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Biosurfactants are amphipathic molecules that can be applied in a wide range of areas. The cost of production limits the industrial application of biosurfactants. Nevertheless, the biosurfactant productivity can be easily enhanced by inducers. This work aimed to investigate the effect of hydrophobic inducers on surfactin production by B. subtilis ATCC 6633 using cassava wastewater as low-cost culture medium. The submerged cultivation was carried out at 30 °C, 150 rpm for 72 h. The fermentation parameters used were bacterial growth, consumption of sugars, and surfactin production, including surfactin homologues. The surface tension decreased by 40% after 12 h, when compared to control. Depletion of sugars was observed in all experiments. Palmitic acid led to the highest yield in terms of surfactin production (≈ 1.3 g·L- 1 of pure surfactin). The inducers triggered the production of new surfactin homologues, that represent, potentially, new biological activities.

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The global production of cassava was estimated at ca. 303 million tons. Due to this high production, the cassava processing industry (cassava flour and starch) generates approximately ca. 0.65 kg of solid residue and ca. 25.3 l of wastewater per kg of fresh processed cassava root. The composition of the liquid effluent varies according to its origin; for example, the effluent from cassava flour production, when compared to the wastewater from the starch processing, presents a higher organic load (ca. 12 times) and total cyanide (ca. 29 times). It is worthy to highlight the toxicity of cassava residues regarding cyanide presence, which could generate disorders with acute or chronic symptoms in humans and animals. In this sense, the development of simple and low-cost eco-friendly methods for the proper treatment or reuse of cassava wastewater is a challenging, but promising path. Cassava wastewater is rich in macro-nutrients (proteins, starch, sugars) and micro-nutrients (iron, magnesium), enabling its use as a low-cost culture medium for biotechnological processes, such as the production of biosurfactants. These compounds are amphipathic molecules synthesized by living cells and can be widely used in industries as pharmaceutical agents, for microbial-enhanced oil recovery, among others. Amongst these biosurfactants, surfactin, rhamnolipids, and mannosileritritol lipids show remarkable properties such as antimicrobial, biodegradability, demulsifying and emulsifying capacity. However, the high production cost restricts the massive biosurfactant applications. Therefore, this study aims to present the state of the art and challenges in the production of biosurfactants using cassava wastewater as an alternative culture medium.

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Biosurfactants can be widely used in industries as pharmaceutical agents, for microbial enhanced oil recovery, crop biostimulation, among others. Surfactin and rhamnolipids are well-known biosurfactants. These compounds have several advantages over chemical surfactants, however they are not economically competitive, since their production cost is up to 12 times higher than chemical surfactants. In this sense, an interesting approach is to replace synthetic culture medium, which represents ≈ 30% of the production cost by agro-industrial wastes. In addition, biosurfactant productivity can be easily enhanced by inductor supplementation into culture medium that triggers biosurfactant metabolism. Biosurfactant inducers are mainly a pool of hydrophobic molecules (e.g. olive oil-saturated and unsaturated fatty acids, proteins and vitamins). Nevertheless, there is little information on inducer effects of specific molecules (e.g. oleic acid). In general, hydrophobic inducers lead to higher fatty acid chain lengths (biosurfactant chemical structure). Therefore, the aim of this review was to critically discuss the current state of the art and future trends on biosurfactant production, in particular biosurfactant inducers. Taking into account the last 10 years, there is a clear lack of information on correlation between "inducers" or "hydrophobic inducers" AND "biosurfactants", since only 13 documents were found (Scopus database). Thus, it is essential to deeply investigate all inducer effects on biosurfactant production, mainly yield and chemical structure.

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The development of nanovehicles for intracellular drug delivery is strongly bound to the understating and control of nanoparticles cellular uptake process, which in turn is governed by surface chemistry. In this study, we explored the synthesis, characterization, and cellular uptake of block copolymer assemblies consisting of a pH-responsive poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) core stabilized by three different biocompatible hydrophilic shells (a zwitterionic type poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) layer, a highly hydrated poly(ethylene oxide) (PEO) layer with stealth effect, and an also proven nontoxic and nonimmunogenic poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) layer). All particles had a spherical core-shell structure. The largest particles with the thickest hydrophilic stabilizing shell obtained from PMPC40-b-PDPA70 were internalized to a higher level than those smaller in size and stabilized by PEO or PHPMA and produced from PEO122-b-PDPA43 or PHPMA64-b-PDPA72, respectively. Such a behavior was confirmed among different cell lines, with assemblies being internalized to a higher degree in cancer (HeLa) as compared to healthy (Telo-RF) cells. This fact was mainly attributed to the stronger binding of PMPC to cell membranes. Therefore, cellular uptake of nanoparticles at the sub-100 nm size range may be chiefly governed by the chemical nature of the stabilizing layer rather than particles size and/or shell thickness.

