6 research outputs found
Chitosan-FastOs® BG membrane-guides for nervous tissue regeneration
Mestrado em Materiais e Dispositivos BiomédicosThree-dimensional (3D) biodegradable composite porous scaffolds made of a
biopolymer matrix (chitosan) and a bioactive glass (FastOs®BG-Z4) were fabricated via
freeze drying as guides for nerve tissue engineering applications. For this purpose, chitosan
was dissolved in aqueous solutions of lactic acid (LA, 1 wt.%) to reach a final
concentration of 2 wt.%. Subsequently FastOs®BG-Z4 in powder form was added to
chitosan solution in a chitosan/Fasto®BG-Z4 weight ratio of 50/50. The
Chitosan/FastOs®BG-Z4 systems were cross-linked via adding different concentrations
(0.01, 0.05 and 0.5 wt.%) of two kinds of cross-linking agents, genipin, a natural
component, and glutaraldehyde, a synthetic agent, to stiffen the chitosan network. The final
mixtures were then frozen at two temperatures, 20ºC and 80ºC followed by freezedrying
to obtain porous scaffolds.
For achieving the optimal Chitosan/FastOs®BG-Z4 scaffolds, the influences of adding
FastOs®BG-Z4 powder and/or different amounts of crosslinking agents on the rheological
properties of chitosan/LA solutions were firstly investigated by rheological measurements.
The results showed that a strong and stable gel could not be obtained even when the
highest amount of cross-linking agents (0.5 wt.%) was added to the 2 wt.% chitosan
solution, while effective cross-linking occurred in the presence of FastOs®BG-Z4 powder.
Therefore, it was concluded that FastOs®BG-Z4 plays an active role on chitosan
complexation. The positive interactions between chitosan and the surface of FastOs®BGZ4
particles and/or the ionic species leached out to the solution needs to be further
investigated in future work.
The microstructural features of porous scaffolds were investigated by scanning electron
microscope (SEM), and the porosity assessment was made by ethanol replacement method.
The mechanical properties of porous scaffolds were investigated under
compression/swelling tests with samples immersed in phosphate-buffered saline (PBS)
solution. In vitro degradation tests were also performed by immersing the samples in
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phosphate-buffered saline (PBS) solution for 2 months tests and the degradation degree
was evaluated through the undergone weight changes.
The results showed some common features among genipin or glutaraldehyde as crosslinking
agents: increasing their amounts from 0.01 to 0.5 wt.% led to reductions in gelling
time, porosity fraction, swelling and degradation rate, while cross-linking degree increased.
However, their effects on pore size and compression strength of the scaffolds diverged. For
genipin pore size decreased and consequently the compression strength increased, while
for glutaraldehyde pore size always increased with added amounts, but compression
strength was improved with concentration increasing from 0.01 to 0.05 wt.%, decreasing
when the added amount was further increased to 0.5 wt.%.
Moreover, 20ºC was selected as the most suitable freezing temperature when
considering the porous microstructural features and the intended applications.A presente tese relata acerca do fabrico e caracterização de compósitos porosos
tridimensionais (3D) biodegradáveis baseados em quitosano, como matriz biopolimérica,
carregada com partículas de um vidro bioativo (Fastos®BG-Z4). Para este efeito, o
quitosano foi dissolvido em solução aquosa de ácido láctico (LA, 1% em peso) até atingir
uma concentração final de 2% em peso. Subsequentemente o Fastos®BG-Z4 em forma de
pó foi adicionado à solução de quitosano em uma proporção em peso de quitosano/
Fastos®BG-Z4 de 50/50. Os sistemas quitosano/Fastos®BG-Z4 foram reticulados por meio
de adição de diferentes percentagens em peso (0.01, 0.05 e 0.5) de dois tipos de agentes de
ligação cruzada, um componente natural, genipin, e um agente sintético, glutaraldeído. As
misturas finais foram então reticuladas a 60ºC seguido de congelamento a duas
temperaturas diferentes, 20ºC e 80ºC. O gelo foi depois sublimado por liofilização de
modo a obter matrizes porosas para aplicações como guias em engenharia de tecidos
nervosos periféricos.
Com vista à optimização do processo de fabrico e das propriedades das estruturas
porosas de suporte (andaimes) de quitosano/Fastos®BG-Z4, estudaram-se os efeitos da
adição do Fastos®BG-Z4 em pó e/ou de diferentes quantidades de agentes de reticulação
nas propriedades reológicas das soluções de LA/quitosano. Os resultados mostraram a
impossibilidade de obter de um gel de quitosano suficientemente forte e estável mesmo
quando a quantidade mais elevada de agentes de reticulação (0.5% em peso) foi adicionada
à solução de quitosano, em contraste com o que aconteceu com a adição do pó de
Fastos®BG-Z4 na ausência de outros agentes de reticulação. Esta descoberta permitiu
concluir que o Fastos®BG-Z4 desempenha um papel activo na complexação do quitosano.
As interacções positivas entre o quitosano e a superfície das partículas do Fastos®BG-Z4
e/ou as espécies iónicas lixiviadas para a solução precisam de ser melhor investigadas no
futuro.
