Electrospun nanofibers of a degradable poly(ester amide). Scaffolds loaded with antimicrobial agents

A Color Indicator Based on 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide (MTT) and a Biodegradable Poly(ester amide) for Detecting Bacterial Contamination

Bacterial contamination is a hazard in many industries, including food, pharmaceuticals, and healthcare. The availability of a rapid and simple method for detecting this type of contamination in sterile areas enables immediate intervention to avoid or reduce detrimental effects. Among these methods, colorimetric indicators are becoming increasingly popular due to their affordability, ease of use, and quick visual interpretation of the signal. In this article, a bacterial contamination indicator system was designed by incorporating MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) into an electrospun PADAS matrix, which is a biodegradable poly(ester amide) synthesized from L-alanine, 1,12-dodecanediol, and sebacic acid. Uniaxial stress testing, thermogravimetric analysis and scanning electron microscopy were used to examine the mechanical properties, thermal stability, and morphology of the mats, respectively. The capacity for bacterial detection was not only analyzed with agar and broth assays but also by replicating important environmental conditions. Among the MTT concentrations tested in this study (0.2%, 2%, and 5%), it was found that only with a 2% MTT content the designed system produced a color response visible to the naked eye with optimal intensity, a sensitivity limit of 104 CFU/mL, and 86% cell viability, which showed the great potential for its use to detect bacterial contamination. In summary, by means of the process described in this work, it was possible to obtain a simple, low-cost and fast-response bacterial contamination indicator that can be used in mask filters, air filters, or protective clothing.

Amorphous solid dispersions of curcumin in a poly(ester amide): Antiplasticizing effect on the glass transition and macromolecular relaxation dynamics, and controlled release

In order to exploit the pharmacological potential of natural bioactive molecules with low water solubility, such as curcumin, it is necessary to develop formulations, such as amorphous polymer dispersions, which allow a constant release rate and at the same time avoid possible toxicity effects of the crystalline form of the molecule under scrutiny. In this study, polymer dispersions of curcumin were obtained in PADAS, a biodegradable semicrystalline copolymer based on 1,12-dodecanediol, sebacic acid and alanine. The dispersions were fully characterized by means of differential scanning calorimetry and broadband dielectric spectroscopy, and the drug release profile was measured in a simulated body fluid. Amorphous homogeneous binary dispersions were obtained for curcumin mass fraction between 30 and 50%. Curcumin has significantly higher glass transition temperature Tg (≈ 347 K) than the polymer matrix (≈274-277 K depending on the molecular weight), and dispersions displayed Tg's intermediate between those of the pure amorphous components, implying that curcumin acts as an effective antiplasticizer for PADAS. Dielectric spectroscopy was employed to assess the relaxation dynamics of the binary dispersion with 30 wt% curcumin, as well as that of each (amorphous) component separately. The binary dispersion was characterized by a single structural relaxation, a single Johari-Goldstein process, and two local intramolecular processes, one for each component. Interestingly, the latter processes scaled with the Tg of the sample, indicating that they are viscosity-sensitive. In addition, both the pristine polymer and the dispersion exhibited an interfacial Maxwell-Wagner relaxation, likely due to spatial heterogeneities associated with phase disproportionation in this polymer. The release of curcumin from the dispersion in a simulated body fluid followed a Fickian diffusion profile, and 51% of the initial curcumin content was released in 48 h.

Dual-Function Fibrous Co-Polypeptide Scaffolds for Neural Tissue Engineering

This paper reports dual-function (high cell attachment and cell viability) fibrous scaffolds featuring aligned fibers, displaying good biocompatibility and no cytotoxicity. These scaffolds are fabricated through the electrospinning of a co-polypeptide comprising molar equivalents of N₆ -carbobenzyloxy-l-lysine and γ-benzyl-l-glutamate, with the lysine moieties enhancing cell adhesion and the neural-stimulating glutamate moieties improving cell viability. These new scaffolds allow neural cells to attach and grow effectively without any special surface treatment or coating. Pheochromocytoma (PC-12) cells grown on these scaffolds exhibit better neuronal activity and longer neurite length, relative to those grown on scaffolds prepared from their respective homo-polypeptides. When the scaffolds are partially hydrolyzed such that they present net positive charge and increased hydrophilicity, the cell viability and neurite growth both increase further. Accordingly, these novel co-polypeptide fibrous scaffolds have potential applications in neural tissue engineering.

