Research of Preparation Conditions for Regeneration of Hydroxyapatite and Influence on Crystalline Forms

The process of hydroxyapatite (HAp) precipitation in ionic liquid (ChCl-urea) was studied and the influence of various factors on the crystalline forms and yields of HAp were analysed. It was concluded that Na-citrate made the regenerated HAp appear as a long cylindrical crystal (perfect rod-like grain) when chosen to be an additive/surfactant. The optimum conditions for HAp precipitation (regenerated HAp) were applied to extract HAp from chicken bone in ChCl-urea (product HAp). The product HAp was characterized by FTIR, SEM XRD and Particle Size Analyser. The results showed that there is no obvious difference between HAp extracted from chicken bone (product HAp) and regenerated HAp regarding crystalline forms and compositions. The product HAp is relatively pure, and its average particle size is 555.6 nm, meaning that this product has the application value

Keratin: dissolution, extraction and biomedical application

Keratinous materials such as wool, feathers and hooves are tough unique biological co-products that usually have high sulfur and protein contents. A high cystine content (7–13%) differentiates keratins from other structural proteins, such as collagen and elastin. Dissolution and extraction of keratin is a difficult process compared to other natural polymers, such as chitosan, starch, collagen, and a large-scale use of keratin depends on employing a relatively fast, cost-effective and time efficient extraction method. Keratin has some inherent ability to facilitate cell adhesion, proliferation, and regeneration of the tissue, therefore keratin biomaterials can provide a biocompatible matrix for regrowth and regeneration of the defective tissue. Additionally, due to its amino acid constituents, keratin can be tailored and finely tuned to meet the exact requirement of degradation, drug release or incorporation of different hydrophobic or hydrophilic tails. This review discusses the various methods available for the dissolution and extraction of keratin with emphasis on their advantages and limitations. The impacts of various methods and chemicals used on the structure and the properties of keratin are discussed with the aim of highlighting options available toward commercial keratin production. This review also reports the properties of various keratinbased biomaterials and critically examines how these materials are influenced by the keratin extraction procedure, discussing the features that make them effective as biomedical applications, as well as some of the mechanisms of action and physiological roles of keratin. Particular attention is given to the practical application of keratin biomaterials, namely addressing the advantages and limitations on the use of keratin films, 3D composite scaffolds and keratin hydrogels for tissue engineering, wound healing, hemostatic and controlled drug release.info:eu-repo/semantics/publishedVersio

Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento Cientfíico e Tecnológico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de Nvíel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)

Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications

Nanocellulose already proved to be a highly relevant material for biomedical applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive research, a notable number of emerging applications are still being developed. Interestingly, this drive is not solely based on the nanocellulose features, but also heavily dependent on sustainability. The three core nanocelluloses encompass cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their near future applicability. By analyzing the pristine core nanocellulose, none display cytotoxicity. However, CNF has the highest potential to fail long-term biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being elite materials in the urgent replacement of our petrochemical dependence

Valorization of agro-industrial wastes for the production of biodegradable products based on collagen

184 p.Collagen, which can be extracted from livestock and fish processing industry residues, has been widely used in food, cosmetic, pharmaceutical and biomedical applications due to its structural and biological properties as well as its abundance and versatility in forming physical shapes. Furthermore, collagen can be combined with other components to open up new application areas. In this context, the overall objective of this doctoral thesis was to develop products based on collagen, obtained from bovine and porcine skin wastes, with improved properties, incorporating other compounds, some of them also extracted from biowastes, and employing different processing methods. The information about collagen and the materials and characterization methods employed throughout the work are explained in the first two chapters. In chapter 3, citric acid was used to facilitate the processing by laboratory rollers and the functional properties of sheets obtained by compression were investigated. In chapters 4 and 5, aloe vera and chitosan were added in collagen based formulations to evaluate their suitability for biomedical applications. In chapter 6, scaffolds with the same formulation than Chapter 5 was prepared by freeze-drying and material properties and environmental impact were analysed. Moreover, in chapter 7, a syringe-based extrusion 3D printer was used to obtain tetrahydrocurcumin-incorporated porcine collagen scaffolds and their potential as sustained THC delivery systems was analyzed. Then, the electrical properties of collagen films were examined. In chapter 8, ZnO nanoparticles were incorporated into collagen formulations processed by solvent casting in order to obtain materials with induced electro-conductive properties, which could be of great relevance for biomedical applications. In chapter 9, wool and choline dihydrogen phosphate or choline serinate containing collagen formulations were prepared by compression molding to develop next generation advanced functional materials for sustainable electronics

