Additive Manufacturing of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/poly(ε-caprolactone) Blend Scaffolds for Tissue Engineering

Additive manufacturing of scaffolds made of a polyhydroxyalkanoate blended with another biocompatible polymer represents a cost-effective strategy for combining the advantages of the two blend components in order to develop tailored tissue engineering approaches. The aim of this study was the development of novel poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/ poly("-caprolactone) (PHBHHx/PCL) blend scaffolds for tissue engineering by means of computer-aided wet-spinning, a hybrid additive manufacturing technique suitable for processing polyhydroxyalkanoates dissolved in organic solvents. The experimental conditions for processing tetrahydrofuran solutions containing the two polymers at different concentrations (PHBHHx/PCL weight ratio of 3:1, 2:1 or 1:1) were optimized in order to manufacture scaffolds with predefined geometry and internal porous architecture. PHBHHx/PCL scaffolds with a 3D interconnected network of macropores and a local microporosity of the polymeric matrix, as a consequence of the phase inversion process governing material solidification, were successfully fabricated. As shown by scanning electron microscopy, thermogravimetric, differential scanning calorimetric and uniaxial compressive analyses, blend composition significantly influenced the scaffold morphological, thermal and mechanical properties. In vitro biological characterization showed that the developed scaffolds were able to sustain the adhesion and proliferation of MC3T3-E1 murine preosteoblast cells. The additive manufacturing approach developed in this study, based on a polymeric solution processing method avoiding possible material degradation related to thermal treatments, could represent a powerful tool for the development of customized PHBHHx-based blend scaffolds for tissue engineering

Polymeric Systems for the Controlled Release of Flavonoids

Flavonoids are natural compounds that are attracting great interest in the biomedical field thanks to the wide spectrum of their biological properties. Their employment as anticancer, anti-inflammatory, and antidiabetic drugs, as well as for many other pharmacological applications, is extensively investigated. One of the most successful ways to increase their therapeutic efficacy is to encapsulate them into a polymeric matrix in order to control their concentration in the physiological fluids for a prolonged time. The aim of this article is to provide an updated overview of scientific literature on the polymeric systems developed so far for the controlled release of flavonoids. The different classes of flavonoids are described together with the polymers most commonly employed for drug delivery applications. Representative drug delivery systems are discussed, highlighting the most common techniques for their preparation. The flavonoids investigated for polymer system encapsulation are then presented with their main source of extraction and biological properties. Relevant literature on their employment in this context is reviewed in relationship to the targeted pharmacological and biomedical applications

Design, preparation and characterization of ulvan based thermosensitive hydrogels

The present study is focused on the exploitation and conversion of sulphated polysaccharides obtainedfrom waste algal biomass into high value added material for biomedical applications. ulvan, a sulphatedpolysaccharide extracted from green seaweeds belonging to Ulva sp. was selected as a suitable materialdue to its chemical versatility and widely ascertained bioactivity. To date the present work representsthe first successful attempt of preparation of ulvan-based hydrogels displaying thermogelling behaviour.ulvan was provided with thermogelling properties by grafting poly(N-isopropylacrylamide) chains ontoits backbone as thermosensitive component. To this aim ulvan was properly modified with acryloylgroups to act as macroinitiator in the radical polymerization of N-isopropylacrylamide, induced by UVirradiation through a “grafting from” method. The thermogelling properties of the copolymer were inves-tigated by thermal and rheological analyses. Sol–gel transition of the copolymer was found to occur at30–31◦C thus indicating the feasibility of ulvan for being used as in-situ hydrogel forming systems forbiomedical application

Renewable Polysaccharides Micro/Nanostructures for Food and Cosmetic Applications

The worldwide diffusion of nanotechnologies into products nowadays has completely revolutionized human life, providing novel comfort and benefits. Their inclusion in food and cosmetic has a heavy impact over the market, allowing the development of higher value products with enhanced properties. Natural origin polymers and in particular polysaccharides represent a versatile platform of materials for the development of micro/nanostructured additives for food and cosmetic products due to their chemical versatility, biocompatibility, and abundance. Here, we review the current applications of polysaccharides-based micro/nanostructures, taking into consideration the precursors’ production, isolation, and extraction methods and highlighting the advantages, possible drawbacks, and market diffusion