Peptide-Based Electrospun Fibers: Current Status and Emerging Developments

Electrospinning is a well-known, straightforward, and versatile technique, widely used for the preparation of fibers by electrifying a polymer solution. However, a high molecular weight is not essential for obtaining uniform electrospun fibers; in fact, the primary criterion to succeed is the presence of sufficient intermolecular interactions, which function similar to chain entanglements. Some small molecules able to self-assemble have been electrospun from solution into fibers and, among them, peptides containing both natural and non-natural amino acids are of particular relevance. Nowadays, the use of peptides for this purpose is at an early stage, but it is gaining more and more interest, and we are now witnessing the transition from basic research towards applications. Considering the novelty in the relevant processing, the aim of this review is to analyze the state of the art from the early 2000s on. Moreover, advantages and drawbacks in using peptides as the main or sole component for generating electrospun nanofibers will be discussed. Characterization techniques that are specifically targeted to the produced peptide fibers are presented.

Ceiba pentandra cellulose crosslinked with citric acid for drug release systems

An alternative for the production of drug delivery system is proposed based on the Ceiba pentandra milkweed. The kapok cellulose was chemically crosslinked with citric acid (CA) at different CA proportions, and loaded with chlorhexidine diacetate (CHX) at different concentrations. Cellulose crosslinking was followed with FTIR and XPS analysis, and the CHX loading was determined using elemental analysis. In vitro studies showed a burst release within the first 2-3 h and the drug release kinetics was described with several models. In addition, the crosslinked Ceiba pentandra fibers did not exhibit a cytotoxic effect on human dermic fibroblasts. Results indicate that the crosslinked Ceiba pentandra fibers are a feasible material for the production of systems for drug release applications.

Modification of Ceiba pentandra cellulose for drug release applications

Tubular fibers (raw and wax-free) from Ceiba pentandra (CP) were cross-linked with butane-1,2,3,4-tetracarboxylic acid (BTCA) at different concentrations to obtain a porous biodegradable medium for drug release applications. Chlorhexidine diacetate (CHX) was added to the cross-linked fibers for drug release studies. The Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy results indicated that the cross-linked fibers with a 5:1 fiber:BTCA ratio presented the higher cross-linking density. CHX was added at different concentrations (8% and 16% wt/wt); the elemental analysis indicated that CHX was loaded up to 7.99 wt%. In vitro studies showed a burst release of CHX within the first 3 h. CHX release kinetics was described using several models, with the Korsmeyer–Peppas equation, which adjusted better to the experimental data. The results indicated that the CP fibers are a feasible material for drug release applications.

Electrospun poly(lactic acid) fibers containing novel chlorhexidine particles with sustained antibacterial activity

The treatment of persistent infections often requires a high local drug concentration and sustained release of antimicrobial agents. This paper proposes the use of novel electrospinning of poly(lactic acid) (PLA) fibers containing uncoated and encapsulated chlorhexidine particles. Chlorhexidine particles with a mean (SD) diameter of 17.15 ± 1.99 μm were fabricated by the precipitation of chlorhexidine diacetate with calcium chloride. Layer-by-layer (LbL) encapsulation of the chlorhexidine particles was carried out to produce encapsulated particles. The chlorhexidine particles had a high chlorhexidine content (90%), and when they were electrospun into PLA fibers a bead-in-string structure was obtained. The chlorhexidine content in the fibers could be tuned and a sustained release over 650 h was produced, via chlorhexidine particle encapsulation. Chlorhexidine release was governed by the polyelectrolyte multilayer encapsulation as demonstrated by SEM and confocal imaging. The incorporation of uncoated and encapsulated chlorhexidine particles (0.5% and 1% wt/wt chlorhexidine) into the fibers did not cause toxicity to healthy fibroblasts or affect cell adhesion to the fibers over a period of 5 days. The chlorhexidine-containing fibers also demonstrated sustained antibacterial activity against E. coli via an agar diffusion assay and broth transfer assay. Therefore, the chlorhexidine-containing PLA fibers may be useful in the treatment of persistent infections in medicine and dentistry.