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As características microestruturais dos materiais porosos foram investigadas por
microscopia electrónica de varrimento (SEM), e a porosidade foi determinada pelo método
de substituição de etanol. As propriedades mecânicas dos compósitos porosos imersos em
solução (PBS) de solução salina tamponada com fosfato foram investigadas através de
testes de compressão/inchamento. Realizaram-se também testes de degradação in vitro por
imersão das amostras na mesma solução de PBS durante 2 meses, e o grau de degradação
foi avaliado através das alterações de peso sofridas pelas amostras.
Os resultados mostraram algumas características comuns entre o genipin e o
glutaraldeído como agentes de reticulação: o aumento das quantidades adicionadas
(0.010.5% em peso) levou a reduções no tempo de gelificação, na fracção de porosidade,
no grau de inchamento, e na taxa de degradação, enquanto o grau de reticulação aumentou.
No entanto, os seus efeitos sobre o tamanho dos poros e a resistência à compressão dos
suportes porosos divergiram. O tamanho de poro diminuiu no caso do genipin, o que se
traduziu em consequentes aumentos da resistência à compressão; enquanto o tamanho dos
poros aumentou sempre com as quantidades adicionadas no caso do glutaraldeído, pelo que
só foram registadas melhorias na resistência à compressão na gama de concentrações entre
0.010.05% em peso, diminuindo quando a quantidade adicionada foi aumentada para 0,5
% em peso.
Verificou-se ainda que a temperatura de 20ºC era a que permitia obter as
microestruturas porosas mais adequadas para as aplicações almejadas
Janus Nanocomposite Hydrogels for Chirality-Dependent Cell Adhesion and Migration
Recently,
there has been much interest in the chirality-dependent cell affinity
to enantiomorphous nanomaterials (NMs), since, at the nanoscale level,
enantiomers of (bio)molecules have different effects on cell behaviors.
In this respect, this study used enantiomorphous NMs with which to
generate the Janus nanocomposite (NC) hydrogels as multifunctional
biomaterials for studying chirality-dependent cell adhesion and cell
migration. These Janus NC hydrogels possess two enantiomorphous NC
hydrogels, in which the different halves of the hydrogel contain the
opposite enantiomers of a biopolymer functionalized nanomaterials.
Thus, the enantiomers contact each other only at the midline of the
hydrogel but are otherwise separated, yet they are present in the
same system. This advanced system allows us to simultaneously study
the impact that each enantiomer of a biopolymer has on cell behavior
under the same reaction conditions, at the same time, and using only
a single biomaterial. Our results show that cells have higher affinity
for and migrate toward the part of the Janus NC hydrogel containing
the biopolymer enantiomer that the cells prefer
Functional Nanomaterials on 2D Surfaces and in 3D Nanocomposite Hydrogels for Biomedical Applications
An emerging approach to improve the physicobiochemical properties and the multifunctionality of biomaterials is to incorporate functional nanomaterials (NMs) onto 2D surfaces and into 3D hydrogel networks. This approach is starting to generate promising advanced functional materials such as self-assembled monolayers (SAMs) and nanocomposite (NC) hydrogels of NMs with remarkable properties and tailored functionalities that are beneficial for a variety of biomedical applications, including tissue engineering, drug delivery, and developing biosensors. A wide range of NMs, such as carbon-, metal-, and silica-based NMs, can be integrated into 2D and 3D biomaterial formulations due to their unique characteristics, such as magnetic properties, electrical properties, stimuli responsiveness, hydrophobicity/hydrophilicity, and chemical composition. The highly ordered nano- or microscale assemblies of NMs on surfaces alter the original properties of the NMs and add enhanced and/or synergetic and novel features to the final SAMs of the NM constructs. Furthermore, the incorporation of NMs into polymeric hydrogel networks reinforces the (soft) polymer matrix such that the formed NC hydrogels show extraordinary mechanical properties with superior biological properties
Cell Growth on (“Janus”) Density Gradients of Bifunctional Zeolite L Crystals
Nanoparticle
density gradients on surfaces have attracted interest
as two-dimensional material surfaces that can mimic the complex nano-/microstructure
of the native extracellular matrix, including its chemical and physical
gradients, and can therefore be used to systematically study cell–material
interactions. In this respect, we report the preparation of density
gradients made of bifunctional zeolite L crystals on glass surfaces
and the effects of the density gradient and biopolymer functionalization
of zeolite L crystals on cell adhesion. We also describe how we created
“Janus” density gradient surfaces by gradually depositing
two different types of zeolite L crystals that were functionalized
and loaded with different chemical groups and guest molecules onto
the two distinct sides of the same glass substrate. Our results show
that more cells adhered on the density gradient of biopolymer-coated
zeolites than on uncoated ones. The number of adhered cells increased
up to a certain surface coverage of the glass by the zeolite L crystals,
but then it decreased beyond the zeolite density at which a higher
surface coverage decreased fibroblast cell adhesion and spreading.
Additionally, cell experiments showed that cells gradually internalized
the guest-molecule-loaded zeolite L crystals from the underlying density
gradient containing bifunctional zeolite L crystals