1. Introduction
The discovery of new bioactive molecules holds significant importance for combating numerous diseases and infections. Among them, in recent years, the research has been focused particularly on the identification of molecules of natural origin [
1,
2,
3,
4]. Biosurfactants (BSs), or tensio-active biomolecules, are the product of biosynthesis of a great number of different microorganisms, from bacteria (
Acinetobacter,
Bacillus, and
Pseudomonas) to filamentous fungi (
Aspergillus,
Fusarium,
Penicillium,
Trichoderma,
Ustilago) and yeast (
Kluyveromyces,
Pseudozyma,
Rhodotorula,
Torulopsis,
Saccharomyces,
Candida), among others in addition to some animals and plants [
5,
6,
7,
8,
9]. They can be released extracellularly or be located on cellular cell surfaces. The type and output of the produced biosurfactant are usually species-specific and depends on the substrate used for the microbial growth and their environmental production conditions [
10]. They are produced primarily as secondary metabolites and can play important roles in localization, survival and growth of the producing microorganisms, such as motility, metabolism, attachment/detachment to surfaces, defence from microbial antagonists, biofilm production and backdown and resistance to toxic compounds [
11,
12].
These mixture surface-active molecules are composed structurally by a hydrophobic tail (unsaturated or saturated fatty acids hydrocarbon chains) and a hydrophilic head (peptide cations, or anions or mono-, di-, or polysaccharides), and are able to form micelles (
Figure 1).
For this amphipathic nature and unique structural arrangement, biosurfactants display various physicochemical properties such as excellent surface activity, effective critical micelle concentration and the ability to form microemulsions, humectant, foaming and cleaning activity (
Figure 2) [
13,
14].
In addition, several biosurfactants have other interesting biological properties such as strong antibacterial, antifungal, and antiviral activity as well as antioxidant, anticancer and immunomodulatory activities [
12,
15,
16].
For these reasons, in the last two decades, microbial surfactants have been extensively studied, industrially produced and, thanks to their various commercial attractions, applied in many fields worldwide ranging from paint to petroleum, detergents to water treatment, food to pharmaceutics, cosmetics and biomedicine [
10,
15,
17,
18].
Unfortunately, their large-scale production currently is disadvantageous and is mainly constrained by the high costs related to their downstream processes (over 60-80% of the total costs), such as long and difficult separation and purification steps that are required for some specific applications (e.g., pharmaceutical) [
19,
20,
21,
22]. However, it is believed that the implementation of some alternative strategies such as the selection of new microorganism producers from renewable substrates, such as waste from agro-food processing and the dairy industry, from vegetable oils and animal fat together with the improvement of fermentation, extraction and purification techniques can increase their commercial potential [
22,
23,
24].
In 2022, the biosurfactant global market reached USD 1.2 billion. This is forecast to have a compound annual growth rate (CAGR) of 11.2%, increasing to USD 1.9 billion by 2027 [
25].
This increase reflects the general attitude worldwide in encouraging the use of nonharmful and eco-friendly products. In fact, for their potential benefits, in recent years, biosurfactants have boomed as an perfect alternative for the chemically synthesised surfactant. Compared to chemical surfactants, biosurfactants have several interesting features and advantages which include biodegradability, high specificity, low toxicity, tolerance to extreme conditions, higher efficiency and an environment-friendly nature [
17,
24,
26]. In addition, their chemical composition can be modified through genetic engineering manipulation as well as metabolic end products alteration of the producing strains using biotechnological and biochemical techniques to tailor them to specific functional requirements [
27,
28].
Biosurfactants are typically classified based on their microbial origin and their chemical structure (
Figure 3) [
29].
They are mainly categorised into two major classes: low molecular weight molecules which comprise lipopeptides, glycolipids, fatty acids and high molecular weight which comprise polymers and particulates materials [
10,
11,
12].
The low molecular weight biosurfactants lower both surface and interfacial tensions at the surfaces, whereas the later are typically highly efficient in stabilising emulsions [
14,
30].
Lipopeptides and glycolipids represent the most promising types of biosurfactants for pharmaceutical, therapeutic, and biotechnological industries [
31,
32,
33].
Numerous reviews and books have been dedicated to the production, characterization, and application of biosurfactants in diverse fields [
34,
35,
36,
37]. However, special attention should be paid to the potential and real use of these molecules in the biomedical and pharmaceutical fields.