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The prospective use of the block copolymers poly(ethylene oxide)113-b-poly[2-(diethylamino)ethyl methacrylate]50 (PEO113-b-PDEA50) and poly[oligo(ethylene glycol)methyl ether methacrylate]70-b-poly[oligo(ethylene glycol)methyl ether methacrylate10-co-2-(diethylamino)ethyl methacrylate47-co-2-(diisopropylamino)ethyl methacrylate47] (POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47)) as nonviral gene vectors was evaluated. The polymers are able to properly condense DNA into nanosized particles (RH ≈ 75 nm), which are marginally cytotoxic and can be uptaken by cells. However, the green fluorescent protein (GFP) expression assays evidenced that DNA delivery is essentially negligible meaning that intracellular trafficking hampers efficient gene release. Subsequently, we demonstrate that cellular uptake and particularly the quantity of GFP-positive cells are substantially enhanced when the block copolymer polyplexes are produced and further supplemented by BPEI chains (branched polyethylenimine). The dynamic light scattering/electrophoretic light scattering/isothermal titration calorimetry data suggest that such a strategy allows the adsorption of BPEI onto the surface of the polyplexes, and this phenomenon is responsible for increasing the size and surface charge of the assemblies. Nevertheless, most of the BPEI chains remain freely diffusing in the systems. The biological assays confirmed that cellular uptake is enhanced in the presence of BPEI and principally, the free highly charged polymer chains play the central role in intracellular trafficking and gene transfection. These investigations pointed out that the transfection efficiency versus cytotoxicity issue can be balanced by a mixture of BPEI and less cytotoxic agents such as for instance the proposed block copolymers.

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The intracellular delivery of nucleic acids requires a vector system as they cannot diffuse across lipid membranes. Although polymeric transfecting agents have been extensively investigated, none of the proposed gene delivery vehicles fulfill all of the requirements needed for an effective therapy, namely, the ability to bind and compact DNA into polyplexes, stability in the serum environment, endosome-disrupting capacity, efficient intracellular DNA release, and low toxicity. The challenges are mainly attributed to conflicting properties such as stability vs efficient DNA release and toxicity vs efficient endosome-disrupting capacity. Accordingly, investigations aimed at safe and efficient therapies are still essential to achieving gene therapy clinical success. Taking into account the mentioned issues, herein we have evaluated the DNA condensation ability of poly(ethylene oxide)113-b-poly[2-(diisopropylamino)ethyl methacrylate]50 (PEO113-b-PDPA50), poly(ethylene oxide)113-b-poly[2-(diethylamino)ethyl methacrylate]50 (PEO113-b-PDEA50), poly[oligo(ethylene glycol)methyl ether methacrylate]70-b-poly[oligo(ethylene glycol)methyl ether methacrylate10-co-2-(diethylamino)ethyl methacrylate47-co-2-(diisopropylamino)ethyl methacrylate47] (POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47), and poly[oligo(ethylene glycol)methyl ether methacrylate]70-b-poly{oligo(ethylene glycol)methyl ether methacrylate10-co-2-methylacrylic acid 2-[(2-(dimethylamino)ethyl)methylamino]ethyl ester44} (POEGMA70-b-P(OEGMA10-co-DAMA44). Block copolymers PEO113-b-PDEA50 and POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47) were evidenced to properly condense DNA into particles with a desirable size for cellular uptake via endocytic pathways (R(H) ≈ 65-85 nm). The structure of the polyplexes was characterized in detail by scattering techniques and atomic force microscopy. The isothermal titration calorimetric data revealed that the polymer/DNA binding is endothermic; therefore, the process in entropically driven. The combination of results supports that POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47) condenses DNA more efficiently and with higher thermodynamic outputs than does PEO113-b-PDEA50. Finally, circular dichroism spectroscopy indicated that the conformation of DNA remained the same after complexation and that the polyplexes are very stable in the serum environment.

