Synthesis and characterization of Fatty acid/amino Acid self-assemblies.

In this paper, we discuss the synthesis and self-assembling behavior of new copolymers derived from fatty acid/amino acid components, namely dimers of linoleic acid (DLA) and tyrosine derived diphenols containing alkyl ester pendent chains, designated as "R" (DTR). Specific pendent chains were ethyl (E) and hexyl (H). These poly(aliphatic/aromatic-ester-amide)s were further reacted with poly(ethylene glycol) (PEG) and poly(ethylene glycol methyl ether) of different molecular masses, thus resulting in ABA type (hydrophilic-hydrophobic-hydrophilic) triblock copolymers.

The support of bone marrow stromal cell differentiation by airbrushed nanofiber scaffolds.

Nanofiber scaffolds are effective for tissue engineering since they emulate the fibrous nanostructure of native extracellular matrix (ECM). Although electrospinning has been the most common approach for fabricating nanofiber scaffolds, airbrushing approaches have also been advanced for making nanofibers. For airbrushing, compressed gas is used to blow polymer solution through a small nozzle which shears the polymer solution into fibers.

Ethylene oxide's role as a reactive agent during sterilization: effects of polymer composition and device architecture.

Sterilization conditions need to be optimized to effectively neutralize the bioburden while using short exposure times for minimizing the changes in chemical composition, material properties and device architecture. Towards this goal, effects of ethylene oxide (EtO) exposure parameters such as time, temperature, humidity, and EtO concentration on the polymer properties were investigated by monitoring the changes in composition, and the morphology of different types of structures in a family of poly(ethylene glycol) (PEG)-containing tyrosine-derived polycarbonates. EtO was found to esterify the carboxyl groups present in the desaminotyrosyl-tyrosine groups.

Gas-Foamed Scaffold Gradients for Combinatorial Screening in 3D.

Current methods for screening cell-material interactions typically utilize a two-dimensional (2D) culture format where cells are cultured on flat surfaces. However, there is a need for combinatorial and high-throughput screening methods to systematically screen cell-biomaterial interactions in three-dimensional (3D) tissue scaffolds for tissue engineering. Previously, we developed a two-syringe pump approach for making 3D scaffold gradients for use in combinatorial screening of salt-leached scaffolds.

The fate of ultrafast degrading polymeric implants in the brain.

We have recently reported on an ultrafast degrading tyrosine-derived terpolymer that degrades and resorbs within hours, and is suitable for use in cortical neural prosthetic applications. Here we further characterize this polymer, and describe a new tyrosine-derived fast degrading terpolymer in which the poly(ethylene glycol) (PEG) is replaced by poly(trimethylene carbonate) (PTMC). This PTMC containing terpolymer showed similar degradation characteristics but its resorption was negligible in the same period.

Interplay of anionic charge, poly(ethylene glycol), and iodinated tyrosine incorporation within tyrosine-derived polycarbonates: Effects on vascular smooth muscle cell adhesion, proliferation, and motility.

Regulation of smooth muscle cell adhesion, proliferation, and motility on biomaterials is critical to the performance of blood-contacting implants and vascular tissue engineering scaffolds. The goal of this study was to examine the underlying substrate-smooth muscle cell response relations, using a selection of polymers representative of an expansive library of multifunctional, tyrosine-derived polycarbonates. Three chemical components within the polymer structure were selectively varied through copolymerization: (1) the content of iodinated tyrosine to achieve X-ray visibility; (2) the content of poly(ethylene glycol) (PEG) to decrease protein adsorption and cell adhesivity; and (3) the content of desaminotyrosyl-tyrosine (DT), which regulates the rate of polymer degradation.

Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle.

A semi-empirical method based on the mass-per-flexible-bond (M/f) principle was used to quantitatively explain the large range of glass transition temperatures (T(g)) observed in a library of 132 L-tyrosine derived homo, co- and terpolymers containing different functional groups. Polymer class specific behavior was observed in T(g) vs. M/f plots, and explained in terms of different densities, steric hindrances and intermolecular interactions of chemically distinct polymers.

Angiogenic competency of biodegradable hydrogels fabricated from polyethylene glycol-crosslinked tyrosine-derived polycarbonates.

Synthetic biomaterials can be used as instructive biological milieus to guide cellular behaviour and function. To further realize this application, we synthesized a series of structurally similar hydrogels and tested their ability to modulate angiogenesis. Hydrogels were synthesized from poly(DTE-co-x% DT carbonate) crosslinked by y% poly(ethylene glycol) (PEG).

Iodine inhibits antiadhesive effect of PEG: implications for tissue engineering.

Background: The success of a biomaterial implant may be affected by the surface chemistry's impact on protein adsorption. We have developed a series of poly(ethylene glycol) (PEG) containing, tyrosine-derived polycarbonates, which have been rendered radio-opaque by the iodination of tyrosine units in the copolymer backbone for use in resorbable biomedical implants including vascular stents and grafts. We tested the hypothesis that protein adsorption along with seeding, growth, and migration of human aortic smooth muscle cells (SMC) and human aortic endothelial cells (EC) will be modified by the presence of iodine and PEG within the polymer composition.

Viscoelastic properties of fibrinogen adsorbed to the surface of biomaterials used in blood-contacting medical devices.

The hemocompatibility of polymeric vascular implants is in part dependent on the propensity of fibrinogen to adsorb to the implant surface. Fibrinogen surface adsorption was measured in real time using a quartz crystal microbalance with dissipation monitoring (QCM-D). Six new, biodegradable tyrosine-derived polycarbonates were used as test surfaces.

Nontoxic block copolymer nanospheres: design and characterization.

Biodegradable polymers capable of self-assembly into hollow nanospheres of less than 100 nm have significant potential for biotechnology applications such as drug delivery and gene therapy. Here we describe the synthesis of a novel ABA-type triblock copolymer made from a hydrophobic tyrosine-derived core and two hydrophilic poly(ethylene glycol) end groups (poly(ethylene glycol)-block-oligo(desaminotyrosyltyrosine octyl ester suberate)-block-poly(ethylene glycol)). We describe the self-assembly of this triblock copolymer and characterize its particles as 100 nm size vesicular nanospheres.

Small changes in the polymer structure influence the adsorption behavior of fibrinogen on polymer surfaces: validation of a new rapid screening technique.

Numerous studies conclude that the selective adsorption of plasma proteins on materials contacting blood or tissue affects all subsequent interactions related to the biocompatibility of artificial surfaces. However, there are only a few studies available, which clearly demonstrate that there is a correlation between surface chemistry and selective protein adsorption. Detailed knowledge of such correlations would facilitate the design of biocompatible materials.

Structure-activity relationship for chemical skin permeation enhancers: probing the chemical microenvironment of the site of action.

Studies were previously conducted in our laboratory on the influence of n-alkanols, 1-alkyl-2-pyrrolidones, N,N-dimethlyalkanamides, and 1,2-alkanediols as skin permeation enhancers on the transport of a model permeant, corticosterone (CS). The experiments were conducted with hairless mouse skin (HMS) in a side-by-side, two-chamber diffusion cell, with enhancer present in an aqueous buffer in both chambers. The purpose of the present study was to extend these studies and investigate in greater detail the hypothesis that a suitable semipolar organic phase may mimic the microenvironment of the site of enhancer action, and that the enhancer partitioning tendency into this organic phase may be used to predict the enhancer potency.