Effects of Block Lengths and Initial Water Content on the Swelling and Degradative Characteristics of an Injectable Poly
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Effects of Block Lengths and Initial Water Content on the Swelling and Degradative Characteristics of an Injectable Poly(propylene fumarate-co-ethylene glycol) Block Copolymer Hydrogel
Albert K. Shung and Antonios G. Mikos Department of Bioengineering, Rice University, MS142 Houston, TX 77251-1892, USA. ABSTRACT The overall goal of this project is to develop an in-situ polymerizable, biodegradable material for use in cardiovascular applications that minimizes non-specific cell adhesion and contains functional moieties for the attachment of peptides to induce specific cell attachment. A novel block copolymer has been developed incorporating poly(propylene fumarate) (PPF) and poly(ethylene glycol) which satisfies these criteria. PPF is a new biodegradable polymer currently being investigated for orthopedic and cardiovascular applications while PEG is a hydrophilic polymer that has been extensively studied for biomedical applications. The copolymer is chemically crosslinked with PEG diacrylate using an ammonium persulfate-ascorbic acid redox initiator system to form the hydrogel. The PEG and PPF block lengths can be varied to modulate the properties of the hydrogel formed. In this study, the following three parameters were studied, (1) PPF block length, (2) PEG block length, and (3) initial water content, were varied to examine their effects on swelling, degradation and elastic modulus. A factorial experimental design was implemented to assess which of these three parameters had the greatest impact on swelling, degradation and elastic modulus. Swelling was found to be most affected by the initial water content followed by PEG block length and PPF block length. The swelling of the hydrogels ranged from 48% water uptake with low initial water content to up to 77% water uptake with the high initial water content. After three weeks, degradation of the hydrogels ranged from 4-13% mass fraction lost. Elastic modulus was determined by tensile testing of the various hydrogel formulations and ranged from 0.4 to 7.7 MPa.
INTRODUCTION
Atherosclerosis, the buildup of atherosclerotic plaque in the arteries, affects millions of Americans each year. This cardiovascular disorder can lead to chronic heart disease and eventually, myocardial infarction, which can lead to death. One of the most effective and popular methods of treating atherosclerosis is a procedure known as Percutaneous Transluminal Coronary Angioplasty (PTCA), more commonly known as balloon angioplasty. However, in 30-60% of PTCA procedures, retreatment of the patients is necessary due to restenosis or reocclusion of the blood vessel [1]. Current solutions include the use of metallic stents as means to mechanically keep the artery patent, however, results have been mixed at best. Not only are these stents nonMM1.4.1
degradable, but also, because of the natural stiffness of the metals, compliance mismatch can occur. The difference in mechanical properties between the flexible artery and the stiffness of metals can lead to continual stress at the implantation site le
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