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A set of seven different palladium nanoparticle (PdNP) systems stabilized by small amounts (1.0mg/mL) of structurally related macromolecular capping agents were comparatively tested as catalyst in p-nitrophenol (Nip) reduction and Suzuki cross-coupling reactions. The observed rate constants (kobs) for Nip reduction were in the range of 0.052-3.120×10(-2)s(-1), and the variation reflected the effects of polymer chain conformation, ionic strength and palladium-polymer complex coordination. Macromolecules featuring pendant pyridyl moieties or inverse temperature-dependent solubility were found to be unsuitable capping agents for PdNPs catalysts, despite being active. The catalytic activity in Suzuki cross-coupling reactions followed the same behavior; the most active particles in the Nip reaction also mediated the cross-coupling reaction providing the expected products in quantitative yields under relatively mild conditions after only 4h at 50°C. Experiments involving the successive addition of reactants and catalyst recovery/re-use indicated that the recycling potential was comparable to those of the standards used in this field.

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The single-step/single-phase synthesis of hybrid organic-inorganic core-shell gold nanoparticles (AuNPs), facilitated by amino-functionalized amphiphilic block copolymers that simultaneously play the roles of reductant and stabilizer, was investigated in this study. Experiments were devised with emphasis on the pH-responsive poly(ethylene oxide)-b-poly(2,3-dihydroxypropyl methacrylate)-b-poly[2-(diisopropylamino)ethyl methacrylate] triblock copolymer, which allows direct chemical cross-linking of the micellar structures to be performed. The polymer structure-reactivity relationship associated with the AuNP formation was established using a set of six structurally related macromolecules. AuNP formation was dependent on the aqueous dissociation equilibrium involving tertiary amino groups, the Au(III) speciation, and electrochemical redox potentials. The effects of these parameters on the synthesis of AuNPs change as the solution pH is increased from pH 3.3 (molecularly dissolved polymer chains; no AuNP formation) to 6.8 or higher (polymer chains self-assembled into spherical micelles; stable gold sols are produced), and Au(III) reduction potentials shift toward the cathodic region while the oxidation potential of deprotonated amino groups decreases. Sigmoidal nanoparticle growth kinetics was observed in all cases after a characteristic induction period. Stable, well-defined, uniform polymer-coated gold colloids with localized surface plasmon resonance centered at 53 0nm can be conveniently produced in one-pot, two-reactant, no work-up reactions when the stoichiometry is [N]/[Au]=3.5-25.0.

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The development of organic solvent-free methods for the encapsulation of hydrophobic molecules is necessary for advances in micelle-mediated drug delivery. In this study we investigated the film/contact approach in which the use of organic solvents is limited to the preparation of a dry film before encapsulation. Unloaded micelles of five structurally related block copolymers were placed in contact with thin homogeneous films of two hydrophobic triazene anticancer compounds (1-(4-amidophenyl)-3-(4-acetylphenyl)triazene (1) and corresponding triazenido complex with triphenylphosphanegold(I) fragment (2)). The micelle surface becomes saturated with the drug, which eventually penetrates as a front into the core. Because the drug interacts with both the shell and the core microenvironments of micelle during the process, the maximum loading capacities were very sensitive to block copolymer micelle composition, ranging from 2.2 to 20.4% (wt./wt. of polymer). We conclude that micelles with poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) cores are the best option for the encapsulation of triazene compounds because i) they are prepared in absence of organic phase; ii) the drug concentration in the particles is high enough for a therapeutic effect and iii) the responsiveness properties of PDPA is appropriate for practical applications in pH-triggered drug release systems.

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Selective protein fouling on block copolymer micelles with well-known potential for tumour-targeting drug delivery was evidenced by using dynamic light scattering measurements. The stability and interaction of block copolymer micelles with model proteins (BSA, IgG, lysozyme and CytC) is reported for systems featuring a hydrophobic (poly[2-(diisopropylamino)-ethyl methacrylate]) (PDPA) core and hydrophilic coronas comprising poly(ethylene oxide)/poly(glycerol monomethacrylate) (PEO-b-PG2MA) or poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC). The results revealed that protein size and hydrophilic chain density play important roles in the observed interactions. The PEO(113)-b-PG2MA(30)-b-PDPA(50) nanoparticles are stable and protein adsorption is prevented at all investigated protein environments. The successful protein-repellent characteristic of these nanoparticles is attributed to a high hydrophilic surface chain density (>0.1 chains per nm(2)) and to the length of the hydrophilic chains. On the other hand, although PMPC also has protein-repellent characteristics, the low surface chain density of the hydrophilic shell is supposed to enable interactions with small proteins. The PMPC(40)-b-PDPA(70) micelles are stable in BSA and IgG environments due to weak repulsion forces between PMPC and the proteins, to the hydration layer, and particularly to a size-effect where the large BSA (R(H) = 4.2 nm) and IgG (R(H) = 7.0 nm) do not easily diffuse within the PMPC shell. Conversely, a clear interaction was observed with the 2.1 nm radius lysozyme. The lysozyme protein can diffuse within the PMPC micellar shell towards the PDPA hydrophobic core in a process favored by its smaller size and the low hydrophilic PMPC surface chain density (∼0.049 chains per nm(2)) as compared to PEO-b-PG2MA (∼0.110 chains per nm(2)). The same behavior was not evidenced with the 2.3 nm radius positively charged CytC, probably due to its higher surface hydrophilicity and the consequent chemical incompatibility with PDPA.

