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Materials, Volume 4, Issue 10 (October 2011), Pages 1632-1905

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Research

Jump to: Review

Open AccessArticle Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers
Materials 2011, 4(10), 1632-1647; doi:10.3390/ma4101632
Received: 22 August 2011 / Revised: 2 September 2011 / Accepted: 19 September 2011 / Published: 27 September 2011
Cited by 11 | PDF Full-text (1102 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a study of the nematic (N)–isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy)-ω-(1-pyrenimine-benzylidene-4’-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the
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In this work, a study of the nematic (N)–isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy)-ω-(1-pyrenimine-benzylidene-4’-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB) phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU)–isotropic (I) phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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Open AccessArticle Polyacylurethanes as Novel Degradable Cell Carrier Materials for Tissue Engineering
Materials 2011, 4(10), 1705-1727; doi:10.3390/ma4101705
Received: 10 September 2011 / Accepted: 21 September 2011 / Published: 6 October 2011
Cited by 5 | PDF Full-text (566 KB) | HTML Full-text | XML Full-text
Abstract
Polycaprolactone (PCL) polyester and segmented aliphatic polyester urethanes based on PCL soft segment have been thoroughly investigated as biodegradable scaffolds for tissue engineering. Although proven beneficial as long term implants, these materials degrade very slowly and are therefore not suitable in applications in
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Polycaprolactone (PCL) polyester and segmented aliphatic polyester urethanes based on PCL soft segment have been thoroughly investigated as biodegradable scaffolds for tissue engineering. Although proven beneficial as long term implants, these materials degrade very slowly and are therefore not suitable in applications in which scaffold support is needed for a shorter time. A recently developed class of polyacylurethanes (PAUs) is expected to fulfill such requirements. Our aim was to assess in vitro the degradation of PAUs and evaluate their suitability as temporary scaffold materials to support soft tissue repair. With both a mass loss of 2.5–3.0% and a decrease in molar mass of approx. 35% over a period of 80 days, PAUs were shown to degrade via both bulk and surface erosion mechanisms. Fourier Transform Infra Red (FTIR) spectroscopy was successfully applied to study the extent of PAUs microphase separation during in vitro degradation. The microphase separated morphology of PAU1000 (molar mass of the oligocaprolactone soft segment = 1000 g/mol) provided this polymer with mechano-physical characteristics that would render it a suitable material for constructs and devices. PAU1000 exhibited excellent haemocompatibility in vitro. In addition, PAU1000 supported both adhesion and proliferation of vascular endothelial cells and this could be further enhanced by pre-coating of PAU1000 with fibronectin (Fn). The contact angle of PAU1000 decreased both with in vitro degradation and by incubation in biological fluids. In endothelial cell culture medium the contact angle reached 60°, which is optimal for cell adhesion. Taken together, these results support the application of PAU1000 in the field of soft tissue repair as a temporary degradable scaffold. Full article
(This article belongs to the Special Issue Biodegradability of Materials in Biomedical Applications 2011)
Open AccessArticle Chitin-Methacrylate: Preparation, Characterization and Hydrogel Formation
Materials 2011, 4(10), 1728-1746; doi:10.3390/ma4101728
Received: 11 August 2011 / Revised: 20 September 2011 / Accepted: 27 September 2011 / Published: 6 October 2011
Cited by 9 | PDF Full-text (1124 KB) | HTML Full-text | XML Full-text
Abstract
Chitin-methacrylate (CM) was prepared by the reaction of methacrylic acid on chitin in 5% LiCl/DMAc in the presence of N,N’-dicyclocarbodiimide and dimethylaminopyridine. The resultant chitin-methacrylate product was isolated in 61% yield and was found to be readily water-soluble. The derivative was found to
