Ana C. Fonseca

The quest for sustainable polyesters – insights into the future

Polyesters from renewable resources are an expanding area with a burgeoning scientific activity, nevertheless little has been reviewed about this particular class of polymers. The present appraisal intends to contribute to fill this literature gap by reviewing recent aspects related to the most promising renewable-based polyesters. Emphasis will be placed on bio-based polyesters that, given their comparable properties, may replace polymers derived from fossil fuel feedstock, and on bio-based polyesters with completely innovative properties for novel applications. Furthermore, the sources of renewable monomers will also be reviewed, together with the most relevant eco-friendly synthetic approaches used in polycondensation reactions leading to polyesters.

Biobased polyesters and other polymers from 2,5-furandicarboxylic acid: a tribute to furan excellency

Motivated by the general concern about sustainability and environmental issues, an intense search for renewable-based polymers has grown exponentially in recent years. This search definitely spotlighted polyesters derived from 2,5-furandicarboxylic acid, among other polymers, as some of the most promising, especially due to the resemblance of this renewable monomer to the well-known petroleum-based terephthalic acid, as well as owing to the possibility of preparing innovative materials. The huge number of recent papers and patents about this family of polymers explore aspects as diverse as synthesis with other renewable-based monomers, leading to the preparation of materials with enhanced thermo-mechanical, biodegradability and liquid crystalline properties, among other features. Additional aspects pursued in such studies are innovation in the synthetic approaches or their optimisation, as well as the development of applications for everyday-life objects for example packaging materials, especially bottles, textiles, coating, and toners, among many other uses. Despite this intense activity, little has been reviewed recently about this unique family of polyesters or derived polymers, as the only reviews on the subject date back to the last century. In this perspective, the present review aims at contributing to filling this literature gap, covering recent aspects related with challenges in developing polyesters, polyamides, or other polymers from 2,5-furandicarboxylic acid and their precursors. Emphasis is placed on monomer synthesis, polymerisation reactions, catalysts and applications.

Drug delivery systems: Advanced technologies potentially applicable in personalized treatments

Advanced drug delivery systems (DDS) present indubitable benefits for drug administration. Over the past three decades, new approaches have been suggested for the development of novel carriers for drug delivery. In this review, we describe general concepts and emerging research in this field based on multidisciplinary approaches aimed at creating personalized treatment for a broad range of highly prevalent diseases (e.g., cancer and diabetes). This review is composed of two parts. The first part provides an overview on currently available drug delivery technologies including a brief history on the development of these systems and some of the research strategies applied. The second part provides information about the most advanced drug delivery devices using stimuli-responsive polymers. Their synthesis using controlled-living radical polymerization strategy is described. In a near future it is predictable the appearance of new effective tailor-made DDS, resulting from knowledge of different interdisciplinary sciences, in a perspective of creating personalized medical solutions.

New unsaturated copolyesters based on 2,5-furandicarboxylic acid and their crosslinked derivatives

The synthesis and characterisation of a novel family of unsaturated polyesters (UPs) and their crosslinked resins (UPRs) based on 2,5-furandicarboxylic acid (FDCA) are reported. Their original features stem from the use of FDCA as the aromatic monomer, and also from the fact that UPs are entirely based on renewable resources, oppositely to most reported materials which are typically based on petrochemicals or instead they are derived from both petrochemicals and a percentage of renewables. Additionally, instead of styrene, 2-hydroxyethylmethacrylate (HEMA) was used as the reactive solvent to obtain the UPRs. These novel resins showed adequate thermal and mechanical behavioural tendencies similar to petrochemical ones, namely high glass transition temperature (up to 104 °C) and good thermal stability (up to 230 °C). These characteristics enhance their prospects of being a successful renewable-based material.

Recent Developments in Antimicrobial Polymers: A Review

Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.

Dynamic Mechanical Thermal Analysis of Polymer Composites Reinforced with Natural Fibers

ABSTRACT The preparation of high performance materials using renewable resources is a prime goal in materials science. Composites are amply recognized as an effective route to achieve a new portfolio of advanced materials with high performance. The comprehensive understanding of the structure/properties relationships is crucial to achieve such goal. Therefore, the detailed characterization of the viscoelastic properties of composites is an essential step in the development process. This review describes the use of Dynamic Mechanical Thermal Analysis (DMTA) in the viscoelastic characterization of composites, and a brief description about the utility of the DMTA in the study of their structure/properties relationships is given. The paper is focused on the discussion of the most relevant publications in the area.

