132 research outputs found
Degradation studies of hydrophilic, partially degradable and bioactive cements (HDBCs) incorporating chemically modified starch
The degradation rate in Hydrophilic, Degradable and Bioactive Cements (HDBCs) containing starch/cellulose acetate blends (SCA) is still low. In order to increase degradation, higher amounts of starch are required to exceed the percolation threshold. In this work, gelatinization, acetylation and methacrylation of corn starch were performed and assessed as candidates to replace SCA in HDBCs. Formulations containing methacrylated starch were prepared with different molar ratios of 2-hydroxyethyl methacrylate and methyl methacrylate in the liquid component and the amount of residual monomer released into water was evaluated. The concentration of reducing sugars, percentage of weight loss and morphologic analyses after degradation all confirmed increased degradation of HDBC with alpha-amylase, with the appearance of pores and voids from enzymatic action. Methacrylated starch therefore is a better alternative to be used as the solid component of HDBC then SCA, since it leads to the formation of cements with a lower release of toxic monomers and more prone to hydrolytic degradation while keeping the other advantages of HDBCs.The authors acknowledge to Foundation for Science and Technology (FCT), who supported this study through funds from project Concept2Cement (POCTI/CTM/60735/2004)
The effect of water uptake on the behaviour of hydrophilic cements in confined environments
Physiological fluids will be in contact with the implant components from the first moments after a surgery. Therefore, the study of the
effect of water on the properties of the bone cements that are part of the arthroplasty procedure is of critical importance to predict the
long-term performance of the whole system. In our research group, we have developed a novel concept, the hydrophilic, partially
degradable and bioactive cements which uptake considerably more water than standard bone cements. In this paper, we aimed to study the
effect of water uptake (WU) by these cements on their behaviour. The tests were carried out in confined cavities, which represent more
accurately the in vivo situation the cement will face (constrained by the bone and prosthesis surfaces). We observed that the equilibrium
WU decreased up to 60% (as compared to non-confined situations), depending of the formulation. This decrease resulted in a latent
tendency of the cements to swell, and the hindering of such swelling generated a swelling pressure against the constraining walls. The
pressure, and consequent press-fitting effect, could be controlled by a number of mechanisms, and resulted in higher stability of the
hydrophilic cements, expressed as an increase in the push-out force, required to extract the specimens from such constrained cavities. This
effect was only observed in hydrophilic cements, not in commercial, hydrophobic ones used as controls. We conclude that such cements
will provide an additional and very useful source of immediate adhesion in the short-term after surgery: water induced press fitting
A review on the polymer properties of hydrophilic, partially degradable and bioactive acrylic cements (HDBC)
Acrylic bone cements were developed around 50 years ago for the fixation of hip prostheses during arthroplasty. Over
the intervening years, a series of drawbacks have been disclosed that have fostered intensive research on the development
of novel or alternative formulations to the standard acrylic cements. Here, we will review the development and
characterization of a novel class of cements, the Hydrophilic, partially Degradable and Bioactive Cements (HDBCs), an
example of multifunctional cements. They were developed to have improved biocompatibility and initial fixation to the
prosthesis and to induce the growth of bone on the surface of the cement and within pores generated by the degradation of
the solid component. HDBCs have higher water uptake than typical acrylic cements, leading to press-fitting inside
constrained cavities. They are tougher, albeit less stiff and strong than hydrophobic cements, and their mechanical
properties may be easily adjusted by small changes in composition. Last, the simultaneous bioactive and degradable
character of HDBCs have been shown to allow in vitro growth of calcium phosphates into pores within the bulk of the
cement
The in vitro bioactivity of two novel hydrophilic, partially degradable bone cements
Composite bone cements were prepared with bioactive glasses (MgO–SiO2–3CaO Æ P2O5) of different reactivities. The matrix of these
so-called hydrophilic, partially degradable and bioactive cements was composed of a starch/cellulose acetate blend and poly(2-hydroxyethyl
methacrylate). The addition of 30 wt.% of glasses to this system made them bioactive in acellular medium: a dense apatite layer
formed on the surface after 7 days of immersion in simulated body fluid. This was demonstrated both by microscopic and infrared spectroscopic
techniques. The composition of the glass and, consequently, its structure was found to have important effects on the rate of the
apatite formation. The combination of reactivity obtained by one formulation with the hydrophilic and degradable character of these
cements makes them a very promising alternative to conventional acrylic bone cements, by allowing a better stabilization of the implant
and a stronger adhesion to the bone
Innovative approach for producing injectable, biodegradable materials using chitooligosaccharides and green chemistry
Although there are a number of injectable biomaterials currently under development, they present some drawbacks
such as being based on synthetic polymers, needing toxic or aggressive synthesis procedures or using raw materials
with low availability and/or high production costs. Having this in mind, a novel injectable biomaterial using
chitooligosaccharides as starting materials was developed. This system uses a widely available and cheap polymer
from marine biomass (chitosan), which can be turned into an injectable material by water-based and ecologically
friendly reactions. Chitooligosaccharides were functionalized with methacrylic groups, to allow in situ crosslinking.