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Chitin-methacrylate (CM) was prepared by the reaction of methacrylic acid on chitin in 5% LiCl/DMAc in the presence of N,N’-dicyclocarbodiimide and dimethylaminopyridine. The resultant chitin-methacrylate product was isolated in 61% yield and was found to be readily water-soluble. The derivative was found to be a mixture of methacrylate and methacrylic-dimethylaminopyridine complex substituents at the C-6 position in approximately equal amounts. In order to evaluate the activity of the methacrylate double bond, a chitin-methacrylate water solution was photo-crosslinked in the presence of Irgacure 2959 photo-initiator to generate CM-hydrogel. The CM-hydrogel was evaluated for its biodegradability characteristics by enzymatic degradation with lysozyme solutions of varying concentrations. Completely water-soluble products were obtained within 48 h. In vitro cytotoxicity assays of the CM-hydrogel and its extract against three cell lines, NCTC clone 929, IMR-90 and MG-63, indicated the hydrogel was non-cytotoxic with cells able to adhere and proliferate well on the hydrogel. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
Open AccessArticle Mechanical Properties of Titanium Nitride Nanocomposites Produced by Chemical Precursor Synthesis Followed by High-P,T Treatment
Materials 2011, 4(10), 1747-1762; doi:10.3390/ma4101747
Received: 12 September 2011 / Revised: 27 September 2011 / Accepted: 28 September 2011 / Published: 6 October 2011
Cited by 10 | PDF Full-text (863 KB) | HTML Full-text | XML Full-text
Abstract
We investigated the high-P,T annealing and mechanical properties of nanocomposite materials with a highly nitrided bulk composition close to Ti3N4. Amorphous solids were precipitated from solution by ammonolysis of metal dialkylamide precursors followed by heating at 400–700 °C in
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We investigated the high-P,T annealing and mechanical properties of nanocomposite materials with a highly nitrided bulk composition close to Ti3N4. Amorphous solids were precipitated from solution by ammonolysis of metal dialkylamide precursors followed by heating at 400–700 °C in flowing NH3 to produce reddish-brown amorphous/nanocrystalline materials. The precursors were then densified at 2 GPa and 200–700 °C to form monolithic ceramics. There was no evidence for N2 loss during the high-P,T treatment. Micro- and nanoindentation experiments indicate hardness values between 4–20 GPa for loads ranging between 0.005–3 N. Young's modulus values were measured to lie in the range 200–650 GPa. Palmqvist cracks determined from microindentation experiments indicate fracture toughness values between 2–4 MPa·m1/2 similar to Si3N4, SiC and Al2O3. Significant variations in the hardness may be associated with the distribution of amorphous/crystalline regions and the very fine grained nature (~3 nm grain sizes) of the crystalline component in these materials. Full article
(This article belongs to the Special Issue Hard Materials: Advances in Synthesis and Understanding)
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Open AccessArticle Gelation and Retrogradation Mechanism of Wheat Amylose
Materials 2011, 4(10), 1763-1775; doi:10.3390/ma4101763
Received: 1 July 2011 / Revised: 24 September 2011 / Accepted: 27 September 2011 / Published: 10 October 2011
Cited by 11 | PDF Full-text (1283 KB) | HTML Full-text | XML Full-text
Abstract
The flow behavior, dynamic viscoelasticity, and optical rotation of aqueous solutions of wheat amylose were measured using a rheogoniometer and a polarimeter. The amylose solutions, at 25 °C, showed shear-thinning behavior at a concentration of 1.2%, but plastic behavior at 1.4 and 1.6%,
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The flow behavior, dynamic viscoelasticity, and optical rotation of aqueous solutions of wheat amylose were measured using a rheogoniometer and a polarimeter. The amylose solutions, at 25 °C, showed shear-thinning behavior at a concentration of 1.2%, but plastic behavior at 1.4 and 1.6%, the yield values of which were estimated to be 0.6 and 1.0 Pa, respectively. The viscosity of the wheat amylose increased a little with increase in temperature up to 10 or 20 °C at 1.2% or 1.4 and 1.6%, which was estimated to be a transition temperature. The elastic modulus increased with increase in concentration, and increased with increasing temperature up to 20, 25 and 30 °C, which was estimated to be a transition temperature, respectively, then decreased gradually but stayed at a large value even at high temperature (80 °C). A very low elastic modulus of the wheat amylose was observed upon addition of urea (4.0 M) and in alkaline solution (0.05 M NaOH) even at low temperature. The optical rotation of wheat amylose solution increased a little with decreasing temperature down to 25 °C, then increased rapidly with further decrease in the temperature. The mode of gelation mechanism of amylose molecules, which was previously proposed, was confirmed and a retrogradation mechanism of wheat amylose was proposed. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