The main objective of this review is to present a comprehensive update on the latest advancements, research findings, and insights into how biosurfactants can be utilized in the pharmaceutical and biomedical fields, building upon the previous literature output [
12]. By examining the recent literature, primarily within the past couple of years, this review aims to shed light on the current state of knowledge and identify emerging trends or promising directions in the application of biosurfactants in the pharmaceutical and biomedical sectors. Particular attention will be directed towards the latest and cutting-edge applications of biosurfactants, with a particular focus on areas such as innovative coatings, drug and gene delivery, wound healing and anticancer. By examining the most recent advancements in the field, this review will shed light on the innovative uses of biosurfactants and their potential in improving the efficacy of drugs and conventional treatments.
2. Biosurfactants: A Real Prospect for biomedical and pharmaceutical use?
The discovery and selection of bioactive molecules is one of the main challenges of the modern era in the fight against many diseases and infections. Biosurfactants are very valuable and important products for possible biomedical and pharmaceutical applications (
Figure 4) and especially, lipopeptides and glycolipids are of particular interest. They are characterised by antibacterial, antifungal and antiviral activities, in addition to anticancer, immunological and neurological properties. They are also able to increase in the electrical conductance of bimolecular lipid membranes and the inhibition of fibrin clot formation. Moreover, their ability to decrease surface tensions between immiscible or miscible liquids, blocking hydrogen-bonding and augmenting hydrophilic/hydrophobic interactions, they can be used as antiadhesive/antibiofilm agents on medical devices and applications in transplantation [
36,
38]. Furthermore, BSs are not only applied to enhance some physical-chemical properties of some pharmaceutical formulations but also to improve the efficacy and performance of these pharmaceutical products. In synergy with nanotechnology, BSs also plays essential roles in the development of micro/nano-based drug delivery systems, self-emulsifying drug delivery systems (SEDDS) and liposomes, controlling the particle size and the stability or solubility of drugs in liquid, semi-solid, and solid formulations [
39].
It should be remembered that some biosurfactants can be produced by pathogenic microorganisms such as
Pseudomonads aeruginosa and their biosynthesis is related to the potential pathogenicity of the producing strain/s and, for these reasons, precautions are essential to avoid allergic reactions and potential skin irritations [
34].
Finally, despite their extensive range of applications, it is essential to thoroughly assess the safety of each biosurfactant before considering using it within clinical application., A limited number of studies conducted on animal models to investigate their
in vivo toxicity and biological activities however highlighted significant challenges in utilising them as therapeutic agents [
40,
41].
A recent study by Rana et al. (2021) evaluated the toxicity of polymeric nanoparticles loaded with a novel biosurfactant product from
Candida parapsilosis in a rodent model. Biochemical, haematological, and histopathological evaluations. The findings indicated that there were no noteworthy variations in haematological parameters between the control and treated groups and only minor, yet not significant, alterations in biochemical parameters. In addition, no toxicological characteristics were observed in the tissue samples, suggesting that the biosurfactant encapsulated within PLA-PEG copolymeric nanoparticles presents a secure and suitable platform for potential biomedical applications [
41]. Other recent toxicity profile testing for rhamnolipid BSs produced by
Marinobacter and
Pseudomonas strains showed no cytotoxicity using
in vitro models of human liver and skin cells and no mutagenic/anti-mutagenic potential or significant antioxidant capabilities [
42].
Adu et al. (2023) very recently reported on the safety and lack of cytotoxicity of sophorolipids and rhamnolipids (RLs) BSs which showed insignificant effects on human keratinocyte cell line morphology, viability and the production of pro-inflammatory cytokines and potential for use in skincare applications [
43].
3. Biosurfactants for innovative coatings
It is well known that indwelling medical devices are widely used in the healthcare industry and have significantly contributed to improve the treatment of multiple pathologies and the quality of life of patients. However, they can constitute a favourable substrate for the adhesion and growth of microorganisms as biofilms, which are one of the main causes of healthcare-associated infections [
44]. In contact with human body fluids, implants are rapidly covered by a conditioning film (composed of proteins, other organic molecules and ions) that attracts microorganisms. After deposition, microbial cells adhere to surfaces, forming micro-colonies that grows as complex communities embedded within an exopolysaccharide matrix. In their sessile form, microbial cells acquire a typical physiological state, becoming more resistant to host defence mechanisms and up to 1000-fold less susceptible to various antimicrobial agents [
45].
