B'reshith

The Hebrew word "b'reshith" (בְּרֵאשִׁית) means "in the beginning". It is the first word and title of the Book of Genesis, and it describes a process of creation. The four authors were present at the beginning of Langer labs, and the purpose of this essay is to convey the scientific and technological zeitgeist that existed in the late 1970s and early 1980s, when Bob Langer began his exceptionally creative work. While Langer labs has branched into many other areas, Bob's unique ability to recognize important problems and entice people to look beyond their own disciplines to solve them was evident from the start. We focus on the two areas of most interest to Bob at the time, namely controlled release of macromolecules from polymers, and removal of heparin in order to prevent uncontrolled bleeding during surgery.

Synthesis of thermoresponsive polymers for drug delivery

A protocol for synthesizing thermosensitive copolymers of N-isopropylacrylamide (NIPAM) and N-vinylpyrrolidone (VP), cross-linked with N,N'-methylene-bis-acrylamide (MBA) has been described in this chapter. The copolymers have been formed at different concentrations of NIPAM and VP and at two different temperatures (70 °C and 30 °C). The lower critical solution temperature (LCST) of the samples has been measured, and the size of the particles formed with the highest concentration of NIPAM and lowest concentration of VP (MG1 and NG1) has been measured at three different temperatures of 25 °C, 35 °C, and 37 °C. Both MG1 and NG1 showed the lowest size at 37 °C. The MG1 and NG1 samples were further characterized using TEM and SEM. The MG1 particles were subsequently used for protein drug delivery, using BSA as a model. The release profile showed the best fit with the zero-order model. Finally, cytotoxicity studies of the synthesized MG1 and NG1 particles were carried out, using in vitro MTT assay, so as to determine the overall biocompatibility of the materials.

The Effect of Ultrasound Wave on Levothyroxine Release from Chitosan Nanoparticles

A nanoparticle polymer has been developed as a potential platform for drug delivery. Chitosan nanoparticles were prepared with tripolyphosphate (TPP) by the ionic crosslinking method. The particle size of chitosan nanoparticles was in the range of 190-250 nm and encapsulation efficiencies of levothyroxine were 85%. The particle size was determined by photon correlation spectroscopy (PCS). Shape and surface morphology were determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). They revealed fairly spherical shape of nanoparticles. A non-invasive way to deliver drugs to the deepest parts of the human body is ultrasound. To study how ultrasound causes levothyroxine to be released from chitosan nanoparticles, cumulative release was examined. In this report, we explore the effect of ultrasound and tripolyphosphate (TPP) concentration on release behavior of levothyroxine from chitosan nanoparticles. The drug release from chitosan nanoparticles was enhanced using the ultrasound wave.

Can sonication enhance release from liquid-core capsules with a hydrogel membrane?

The objective is to investigate the influence of sonication on the mechanical and release properties of hydrogel capsules. A new fabrication process is developed to fabricate millimetric capsules made of a highly-viscous liquid core protected by a thin hyperelastic alginate membrane. At high intensities and/or long exposure times, sonication can lead to the capsule rupture, because it induces fatigue in the membrane. Below the breakup threshold, no remnant effect of sonication is, however, measured on the capsule mechanical properties. The release is studied by sonicating capsules filled with blue dextran suspended in an aqueous solution. The mass release that results from sonication is found to be proportional to the sonication duration time and pressure wave amplitude. A possible physical interpretation is that the acoustic streaming flow induced by the ultrasonic wave enhances convection in the vicinity of the capsule membrane and thus mass release. We have finally quantified the passive release subsequent to low-intensity sonications: it is on average identical to the one measured on non-sonicated capsules. Overall the membrane therefore recovers its physical and mechanical properties after sonication. If sonication leads to an increase in porosity of the capsule membrane, the increase is temporary and reverses back at the end of the ultrasonic stimulation.

