Ana Lima

Production methodologies of polymeric and hydrogel particles for drug delivery applications

Introduction: Polymeric particles are ideal vehicles for controlled delivery applications due to their ability to encapsulate a variety of substances, namely low- and high-molecular mass therapeutics, antigens or DNA. Micro and nano scale spherical materials have been developed as carriers for therapies, using appropriated methodologies, in order to achieve a prolonged and controlled drug administration. Areas covered: This paper reviews the methodologies used for the production of polymeric micro/nanoparticles. Emulsions, phase separation, spray drying, ionic gelation, polyelectrolyte complexation and supercritical fluids precipitation are all widely used processes for polymeric micro/nanoencapsulation. This paper also discusses the recent developments and patents reported in this field. Other less conventional methodologies are also described, such as the use of superhydrophobic substrates to produce hydrogel and polymeric particulate biomaterials. Expert opinion: Polymeric drug delivery systems have gained increased importance due to the need for improving the efficiency and versatility of existing therapies. This allows the development of innovative concepts that could create more efficient systems, which in turn may address many healthcare needs worldwide. The existing methods to produce polymeric release systems have some critical drawbacks, which compromise the efficiency of these techniques. Improvements and development of new methodologies could be achieved by using multidisciplinary approaches and tools taken from other subjects, including nanotechnologies, biomimetics, tissue engineering, polymer science or microfluidics.

Synthesis of temperature-responsive Dextran-MA/PNIPAAm particles for controlled drug delivery using superhydrophobic surfaces

ABSTRACTPurposeTo implement a bioinspired methodology using superhydrophobic surfaces suitable for producing smart hydrogel beads in which the bioactive substance is introduced in the particles during their formation.Methods Several superhydrophobic surfaces, including polystyrene, aluminum and copper, were prepared. Polymeric solutions composed by photo-crosslinked dextran-methacrylated and thermal responsive poly(N-isopropylacrylamide) mixed with a protein (insulin or albumin) were dropped on the superhydrophobic surfaces, and the obtained millimetric spheres were hardened in a dry environment under UV light.ResultsSpherical and non-sticky hydrogels particles were formed in few minutes on the superhydrophobic surfaces. The proteins included in the liquid formulation were homogeneously distributed in the particle network. The particles exhibited temperature-sensitive swelling, porosity and protein release rate, with the responsiveness tunable by the dextran-MA/PNIPAAm weight ratio.ConclusionsThe proposed method permitted the preparation of smart hydrogel particles in one step with almost 100% encapsulation yield. The temperature-sensitive release profiles suggest that the obtained spherical-shaped biomaterials are suitable as protein carriers. These stimuli-responsive beads could have potential to be used in pharmaceutical or other biomedical applications, including tissue engineering and regenerative medicine.

Bioinspired methodology to fabricate hydrogel spheres for multi-applications using superhydrophobic substrates

Inspired by the rolling of water drops over the lotus leaf, we propose a new biomimetic fabrication process for hydrogel and polymeric spheres over a superhydrophobic substrate. This method may be potentially applied in tissue engineering or as support for cell expansion, cell encapsulation and as spherical structures for controlled release of molecule.

Biomimetic Methodology to Produce Polymeric Multilayered Particles for Biotechnological and Biomedical Applications

The authors acknowledge the financial support from Fundacao para a Ciencia e Tecnologia (FCT) through the PhD grants SFRH/BD/71395/2010 and SFRH/BD/61390/2009, Fundo Social Europeu (FSE) and Programa Operacional Potencial Humano (POPH) Portugal, and MICINN (SAF2011-22771 and PRI-AIBPT-2011-1211) Spain.

Micro/nano-structured superhydrophobic surfaces in the biomedical field: part II: applications overview

The properties of surfaces define the acceptance and integration of biomaterials in vivo, as well as the materials efficiency when used at research or manufacturing levels. The presence of micro/nano-topographical structures and low surface energies could bring several advantages when highly repellent surfaces are employed in the biomedical field. Biomimetic superhydrophobic surfaces have been explored for diverse applications: as an intrinsic characteristic of biomaterials to be implanted; as materials that exhibit special interactions with biological entities; or to be used in ex vivo applications. This article aims to focus on the main motivations and requirements in the biomedical field that pushed for the utilization of superhydrophobic surfaces as suitable alternatives, as well as the great evolution of applications that have emerged in the last few years.

Pectin-coated chitosan microgels crosslinked on superhydrophobic surfaces for 5-fluorouracil encapsulation

5-Fluorouracil (5-FU)-loaded chitosan microgels for oral and topical chemotherapy were prepared applying a superhydrophobic surface-based encapsulation technology. Drug-loaded chitosan dispersions were cross-linked and then coated with drug-free chitosan or pectin layers at the solid-air interface in a highly efficient and environment-friendly way. The size of the microgels (with diameters of ca. 280 and 557 μm for the chitosan seeds and pectin-coated microgels respectively) was the lowest obtained until now using similar biomimetic methodologies. The microgels were characterized regarding 5-FU release profiles in vitro in aqueous media covering the pH range of the gastrointestinal tract, and cytotoxicity against two cancer cell lines sensitive to 5-FU. Owing to their control of 5-FU release in acidic medium, calcium pectinate-coated microgels can be considered as suitable for oral administration. Growth inhibition of cancer cells by 5-FU was greater when incorporated to chitosan microgels; these being potentially useful for treatment of skin and colorectal tumors.

