapy often suffers from poor selectivity, systemic toxicity, and multidrug resistance. Nanosponge-based drug delivery systems have emerged as promising carriers for anticancer drugs due to their ability to provide controlled and targeted drug release (58).

Nanosponges can encapsulate chemotherapeutic agents such as paclitaxel, doxorubicin, camptothecin, and tamoxifen, improving their aqueous solubility and reducing adverse effects on healthy tissues. Surface-functionalized nanosponges further enhance tumor targeting through receptor-mediated uptake (59).

Benefits in Cancer Therapy

• Improved drug solubility
• Enhanced tumor targeting
• Sustained drug release
• Reduced systemic toxicity
• Improved therapeutic efficacy

Table 11: Anticancer Drugs Delivered Using Nanosponges

9.2 Antimicrobial Drug Delivery

The emergence of antimicrobial resistance has created a need for more effective drug delivery systems. Nanosponges improve the delivery of antibiotics, antifungal agents, and antiviral drugs by enhancing their stability and maintaining therapeutic concentrations for prolonged periods (60).

Encapsulation within nanosponges protects antimicrobial agents from degradation and improves penetration into infected tissues. This approach may reduce dosing frequency and minimize resistance development.

Applications

• Bacterial infections
• Fungal infections
• Viral diseases
• Biofilm-associated infections

Advantages

• Improved antimicrobial activity
• Enhanced drug stability
• Sustained release
• Reduced frequency of administration

Table 12:. Antimicrobial Applications of Nanosponges

9.3 Anti-inflammatory Drug Delivery

Inflammatory disorders require prolonged therapy, often associated with adverse effects due to repeated administration. Nanosponges offer controlled and localized drug delivery, reducing systemic exposure and improving therapeutic outcomes (61).

Anti-inflammatory drugs such as diclofenac, meloxicam, ibuprofen, and celecoxib have been successfully incorporated into nanosponge systems. Controlled drug release helps maintain therapeutic drug levels over extended periods.

Benefits

• Sustained anti-inflammatory action
• Reduced gastrointestinal side effects
• Improved patient compliance
• Enhanced local drug concentration

9.4 Neurological Disorders

Treatment of neurological diseases is often limited by the blood-brain barrier (BBB), which restricts drug penetration into the central nervous system. Nanosponges have shown potential in enhancing brain delivery of therapeutic agents through improved permeability and controlled release (62).

Nanosponge formulations have been investigated for the treatment of:

• Alzheimer's disease
• Parkinson's disease
• Epilepsy
• Brain tumors
• Neuroinflammatory disorders

Advantages in Neurological Therapy

• Improved BBB penetration
• Sustained drug release
• Enhanced bioavailability
• Reduced systemic toxicity

Table 13: Neurological Applications of Nanosponges

10. ADVANTAGES OF NANOSPONGES

Nanosponges possess several advantages over conventional drug delivery systems due to their unique porous structure and versatile drug-loading capabilities (63).

1. Enhanced Drug Solubility:Nanosponges improve the aqueous solubility of poorly water-soluble drugs through inclusion complex formation and molecular encapsulation.

2. Controlled and Sustained Release:The porous matrix allows gradual drug release, maintaining therapeutic drug concentrations for extended periods.

3. Improved Stability:Encapsulation protects drugs from hydrolysis, oxidation, photodegradation, and enzymatic degradation.

4. Reduced Toxicity:Targeted and controlled drug delivery minimizes exposure of healthy tissues to drugs, reducing adverse effects.

5. High Drug Loading Capacity:Large internal cavities facilitate efficient incorporation of therapeutic molecules.

6. Versatility: Nanosponges are versatile nanostructured carriers capable of encapsulating hydrophobic and hydrophilic drugs, proteins, peptides, anticancer agents, and antimicrobial agents.

11. Challenges and Limitations

Despite their numerous advantages, nanosponge systems face several challenges that limit their widespread clinical and commercial application (64).

11.1 Manufacturing Challenges:Large-scale production of nanosponges remains difficult due to complex synthesis procedures, reproducibility issues, and process optimization requirements.

11.2 Drug Loading Limitations:Not all drugs are suitable for nanosponge encapsulation. Drug loading depends on molecular size, polarity, and affinity toward the polymer matrix.

11.3 Toxicity Concerns:Although generally considered biocompatible, long-term toxicity and biodistribution studies remain limited for several nanosponge formulations.

11.4 Regulatory Challenges:The absence of standardized regulatory guidelines for nanosponge-based formulations delays product approval and commercialization.

11.5 Stability Issues:Certain nanosponge formulations may experience aggregation, particle growth, or drug leakage during storage.

11.6 Cost of Production:Advanced preparation methods and specialized characterization techniques increase manufacturing costs.

12. Future Perspectives

Nanosponge technology has emerged as a versatile and promising platform in advanced drug delivery. Although significant progress has been made in recent years, continuous innovations in material science, nanotechnology, biotechnology, and pharmaceutical engineering are expected to further expand the scope of nanosponges in clinical medicine. Future research is directed toward developing safer, smarter, and more efficient nanosponge systems capable of overcoming current limitations and addressing unmet therapeutic needs (65)

Figure 4 : Future presepective of Nanosponge