Additive Manufacturing of Poly(Methyl Methacrylate) Biomedical Implants with Dual-Scale Porosity

The development of bone permanent implants with a porous structure favoring their integration with the surrounding tissues is emerging as an attractive field of application of additive manufacturing (AM). This article reports on the investigation of the suitability of a hybrid AM technique, that is, computer-aided wet-spinning (CAWS), to fabricate novel poly(methyl meth- acrylate) (PMMA) constructs as porous implant prototypes. The optimization of the processing parameters to fabricate PMMA samples with a predefined internal porous structure and different external shapes is described. The study demonstrates that tailoring post-processing conditions represents a powerful tool to optimize samples macroscopic aspect, micromorphology, and mechanical properties. In particular, the possibility of obtaining a dual-scale porosity through the integration of the macroporous structure determined by the material lay-down pattern with a submicrometric porosity resulting from the phase inversion process governing polymer solidification, together with the possibility of purifying the employed commercial material from residual monomer during coagulation in ethanol, are reported as note- worthy advantages of CAWS over other AM techniques. A natural progression of this work is the development of relevant complex anatomical prototypes with tailored porosity by processing digital data obtained from computer tomography imaging of bone defects

Levofloxacin-loaded star poly(ε-caprolactone) scaffolds by additive manufacturing

The employment of a tissue engineering scaffold able to release an antimicrobial agent with a controlled kinetics represents an effective tool for the treatment of infected tissue defects as well as for the prevention of scaffolds implantation-related infectious complications. This research activity was aimed at the development of additively manufactured star poly(ε-caprolactone) (*PCL) scaffolds loaded with levofloxacin, investigated as antimicrobial fluoroquinolone model. For this purpose a computer-aided wet-spinning technique allowing functionalizing the scaffold during the fabrication process was explored. Scaffolds with customized composition, microstructure and anatomical external shape were developed by optimizing the processing parameters. Morphological, thermal and mechanical characterization showed that drug loading did not compromise the fabrication process and the final performance of the scaffolds. The developed *PCL scaffolds showed a sustained in vitro release of the loaded antibiotic for 5 weeks. The proposed computer-aided wet-spinning technique appears well suited for the fabrication of anatomical scaffolds endowed with levofloxacin-releasing properties to be tested in vivo for the regeneration of long bone critical size defects in a rabbit model

Design, Preparation, and Characterization of Thermoresponsive Hybrid Nanogels Using a Novel Ulvan-Acrylate Crosslinker as Potential Carriers for Protein Encapsulation

The aim of the present study is the design and development of thermoresponsive nanogels based on ulvan, a sulphated heteropolysaccharide of algal origins with unique biological and chemical properties. Hybrid nanogels are successfully synthesized by means of UV-initiated radical copolymerization of N-vinylcaprolactam with an ulvan derivate as a novel crosslinker. In nanogels, the ulvan-grafted poly(N-vinylcaprolactam) chains represent the thermoresponsive component. The most promising candidates, selected after a thorough physical-chemical characterization of nanogels in terms of size and responsivity to thermal variation at physiological conditions, are loaded with bovine serum albumin (BSA) as model bioactive compound. The developed nanogels display BAS loading efficiency values similar to those obtained by using synthetic crosslinkers, and thus indicating the suitability of the developed ulvan-acrylate to act as novel macromolecular crosslinker for thermoresponsive nanogels preparation

A novel Electrospinning Procedure for the Production of Straight Aligned and Winded Fibers

An electrospinning procedure allowing the spinning of a straight jet of polymer solution was developed. By using proper collector devices, it enables to collect winded and aligned fibers and to prepare polymeric constructs developing along the Z axis. The reported results are expected to provide basic understandings on which parameters are controlling the stability/instability of the process and implement new applications of electrospinning with specific reference to the preparation of well defined three-dimensional structure