The degree of substitution, as determined by 1H NMR, varied between 5 and 50%. The system was
characterized in terms of kinetics of gel formation, rheology, degradation behavior and in vitro cytotoxicity. The
gelation time could be easily tailored between 1.5 and 60 min by changing the conditions of the methacrylation
reaction, and the final gel presented rheological properties typical of strong gels, that is, shear stresses in the kPa
range. The cross-linked gel was degradable and nontoxic, presenting indeed an interesting cytokinetic effect.
Injectable materials based on chitooligosaccharides are, therefore, an innovative system combining adequate
biological performance, ease of preparation, and an ecologically friendly concept of production.The authors thank Dr. Mar Fernandez for the cytotoxicity tests. L.F.B. thanks the European Commission for supporting this work through a Marie Curie-IIF fellowship
Injectable hydrogels based on chitosan
Oligo-D-glucosamine (‘‘oligomer’’ of chitosan) seems well suited for injectable, biodegradable systems (IBS), due to their solubility in water, easier funtionalization and the possibility of working at
high concentrations. Chitosan was enzymatically degraded with a commercial enzyme (Multifect Pectinase FE) at 508C and pH 5.5 during 17h, adapting a previous procedure. The oligomers were precipitated in ethanol and analysed by MALDI-TOF/MS and FTIR. They were then functionalized by reaction with methacrylic anhydride (MethA), varying ratio of amount of substance of MethA : amount of substance of -NH2 groups in the oligomer. The obtained methacrylamide-
oligomers were polymerized with a potassium persulfate/ vitamin C initiation system. Both the modified oligomers and the polymerized product were analysed by FTIR and NMR. [...]info:eu-repo/semantics/publishedVersio
Incorporation of alpha-amylase enzyme and a bioactive filler into hydrophilic, partially degradable, and bioactive cements (HDBCs) as a new approach to tailor simultaneously their degradation and bioactive behavior
Hydrophilic, partially degradable, and bioactive cements (HDBCs) are starch-containing cements intended to
degrade partially in the human body and, in so doing, allow for bone ingrowth inside the pores formed during
degradation. Therefore, the study of degradation and bioactivity behavior was performed to assess the suitability
of the current HDBCs formulations to achieve those aims. The degradation profile of HDBCs was studied under
different conditions, including incubation in phosphate-buffered saline (PBS) and PBS supplemented with R-amylase
at different concentrations. Thermostable R-amylase was also added to some formulations to allow control of the
degradation rate and its extent. In a second stage the simultaneous phenomena of enzymatic degradation and
bioactivity (both in vitro) was studied. We observed that the degradation of starch present in HDBCs can be
easily controlled by the amount of R-amylase added to the cement and high values of degradation may be achieved
if high enough quantities of enzyme are incorporated. However, the maximum degradation extent is much more
dependent on the total amount of starch present in the formulation than on the amount of enzyme added to it: for
full pore connectivity, the amount of starch should be higher than the percolation threshold for a 3D specimen.
Nonetheless, calcium phosphate was able to nucleate and spread in inner pores of the cement, formed due to
degradation, if they were interconnected. For a more thorough covering of the pores with calcium phosphates the
amount of starch present in HDBCs should be increased to be higher than the percolation threshold
New hydrophilic, partially degradable and bioactive cements (HDBC) to improve interface with bone
[Excerpt] Acrylic bone cements aim to fix prosthesis to bone during hip arthroplasty. The commercial acrylic bone cements perform their function, however at the long term they fail due to aseptic loosening
of two interfaces: prosthesis-cement and cement bone. To minimize these problems, the bone growth should be promoted on the surface and inside of the partially degradable bone cement. In our work five different formulations were developed containing in the powder a biodegradable component such as modified
corn starch with acrylic segments (methacrylated starch) as well cellulose acetate blended with corn starch (SCA). These components reacted with acrylic monomers (methylmethacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA)) to produce hydrophilic partially degradable bone cements by radical polymerization. Diverse molar ratios MMA/HEMA as well the amount of initiator/ activator were employed in such cements. [...]info:eu-repo/semantics/publishedVersio
Micropatterning of bioactive glass nanoparticles on chitosan membranes for spatial controlled biomineralization
[Excerpt] Objectives: Chitosan membranes were patterned with bioactive glass nanoparticles (BG-NPs) capable of bone regeneration by a Microcontact Printing technique, in order to spatially control biomineralization and also cell adhesion and proliferation. [...
Bioinert, biodegradable and injectable polymeric matrix composites for hard tissue replacement: state of the art and recent developments
The present review paper examines the use of different types of polymeric matrix composites in hard tissue replacement applications.
The review presents the actual state of the art in the fields of bioinert composites for permanent applications, biodegradable
matrix composites for temporary applications and the emerging area of injectable composites.In all cases some recent developments
are also discussed.The paper starts with an introduction to locate the reader. Bone–analogue composites are then extensively
discussed.Several other systems based on an inert polymeric matrix are described, focusing on their proposed applications.A great
emphasis is afterwards given to biodegradable matrix systems.The most widely used synthetic bioresorbable systems are analysed
and compared with an example of natural origin degradable composites–starch based composites.Finally, composite systems that
are non-processable by melt based routes and in many cases injectable are discussed in detail, including several recent developments
on this emerging area of research
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