One of the most appealing applications of biosurfactants is their use as coating agents in order to prevent biofilm formation on medical devices. They can be utilised to create thin, uniform films on various surfaces, providing numerous benefits, such as enhanced wetting and reduced surface tension, impairing microbial adhesion (
Figure 5). With ongoing research and advancements in biosurfactant production and formulation techniques, surface coating methods (such as physical adsorption, bulk incorporation or covalent grafting) have been proposed and used to attach these molecules on a wide range of materials. Moreover, biosurfactant-based coatings exhibit excellent biocompatibility and biodegradability, making them attractive alternatives to conventional synthetic coatings [
46,
47,
48].
In a recent work by Kannan et al. (2021), liposomes encapsulated with a lipopeptide produced by the human skin bacterium
Paenibacillus thiaminolyticus and copper oxide nanoparticles were able to strongly interfere with Methicillin-resistant
Staphylococcus aureus (MRSA) and
Pseudomonas aeruginosa biofilm formation on urinary catheters. EL-LP-CuNPs possessed a marked antibacterial activity with Minimal Inhibitory Concentrations (MICs) of 105 μg/mL (for MRSA) and 89 μg/mL (for
P. aeruginosa), stimulated reactive oxygen species (ROS) production and accumulation, decreased carotenoid synthesis and exopolysaccharides secretion as well as induced a profound collapse of the cell arrangement and severe destruction on cell walls [
49]. The same year, different type of biosurfactants (rhamnolipids, sophorolipids and lipopeptides) were used as anti-adhesive molecules to counteract the colonisation of medical grade silicone by a cell combination of
Staphylococcus spp. and
Candida albicans cultures. The BSs coating films, obtained by physical adsorption, significantly limited microbial adhesion, and markedly inhibited the formation of the dual species biofilms in a range from 74% to 95% up to 3 days, while reducing their cell viability, metabolic activity and biomass yield at the same time and thus kept silicone surfaces free from microbial contamination, as was confirmed by SEM observations [
50]. In another study by Cheffi et al. (2021), lipopeptides Bios-PHKT produced by a
Halomonas venusta strain isolated from contaminated seawater showed an interesting antiadhesive activity towards Gram-negative and Gram-positive human pathogens due to the electrostatic repulsion between the BSs coating films on the polystyrene surfaces and bacterial cells. The inhibition of cell adhesion increased in function of Bios-PHKT concentration reaching a near-constant level from 0.5 mg/mL onwards, with a maximum of effect against
Escherichia coli (72.3% reduction in cell biomass) [
51].
Very recently, rhamnolipids were employed by Sharaf et al. (2022) for the preparation of biosurfactant-coated iron oxide nanoparticles as a innovative multitarget approach to combat some food-borne
Escherichia coli serotypes and MRSA. In particular, the antibiofilm and antiadhesive properties of rhamnolipids coated Fe
3O
4 nanoparticles (NPs) were combined with two antimicrobial drugs, gallic acid (GA) and p-coumaric acid (p-CoA). The biosurfactant-coated iron oxide nanoparticles (RHL-Fe
3O
4@PVA@p-CoA/G) significantly interfered with growth and significantly limited biofilm formation downregulating operon I
caABCD, responsible for the formation of the slime layer in
S. aureus, and
CsgBAC, responsible for the production of curli fimbriae
E. coli [
52]. In another study, a glycopeptide biosurfactant produced by
Lactobacillus delbrueckii alpha2 was applied at different concentrations (from 2.5 mg/mL to 25 mg/mL) on polystyrene surfaces for the evaluation of its antiadhesive potential against four pathogenic strains (
Klebsiella spp.,
Bacillus spp.,
S. aureus,
E. coli, and
Pseudomonas spp.) with percentages of inhibition ranging from 56% to 71% at 25 mg/mL concentration. In addition, the authors demonstrated that a glycoprotein-coating of medical grade silicone tubes was effective in preventing the growth of
S. aureus and E. coli biofilms [
53].
In this year, Findose et al. (2023) evaluated the protective effect of a rhamnolipids coating against the attachment and the formation of biofilms in ESKAPE pathogens such as
Acinetobacter baumannii and
Enterococcus faecium. The pre-treatment of 96-well plates with BSs prevented the deposition and adhesion of bacterial cells on surfaces in a concentration-dependent and strain-dependent manner with the most significant results at concentration of 31.2 μg/mL for
E. faecium with a reduction of 91% and at 250 μg/mL for
Ac. baumannii with a reduction of 76% [
54].
Section 6 elucidates a collection of recently patented and ground-breaking methodologies utilised for the functionalization of biomaterials with biosurfactants, as evidence of the strong scientific interest in these anti-adhesive coatings.
