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Novel polymeric delivery systems for pharmaceutical and biomedical applications: from synthesis to in vivo feasibility studies
No full textA polymer is a molecule with high molecular weight constituted by identical or different repeating units (monomers) hold together as a chain by covalent bonds. Nucleic acids, polysaccharides and proteins are biological macromolecules essential for living organism with inner biocompatibility and essential biological activity for health. The biomedical and pharmaceutical applications of natural polymers face some limitations associated to difficult isolation and purification processes connected to the risk of immunological reactions once applied in the human body. The design of synthetic polymers takes inspiration from the main features of natural polymers, with the final goal to overcome their limitations and meet the therapeutic medical needs of patients. The combination of natural and synthetic polymers results in biomaterials with unique and complementary characteristics. The main goal of the present thesis is the development of new biomaterials composed of hybrid and synthetic polymers formulated as hydrogels and nanoparticles for application in drug delivery, tissue engineering, and brain targeting. The central theme of this thesis is presented in Chapter 2. Temperature responsive polymers belong to the class of smart polymers, that, in aqueous solutions, lead to the formation of stimuli responsive hydrogels. For biomedical and pharmaceutical applications, hydrogels must satisfy precise properties that are explained in this section. The chapter mainly focuses on the use of hydrogels for protein release, the ways proteins can be loaded and subsequently delivered in a controlled way from the gel network are explained. The application of hydrogels in tissue engineering is presented and deeply investigated in the following Chapter 3, with particular emphasis on the most recent applications in cartilage repair. After a brief presentation of natural and synthetic hydrogels, the discussion converges on the use of gel networks for the delivery of bioactive molecules such as growth factors mostly involved as signaling and stimulating molecules for cells proliferation, growth and differentiation. Growth factors are rapidly degraded in physiological conditions, being therefore unable to reach the injury site and to unroll their work. The encapsulation into polymeric scaffolds is an efficacious approach to overcome these disadvantages and provide an in-situ release of bioactive proteins. Other strategies for cartilage restoration regards the encapsulation of genetic material encoding for growth factors and the enclosure of platelet rich plasma (PRP) into the hydrogel scaffold.\ud
Chapter 4 introduces the principal biomaterial of this thesis. The aim of the work is to develop a fast-gelling hydrogels composed of a central hydrophilic block of poly ethylene glycol (PEG) flanked by two thermosensitive chains of poly(hydroxypropyl methacrylamide) (p(HPMAm-lac)) derivatized with vinyl groups and cross-linked, by Michael addition with thiolated hyaluronic acid (HA-SH) in a vinyl sulfone- thiol groups ratio of 1:1. Vinyl sulfonated triblock copolymers were highly reactive towards thiol groups giving rise to hydrogels with rapid gelation time and with complete conversion of vinyl sulfone groups. The hydrogels showed increasing G’ values, decreasing gelation temperature (considered as temperature at which G’=G’’), greater swelling and faster degradation kinetics at decreasing thiolation degree of hyaluronic acid. Cells viability, evaluated by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay for 21 days on mouse bone marrow stromal cell (BMSCs) and NIH 3T3 mouse embryonic fibroblasts, showed that cells viability was preserved, and cells maintained their shape for the considered timescale.\ud
Chapter 5 reports on the in vivo biocompatibility study of the tandem cross-linked vinyl sulfone bearing p(HPMA-lac)-PEG-p(HPMA-lac) based hydrogel when injected into Balb/c mice. The hydrogel was easily injected both intramuscularly and subcutaneously and immediately cross-linked in a stable network at the site of administration, as confirmed by ultranosography monitoring. Bone marrow cells of mice treated with hydrogels, after been cultured in medium, showed an important decrease of pro-inflammatory cytokines and chemokines. The decrease is time–dependent, possibly due to the anti-inflammatory effect of hyaluronic acid released during the degradation of the hydrogel. It was concluded that the presented cross-linked hydrogel was a good candidate for tissue engineering applications and for drug delivery.\ud
The feasibility of the application of the vinyl sulfone bearing p(HPMA-lac)-PEG-p(HPMA-lac) based hydrogels in articular cartilage defects is the topic of Chapter 6, where the hydrogel was loaded with platelet rich plasma extracted from equine blood samples. In vitro studies and rheological analysis showed that the hydrogel provided a protective and strong network and increased the mechanical strength of platelet derived fibrin gel. The release studies focused on PDGF-BB and TGF-β1 and is an ongoing work, as well as the viability and proliferation of equine mesenchymal stem cells.\ud