Eletrosíntese de nanopartículas metálicas 1-D de DES usando modelos anódicos porosos

Doutoramento em Ciência e Engenharia de MateriaisO método de síntese de nanoparticulas 1-D assistido por um modelo tornou-se um tópico em voga na química após o desenvolvimento de filmes anódicos com poros bem ordenados. Contudo, a maioria dos trabalhos nesta área tem sido feita utilizando filmes porosos destacados devido à presença de uma barreira no fundo dos poros. No entanto, esta estratégia segue demasiados passos, o que aumenta o seu custo, torna mais difícil a execução e impõe várias limitações. Consequentemente, existe a necessidade de uma técnica que permita o enchimento (electrofilling) dos tubos sem remover a camada barreira – esta tese representa o nosso contributo para esse trabalho. Utilizámos uma técnica mais simples que permite a electrodeposição e “electrofilling” de nanoestruturas directamente nos modelos sobre o substrato metálico, utilizando solventes eutécticos profundos à base de cloreto de colina como electrólito. Relativamente à água, os solventes eutécticos profundos demonstram superior estabilidade térmica e uma janela electroquímica mais alargada, o que aumenta o número de materais secundários depositados. Como materiais a investigar foram escolhidos titânia e alumina dada a sua capacidade para formar estruturas porosas altamente ordenadas, propriedades eletroquímicas distintas e uso generalizado em síntese assistida por padrão. O estudo aqui apresentado encontra-se dividido em duas etapas. Primeiramente, a influência da camada barreira foi investigada em sistemas modelo através da utilização de filmes barreira densos na superfície dos elétrodos. Para os filmes de alumina e titânia, identificaram-se vários parâmetros que afectam a electrodeposição, dos quais se destacam a influência da voltagem de anodização, a espessura da camada de barreira, a dupla camada eléctrica e o perfil de corrente. Durante esta etapa detectaram-se efeitos nefastos, como a formação de uma densa camada orgânica na superfície do eléctrodo, que foram ultrapassados aumentando a temperatura ou alternando o potencial aplicado. A segunda etapa consistiu em passar de elétrodos planos (primeira etapa) para modelos porosos (segunda etapa). Foi realizado, com sucesso, o preenchimento dos poros de alumina e dos poros de titânia. Parâmetros como o perfil de corrente, temperatura de solução, entre outras, foram ajustadas para melhorar o fator de preenchimento e a homogeneidade do preenchimento. Foi desenvolvido um processo de preenchimento de moldes de alumina anódica em duas etapas, nucleação AC (1º passo) e preenchimento galvanostático (2º passo). Foram utilizadas três condições diferentes de modelos de titânia anódica porosa no “electrofilling”. O primeiro é sem modificação e demonstrou que a electroredução do zinco ocorre de forma aleatória ao longo de todo o comprimento do poro, o que leva ao fecho do poro e a um enchimento não homogéneo. A segunda modificação, cristalização total por têmpera, permite a preparação de estruturas coaxiais devido à deposição uniforme de zinco nas paredes dos poros. A última modificação foi a cristalização selectiva do fundo do poro. Foi descoberto que uma anodização adicional em eletrólitos não agressivos leva à cristalização da parte barreira dos tubos (fundo) e, consequentemente, a maior condutividade na parte inferior do que nas paredes. Este efeito permite um enchimento ascendente dos modelos porosos de titânia. As estratégias aqui apresentadas alargam a gama de possibilidades para a aplicação de modelos porosos anódicos na electrodeposição de diferentes nanoestruturas.The template assisted method of 1-D nanoparticles synthesis has become a hot topic in Chemistry after the development of high-ordered porous anodic films. Most studies in this field have focused on the use of detached porous films due to the presence of the barrier layer on the pore bottom. However, this strategy follows a great number of steps, which raises its cost while decreasing convenience of operation and imposing several limitations. Consequently, there is a need for a technique which allows electrofilling of tubes without removing the barrier layer – this thesis represents our contribution to that enterprise. We have devised a simpler technique which allows electrodeposition of nanostructures directly in the templates on metallic substrate, using choline chloride based deep eutectic solvents (DES) as electrolyte. Compared to water, DES have improved thermal stability and a wider electrochemical window, dramatically increasing the number of possible secondary materials deposited. Titania and alumina were chosen as materials under study due to their known capacity to form highly-ordered porous structures, different electrochemical profiles and widespread use in template assisted synthesis. The present work is divided in two parts. First, the influence of the barrier layer has been investigated by using dense barrier films on the electrode surface as a model system. For both alumina and titania films, several parameters affecting the electrodeposition of zinc have been identified, notably the influence of the anodization voltage, barrier layer thickness, electrical double layer and current profile. During this stage, some negative effects have been detected, such as a dense organic layer formation on electrode surface, a hurdle which has been overcome by either increasing the temperature or applying the alternating potential. The second stage consisted in transferring the method from the flat electrodes (the first stage) to the porous templates. The successful filling of both porous alumina and porous titania, has been achieved. Parameters such as current profile, solution temperature, among others, have been tuned to improve the fill factor and homogeneity of the filling. A two-step porous anodic alumina template filling with AC nucleation (1st step) and galvanostatic filling (2nd step) has been developed. Three different types of porous anodic titania templates have been used for electrofilling. The first one was used as-prepared, showing that zinc electroreduction occurs in random places along all pore length, resulting in pore sealing and non-homogeneous filling. The second modification, full crystallization by annealing, allows the preparation of coaxial structures due to uniform zinc deposition on the pore walls. The last modification is selective bottom crystallization. It has been found that additional anodization in unaggressive electrolytes leads to crystallization of the barrier (bottom) part of the tubes and, thus, to higher conductivity of the bottom part than that of the walls. This effect allows a bottom-up filling of the titania porous template. The strategies presented here widen the range of possibilities for the application of porous anodic templates in the electrodeposition of different nanostructures