6. Utilizing biosurfactants as adjuvants in medicine: drug delivery systems
Drug delivery systems play a crucial role in pharmaceutical and medicinal sciences, serving as formulations or devices/vehicles that enable controlled administration and release of the active ingredients to specific parts of the body, via various routes depending on the desired effect and the nature of the disease, thereby enhancing efficiency and safety [
38]. These numerous advantages offered by these systems include optimal drug loading capacity without loss of the drug, aqueous solubility and improvement in bioavailability as well as facilitated and controlled transport of the active substance across membranes to the intended site, maximizing efficacy [
125]. Nanoparticles, nanoemulsions, microemulsions and liposomes are distinct types of drug delivery systems utilized in various medical applications. Nanoparticles are dispersed particulates or solid particles that have a size range of 10-1000nm. They can be prepared as nanospheres, or nanocapsules. Nanoparticles have been used in various treatment strategies, including drug delivery, due to their unique physical properties, their potential use in controlled release and their ability to protect drugs or other molecules with biological activity against their neighbouring environment, improves their bioavailability and therapeutic index [
126].
Nanoemulsions and microemulsions are therefore colloidal systems composed of oil, water, and surfactants. They have small droplet sizes and can enhance drug solubility and stability [
127]. Liposomes are vesicles formed by hydrating a mixture of cholesterol and phospholipids. They improve drug efficacy by delaying clearance from the circulation system and protecting the drug from their biological environment [
128].
Biosurfactants can be employed in drug delivery due to their unique surface-active properties and benefits. Overall, the use of biosurfactants in drug delivery holds promise for improving drug solubility, achieving controlled release, ensuring biocompatibility, providing protection, and enabling targeted delivery. These advantages make biosurfactants attractive candidates for developing innovative and efficient drug delivery systems.
An investigation on the effect of two biosurfactants (BS) produced by
Lactobacillus gasseri BC9 and
Lactobacillus crispatus BC1 and on the skin permeation profile of hydrocortisone (HC). Both BSs increased the solubility of HC particularly at concentrations above their critical micellar concentrations (CMC). At concentrations below the CMC, drug permeation through the skin was improved due to the formation of a superficial lipophilic environment and the interaction between BS and the stratum corneum (SC). When skin hydration tests and differential scanning calorimetry (DSC) analysis were carried out to further investigate BS interaction with the outermost layer of the skin the data showed that both BS products may be considered as new promising green excipients for drug permeation enhancement through the skin [
129]. In another study by the same research group to explore the potential of
L. gasseri BC9 biosurfactant as natural excipients to enhance the hydrocortisone solubility and nasal delivery and its mucoadhesive properties at concentrations both below and above the CMC. Diffusion studies performed using sheep nasal mucosa with BC9-BS at a concentration below the CMC indicated that BC9-BS interacted with the nasal mucosa components, leading to increased drug solubilization and permeation at lower concentrations and suggesting that BC9-BS has a potential as a promising alternative to chemical surfactants for nasal drug delivery applications [
130]. Lipopeptides produced by
Bacillus velezensis showed antibacterial activity on the surface of both vegetative cells and spores. Strains with the highest levels of activity also exhibited detectable lipopeptide micelles, which were heat and gastric stable and able to entrap other antimicrobials produced by the host bacterium itself. In addition, the naturally produced micelle formulations were able to entrap other antimicrobial compounds, such as vancomycin, resveratrol and clindamycin, and the incorporation of antibiotics into micelles increased their activity, suggesting their potential use to enhance drug delivery [
131]. In a study by Lassenberger et al. (2021), silk-based composite hydrogels incorporating anionic biosurfactant assemblies (sophorolipids SL-C18:0 and SL-C18:1) were generated to enhance the properties of silk fibroin. The inclusion of sophorolipids assemblies accelerated the gelation of silk fibroin suggesting promising potential for improving the functionality and mechanical properties of SF-based hydrogels. These advancements present exciting opportunities for controlled cell culture applications, tissue engineering, and drug delivery [
132].
Interestingly, sophorolipids have also been used as green delivery carriers to create scalable, cost-effective, and environmentally friendly nanopesticide systems for agronomic applications [
133].
6.1. Nanoparticles
Biosurfactants have emerged as highly promising candidates for the development and synthesis of eco-friendly bioactive nanoparticles, thereby replacing synthetic surfactants. Numerous studies in recent years have described the use of biosurfactants as substitutes for conventional surfactants in the field of nanoparticle synthesis, exhibiting significant promise for applications in biomedical science, including antimicrobial activity, drug delivery, controlled release, anticancer activity [
86,
134,
135,
136,
137,
138].