Chapter 7 presents a thermosensitive triblock copolymer of p(HPMA-lac)-PEG-p(HPMA-lac) partly functionalized with methacrylic, acrylic and vinyl sulfone groups and cross-linked with thiolated hyaluronic acid (HA-SH) to form in situ jellying hydrogel. The controlled release of the glycopeptide vancomycin in phosphate buffer (PBS buffer, 150 mM, pH 7.4) at 37 °C was achieved for at least 5 days. Vancomycin, released from hydrogels, was tested for its antimicrobial activity on a gram positive bacterium, Staphylococcus Aureus, whose growth was inhibited by released vancomycin to the same extent vancomycin positive control solutions. Hydrogels with higher amount of hyaluronic acid released vancomycin with slower rates compared to hydrogels with lower polysaccharide content. An ionic interaction between the positive charged vancomycin and the negative hyaluronic acid was postulated and demonstrated. This hypothesis was confirmed by release studies in borate buffered saline (BBS buffer, 10 mM, pH 8.5) at 37°C, where the vancomycin is negative charged and was diffusionally and more rapidly released as compared to hydrogels at pH 7.4. Moreover, it was found that the encapsulation into hydrogel networks prevented vancomycin deamidation. The developed hydrogel system proved efficacious as a potential antibacterial depot to prevent orthopaedic implant associated infections.\ud
The topic of stimuli sensitive polymers inspired the research described in Chapter 8, where a novel dual responsive triblock copolymer system, sensitive to themperature and controllably degradable at acidic pH, composed of a central chain of polyethylene glycol (PEG) flanked by two identical chains with pendent cyclic ortho ester groups, was developed. The side chains give the acid sensitive behavior to the polymer while, the copolymerization with PEG middle block resulted in thermosensitive gel forming polymers. Several triblock copolymers with different molecular weight were prepared and formulated as physical hydrogel networks held together by secondary forces (mainly hydrophobic interactions). The molecular weights of the polymers and the amount of polymers into the hydrogels directly influenced the gelation times of the hydrogels. The perspective is to evaluate the swelling behavior of the hydrogels at different pHs and to stabilize the polymer network by the use of chemical cross-links to ensure higher mechanical strength. One examples of chemical cross-link is the Michael addition reaction among acrylic, methacrylic or vinyl sulfone groups and thiolated ones. In-vitro viability on mesenchimal cells will be investigated to assure the lack of toxicity and the potential feasibility of the hydrogels for in-vivo applications. Recently, several studies reported on nanohydrogels systems for biomedical applications. Nanohydrogels are hydrogel based nanoparticles in the nanometer scale from tens to hundreds of nanometers that combine the advantages of hydrogels and nanoparticles for drug formulation and delivery, which include controllable drug release, high stability in physiological media, distinct responsiveness to environmental factors such as pH and temperature, high cellular uptake due to the endocytosis mechanisms, long half-life in circulation by appropriate surface modification and drug targeting by conjugation of ligand onto the surface of hydrogel nanoparticles. Future development of the poly ortho esters-PEG- poly ortho esters triblock copolymers as nanohydrogel systems is an attractive perspective.\ud
In Chapter 9 a new adenosine conjugated polylactic-co-glycolic acid-polyethylene glycol PLGA-PEG block copolymer formulated in the form of solid nanoparticle for brain targeting was investigated and developed. The nanoparticle core consisted of hydrophobic PLGA shielded by an external corona of PEG surface decorated with adenosine, chosen as model ligand to specifically target nucleoside transporters present on the blood brain barrier (BBB). Adenosine was linked to the PEG via its amino group in position 6’ of the adenine. Homogenous polymer distribution, particle size of 200 nm and spherical shape were assessed. Rhodamine 6G, a highly fluorescent dye was encapsulated into the polymeric nanoparticle and used for in vivo studies to determine circulation time and brain uptake of the nanoparticles upon intravenous administration in mice. Release studies from nanoparticles are ongoing. In vitro stability, cell viability, haemolysis and platelet aggregation of nanoparticles will be tested.\ud
Further development of this research topic will be the development of PLGA-PEG-Adenosine copolymers conjugated via the hydroxyl group in position 5’ of adenosine ribose, which, according to structure activity relationship studies (SAR) is not involved in the binding of adenosine with transporters
Gelling Thermosensitive Hydrogels for Protein Delivery Applications
No full textHydrogels cover an extremely broad variety of medical, biological and pharmaceutical applications, chemical composition and gelation mechanisms. They range from chemically to physically crosslinked networks of synthetic or natural polymers, can be manufactured into materials of different shapes and dimensions (from macroscopic depots to nanogels/nanofibers) and formulated in such a way that they become degradable in a specific controllable manner. Research on the controlled release of proteins and peptides covers a sizeable portion of the work on hydrogels. Pharmaceutical proteins have increased remarkably in number and frequency of use. However, their delicate three-dimensional structure is a major limitation to the use of pharmaceutical proteins, as they suffer from poor stability, due to proteolytic and chemical degradation as well as physical unfolding and aggregation. This instability leads to loss of activity and often elicits an immune response. Injectable hydrogel-based controlled release delivery systems are among the approaches implemented to enhance protein’s pharmacokinetic and pharmacodynamic properties. Hydrogels are crosslinked networks of hydrophilic polymers capable of retaining large amounts of water yet remaining insoluble and maintaining their three-dimensional structure. They can entrap, protect from degradation and slowly release proteins in a controlled fashion in order to maintain a therapeutic effective concentration of the protein drug in the surrounding tissues or in the circulation over an extended period of time. This chapter is intended as a small cross section of the multidisciplinary and exciting research ongoing in the area of hydrogels for protein delivery, with particular emphasis on in-situ gelling thermosensitive hydrogels