Fed-Batch Synthesis of Poly(3-Hydroxybutyrate) and Poly(3-Hydroxybutyrate-co-4-Hydroxybutyrate) from Sucrose and 4-Hydroxybutyrate Precursors by Burkholderia sacchari Strain DSM 17165

Based on direct sucrose conversion, the bacterium Burkholderia sacchari is an excellent producer of the microbial homopolyester poly(3-hydroxybutyrate) (PHB). Restrictions of the strain’s wild type in metabolizing structurally related 3-hydroxyvalerate (3HV) precursors towards 3HV-containing polyhydroxyalkanoate (PHA) copolyester calls for alternatives. We demonstrate the highly productive biosynthesis of PHA copolyesters consisting of 3-hydroxybuytrate (3HB) and 4-hydroxybutyrate (4HB) monomers. Controlled bioreactor cultivations were carried out using saccharose from the Brazilian sugarcane industry as the main carbon source, with and without co-feeding with the 4HB-related precursor γ-butyrolactone (GBL). Without GBL co-feeding, the homopolyester PHB was produced at a volumetric productivity of 1.29 g/(L·h), a mass fraction of 0.52 g PHB per g biomass, and a final PHB concentration of 36.5 g/L; the maximum specific growth rate μmax amounted to 0.15 1/h. Adding GBL, we obtained 3HB and 4HB monomers in the polyester at a volumetric productivity of 1.87 g/(L·h), a mass fraction of 0.72 g PHA per g biomass, a final PHA concentration of 53.7 g/L, and a μmax of 0.18 1/h. Thermoanalysis revealed improved material properties of the second polyester in terms of reduced melting temperature Tm (161 °C vs. 178 °C) and decreased degree of crystallinity Xc (24% vs. 71%), indicating its enhanced suitability for polymer processing

Development and characterization of highly stable silver nanoparticles as novel potential antimicrobial agents for wound healing hydrogels

Recurrent microbial infections are a major cause of surgical failure and morbidity. Wound healing strategies based on hydrogels have been proposed to provide at once a barrier against pathogen microbial colonization, as well as a favorable environment for tissue repair. Nevertheless, most biocompatible hydrogel materials are more bacteriostatic than antimicrobial materials, and lack specific action against pathogens. Silver-loaded polymeric nanocomposites have efficient and selective activity against pathogenic organisms exploitable for wound healing. However, the loading of metallic nanostructures into hydrogels represents a major challenge due to the low stability of metal colloids in aqueous environments. In this context, the aim of the present study was the development of highly stable silver nanoparticles (AgNPs) as novel potential antimicrobial agents for hyaluronic acids hydrogels. Two candidate stabilizing agents obtained from natural and renewable sources, namely cellulose nanocrystals and ulvan polysaccharide, were exploited to ensure high stability of the silver colloid. Both stabilizing agents possess inherent bioactivity and biocompatibility, as well as the ability to stabilize metal nanostructures thanks to their supramolecular structures. Silver nitrate reduction through sodium borohydride in presence of the selected stabilizing agents was adopted as a model strategy to achieve AgNPs with narrow size distribution. Optimized AgNPs stabilized with the two investigated polysaccharides demonstrated high stability in phosphate buffer saline solution and strong antimicrobial activity. Loading of the developed AgNPs into photocrosslinked methacrylated hyaluronic acid hydrogels was also investigated for the first time as an effective strategy to develop novel antimicrobial wound dressing materials.This research was supported by the Portuguese Foundation for Science and Technology (FCT) under the projects PTDC/BII-BIO/28870/2017 and POCI-01-0145-FEDER-007038 (UID/Multi/ 50026/2013), and by the European Regional Development Fund (FEDER) through the “COMPETE”— Operational Program for Competitiveness factors (FCOMP-01-0124-FEDER-028120). A.R.F. thanks FCT through the Post-Doctoral scholarship SFRH/BPD/100760/2014