6.1.1. Nanoparticles with antibacterial activity
The utilisation of biosurfactants for the production of nanoparticles with antibacterial activity offers a promising avenue in nanotechnology and biomedical applications. On the one hand biosurfactant-based nanoparticles have demonstrated a great potential in combating bacterial infections, as they can efficiently target and destroy bacterial cells through multiple mechanisms. Biosurfactants can act as stabilisers, reducing agents, and templates in the synthesis of nanoparticles, enabling precise control over their size, shape, and surface properties. On the other hand, the internalisation into the metal nanoparticles contributes to a further increase in the antimicrobial activity of BSs, enhancing their biodistribution and limiting unfavourable interactions with unspecific targets. For example, in Chauhan et al. (2022) lipopeptides OXDC12 silver-nanoparticles possessed remarkable antibacterial activities against Gram-negative
Salmonella typhimurium,
Klebsiella pneumnoniae and
E. coli strains, with MIC values lower than the lipopeptides mixture alone [
139]. In 2020, Shikha and collaborators developed a gold nanoparticles (AuNps) green synthesis using sophorolipids (SL) as non-toxic reducing and stabilising agent and demonstrated the higher efficacy of the obtained AuNPs-SL in inhibiting the metabolic activity of viable Gram-negative
Vibrio cholerae and
E. coli cells as well as in killing
V. cholerae in its non-multiplying stage, compared to AuNPs or SL alone. In addition, authors showed that the bactericidal activity of AuNPs-SL on
V. cholerae cells was attributable to inhibiting the respiratory chain dehydrogenases or inducing morphological changes that led to cell membrane disruption and intracellular fluid leakage [
140]. In another study rhamnolipids were applied to synthesise CuO nanoparticles to counteract multi-drug-resistant pathogens. RL-CuO NPs showed an excellent antibacterial activity both against Gram-positive strains, such as
Streptococcus mutans,
S. aureus,
Enterococcus faecalis and Gram-negative strains, such as
Shigella dysentriae and
Salmonella typhi with MIC values at concentrations around 7.8 µg/mL and 250 µg/mL respectively, demonstrating that RL and CuO NPs can combine their activities in synergy increasing cell membrane permeability and promoting bacterial cell inactivation [
141].
In recent a work by Falakaflaki et al. (2022), a cryogel nanocomposite scaffold enriched with the antimicrobial agent usnic acid encapsulated in rhamnolipid (RH) biosurfactant nanoparticles were designed with dual purpose for antimicrobial activity against
Staphylococcus aureus biofilm and bone regeneration. Rhamnolipid biosurfactant in the preparation of nanovesicles improved usnic acid solubility and enhanced the antimicrobial effects of the drug. In particular, the biocompatible usnic acid/rhamnolipid containing cryogel scaffolds had an osteogenic effect and an increase in expression of bone repair markers was detected by RT-PCR. Strong antibacterial effects of the scaffold on
S. aureus, with an inhibition zone of 1.4 ± 0.2 cm, and antibiofilm activity of 43.7 ± 1.6% were demonstrated [
142].
6.1.2. Nanoparticles for drug delivery
Numerous investigations have been carried out on the application of rhamnolipids or lipopeptides in nanoparticles’ stabilisation for their use in the drug delivery field, with particular interest toward cancer therapy and transdermal administration.
For example, Müller et al. (2017) used several rhamnolipids as nano-carriers for different hydrophobic drugs like dexamethasone, Nile red, or tacrolimus to skin delivery in
ex vivo studies and demonstrated that rhamnolipids nanoparticles efficiently deliver Nile red into the skin without causing toxic effects at concentrations higher than CMC values [
143]. In a paper by Lewińska et al (2022), poly(D,L-lactide) nanoparticles stabilised by surfactin were developed for potential administration transdermally. The nanoprecipitation approach was used to obtain nanoparticles. Skin permeability tests obtained on pig ear skin proved the enhanced ability of nanoparticles to penetrate deeper into the epidermis, demonstrating the suitability of surfactin-stabilised poly(D,L-lactide) nanoparticles as biocompatible options for transdermal applications [
144].
