Derick C. Miller

Endothelial and vascular smooth muscle cell function on poly(lactic-co-glycolic acid) with nano-structured surface features.

Biomaterials that successfully integrate into surrounding tissue should match not only the tissues mechanical properties, but also its topography. The cellular response to a biomaterial may be enhanced in synthetic polymer formulations by mimicking the surface roughness created by the associated nano-structured extra-cellular matrix components of natural tissue. As a first step towards this endeavor, the goal of the present in vitro study was to use these design parameters to develop a synthetic, nano-structured, polymeric biomaterial that promotes cell adhesion and growth for vascular applications. In a novel manner, poly(lactic-co-glycolic acid) (PLGA) (50/50wt% mix) was synthesized to possess a range (from micron to nanometer) of surface features. Reduction of surface features was accomplished by treating conventional PLGA with various concentrations of NaOH for select periods of time. Results from cell experiments indicated that, compared to conventional PLGA, NaOH treated PLGA enhanced vascular smooth muscle cell adhesion and proliferation. However, PLGA prepared by soaking in NaOH decreased endothelial cell adhesion and proliferation compared to conventional PLGA. After further investigation, this finding was determined to be a result of chemical (and not topographical) changes during polymer synthesis. Surface chemistry effects were removed while retaining nano-structured topography by using polymer/elastomer casting methods. Results demonstrated that endothelial and smooth muscle cell densities increased on nano-structured cast PLGA. For these reasons, the present in vitro study provided the first evidence that nano-structured surface features can significantly improve vascular cell densities; such design criteria can be used in the synthesis of the next-generation of more successful tissue-engineered vascular grafts.

Nano-structured polymers enhance bladder smooth muscle cell function

It is the hypothesis of the present study that a biocompatible material which mimics the nanometer topography of native bladder tissue will enhance cellular responses and lead to better tissue integration in vivo. Previous in vitro studies have verified the ability to successfully reduce the surface feature dimensions of poly(lactic-co-glycolic acid) (PLGA) and poly(ether urethane) (PU) films into the nanometer regime via chemical etching procedures. Results from these studies also provided the first evidence that bladder smooth muscle cell adhesion was enhanced on chemically treated nano-structured polymeric surfaces compared to their conventional counterparts. Although cell adhesion is necessary for a biomaterials success, subsequent cell functions (such as long-term cell growth and proliferation) are also critical for tissue ingrowth and long-term implant survival. The present in vitro study, therefore, investigated the function of bladder smooth muscle cells on these novel, nano-structured polymers over the expanded periods of 1, 3 and 5 days. Results indicated that cell number was influenced by both surface roughness and surface chemistry changes; the important contributor, however, was increased nanometer surface roughness. This claim is supported by the fact that cell number was enhanced on nano-structured compared to conventional PLGA and PU once chemistry changes were eliminated using casting techniques.

Enhanced functions of vascular and bladder cells on poly-lactic-co-glycolic acid polymers with nanostructured surfaces

Polymers currently utilized for tissue engineering applications do not possess surfaces with nanostructured features. However, the tissue that the polymers will replace is composed of proteins that have nanometer dimensions. Undoubtedly, in situ, cells are accustomed to interacting with surface roughness values in the nanometer regime due to the presence of such proteins in natural tissue. Therefore, the objective of this paper was to design, synthesize and evaluate (using in vitro cellular models) poly-lactic-co-glycolic acid (PLGA) with nanostructured surface features to serve as the next generation of more efficient tissue engineered materials. For this purpose, nanostructured PLGA was created by treating conventional PLGA with various concentrations of NaOH for select periods of time. To eliminate surface chemistry changes created though the etching process, PLGA was cast from silastic molds of NaOH-treated nanostructured PLGA. Results provided the first evidence of increased numbers of vascular cells (specifically, endothelial and aortic smooth muscle cells) and bladder smooth muscle cells on nanostructured compared with conventional PLGA substrates. For this reason, the present results suggest, for the first time, that PLGA should incorporate a high degree of nanostructured surface roughness to enhance tissue regeneration for vascular and bladder applications.