Peripheral Nerve Regeneration: Current Status and New Strategies Using Polymeric Materials

Experiments concerning peripheral nerve regeneration have been reported since the end of the 19th century. The need to implement an effective surgical procedure in terms of functional recovery has resulted in the appearance of several approaches to solve this problem. Nerve autograft was the first approach studied and is still considered the gold standard. Since autografts require donor harvesting, other strategies involving the use of natural materials have also been studied. Nevertheless, the results were not very encouraging and attention has moved towards the use of nerve conduits made from polymers, whose properties can be easily tailored and which allow the nerve conduit to be easily processed into a variety of shapes and forms. Some of these materials are already approved by the US Food and Drug Administration (FDA), as is presented here. Furthermore, polymers with conductive properties have very recently been subject to intensive study in this field, since it is believed that such properties have a positive influence in the regeneration of the new axons. This manuscript intends to give a global view of the mechanisms involved in peripheral nerve regeneration and the main strategies used to recover motor and sensorial function of injured nerves.

Recent advances in smart biotechnology: Hydrogels and nanocarriers for tailored bioactive molecules depot

Over the past ten years, the global biopharmaceutical market has remarkably grown, with ten over the top twenty worldwide high performance medical treatment sales being biologics. Thus, biotech R&D (research and development) sector is becoming a key leading branch, with expanding revenues. Biotechnology offers considerable advantages compared to traditional therapeutic approaches, such as reducing side effects, specific treatments, higher patient compliance and therefore more effective treatments leading to lower healthcare costs. Within this sector, smart nanotechnology and colloidal self-assembling systems represent pivotal tools able to modulate the delivery of therapeutics. A comprehensive understanding of the processes involved in the self-assembly of the colloidal structures discussed therein is essential for the development of relevant biomedical applications. In this review we report the most promising and best performing platforms for specific classes of bioactive molecules and related target, spanning from siRNAs, gene/plasmids, proteins/growth factors, small synthetic therapeutics and bioimaging probes.

Poly(ester amide)s based on l-lactic acid oligomers and glycine: the role of the central unit of the l-lactic acid oligomers and their molecular weight in the poly(ester amide)s properties

Novel biodegradable poly(ester amide)s (PEAs) based on l-lactic acid (l-LA) oligomers and glycine were successfully synthesized, through an easy and fast procedure, making use of inexpensive starting materials. The l-LA oligomers were prepared with different central units and different molecular weights in order to access the influence of such parameters in the final properties of the PEAs’. Both the central unit of the l-LA oligomer and its molecular weight have important influence in the PEAs’ final properties. The thermal stability is lower for the PEAs containing the l-LA with the shortest central unit and for the PEAs based on the l-LA oligomers of high molecular weight. The PEAs exhibit a semi-crystalline nature, except those derived from the l-LA oligomers with high molecular weight, which have an amorphous character. Both hydrolytic and enzymatic degradation are more pronounced in PEAs synthesized from the l-LA oligomers with low molecular weight. Different mechanisms of degradation were found for the PEAs: bulk erosion and surface erosion, for hydrolytic degradation and enzymatic degradation tests, respectively.

The impact of a designed lactic acid-based crosslinker in the thermochemical properties of unsaturated polyester resins/nanoprecipitated calcium carbonate composites

Unsaturated polyester composites (UPCs) were prepared from biobased unsaturated polyester resins (UPRs) and nanoprecipitated calcium carbonate (NPCC). The UPRs were obtained from the crosslinking reaction of an unsaturated polyester (UP) made from renewable monomers and styrene (St) or a mixture of St with a designed lactic acid-based crosslinker (BPPC). The UPCs were obtained by adding the NPCC to the formulations. Aspects of the composition of the UPs and of the BPPC were confirmed by FTIR and 1H NMR spectroscopies. Different UPCs were prepared and the influences of the addition of NPCC and of the amount of BPPC on their thermomechanical properties were evaluated. The BPPC has a major influence on the properties of the UPCs, namely a significant improvement of mechanical properties and of the thermal stability of UPCs. Both results suggest that the BPPC may be acting as a compatibilizer between the polymer matrix and the filler.