As for cancer therapy applications, in 2019, rhamnolipids nanoparticles loaded with hydrophobic photosensitizer were injected into the SCC7 cancer bearing mice. Interestingly, nanoparticles promoted both a significant accumulation of “pheophorbide a” into the targeted tissue and cancer suppression by photody-namic-therapy [
145]. In 2020, the lipopeptide from
Acinetobacter junii B6 was used to produce gold nanoparticles, which cytotoxic activity against U87, A549 and MCF7 cancer cell lines was dose dependant with IC50 values of 89.08 ± 0.4 μg/mL, 646.12 ± 0.5 μg/mL and 3.37 ± 0.1 μg/mL [
146]. Another study explored the possibility to use rhamnolipids for the preparation of double emulsion nanoparticles (NP) containing doxorubicin and erlotinib (RL-NP-DOX-ER) as a drug delivery system for a combination therapy, to provide efficient drug delivery to tumour tissue with a synergistic effect. The double emulsion method enabled simultaneous loading of hydrophilic doxorubicin and hydrophobic erlotinib in the NPs, and biosurfactants provided stable surface coating. The resulting nanoparticles demonstrated rapid cellular uptake and synergistic killing of tumour cells. Notably, RL-NP-DOX-ERL exhibited enhanced tumour suppression compared to control groups treated with free drugs or nanoparticles containing a single drug, highlighting the potential of double emulsion nanoparticles and rhamnolipid coating for efficient tumour combination therapy [
147].
In the work proposed by Wadhawan et al. (2022), a novel biosurfactant isolated from
C. parapsilosis loaded into polymeric nanoparticles was investigated as a promising therapeutic system against MDA-MB-231 breast cancer cells. The nanoparticles were prepared using a polymer material called PLA-PEG (polylactic acid-polyethylene glycol), which contained BS concentrations ranging from 1.25 to 20 μg/ml, and compared with pure nanoparticles without biosurfactant and nanoparticles conjugated with folic acid (FA) to targeting cancer cells. The formulation with folic acid showed maximal internalization and superior cytotoxicity compared to non-targeted formulations against MDA-MB-231 cells. In addition, this formulation was observed to induce apoptosis in the breast cancer cell line, thereby killing the cancer cells. It is important to note that these results were specific to the MDA-MB-231 breast cancer cell line used in the study and further studies would be required to determine the cytotoxic and apoptotic effects of the biosurfactant-loaded nanoparticles in other cancer cell lines or
in vivo models [
148].
6.2. Microemulsions and nanoemulsions
Micro- and nanoemulsions are dispersed systems extensively utilized for effective and precise drug delivery via different administration routes. Interestingly, the disparity between micro- and nanoemulsions is not solely determined by their size scale, as the names imply, as both systems can contain droplets with diameters below 100 nm. The primary distinction between these systems lies in the method of achieving droplet size: nanoemulsions involve a mechanical reduction process, whereas microemulsions form spontaneously [
149]. A microemulsion delivery system based on commercial biosurfactant sophorolipids (SLs) was developed to improve the solubility and stability of Xanthohumol, a compound with numerous physiological activities such as antioxidant, antimicrobial, anticancer, anti-inflammatory, anti-osteoporosis, and neuroprotective. The SL-based microemulsion system increased the solubility of Xanthohumol by about 4000 times and extended its half-life to over 150 days, making it a potential green solubilization and delivery method for Xanthohumol and other hydrophobic drugs [
150].
In a study published in 2022, submicron emulsions (ESEs) loaded with etoposide, a traditional anticancer chemotherapeutic agent, were prepared using lactonic sophorolipid (LSL) and acidic sophorolipid (ASL), compared to the chemical surfactant Tween-80. Results showed that ASL exhibited superior properties and activities compared to LSL and Tween-80 in ESE formation. The ASL-ESE demonstrated higher drug loading capacity and slower drug release rate. It also significantly increased antitumour activity against the ovarian cancer cell line A2780 through apoptosis when compared to Tween-ESE and commercial etoposide injections. Additionally, ASL-ESE showed no haemolysis and displayed comparable long-term and autoclaving stability to Tween-ESE, suggesting the exceptional capabilities of ASL in ESE formation, efficacy enhancement, and safety improvement [
151].
Stable oil-in-water nanoemulsions were prepared combining different biosurfactants (plant-derived saponin and microbial rhamnolipid and surfactin) using high-energy ultrasonication techniques. The rhamnolipid-surfactin system formed a more stable nanoemulsion compared to the combinations rhamnolipid-saponin and surfactin-saponin. The study suggested that the optimal synergy between mixed-biosurfactants at the oil-water interface leading to stable nanoemulsion is primarily dictated by the type and composition of the biosurfactants used in the formulation. In addition, antimicrobial and scavenging investigations of stable nanoemulsions revealed that two-biosurfactant systems showed comparable efficacies to single biosurfactant nanoemulsions [
152].