Technological advances in nanoscale biomaterials: the future of synthetic vascular graft design

Currently, autologous veins are the first choice for patients in need of bypass grafting materials. However, due to either pre-existing conditions or previous bypass surgery, some patients lack the necessary amount of host tissue for such procedures. Unfortunately, current synthetic vascular grafts of less than 6 mm in diameter have been plagued by a variety of problems. For this reason, there has been significant research aimed at finding more suitable small-diameter vascular graft materials. In order to improve vascular cell functions on such synthetic materials, several techniques are currently under development that attempt to mimic the natural nanometer architecture of the vascular basement membrane. This review presents several processes including colloidal lithography, chemical etching, electrospinning and solid free-form fabrication that could play a role in the future of vascular nanostructured biomaterial development.

Mechanisms controlling increased vascular cell adhesion to nano-structured polymer films

Previous research has shown that increasing the nanometer surface roughness of poly(lactic-co-glycolic acid) (PLGA) films promotes vascular endothelial and smooth muscle cell adhesion. The goal of this in vitro research was to understand the mechanism(s) behind these observed responses. In order to elucidate the adhesive factors for vascular cell adhesion on nano-structured PLGA, substrates of various surface feature dimensions were exposed to serum-containing media overnight. The adsorbed proteins were then desorbed using a stripping buffer and the amount, as well as type, of proteins initially adsorbed were analyzed. Furthermore, cellular adhesion studies were preformed in order to correlate the link between specific protein adsorption and subsequent cellular response. Results showed that nano-structured PLGA adsorbed significantly more vitronectin and fibronectin when compared to conventional PLGA. Additionally, vascular cell adhesion studies demonstrated that both vascular smooth muscle cell and endothelial cell density increased on vitronectin and fibronectin pre-adsorbed onto nano-structured (compared to conventional) PLGA. In combination, these results provide insights into the mechanism(s) of increased vascular cell adhesion on nano-structured PLGA important for tissue engineering applications.

In Vitro Vascular Cell Adhesion and Proliferation on Alkaline Degraded Poly-lactic/glycolic Acid Polymers

Abstract : The objective of the present in vitro study was to determine vascular endothelial and smooth muscle cell responses to poly(lactic-co-glycolic acid) (PLGA) films that were exposed apriori to various degrees of alkaline degradation. To model the alkaline environment of blood in arteries PLGA films were separately soaked in select concentrations (from 0.1 - 10N) of NaOH for various periods of time (from 10 minutes to 1 hour). Vascular endothelial and smooth muscle cells were then separately allowed to adhere and/or proliferate on the different PLGA degraded surfaces. Results provided the first evidence that smooth muscle adhesion and proliferation increased with larger amounts of alkaline PLGA degradation. In contrast endothelial cell adhesion and proliferation decreased with increasing amounts of alkaline PLGA degradation. In this manner, the present in vitro study suggests a possible mechanism for insufficient endothelialization on PLGA vascular implants in vivo.

Enhanced functions of cells on polymers with nanostructured surfaces

Polymers currently utilized for tissue engineering applications do not possess surfaces with nano-structured features. In contrast, the tissue that the polymers will regenerate is composed of proteins that have nanometer dimensions. Undoubtedly, the presence of proteins in natural tissue provide for surface roughness values in the nanometer regime. For this reason, the objective of the present study was to design, synthesize, and evaluate (using in vitro cellular models) poly-lactic-co-glycolic acid (PLGA) for use as the next generation of more efficient tissue engineered materials. Results provided the first evidence that osteoblasts (bone-forming cells), chondrocytes (cartilage synthesizing cells), aortic smooth muscle cells, and bladder smooth muscle cells adhered and proliferated more on nanostructured compared to conventionally structured PLGA substrates. For this reason, the present results suggest that to enhance tissue regeneration, PLGA should incorporate a high degree of nano-structured surface features.

Nano-structured poly-lactic-co-glycolic acid polymer surface features increase cell functions

Polymers currently utilized for tissue engineering applications do not possess surfaces with nanostructured features. In contrast, the tissue that the polymers will regenerate is composed of proteins that have nanometer dimensions. Undoubtedly, the presence of proteins in natural tissue provide for surface roughness values in the nanometer regime. For this reason, the objective of the present study was to design, synthesize, and evaluate (using in vitro cellular models) the ability of poly-lactic-co-glycolic acid (PLGA) as the next generation of more efficient tissue engineering materials. Results provided the first evidence that osteoblasts (bone-forming cells), chondrocytes (cartilage synthesizing cells), aortic smooth muscle cells, and bladder smooth muscle cells adhered and proliferated more on nanostructured compared to conventional PLGA substrates. For this reason, the present results suggest that to enhance tissue regeneration, PLGA should incorporate a high degree of nanostructured surface features.