Using Biomaterials to Reduce Fibrous Encapsulation of Biomedical Implants

Fibrous encapsulation, commonly referred to as scar formation, can cause failure in many biomedical implants, such as in the artificial pancreas for type I diabetes treatment. Scar tissue prevents wastes and nutrients from being able to be exchanged in the implant, ultimately rendering the treatment painful or ineffective. For example, one potential therapeutic for type I diabetes involves using a polymer to protect insulin-producing cells. This artificial pancreas provides diabetics with their much needed insulin on-demand. If scar tissue forms around this artificial pancreas, the device loses the ability to deliver insulin and becomes useless. Our goal is to reduce the fibrous encapsulation of implants using biomaterials and improve the understanding of how cells involved in scar formation respond to biomaterials. We show that our materials can reduce fibrous capsule formation by inhibiting certain physiological pathways. This research will not only improve the success of the artificial pancreas, but other biomaterials

Influence of Lysine-Based Biomaterials on Fibroblast to Myofibroblast Differentiation

Fibrous encapsulation occurs as a result of implantation of devices such as pacemakers, artificial breast implants, and microencapsulated islet cells used in type 1 diabetes treatment. The foreign body response (FBR) is responsible for the development of a fibrous capsule, which is often detrimental to the function of the implanted device and therefore affected patients. One event leading to fibrous capsule formation is contraction of collagen by myofibroblasts. The objective of this project was to significantly reduce the thickness of the fibrous capsule by limiting fibroblast to myofibroblast differentiation. It was hypothesized that using lysine-based biomaterials with amidine-like functional group modifications would inhibit matrix metalloproteinase (MMP) activity, a precursor to myofibroblast formation. MMP Inhibition would impede cleavage of latent transforming growth factor beta (L-TGF-β) to transforming growth factor beta (TGF-β), a cytokine that stimulates fibroblast to myofibroblast differentiation. Cell staining was performed on NIH 3T3 fibroblasts cultured on each biomaterial and stimulated by L-TGF-β and TGF-β to evaluate material performance. Fibroblast viability was found to be \u3e70% on each material. These biomaterials have potential for use as a coating of microencapsulated islet cells for diabetes therapy. This study is also important for furthering understanding of the biology involved in fibrous capsule formation

Competing interactions in artificial spin chains

The low-energy magnetic configurations of artificial frustrated spin chains are investigated using magnetic force microscopy and micromagnetic simulations. Contrary to most studies on two-dimensional artificial spin systems where frustration arises from the lattice geometry, here magnetic frustration originates from competing interactions between neighboring spins. By tuning continuously the strength and sign of these interactions, we show that different magnetic phases can be stabilized. Comparison between our experimental findings and predictions from the one-dimensional Anisotropic Next-Nearest-Neighbor Ising (ANNNI) model reveals that artificial frustrated spin chains have a richer phase diagram than initially expected. Besides the observation of several magnetic orders and the potential extension of this work to highly-degenerated artificial spin chains, our results suggest that the micromagnetic nature of the individual magnetic elements allows observation of metastable spin configurations.Comment: 5 pages, 4 figure

Cosmological evolution with a logarithmic correction in the dark energy entropy

In a thermodynamical model of cosmological FLRW event horizons for the dark energy (DE), we consider a logarithmic corrective term in the entropy to which corresponds a new term in the DE density. This model of $\Lambda (t)$ in an interacting two-component cosmology with cold dark matter (DM) as second component leads to a system of coupled equations, yielding, after numerical resolution, the evolutions of $\Lambda (t)$, the Hubble $H(t)$, vacuum density $\Omega \_{\Lambda}(t)$, deceleration $q(t)$ and statefinder $R(t)$ and $S(t)$ parameters. Its results, compatible with an initial inflation and the current observations of the so-called "concordance model", predict a graceful exit of early inflation and the present acceleration and solve in the same time the age and coincidence problems. Moreover they account for the low-$l$ CMBR power spectrum suppression.Comment: 17 pages, 3 figures, submitted to JCA

SnIa Constraints on the event-horizon Thermodynamical model of Dark Energy

We apply the thermodynamical model of the cosmological event horizon of the spatially flat FLRW metrics to the study of the recent accelerated expansion phase and to the coincidence problem. This model, called "ehT model" hereafter, led to a dark energy (DE) density $\Lambda$ varying as $r^{-2},$ where $r$ is the proper radius of the event horizon. Recently, another model motivated by the holographic principle gave an independent justification of the same relation between $\Lambda$ and $r$. We probe the theoretical results of the ehT model with respect to the SnIa observations and we compare it to the model deduced from the holographic principle, which we call "LHG model" in the following.Our results are in excellent agreement with the observations for $H\_{0}=64kms^{-1}Mpc^{-1}$, and $\Omega \_{\Lambda }^{0}=0.63\_{-0.01}^{+0.1}$, which leads to $q\_{0}=-0.445$ and $z\_{T}\simeq 0.965$

Static cylindrical symmetry and conformal flatness

We present the whole set of equations with regularity and matching conditions required for the description of physically meaningful static cylindrically symmmetric distributions of matter, smoothly matched to Levi-Civita vacuum spacetime. It is shown that the conformally flat solution with equal principal stresses represents an incompressible fluid. It is also proved that any conformally flat cylindrically symmetric static source cannot be matched through Darmois conditions to the Levi-Civita spacetime. Further evidence is given that when the Newtonian mass per unit length reaches 1/2 the spacetime has plane symmetry.Comment: 13 pages, Late

Expansion-Free Evolving Spheres Must Have Inhomogeneous Energy Density Distributions

In a recent paper a systematic study on shearing expansion-free spherically symmetric distributions was presented. As a particular case of such systems, the Skripkin model was mentioned, which corresponds to a nondissipative perfect fluid with a constant energy density. Here we show that such a model is inconsistent with junction conditions. It is shown that in general for any nondissipative fluid distribution, the expansion-free condition requires the energy density to be inhomogeneous. As an example we consider the case of dust, which allows for a complete integration.Comment: 8 pages, Latex. To appear in Phys. Rev.D. Typos correcte