Raman Microspectroscopy Study of the Hydrolytic Degradation of Polyanhydride Network Polymers.

Raman microspectroscopy was employed in this work to study the degradation of a polyanhydride network polymer synthesized from 4-pentenoic anhydride and pentaerythritol tetrakis(3-mercaptopropionate) monomers in order to illustrate the utility of this method and improve the understanding of the polyanhydride degradation and erosion. Disk-shaped polymer samples were immersed in buffer solutions for different periods of time, and hydrolytic degradation was monitored spatially and temporally via kinetic Raman studies at various depths of penetration into the samples. Erosion, meanwhile, was monitored via mass loss measurements. Dispersive Raman microspectroscopy is shown to be a particularly valuable tool for the study of the hydrolytic degradation of these materials. It confirms that these thiol-ene polyanhydrides are indeed surface eroding, while also revealing that degradation starts to occur at the core of samples on a short time scale (less than 5 h). At any given degradation time, there is a concentration gradient of the unreacted anhydride, with the unreacted anhydride concentration increasing from the outer edge to the center of the polymer samples. Further, the anhydride functionality is found to decrease approximately linearly with degradation time at all depths in the samples, though the degradation rate does appear to increase slightly as degradation occurs.

Surface Eroding, Semicrystalline Polyanhydrides via Thiol-Ene "Click" Photopolymerization.

Surface eroding and semicrystalline polyanhydrides, with tunable erosion times and drug delivery pharmacokinetics largely dictated by erosion, are produced easily with thiol-ene "click" polymerization. This strategy yields both linear and cross-linked network polyanhydrides that are readily and fully cured within minutes using photoinitiation, can contain up to 60% crystallinity, and have tensile moduli up to 25 MPa for the compositions studied. Since they readily undergo hydrolysis and exhibit the oft-preferred surface erosion mechanism, they may be particularly useful in drug delivery applications. The polyanhydrides were degraded under pseudophysiological conditions and cylindrical samples (10 mm diameter × 5 mm height) were completely degraded within ∼10 days, with the mass-time profile being linear for much of this time after a ∼24 h induction period. Drug release studies, using lidocaine as a model, showed pharmacokinetics that displayed a muted burst release in the early stages of erosion, but then a delayed release profile that is closely correlated to the erosion kinetics. Furthermore, cytotoxicity studies of the linear and cross-linked semicrystalline polyanhydrides, and degradation products, against fibroblast cells indicate that the materials have good cytocompatibility. Overall, cells treated with up to 2500 mg/L of the semicrystalline polyanhydrides and degradation products show >90% human dermal fibroblast adult (HDFa) cell viability indicative of good cytocompatibility.

Photopolymerized cross-linked thiol-ene polyanhydrides: erosion, release, and toxicity studies.

Several critical aspects of cross-linked polyanhydrides made using thiol-ene polymerization are reported, in particular the erosion, release, and solution properties, along with their cytotoxicity toward fibroblast cells. The monomers used to synthesize these polyanhydrides were 4-pentenoic anhydride and pentaerythritol tetrakis(3-mercaptopropionate). Techniques used to evaluate the erosion mechanism indicate a complex situation in which several phenomena, such as hydrolysis rates, local pH, water diffusion, and solubility, may be influencing the erosion process. The mass loss profile, the release rate of a hydrophilic dye, the rate of hydrolysis of the polyanhydride, the hydrolysis product solubility as a function of pH, average pK(a) and its cytotoxicity toward fibroblast cells were all determined. The solubility of the degradation product is low at pH values less than 6-7, and the average pKa was determined to be ~5.3. The cytotoxicity of the polymer and the degradation product was found to be low, with cell viabilities of >97% for the various samples studied at concentrations of ~1000-1500 ppm. These important parameters help determine the potential of the thiol-ene polyanhydrides in various biomedical applications. These polyanhydrides can be used as a delivery vehicle, and although the release profile qualitatively followed the mass loss profile for a hydrophilic dye, the release rate appears to be by both diffusion and mass loss mechanisms.

Engineering injectable, biocompatible, and highly elastic bioadhesive cryogels.

The extracellular matrix (ECM), an integral component of all organs, is inherently tissue adhesive and plays a pivotal role in tissue regeneration and remodeling. However, man-made three-dimensional (3D) biomaterials that are designed to mimic ECMs do not intrinsically adhere to moisture-rich environments and often lack an open macroporous architecture required for facilitating cellularization and integration with the host tissue post-implantation. Furthermore, most of these constructs usually entail invasive surgeries and potentially a risk of infection. To address these challenges, we recently engineered biomimetic and macroporous cryogel scaffolds that are syringe injectable while exhibiting unique physical properties, including strong bioadhesive properties to tissues and organs. These biomimetic catechol-containing cryogels were prepared from naturally-derived polymers such as gelatin and hyaluronic acid and were functionalized with mussel-inspired dopamine (DOPA) to impart bioadhesive properties. We found that using glutathione as an antioxidant and incorporating DOPA into cryogels via a PEG spacer arm led to the highest tissue adhesion and improved physical properties overall, whereas DOPA-free cryogels were weakly tissue adhesive. As shown by qualitative and quantitative adhesion tests, DOPA-containing cryogels were able to adhere strongly to several animal tissues and organs such as the heart, small intestine, lung, kidney, and skin. Furthermore, these unoxidized (i.e., browning-free) and bioadhesive cryogels showed negligible cytotoxicity toward murine fibroblasts and prevented the ex vivo activation of primary bone marrow-derived dendritic cells. Finally, in vivo data suggested good tissue integration and a minimal host inflammatory response when subcutaneously injected in rats. Collectively, these minimally invasive, browning-free, and strongly bioadhesive mussel-inspired cryogels show great promise for various biomedical applications, potentially in wound healing, tissue engineering, and regenerative medicine.