Design of New Azole Molecules to Prevent Metal Leaching from Medical Implants

The aim of this project was to develop new coatings for titanium based implants, most particularly stents, incorporating heterocyclic functional groups in their structure that will have the potential to bind to a titanium surface and prevent or reduce metal corrosion. Many of the current coatings are chemically bound onto metallic surfaces, but this project looks at electropolymerising the coatings onto the surface of the Ti6Al4V stents. Hence, polymerising functional groups have been incorporated with azoles in the structure of the synthesised compounds. Additionally, surface characterisation and preliminary corrosion studies have been carried out on a series of coated TI6Al4V stents. In this study, the compounds synthesised have been divided into three groups. Compounds from series 1 have been synthesised from the core unit 2-(1H-tetrazol-5- yl)pyridine, while compounds from series 2 have been derived from pyrrole or 1,2- dimethyltetrahydrofuran. Series 3 compounds were obtained by reacting compounds 1 and 2 together. This in turn created a series of tetrazole/pyrrole based compounds. A total of 16 compounds are reported in this thesis. The compounds were isolated and identified by spectroscopic techniques (1H and 13C NMR, IR) as well as elemental analysis. A selection of series 3 compounds were subsequently chosen based on their polymerisation properties and coated onto a Ti6Al4V stent surface. The coatings were characterised by microscopy (SEM and AFM) and subjected to electrochemical corrosion testing via Tafel analysis. The preliminary results indicated that some of the synthesised coatings display a good coating ability and improved anti-corrosion properties, relative to coatings currently on the medical device market. Compounds 2-(2,2-diethoxyethane-3amino-pyrrol-1-yl ethyl-(1-tetrazol-5-yl) pyridine and 2-(n-ethylphenylpyrrole-(2H-tetrazol-5-yl) pyridine demonstrated the best reduction in corrosion, with a 5 fold reduction when compared to the uncoated Ti6Al4V stent. New tetrazole/pyrrole based coatings have been synthesised in this project, that have the capabilities of adhering to metallic surfaces and reduce metal corrosion. It is hoped that this exploratory work could lead to an introduction of new corrosion reducing iv coatings onto the medical stent market. However, further research is needed to bring the application of this project to the market

Biopolymers from Natural Resources

This work covers all aspects related to the obtainment, production, design, and processing of biopolymers obtained from natural resources. Moreover, it studies characteristics related to the improvement of their performance to increase their potential application at an industrial level, in line with the concept of a global circular economy. Thus, this work firstly classifies biopolymers obtained from natural resources (e.g., biobased building blocks and biopolymers extracted directly from plants and biomass), and then summarizes several cutting-edge research works focused on enhancing the performance of biopolymers from natural resources to extend their application in the industrial sector, and contribute to the transition to more sustainable plastics