Saccharomyces cerevisiae glycerol/H+ symporter Stl1p is essential for cold/near-freeze and freeze stress adaptation. A simple recipe with high biotechnological potential is given

BackgroundFreezing is an increasingly important means of preservation and storage of microbial strains used for many types of industrial applications including food processing. However, the yeast mechanisms of tolerance and sensitivity to freeze or near-freeze stress are still poorly understood. More knowledge on this regard would improve their biotechnological potential. Glycerol, in particular intracellular glycerol, has been assigned as a cryoprotectant, also important for cold/near-freeze stress adaptation. The S. cerevisiae glycerol active transporter Stl1p plays an important role on the fast accumulation of glycerol. This gene is expressed under gluconeogenic conditions, under osmotic shock and stress, as well as under high temperatures.ResultsWe found that cells grown on STL1 induction medium (YPGE) and subjected to cold/near-freeze stress, displayed an extremely high expression of this gene, also visible at glycerol/H+ symporter activity level. Under the same conditions, the strains harbouring this transporter accumulated more than 400 mM glycerol, whereas the glycerol/H+ symporter mutant presented less than 1 mM. Consistently, the strains able to accumulate glycerol survive 25-50% more than the stl1Δ mutant.ConclusionsIn this work, we report the contribution of the glycerol/H+ symporter Stl1p for the accumulation and maintenance of glycerol intracellular levels, and consequently cell survival at cold/near-freeze and freeze temperatures. These findings have a high biotechnological impact, as they show that any S. cerevisiae strain already in use can become more resistant to cold/freeze-thaw stress just by simply adding glycerol to the broth. The combination of low temperatures with extracellular glycerol will induce the transporter Stl1p. This solution avoids the use of transgenic strains, in particular in food industry.

Micro-/nano-structured superhydrophobic surfaces in the biomedical field: part I: basic concepts and biomimetic approaches

Inspired by natural structures, great attention has been devoted to the study and development of surfaces with extreme wettable properties. The meticulous study of natural systems revealed that the micro/nano-topography of the surface is critical to obtaining unique wettability features, including superhydrophobicity. However, the surface chemistry also has an important role in such surface characteristics. As the interaction of biomaterials with the biological milieu occurs at the surface of the materials, it is expected that synthetic substrates with extreme and controllable wettability ranging from superhydrophilic to superhydrophobic regimes could bring about the possibility of new investigations of cell-material interactions on nonconventional surfaces and the development of alternative devices with biomedical utility. This first part of the review will describe in detail how proteins and cells interact with micro/nano-structured surfaces exhibiting extreme wettabilities.

Free and copolymerized γ-cyclodextrins regulate the performance of dexamethasone-loaded dextran microspheres for bone regeneration

Polymeric particles acting as sources of biological cues to promote tissue regeneration are currently an interesting topic in bone tissue engineering research. In this study, microspheres of dextran-methacrylate (dextran-MA) and γ-cyclodextrins (γ-CD) for the delivery of osteogenic agents were prepared by means of photopolymerization on biomimetic superhydrophobic surfaces. The effects of the incorporation of the γ-CD units as free entities or as structural monomers (acrylamidomethyl-γ-cyclodextrin, γ-CD-NMA) on dexamethasone loading and release performance were evaluated in detail in order to achieve osteogenic differentiation of human stem cells. The copolymerization of dextran-MA with γ-CD-NMA improved the loading capacity of the particles and also provided a sustained release of dexamethasone for several days. The biological studies revealed that such microspheres were cytocompatible and capable of inducing the differentiation of human adipose-derived stem cells (hASCs) to osteoblasts, as determined from an increase of alkaline phosphatase (ALP) activity between days 3 and 7. Such results were also confirmed using ALP staining. Therefore, immobilization of γ-CDs onto the dextran-MA network may be particularly useful for the development of cytocompatible implantable spherical biomaterials for bone tissue engineering purposes.

Sequential ionic and thermogelation of chitosan spherical hydrogels prepared using superhydrophobic surfaces to immobilize cells and drugs

Chitosan is soluble in acidic media, which makes it incompatible for the encapsulation of cells and pH-sensitive molecules. In this work, a mild chitosan-based system with two sequential gelation steps is proposed, where the model drug dexamethasone and L929 cells are immobilized inside hydrogel beads. Superhydrophobic surfaces were used to produce the spherical hydrogel particles that provided favorable conditions to encapsulate cells or bioactive agents. First, the chitosan acidic solution was neutralized with β-glycerophosphate at room temperature to pH 6.2. Suspended cells (or dexamethasone) in the formulation were dispensed in controlled volumes onto biomimetic polystyrene superhydrophobic surfaces, to form spherical shapes. The addition of sodium tripolyphosphate on the top of each sphere induced an ionic gelation process of the chitosan through electrostatic interactions. At 37°C, the hydrophobicity of the chitosan-based formulations increased and a second gelation step occurred, which increased the elastic modulus. In addition, the pH-responsive behavior characteristic of chitosan was maintained. The softness and flexibility of the system can potentially be utilized to implant cells and therapeutic molecules using less invasive procedures.