Charlotte L. Huang

The effect of polyethylene glycol structure on paclitaxel drug release and mechanical properties of PLGA thin films.

Thin films of poly(lactic acid-co-glycolic acid) (PLGA) incorporating paclitaxel typically have slow release rates of paclitaxel of the order of 1 μg day(-1) cm(-2). For implementation as medical devices a range of zero order release rates (i.e. 1-15 μg day(-1) cm(-2)) is desirable for different tissues and pathologies. Eight and 35 kDa molecular weight polyethylene glycol (PEG) was incorporated at 15%, 25% and 50% weight ratios into PLGA containing 10 wt.% paclitaxel. The mechanical properties were assessed for potential use as medical implants and the rates of release of paclitaxel were quantified as per cent release and the more clinically useful rate of release in μg day(-1) cm(-2). Paclitaxel quantitation was correlated with the release of PEG from PLGA, to further understand its role in paclitaxel/PLGA release modulation. PEG release was found to correlate with paclitaxel release and the level of crystallinity of the PEG in the PLGA film, as measured by Raman spectrometry. This supports the concept of using a phase separating, partitioning compound to increase the release rates of hydrophobic drugs such as paclitaxel from PLGA films, where paclitaxel is normally homogeneously distributed/dissolved. Two formulations are promising for medical device thin films, when optimized for tensile strength, elongation, and drug release. For slow rates of paclitaxel release an average of 3.8 μg day(-1) cm(-2) using 15% 35k PEG for >30 days was achieved, while a high rate of drug release of 12 μg day(-1) cm(-2) was maintained using 25% 8 kDa PEG for up to 12 days.

SMAD3 Deficiency Promotes Inflammatory Aortic Aneurysms in Angiotensin II–Infused Mice Via Activation of iNOS

Background Ninety percent of the patients carrying distinct SMAD3 mutations develop aortic aneurysms and dissections, called aneurysms‐osteoarthritis syndrome (AOS). However, the etiology and molecular events downstream of SMAD3 leading to the pathogenesis of aortic aneurysms in these patients still remain elusive. Therefore, we aimed to investigate the vascular phenotypes of SMAD3‐knockout mice. Methods and Results We have shown that angiotensin II–induced vascular inflammation, but not hypertension, leads to aortic aneurysms and dissections, ultimately causing aortic rupture and death in mice. Lipopolysaccharide‐triggered inflammation confirmed that enhanced aortic macrophage recruitment was essential for aneurysm formation in angiotensin II–infused SMAD3‐knockout mice. In contrast, phenylephrine‐triggered hypertension alone was insufficient to induce aortic aneurysms in mice. Using uniaxial tensile and contractility tests, we showed that SMAD3 deficiency resulted in defective aortic biomechanics and physiological functions, which caused weakening of the aortic wall and predisposed the mice to aortic aneurysms. Chromatin immunoprecipitation (ChIP) and re‐ChIP assays revealed that the underlying mechanism involved aberrant upregulation of inducible nitric oxide synthase (iNOS)–derived nitric oxide production and activation of elastolytic matrix metalloproteinases 2 and 9. Administration of clodronate‐liposomes and iNOS inhibitor completely abrogated these aortic conditions, thereby identifying iNOS‐mediated nitric oxide secretion from macrophages as the downstream event of SMAD3 that drives this severe pathology. Conclusions Macrophage depletion and iNOS antagonism represent 2 promising approaches for preventing aortic aneurysms related to SMAD3 mutations and merit further investigation as adjunctive strategies for the life‐threatening manifestations of AOS.

High-throughput screening of PLGA thin films utilizing hydrophobic fluorescent dyes for hydrophobic drug compounds

Hydrophobic, antirestenotic drugs such as paclitaxel (PCTX) and rapamycin are often incorporated into thin film coatings for local delivery using implantable medical devices and polymers such as drug-eluting stents and balloons. Selecting the optimum coating formulation through screening the release profile of these drugs in thin films is time consuming and labor intensive. We describe here a high-throughput assay utilizing three model hydrophobic fluorescent compounds: fluorescein diacetate (FDAc), coumarin-6, and rhodamine 6G that were incorporated into poly(d,l-lactide-co-glycolide) (PLGA) and PLGA-polyethylene glycol films. Raman microscopy determined the hydrophobic fluorescent dye distribution within the PLGA thin films in comparison with that of PCTX. Their subsequent release was screened in a high-throughput assay and directly compared with HPLC quantification of PCTX release. It was observed that PCTX controlled-release kinetics could be mimicked by a hydrophobic dye that had similar octanol-water partition coefficient values and homogeneous dissolution in a PLGA matrix as the drug. In particular, FDAc was found to be the optimal hydrophobic dye at modeling the burst release as well as the total amount of PCTX released over a period of 30 days.