In another work, rhamnolipids were used in combination with tea-tree oil to develop a biocompatible nanoformulation to deliver the herbal drug tanshinone-IIA (TSIIA) which is used for the treatment of acute lung injury (ALI), a severe condition often observed in COVID-19 patients. The nanoemulsion (NE) was optimised using ultrasound, and its efficacy was evaluated in an ALI model induced by lipopolysaccharide. Compared to free medication and blank-NE, TSIIA-NE demonstrated superior efficacy. Furthermore, the loading of TSIIA into the nanoemulsion formulation potentially amplified this effect, possibly due to the inherent pharmacological activities of tea-tree oil and rhamnolipids, as well as the improved
in vivo performance of the nanoformulation [
153].
In a study by Kubendiran et al. (2021) a natural biosurfactant extracted from
Lactobacillus casei (MT012285) was used to develop a biosurfactant-based nano-topical ointment for wound treatment using a blend of
Tridax procumbens infused oil and gelatine-stabilised silver nanoparticles. The prepared ointment exhibited potent antimicrobial activity against clinical pathogens, including
S. aureus,
E. coli,
P. aeruginosa, and
K. pneumoniae minimal haemolytic effects on red blood cells and low cytotoxicity on L929 fibroblastic cell lines. A wound scratch assay revealed a cell migration rate of 62% within 24 hours, suggesting potential for topical wound treatment [
154].
6.3. Liposomes
Biosurfactants have been increasingly utilised in the preparation of liposomes, which are lipid-based nanoparticles used for drug delivery and various biomedical applications, to replace PEG-lipid that may cause hypersensitivity reactions [
155]. Glycolipids, such as rhamnolipids, in particular, can be employed to develop liposomes, as demonstrated with rhamnolipid-modified curcumin-loaded liposomes [
156]. By incorporating biosurfactants into liposome formulations, several advantages can be achieved. Firstly, biosurfactants can enhance the stability and integrity of liposomes, optimise drug delivery efficiency, improve their shelf life, and prevent aggregation [
143,
155,
156]. Furthermore, biosurfactants can enhance the biocompatibility and biodegradability of liposomes, reducing potential toxic effects [
156]. In a recently published study from 2022, researchers explored the use of sophorolipids for the modification of liposomes containing the nutraceutical drug pipeline. The study highlights the effectiveness of sophorolipids in enhancing the stability and dispersion of the liposomal formulation, while also improving the drug loading efficiency [
155].
7. Patents in the biomedical and pharmaceutical fields incorporating biosurfactants
Patents related to the usage of biosurfactants in biomedical, pharmaceutical and related fields have been widely issued, indicating the growing interest and recognition of their therapeutic and functional properties. These patents cover a range of topics, such as the formulation of biosurfactants as antimicrobial, antibiofilm and coating agents, for drug delivery systems, their use in improving the stability and bioavailability of pharmaceuticals, and their application in the synthesis and modification of nanoparticles for targeted therapies.
As confirmation of the interesting antiadhesive and antibiofilm activities of biosurfactants, several methodologies have been patented to covalently bind these molecules to surfaces of various nature in order to prevent biofouling. The broad applicability and versatility of these natural surfactants extend their antiadhesive applications beyond the biomedical field, encompassing all sectors where microbial proliferation needs to be combated (ranging from agriculture and food industries to maritime transportation). In relation to applications employed to tackle microbial infection associated with the use of medical devices, methodologies for covalently linking biosurfactants to different materials have been described. A patent issued in 2022 describes protocols for coating polymeric and metallic materials with biosurfactants from
Pseudomonas aeruginosa,
Bacillus amyloliquefaciens and
Serratia marcescens to inhibit biofilm formation by surface oxidation and the use of silane linkers [
157]. In the same year, another patent was granted describing methods for coating medical devices with irregular and/or curved silicone surfaces via rhamnolipids grafting. This method involves different steps such as another Brazilian patent describing a surfactin production process by isolates of
Bacillus subtilis ATCC 19659 with anti-adhesive and antimicrobial properties against biofilm-forming pathogens on silicone-coated latex pieces [
158].
Very recently a patent concerning albofungin from
Sterptomyces chrestomyceticus BCC 24770 issued as copolymer coating to inhibit fouling by marine microorganisms has demonstrated antibiofilm activity also against ESKAPE bacteria [
159]. In 2022, a patent was issued regarding medical devices, including voice prostheses, with irregular and/or curved silicone surfaces coated with rhamnolipids for the prevention or reduction of biofilm formation on the surface of the medical device. The method described involves surface functionalization of silicone using atmospheric or vacuum plasma discharge of argon with (3-Aminopropyl)triethoxysilane (APTES) or cyclopropylamine, followed by covalent grafting of rhamnolipids using carbodiimide chemistry. Covalent grafting of rhamnolipids on APTES modified silicone surfaces allowed to maintain the anti-biofilm activity up to 72 hours with 80% reduction of
C. albicans biofilm and more than 90% of
S. aureus biofilm [
160].