Ultrasonically enhanced delivery and degradation of PAHs in a polymer-liquid partitioning system by a microbial consortium

The current study examined the effects of ultrasonic irradiation on mass transfer and degradation of PAHs, by an enriched consortium, when delivered from polymeric matrices. Rates of release into methanol under sonicated conditions, relative to unmixed cases, for phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene were increased approximately fivefold, when delivered from Desmopan 9370 A (polyurethane). Similar effects were observed in Hytrel and Kraton D4150 K polymers as well as recycled Bridgestone tires. Enhancements were also displayed as shifts to higher release equilibria under sonicated conditions, relative to non-sonicated cases, agreeing with current knowledge in sonochemistry and attributed to cavitation. Ultrasonic effects on microbial activity were also investigated and cell damage was found to be non- permanent with consortium re-growth being observed after sonic deactivation. Finally, the lumped effect of sonication on degradation of phenanthrene delivered from Desmopan was examined under the absence and presence of sonication. Rates of degradation were found to be increased by a factor of four demonstrating the possibility of using ultrasonic irradiation for improved mass transport in solid-liquid systems. Cellular inactivation effects were not evident, and this was attributed to the attenuation of sonic energy arising from the presence of solid polymer materials in the medium. The findings of the study demonstrate that sonication can be used to improve mass transport of poorly soluble compounds in microbial degradations, and alleviate limiting steps of soil remediation processes proposed in previous research.

Biomaterials approaches to combating oral biofilms and dental disease

Background

Possibilities for biomaterials to impact the dental caries epidemic are reviewed with emphasis placed on novel delivery biomaterials and new therapeutic targets.

Ultrasound degradation of novel polymer contrast agents

This report describes an investigation into factors affecting the degradation of novel poly(lactic-co-glycolic acid) (PLGA) contrast agents. Contrast agents fabricated by two different methods and varying in acoustic properties were compared. The effect of ultrasound frequency (5 and 10 MHz) on degradation of the microcapsules was also studied. High-performance liquid chromatography was used to quantify the production of lactic and glycolic acid to monitor agent degradation. The degradation pattern from the microcapsules was found to be closely related to capsule morphology; the more acoustically efficient capsules (maximum enhancement of 25 dB at 5 MHz with 0.004 mg/mL) degraded at a faster rate than those with lower acoustical efficiency (maximum enhancement of 25 dB at 5 MHz only achieved with 0.6 mg/mL). The capsules also degraded fastest when insonated at the frequency at which they gave highest backscatter. In addition, despite the use of a 50:50 PLGA copolymer, more glycolic than lactic acid was released at early time points, which reflects the greater hydrophilicity of the glycolic acid residues, and greater degradation rate of glycolic acid repeat units. The results from this study provided unique insight into the degradation behavior of hollow PLGA microcapsules, and their potential in ultrasound diagnosis and therapy.

Ultrasound-assisted insulin delivery and noninvasive glucose sensing

Peptides and proteins are emerging as an increasingly important class of drugs as they become more readily available through improvement in recombinant DNA technology and chemical synthesis techniques. The application of peptides and proteins as clinically useful drugs is, however, seriously hampered owing to the substantial delivery problems requiring frequent injections. Considerable effort has been directed therefore to developing painless and convenient methods for delivery of peptides and proteins. In diabetes, in addition to the need of insulin injections there is a need to develop painless and convenient methods to measure blood glucose. This review describes approaches based on the application of ultrasound for noninvasive and painless transdermal glucose sensing and delivery of insulin.

Responsive polymeric delivery systems

This paper discusses the state of the art in a relatively new approach in the field of controlled drug delivery-responsive polymeric drug delivery systems. Such systems are capable of adjusting drug release rates in response to a physiological need. The fundamental principles of externally and self-regulated delivery systems are examined. Special attention is paid to specific clinical settings such as diabetes, presenting the advantages and disadvantages of different approaches.

Mass transport enhancement by ultrasound in non-degradable polymeric controlled release systems

In this work, an attempt was made to characterize mass transport enhancement in non-erodible polymeric matrices, caused by ultrasound. It was found that drug release rates from polymeric matrices exposed to ultrasound, can be controlled by modifying parameters like: ultrasound frequency, molecular weight of the incorporated drug and structure of the polymeric matrix (size of pores in the network). It is suggested that the enhancing effect of ultrasound on drug release from non-erodible polymers is due to the contribution of a convective term, generated by cavitation, without any destructive effect on morphology of the polymer. This phenomenon was found to be more pronounced in systems which are mass-transport limited.