Open AccessArticle Evaluation of Titanium Alloys Fabricated Using Rapid Prototyping Technologies—Electron Beam Melting and Laser Beam Melting
Materials 2011, 4(10), 1776-1792; doi:10.3390/ma4101776
Received: 29 August 2011 / Revised: 28 September 2011 / Accepted: 6 October 2011 / Published: 10 October 2011
Cited by 50 | PDF Full-text (3573 KB) | HTML Full-text | XML Full-text
Abstract
This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each
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This study characterized properties of Ti-6Al-4V ELI (extra low interstitial, ASTM grade 23) specimens fabricated by a laser beam melting (LBM) and an electron beam melting (EBM) system for dental applications. Titanium alloy specimens were made into required size and shape for each standard test using fabrication methods. The LBM specimens were made by an LBM machine utilizing 20 µm of Ti-6Al-4V ELI powder. Ti-6Al-4V ELI specimens were also fabricated by an EBM using 40 µm of Ti-6Al-4V ELI powder (average diameter, 40 µm: Arcam ABÒ) in a vacuum. As a control, cast Ti-6Al-4V ELI specimens (Cast) were made using a centrifugal casting machine in an MgO-based mold. Also, a wrought form of Ti-6Al-4V ELI (Wrought) was used as a control. The mechanical properties, corrosion properties and grindability (wear properties) were evaluated and data was analyzed using ANOVA and a non-parametric method (α = 0.05). The strength of the LBM and wrought specimens were similar, whereas the EBM specimens were slightly lower than those two specimens. The hardness of both the LBM and EBM specimens was similar and slightly higher than that of the cast and wrought alloys. For the higher grindability speed at 1,250 m/min, the volume loss of Ti64 LBM and EBM showed no significant differences among all the fabrication methods. LBM and EBM exhibited favorable results in fabricating dental appliances with excellent properties as found for specimens made by other fabricating methods. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application)
Open AccessArticle Fabrication of κ-Carrageenan Fibers by Wet Spinning: Spinning Parameters
Materials 2011, 4(10), 1805-1817; doi:10.3390/ma4101805
Received: 1 July 2011 / Revised: 26 September 2011 / Accepted: 28 September 2011 / Published: 11 October 2011
Cited by 2 | PDF Full-text (708 KB) | HTML Full-text | XML Full-text
Abstract
This study demonstrates the fabrication of κ-carrageenan fibers by a wet-spinning method and discusses three important spinning parameters: coagulation bath composition, spinning rate and post-spinning mechanical drawing. The as-spun fiber diameter decreased with KCl and ethanol concentration in the coagulation bath. In general,
[...] Read more.
This study demonstrates the fabrication of κ-carrageenan fibers by a wet-spinning method and discusses three important spinning parameters: coagulation bath composition, spinning rate and post-spinning mechanical drawing. The as-spun fiber diameter decreased with KCl and ethanol concentration in the coagulation bath. In general, the ultimate tensile stress and elongation at break both increased for KCl concentration from 0.1 to 0.5 M with and without ethanol, with no significant change above 0.5 M. Spinning rate affected the dope flow and thus the polymer orientation (apparent viscosity) and fiber morphology. At spinning rates between 0.25 mL/min and 0.33 mL/min, the fiber diameter reached a minimum and the fiber surface was smooth. Both an increase and decrease from this spinning rate range increased the fiber diameter and roughness of the fiber surface. Post-spinning drawing of the fiber resulted in even smaller fiber diameter. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)
Open AccessArticle Multi-Echo-Based Echo-Planar Spectroscopic Imaging Using a 3T MRI Scanner
Materials 2011, 4(10), 1818-1834; doi:10.3390/ma4101818
Received: 2 September 2011 / Revised: 6 October 2011 / Accepted: 7 October 2011 / Published: 17 October 2011
Cited by 2 | PDF Full-text (813 KB) | HTML Full-text | XML Full-text
Abstract
The use of spin-echoes has been employed in an Echo-Planar Spectroscopic Imaging (EPSI) sequence to collect multiple phase encoded lines within a single TR in a Multi-Echo-based Echo-Planar Spectroscopic Imaging technique (MEEPSI). Despite the T2 dependence on the amplitude of the spin-echoes,
[...] Read more.