Another invention provides constituents and methods for treating, preventing, or disrupting biofilms formation on surfaces and in various bodily locations. The compositions utilize biological amphiphilic molecules produced by microorganisms (such as glycolipids, lipopeptides, flavolipids, phospholipids, fatty acid ether compounds, , fatty acid ester compounds, and high molecular weight polymers), which can be combined with other biocidal substances such as antibiotics or essential oils to attack and weaken the bacterial biofilm matrix, through enhancing the penetration of the biocidal substance. Such methods can be used to treat or prevent biofilm-related infections in various sites of the body and can also be applied to inert surfaces to inhibit the proliferation of biofilm-forming microbes [
161]. Another Brazilian invention describes the production of surfactin by
Bacillus subtilis isolates with anti-adhesive and antimicrobial properties against biofilm-forming isolates such as
S. aureus,
S. epidermidis and
E. coli on stainless steel and titanium parts used in orthopaedic procedures [
162]. A recent patent published in 2023 describes a method utilizing an extract containing biosurfactants derived from a bacterium, such as
Bacillus,
Streptomyces,
Mycobacterium,
Micrococcus,
Rhodococcus,
Pseudomonas,
Arthrobacter, or
Staphylococcus, as an effective antimicrobial agent against foodborne or plant bacterial or fungal pathogens [
163].
In recent years, there has been growing interest in the use of probiotics that also possess the ability to produce biosurfactants. Patents have been filed to explore the potential of probiotics producing biosurfactants in improving health and wellbeing. By harnessing the synergistic effects of probiotics and biosurfactants, these patents aim to provide novel solutions for a wide range of health concerns, such as enhancement of innate barrier functions in various areas of the body, inhibition of pathogenic biofilm growth and adhesion, promotion of commensal biofilm growth, treatment and prevention of fungal infections, improvement of skin microbiome health, amelioration of skin barrier damage and inflammation, particularly in the context of inflammatory skin diseases like atopic dermatitis, psoriasis, and acne [
164,
165,
166,
167,
168].
As described in section 5, biosurfactants have gained significant attention in the field of drug delivery, leading to their utilization in various patents. Overall, the incorporation of biosurfactants in patents for drug delivery holds great potential for improving therapeutic outcomes and expanding the possibilities of pharmaceutical formulations. A recently issued patent involves the development of nanostructured drug formulations that enhance both the effectiveness and bioavailability of the drugs, particularly in cancer treatment. These formulations utilize biosurfactants derived from microbial sources, replacing synthetic surfactants, to enhance the safety and efficacy of chemotherapy [
169]. Another patent issued in 2023, provides a method for improving the penetration of a therapeutic agent into a microbial biofilm via the administration of a cavitation enhancing agent, followed by the exposure of the biofilm to at least one therapeutic agent. In this patent, it was demonstrated that rhamnolipids in combination with antibiotics has potent activity against persister cells and recalcitrant populations including anaerobically growing cells, non-respiring cells and small colony variants [
170]. A patent issued in 2021 describes a combination treatment of rhamnolipid and niclosamide for non-alcoholic fatty liver disease, nonalcoholic steatohepatitis, including liver cirrhosis, and type 2 diabetes mellitus. By combining rhamnolipids with niclosamide, the water solubility of niclosamide is enhanced, leading to an increase in its oral bioavailability [
171].
Biosurfactants have also emerged as valuable ingredients in the cosmetic field, offering unique properties and benefits for skincare, haircare, and personal care products. Topical therapeutic compositions that utilize microbial biosurfactants have been patented for enhanced wound healing, scar reduction, and improvement of various skin conditions. These compositions and methods have been developed to reduce healing time for skin wounds, diminish the appearance of scars, and provide benefits for conditions like acne, psoriasis, and eczema [
172]. In another patent, natural nano- or micro-emulsions containing rhamnolipids, mannosylerythritol lipids and the methods for producing them have been described for the treatment of the skin, hair follicles, and related conditions as well as for the treatment of skin and hair pigmentation [
173]. Cosmetic compositions and detergents containing biosurfactants have also been recently patented as environmental-friendly alternatives to cosmetic compositions based on non-renewable resources that may contain microplastic [
174,
175].