Application of a Biodegradable Polyesteramide Derived from L-Alanine as Novel Excipient for Controlled Release Matrix Tablets

This pre-formulation study assays the capacity of the polyesteramide PADAS, poly (L-alanine-dodecanediol-L-alanine-sebacic), as an insoluble tablet excipient matrix for prolonged drug release. The flow properties of PADAS were suitable for tableting, and the compressibility of tablets containing exclusively PADAS was evaluated by ESEM observation of the microstructure. The tablets were resistant to crushing and non-friable and they did not undergo disintegration (typical features of an inert matrix). Tablets containing 33.33% sodium diclofenac (DF), ketoprofen (K) or dexketoprofen trometamol (DK-T) as a model drug, in addition with 66.67% of polymer, were formulated, and the absence of interactions between the components was confirmed by differential scanning calorimetry. Dissolution tests showed that PADAS retained DF and K and prolonged drug release, following a Higuchi kinetic. The tablets containing DK-T did not retain the drug sufficiently for prolonged release to be established. Tablets containing DK-T and 66.67, 83.33 or 91.67% PADAS, compressed at 44.48 or 88.96 kN, were elaborated to determine the influence of the polymer amount and of the compression force on DK-T release. Both parameters significantly delayed drug release, except when the proportion of polymer was 91.67%.

Poly(ester amide)s: recent insights into synthesis, stability and biomedical applications

Recent progress in polyesteramides, which are important polymers that can combine the properties of polyesters and polyamides, is described with a focus on synthesis and their application as biomaterials.

New poly(ester urea) derived from L-leucine: electrospun scaffolds loaded with antibacterial drugs and enzymes

Electrospun scaffolds from an amino acid containing poly(ester urea) (PEU) were developed as promising materials in the biomedical field and specifically in tissue engineering applications. The selected poly(ester urea) was obtained with a high yield and molecular weight by reaction of phosgene with a bis(α-aminoacyl)-α,ω-diol-diester monomer. The polymer having L-leucine, 1,6-hexanediol and carbonic acid units had a semicrystalline character and relatively high glass transition and melting temperatures. Furthermore it was highly soluble in most organic solvents, an interesting feature that facilitated the electrospinning process and the effective incorporation of drugs with bactericidal activity (e.g. biguanide derivatives such as clorhexidine and polyhexamethylenebiguanide) and enzymes (e.g. α-chymotrypsin) that accelerated the degradation process. Continuous micro/nanofibers were obtained under a wide range of processing conditions, being diameters of electrospun fibers dependent on the drug and solvent used. Poly(ester urea) samples were degradable in media containing lipases and proteinases but the degradation rate was highly dependent on the surface area, being specifically greater for scaffolds with respect to films. The high hydrophobicity of new scaffolds had repercussions on enzymatic degradability since different weight loss rates were found depending on how samples were exposed to the medium (e.g. forced or non-forced immersion). New scaffolds were biocompatible, as demonstrated by adhesion and proliferation assays performed with fibroblast and epithelial cells.

Biomimetic L-aspartic acid-derived functional poly(ester amide)s for vascular tissue engineering

Functionalization of polymeric biomaterials permits the conjugation of cell signaling molecules capable of directing cell function. In this study, l-phenylalanine and l-aspartic acid were used to synthesize poly(ester amide)s (PEAs) with pendant carboxylic acid groups through an interfacial polycondensation approach. Human coronary artery smooth muscle cell (HCASMC) attachment, spreading and proliferation was observed on all PEA films. Vinculin expression at the cell periphery suggested that HCASMCs formed focal adhesions on the functional PEAs, while the absence of smooth muscle α-actin (SMαA) expression implied the cells adopted a proliferative phenotype. The PEAs were also electrospun to yield nanoscale three-dimensional (3-D) scaffolds with average fiber diameters ranging from 130 to 294nm. Immunoblotting studies suggested a potential increase in SMαA and calponin expression from HCASMCs cultured on 3-D fibrous scaffolds when compared to 2-D films. X-ray photoelectron spectroscopy and immunofluorescence demonstrated the conjugation of transforming growth factor-β1 to the surface of the functional PEA through the pendant carboxylic acid groups. Taken together, this study demonstrates that PEAs containing aspartic acid are viable biomaterials for further investigation in vascular tissue engineering.