New Nanometric Solid Dispersions of Glibenclamide in Neusilin® UFL2
Full text linkTo improve the poor water solubility and dissolution rate of the oral hypoglycemic drug glibenclamide, it was molecularly dispersed in Neusilin® UFL2, an amorphous synthetic form of magnesium aluminometasilicate, at different proportions; the physicochemical and biopharmaceutical properties, as well as the stability of the four different batches recovered were characterized, and it was determined that complete dispersion of glibenclamide in the amorphous polymer was obtained at the drug to Neusilin ratio of 1 to 2.5. Completely amorphous dispersion was proven by Thermal Analysis and X-Ray Powder Diffractometry. Very small particles were obtained, ranging from approximately 200 to 400 nm. The amorphous batches were physically and chemically stable for the entire duration of experiments. The physicochemical properties of the four batches were compared to those of the starting materials and physical mixtures of Neusilin® UFL2 and glibenclamide, the latter showing the typical behaviour of simple mixes, i.e. the additivity of properties of single components. The dissolution studies of the four solid dispersions revealed a very high dissolution rate of the completely amorphous batches (Batches 3 and 4), behaviour that was ascribed to their high Intrinsic Dissolution Rate due to the amorphous characteristics of the solid dispersions, to their very small particle size, and to the presence of polysorbate 80 that improved solid wettability. The technique under investigation thus proved effective for recovering stable amorphous dispersions of very small particle sizes
Influence of pH and method of crystallization on the solid physical form of indomethacin.
No full textThe purpose of this study was to investigate the effect of pH and method of crystallization on the solid physical form of indomethacin (IDM). IDM, a non steroidal anti-inflammatory drug poorly soluble in water, underwent two different crystallization methods: crystallization by solvent evaporation under reduced pressure at 50.0°C (method A), and crystallization by cooling of solution from 50.0 to 5.0°C (method B). In both cases, several aqueous ethanolic solutions of IDM of different pHs were prepared. pHs were adjusted by adding acidic solutions (HCl 2M) or alkali (NaOH or NH4OH 2M) to an aqueous ethanolic solution of IDM. Thus, several batches were recovered after crystallization. The chemical stability of IDM was verified through (1)H NMR and mass spectroscopy (FIA-ESI-MS), that revealed that IDM degraded in strong alkali media (pH ≥ 12). Crystals obtained under different crystallization conditions at pHs of 1.0, 4.5, 7.0, 8.0, 10.0 and chemically stable were thus characterized for crystal habit by scanning electron microscopy, for thermal behaviour by differential scanning calorimetry, and thermogravimetry, and for solid state by X-ray powder diffractometry. Under the Method A, IDM always crystallized into pure metastable alpha form when solutions were acidified or alkalized respectively with HCl and NH4OH. On the contrary, in presence of NaOH, IDM crystallized under a mixture of alpha and sodium trihydrate form, because the presence of the sodium counter ion orientates the crystallization towards the formation of the trihydrate salt. Under the method B, at pH of 1.0, IDM crystallized under the alpha form; at pH 4.5, IDM crystallized under the form alpha in presence of some nuclei of gamma form; at pH 7.0, 8.0, and 10.0 for NH4OH, IDM crystallized under the most stable polymorph gamma form, whereas in presence of NaOH, a mix of alpha, and salt forms was formed whatever the pH of the solution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
In vivo biocompatibility of p(HPMAm-lac)-PEG hydrogels hybridized with hyaluronan
No full textThe present study reports on the biocompatibility in vivo after intramuscular and subcutaneous administration in Balb/C mice of vinyl sulfone bearing p(HPMAm-lac1-2)-PEG- p(HPMAm-lac1-2)/thiolated hyaluronic acid hydrogels, designed as novel injectable biomaterials for potential application in the fields of tissue engineering and regenerative medicine.[3] Ultrasonography, used as a method to study hydrogel gelation and residence time in vivo, showed that, upon injection, the biomaterial efficiently formed a hydrogel by simultaneous thermal gelation and Michael addition cross-linking forming a viscoelastic spherical depot at the injection site. The residence time in vivo (20 days) was found shorter than that observed in vitro (32 days), indicating that the injected hydrogel was resorbed not only by chemical hydrolysis but also by cellular metabolism and/or enzymatic activity. Systemic biocompatibility was tested by analysing routine hematologic parameters at different time points (7, 14 and 21 days post administration) and histology of the main organs including the hematopoietic system. No statistically significant difference between parameters of the saline treated group and those of the hydrogel treated group was found. Importantly, a time-dependent decrease of important pro-inflammatory cytokines (TREM1, TNF-α, IL-1β) in cultured BMCs extracted from hydrogel treated mice was observed, possibly correlated to the anti-inflammatory effect of hyaluronic acid released in time as hydrogel degraded. This in vivo study established the suitability of the proposed hydrogel technology as promising matrix for tissue engineering and drug delivery. The possibility to apply the developed hydrogel technology in vivo will potentially bring advances in the biomedical and pharmaceutical fields
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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