The use of spin-echoes has been employed in an Echo-Planar Spectroscopic Imaging (EPSI) sequence to collect multiple phase encoded lines within a single TR in a Multi-Echo-based Echo-Planar Spectroscopic Imaging technique (MEEPSI). Despite the T2 dependence on the amplitude of the spin-echoes, the Full Width at Half Maximum (FWHM) of the derived multi-echo Point Spread Function (PSF) is shown to decrease, indicating an improved overall spatial resolution without requiring any additional scan time. The improved spatial resolution is demonstrated in the one-dimensional (1D) spatial profiles of the N-Acetyl Aspartate (NAA) singlet along the phase encode dimension in a gray matter phantom. Although the improved spatial resolution comes at the expense of spectral resolution, it is shown in vivo that peak broadening due to T2* decay is more significant than the loss of resolution from using spin-echoes and therefore does not affect the ability to quantify metabolites using the LCModel fitting algorithm. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
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Open AccessArticle The Origin of Tc Enhancement in Heterostructure Cuprate Superconductors
Materials 2011, 4(10), 1835-1845; doi:10.3390/ma4101835
Received: 2 August 2011 / Revised: 24 September 2011 / Accepted: 9 October 2011 / Published: 17 October 2011
Cited by 5 | PDF Full-text (287 KB) | HTML Full-text | XML Full-text
Abstract
Recent experiments on heterostructures composed of two or more films of cuprate superconductors of different oxygen doping levels have shown a remarkable Tc enhancement (up to 50%) relative to single compound films. We provide a simple explanation of the enhancement which arises
[...] Read more.
Recent experiments on heterostructures composed of two or more films of cuprate superconductors of different oxygen doping levels have shown a remarkable Tc enhancement (up to 50%) relative to single compound films. We provide a simple explanation of the enhancement which arises naturally from a collection of experimental works. We show that the enhancement could be caused by a structural change in the lattice, namely an increase in the distance of the apical oxygen from the copper-oxygen plane. This increase modifies the effective off-site interaction in the plane which in turn enhances the d-wave superconductivity order parameter. To illustrate this point we study the extended Hubbard model using the fluctuation exchange approximation. Full article
(This article belongs to the Special Issue New High Tc Superconductor)
Open AccessArticle A New Generation of X-ray Baggage Scanners Based on a Different Physical Principle
Materials 2011, 4(10), 1846-1860; doi:10.3390/ma4101846
Received: 21 September 2011 / Accepted: 28 September 2011 / Published: 17 October 2011
Cited by 4 | PDF Full-text (1083 KB) | HTML Full-text | XML Full-text
Abstract
X-ray baggage scanners play a basic role in the protection of airports, customs, and other strategically important buildings and infrastructures. The current technology of baggage scanners is based on x-ray attenuation, meaning that the detection of threat objects relies on how various objects
[...] Read more.
X-ray baggage scanners play a basic role in the protection of airports, customs, and other strategically important buildings and infrastructures. The current technology of baggage scanners is based on x-ray attenuation, meaning that the detection of threat objects relies on how various objects differently attenuate the x-ray beams going through them. This capability is enhanced by the use of dual-energy x-ray scanners, which make the determination of the x-ray attenuation characteristics of a material more precise by taking images with different x-ray spectra, and combining the information appropriately. However, this still has limitations whenever objects with similar attenuation characteristics have to be distinguished. We describe an alternative approach based on a different x-ray interaction phenomenon, x-ray refraction. Refraction is a familiar phenomenon in visible light (e.g., what makes a straw half immersed in a glass of water appear bent), which also takes place in the x-ray regime, only causing deviations at much smaller angles. Typically, these deviations occur at the boundaries of all objects. We have developed a system that, like other “phase contrast” based instruments, is capable of detecting such deviations, and therefore of creating precise images of the contours of all objects. This complements the material-related information provided by x-ray attenuation, and helps contextualizing the nature of the individual objects, therefore resulting in an increase of both sensitivity (increased detection rate) and specificity (reduced rate of false positives) of baggage scanners. Full article
(This article belongs to the Special Issue X-ray Imaging in Materials Science)
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Open AccessArticle Sol-Gel Behavior of Hydroxypropyl Methylcellulose (HPMC) in Ionic Media Including Drug Release
Materials 2011, 4(10), 1861-1905; doi:10.3390/ma4101861
Received: 20 September 2011 / Revised: 6 October 2011 / Accepted: 13 October 2011 / Published: 24 October 2011
Cited by 24 | PDF Full-text (2273 KB) | HTML Full-text | XML Full-text
Abstract
Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed
[...] Read more.
Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels. Full article
(This article belongs to the Special Issue Carbohydrate Polymers)

Review

Jump to: Research

Open AccessReview Synthesis of Binary Transition Metal Nitrides, Carbides and Borides from the Elements in the Laser-Heated Diamond Anvil Cell and Their Structure-Property Relations
Materials 2011, 4(10), 1648-1692; doi:10.3390/ma4101648
Received: 15 August 2011 / Revised: 13 September 2011 / Accepted: 16 September 2011 / Published: 28 September 2011
Cited by 29 | PDF Full-text (4523 KB) | HTML Full-text | XML Full-text
Abstract
Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary
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Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary transition metal nitrides, carbides and borides focusing on the reaction of the elements at extreme conditions generated within the laser-heated diamond anvil cell. The current knowledge of their structures and high-pressure properties like high-(p; T) stability, compressibility and hardness is described as obtained from experiments. Full article
(This article belongs to the Special Issue Hard Materials: Advances in Synthesis and Understanding)
Open AccessReview Manganese-based Materials Inspired by Photosynthesis for Water-Splitting
Materials 2011, 4(10), 1693-1704; doi:10.3390/ma4101693
Received: 4 August 2011 / Revised: 28 August 2011 / Accepted: 21 September 2011 / Published: 28 September 2011
Cited by 35 | PDF Full-text (533 KB) | HTML Full-text | XML Full-text
Abstract
In nature, the water-splitting reaction via photosynthesis driven by sunlight in plants, algae, and cyanobacteria stores the vast solar energy and provides vital oxygen to life on earth. The recent advances in elucidating the structures and functions of natural photosynthesis has provided firm
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In nature, the water-splitting reaction via photosynthesis driven by sunlight in plants, algae, and cyanobacteria stores the vast solar energy and provides vital oxygen to life on earth. The recent advances in elucidating the structures and functions of natural photosynthesis has provided firm framework and solid foundation in applying the knowledge to transform the carbon-based energy to renewable solar energy into our energy systems. In this review, inspired by photosynthesis robust photo water-splitting systems using manganese-containing materials including Mn-terpy dimer/titanium oxide, Mn-oxo tetramer/Nafion, and Mn-terpy oligomer/tungsten oxide, in solar fuel production are summarized and evaluated. Potential problems and future endeavors are also discussed. Full article
(This article belongs to the Special Issue Advanced Materials for Water-Splitting)
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Open AccessReview Mesenchymal Stem Cells in Combination with Scaffolds for Bone Tissue Engineering
Materials 2011, 4(10), 1793-1804; doi:10.3390/ma4101793
Received: 27 July 2011 / Accepted: 16 August 2011 / Published: 11 October 2011
Cited by 2 | PDF Full-text (192 KB) | HTML Full-text | XML Full-text
Abstract
This article reviews past and current strategies of the use of bone graft substitutes along with the future biologic alternatives that can enhance the functional capabilities of those grafts. Many of these bone graft substitute alternatives include ceramic-based, allograft-based, factor-based and polymer-based whereas
[...] Read more.
This article reviews past and current strategies of the use of bone graft substitutes along with the future biologic alternatives that can enhance the functional capabilities of those grafts. Many of these bone graft substitute alternatives include ceramic-based, allograft-based, factor-based and polymer-based whereas others are cell-based. The ways of achieving the goal of tissue engineering using stem cells and their lineage to regenerate tissue have been detailed with regard to both the generation of sufficient vascular invasion of the tissue to improve oxygen and nutrient supply, and the development of innovative physical/chemical stimuli to induce bone formation with the proper biomaterial to carry the cells. It is imperative to integrate basic polymer science with molecular biology and stem cell biology, in the design of new materials that perform very sophisticated signaling needed for integration and function. Full article
(This article belongs to the Special Issue Orthopaedic Biomaterials)

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