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The internal structure of polystyrene(PS)-shell micelles having core-forming blocks consisting of polydimethylsiloxane (PDMS) or poly[5-(N,N-diethylamino)isoprene] (PAI) was determined in detail by accessing the multilevel structural organization using static and dynamic light scattering and small-angle X-ray scattering techniques. Well-defined PS-b-PDMS and PS-b-PAI diblock copolymers with molar masses in the range of 12.0k-18.2k g/mol were dispersed in cyclohexane, dimethylacetamide, or dimethylformamide. Colloidal nanoparticles exhibiting either swollen core with a large surface area per corona chain that enables the PS chains to assume a random coil conformation with gaussian statistics, or compact core and slightly stretched PS chains in the corona were obtained. Therefore, the results of this study provide an interesting alternative allowing for precise control of the core and corona properties of PS-b-PDMS and PS-b-PAI micelles in selective solvents. Admittedly, such differences in terms of micellar properties can dictate the potential of block copolymer micelles for generating thin films from preformed nano-objects, as well as the capability to function as nanoreactors in organic medium.

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Recent advances in the field of macromolecular engineering applied to the fabrication of nanostructured materials using block copolymer chains as elementary building blocks are described in this feature article. By highlighting some of our work in the area and accounting for the contribution of other groups, we discuss the relationship between the physical-chemical properties of copolymer chains and the characteristics of nano-objects originating from their self-assembly in solution and in bulk, with emphasis on convenient strategies that allow for the control of composition, functionality, and topology at different levels of sophistication. In the case of micellar nanoparticles in solution, in particular, we present approaches leading to morphology selection via macromolecular architectural design, the functionalization of external solvent-philic shells with biomolecules (polysaccharides and proteins), and the maximization of micelle loading capacity by the suitable choice of solvent-phobic polymer segments. The fabrication of nanomaterials mediated by thin block copolymer films is also discussed. In this case, we emphasize the development of novel polymer chain manipulation strategies that ultimately allow for the preparation of precisely positioned nanodomains with a reduced number of defects via block-selective chemical reactivity. The challenges facing the soft matter community, the urgent demand to convert huge public and private investments into consumer products, and future possible directions in the field are also considered herein.

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The self-assembly of linear poly(ethylene oxide)-b-poly(glycerol monomethacrylate)-b-poly[2-(diisopropylamino)ethyl methacrylate] (PEO-b-PG2MA-b-PDPA) triblock copolymer into pH-responsive cross-linkable nanostructures in both organic and aqueous media is reported. Light scattering (LS), electron transmission microscopy (TEM), and nuclear magnetic resonance spectroscopy (NMR) techniques revealed that spherical particles with a core-shell architecture originated upon direct copolymer dissolution in THF, with PG2MA middle blocks occupying the nucleus, and PEO + PDPA segments forming the external layer. The hydroxylated core could be conveniently reticulated to form core cross-linked (CCL) micelles, which swelled without dissociating in presence of water at pH < pK(a) of amino groups. In the absence of stabilizing mechanisms (cross-links), the aggregates first disassembled in response to changes in the solvent selectivity due to water addition and eventually self-assembled again into spherical particles with a three-layered core-shell-corona structure. While pH-responsive PDPA segments were located at the core, PG2MA and PEO blocks composed the inner shell and corona, respectively. The interactions that facilitate micelle existence were reinforced by covalent cross-links in the PG2MA inner shell. Thus, depending on both the solution pH and the presence of cross-links, micelles exhibiting either pH-triggered or diffusion-controlled release mechanisms could be prepared. The encapsulation of enough amounts of guest molecules that interact strongly with the core-forming block led to the formation of cylindrical micelles. These results demonstrate that at least five different types of aggregates can be prepared from this versatile triblock copolymer, thus emphasizing the great potential of combining macromolecular design and sample manipulation strategies to devise functional nanostructures.

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