Chitosan, a chitin-derivative polysaccharide, known for its non-toxicity, biocompatibility and biodegradability, presents limited applications due to its low solubility in neutral or basic pH medium. Quaternization stands out as an alternative to modify this natural polymer, aiming to improve its solubility over a wide pH range and, consequently, expand its range of applications. Quaternization occurs by introducing a quaternary ammonium moiety onto or outside the chitosan backbone, via chemical reactions with primary amino and hydroxyl groups, under vast experimental conditions. The oldest and most common forms of quaternized chitosan involve N,N,N-trimethyl chitosan (TMC) and N-[(2-hydroxy-3-trimethyl ammonium) propyl] chitosan (HTCC) and, more recently, quaternized chitosan by insertion of pyridinium or phosphonium salts. By modifying chitosan through the insertion of a quaternary moiety, permanent cationic charges on the polysaccharide backbone are achieved and properties such as water solubility, antimicrobial activity, mucoadhesiveness and permeability are significantly improved, enabling the application mainly in the biomedical and pharmaceutical areas. In this review, the main quaternized chitosan compounds are addressed in terms of their structure, properties, synthesis routes and applications. In addition, other less explored compounds are also presented, involving the main findings and future prospects regarding the field of quaternized chitosans.
Cellulosic materials have gained a lot of attention in the last decades because of their abundancy, renewability and excellent physicochemical properties. Meanwhile, research on nanofibers has also been increasing with the aim of producing or modifying materials that can have a wide range of applications, such as tissue engineering, drug delivery, protective clothing and wound dressing. In order to produce these fibers, electrospinning is shown to be a promising and extensively used technique. Electrospun cellulosic fibers maintain the optimal characteristics of cellulose while improving its surface area to volume ratio and mechanical properties, in addition to the possibility of surface tailoring of bulk materials. However, there are several limitations related to the utilization of cellulose and most of its derivatives with the electrospinning technique. Poor solubility in most common solvents and inability to melt are major drawbacks. Thus, this review describes mostly recent research in which cellulose and its derivatives have been the feedstock for fabrication of nanofibers by electrospinning, exploring processing details and potential applications.
Surface properties play a key role in how biomaterials interact with the environment. Surface topography has also been reported to be influential in some research, although its effect is still not well elucidated. In this study, nano-roughened polydimethylsiloxane (PDMS) substrates were developed through a chemically etched intermediate surface. Additionally, PDMS substrates containing 10-30 μm diameter micropillars were functionalized with multilayers of chitosan (CHI) and hyaluronic acid (HA) via layer-by-layer. Such substrates were submitted to cell adhesion assays with PC3 tumour cells. The characterization of these substrates was carried out using an atomic force microscopy (AFM), and some roughness parameters were estimated.Through a statistical description of the topography, we investigated the effects of these surface parameters on PC3 cell adhesion. AFM results indicated a significant modification in the PDMS surface topography and the cell adhesion assays suggest that smoother surfaces induce the PC3 cell adhesion, especially the ones with a high Hurst exponent value. In addition to the AFM analysis, the surface modification of the LbL-functionalized substrates was monitored by contact angle and UV-visible measurements. The improved wettability and the significant Alcian Blue absorbance of the functionalized substrates suggest that the HA/CHI film deposition was successfully accomplished. The LbL functionalization increased the cell capture potential of the PDMS substrates, in which lower diameter micropillars favour the cell adhesion mechanism. Although much work is still needed, the findings advance progress towards the fundamental understanding of the role of nanoscale fractal roughness in cell adhesion and can contribute to the development of new biomaterials with applications in biomedical systems, such as biosensors.
Natural polymers are widely known and extensively studied, especially for applications involving biomaterials and medical devices. Such a market has a high-growth potential, associated with the increase in people's average lifetime and the crescent concern for health and prevention by the population worldwide. In spite of this, few products within the medical field made from natural polymers are manufactured on large scale and commercialized. This review aims to provoke a reflection on why there is a missing chain link between the study of these materials and their large-scale production. If there are plenty of research papers published about biopolymers, why are they not available in the market? Initially, we present general statistics about the most commonly studied natural polymers and their applications in the medical field. We then review and analyze the three main processes (in our opinion) involving the production of biomaterials: 3D printing, drying, and sterilization. We present a description of the main processing methods, focusing on the major difficulties and bottlenecks that these processes may present during their use and scale-up. Our main conclusion is that more effort and focus are needed from scientists, in particular chemical and material engineers, to integrate material science with unit operations and close the gap between research and industrial production of natural polymers. This way, we can finally bring decades of development in biopolymers to real-life applications.
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