Novel gradient casting method provides high-throughput assessment of blended polyester poly(lactic-co-glycolic acid) thin films for parameter optimization

Pure polymer films cannot meet the diverse range of controlled release and material properties demanded for the fabrication of medical implants or other devices. Additives are added to modulate and optimize thin films for the desired qualities. To characterize the property trends that depend on additive concentration, an assay was designed which involved casting a single polyester poly(lactic-co-glycolic acid) (PLGA) film that blends a linear gradient of any PLGA-soluble additive desired. Four gradient PLGA films were produced by blending polyethylene glycol or the more hydrophobic polypropylene glycol. The films were made using a custom glass gradient maker in conjunction with a 180 cm film applicator. These films were characterized in terms of thickness, percent additive, total polymer (PLGA+additive), and controlled drug release using drug-like fluorescent molecules such as coumarin 6 (COU) or fluorescein diacetate (FDAc). Material properties of elongation and modulus were also accessed. Linear gradients of additives were readily generated, with phase separation being the limiting factor. Additive concentration had a Pearsons correlation factor (R) of >0.93 with respect to the per cent total release after 30 days for all gradients characterized. Release of COU had a near zero-order release over the same time period, suggesting that coumarin analogs may be suitable for use in PLGA/polyethylene glycol or PLGA/polypropylene glycol matrices, with each having unique material properties while allowing tuneable drug release. The gradient casting method described has considerable potential in offering higher throughput for optimizing film or coating material properties for medical implants or other devices.

Calcium phosphate coated Keratin–PCL scaffolds for potential bone tissue regeneration

The incorporation of hydroxyapatite (HA) nanoparticles within or on the surface of electrospun polymeric scaffolds is a popular approach for bone tissue engineering. However, the fabrication of osteoconductive composite scaffolds via benign processing conditions still remains a major challenge to date. In this work, a new method was developed to achieve a uniform coating of calcium phosphate (CaP) onto electrospun keratin-polycaprolactone composites (Keratin-PCL). Keratin within PCL was crosslinked to decrease its solubility, before coating of CaP. A homogeneous coating was achieved within a short time frame (~10min) by immersing the scaffolds into Ca(2+) and (PO4)(3-) solutions separately. Results showed that the incorporation of keratin into PCL scaffolds not only provided nucleation sites for Ca(2+) adsorption and subsequent homogeneous CaP surface deposition, but also facilitated cell-matrix interactions. An improvement in the mechanical strength of the resultant composite scaffold, as compared to other conventional coating methods, was also observed. This approach of developing a biocompatible bone tissue engineering scaffold would be adopted for further in vitro osteogenic differentiation studies in the future.

Drug-eluting scaffolds for bone and cartilage regeneration

The advances in strategies for bone and cartilage regeneration have been centered on a concept that describes the close relationship between osteogenic cells, osteoconductive scaffolds, delivery growth factors and the mechanical environment. The dynamic nature of the tissue repair process involves intricate mimicry of signals expressed in the biological system in response to an injury. Recently, synergistic strategies involving hybrid delivery systems that provide sequential dual delivery of biomolecules and relevant topological cues received great attention. Future advances in tissue regeneration will therefore depend on multidisciplinary strategies that encompass the crux of tissue repair aimed at constructing the ideal functional regenerative scaffold. Here, functional scaffolds delivering therapeutics are reviewed in terms of their controlled release and healing capabilities.

Collagen-cellulose composite thin films that mimic soft-tissue and allow stem-cell orientation.

Mechanical properties of collagen films are less than ideal for biomaterial development towards musculoskeletal repair or cardiovascular applications. Herein, we present a collagen–cellulose composite film (CCCF) compared against swine small intestine submucosa in regards to mechanical properties, cell growth, and histological analysis. CCCF was additionally characterized by FE-SEM, NMR, mass spectrometry, and Raman Microscopy to elucidate its physical structure, collagen–cellulose composition, and structure activity relationships. Mechanical properties of the CCCF were tested in both wet and dry environments, with anisotropic stress–strain curves that mimicked soft-tissue. Mesenchymal stem cells, human umbilical vein endothelial cells, and human coronary artery smooth muscle cells were able to proliferate on the collagen films with specific cell orientation. Mesenchymal stem cells had a higher proliferation index and were able to infiltrate CCCF to a higher degree than small intestine submucosa. With the underlying biological properties, we present a collagen–cellulose composite film towards forthcoming biomaterial-related applications.Graphical Abstract

Manipulating magnetic 3D spheroids in hanging drops for applications in tissue engineering and drug screening.

Magnetic spheroid manipulation can be carried out in hanging drops to generate distinctly structured heterotypic microtissues through sequential addition of cells or spheroid to homotypic spheroids. These spheroids can also be incorporated in a droplet-based assay to screen for therapeutic efficacy in prolonged studies. This simple and versatile technique can offer potential benefits in tissue engineering and drug screening applications.

Microencapsulation of dye- and drug-loaded particles for imaging and controlled release of multiple drugs

A polymeric microcapsule that can house different drug-loaded particles using a simple emulsion packaging technique is presented. Compared to the neat microparticles, microcapsules simultaneously release multiple drugs in a sustained manner. These microcapsules could provide a means of controlling release of multiple drugs.