Drug Delivery and Drug Efficacy from Amorphous Poly(thioether anhydrides).

The correlation between erosion and drug (lidocaine and 6-mercaptopurine, 6-MP) release from amorphous poly(thioether anhydrides), which are synthesized using radical-mediated thiol-ene polymerization, is reported. Cytotoxicity studies of the polymer toward human fibroblast human dermal fibroblasts adult, melanoma A-375, and breast cancer MCF-7 cells are conducted, and drug efficacy of a cancer and autoimmune disease drug (6-MP) when released from the poly(thioether anhydrides) is examined against two cancerous cell types (A-375 and MCF-7). Erosion and drug release studies reveal that lidocaine release is governed by network erosion whereas 6-MP is released by a combination of erosion and diffusion. The cytotoxicity studies show that all three cell types demonstrate high viability, thus cytocompatibility, to poly(thioether anhydrides). Toxicity to the material is dose dependent and comparable to other polyanhydride systems. The 6-MP cancer drug is shown to remain bioactive after encapsulation in the poly(thioether anhydride) matrix and the polymer does not appear to modify the efficacy of the drug.

Latest Progress in Electrospun Nanofibers for Wound Healing Applications.

Electrospinning is a versatile technique used to create native tissue-like fibrous scaffolds. Recently, it has gained a large amount of attention for generation of bioactive dressing materials suitable for treatment of both chronic and acute wounds. In this Review, we focus on the latest advances made in the application of electrospun scaffolds for bioactive wound healing. We first provide a brief overview of the wound healing process and electrospinning approaches. We then discuss fabrication of scaffolds made from natural and synthetic polymers via electrospinning for effective wound treatment and management. Natural polymers used for wound healing included in our Review cover protein based polymers such as collagen, gelatin, and silk and polysaccharide based polymers such as chitosan, hyaluronic acid, and alginate. In addition, we discuss aliphatic polyesters, super hydrophilic polymers, and polyurethanes as some of the most commonly used synthetic polymers for wound healing and wound dressing applications. Next, we review multifunctional and "smart" scaffolds developed by electrospinning based approaches. We place an emphasis on how flexibility of the electrospinning process enables production of advanced scaffolds such as core-shell fibrous scaffolds, multilayer scaffolds, and surface modified scaffolds. Taken together, it is clear that electrospinning is an emerging technology that provides a unique opportunity for engineering more effective wound dressing, management, and care products.

Quantitative and qualitative toxicological evaluation of thiol-ene "click" chemistry-based polyanhydrides and their degradation products.

Quantitative and qualitative toxicological analyses of crosslinked, surface-eroding polyanhydrides (PAHs) made from thiol-ene "click" polymerizations are reported. The cytotoxicity of these PAHs was investigated against three skin-based cell types; melanoma (A-375), human dermal fibroblast adult (HDFa), and 3T3-J2 (mouse fibroblast) cells, thus providing insight into the potential for these PAHs to be used in dermal drug delivery applications. Apoptosis was evaluated quantitatively and qualitatively using MTT assay and fluorescence microscopic imaging as indication of cytotoxicity. Upon exposure of A-375 and HDFa cells to high concentrations (4000 mg/L) of crosslinked PAH, the respective morphologies remained relatively unchanged compared with nonexposed cells. The 3T3-J2 cell type was more sensitive towards the PAH, exhibiting minimal deformation of cell morphology at 4000 mg/L. The MTT assay and fluorescence imaging revealed that this PAH and its degradation products are highly cytocompatible at high concentrations and cytotoxicity observed is dosage/time dependent. Further, the PAH did not induce inhibition of tested cells' proliferation at high polymer concentration up to 2000 mg/L. The IC50 (concentration of the crosslinked PAH required to inhibit 50% cell viability) for HDFa and A-375 cells was determined to be 4300 ± 70 and 8500 ± 50 mg/L, respectively. The high cytocompatibility of this type of crosslinked PAH, in addition to their degradation products, towards these skin cells (standard and cancer cell types) suggests that the polymer may be viable for dermal-based drug delivery to normal and cancerous diseased tissues. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1936-1945, 2016.

Anhydride-Based Reconfigurable Shape Memory Elastomers.

Soft shape memory polymers typically embody a permanently memorized geometry that cannot be altered, and therefore a new sample must be fabricated each time a new structure is required. We present a shape memory elastomeric composite featuring thermoplastic fibers as a fixing phase and a polyanhydride-based elastomer as the permanent, elastic phase. Interestingly, dynamic covalent exchange reactions at elevated temperatures (T > 50 °C) among the network chains of the elastomer allow near-complete reconfiguration of the permanent shape in the solid state. Together, these features combine to create a shape memory elastomer capable of arbitrary programming of both temporary and permanent shapes.

Noncovalent binding and fluorogenic response of cyanine dyes to DNA homoquadruplex and PNA-DNA heteroquadruplex structures.

Two symmetrical cyanine dyes based on benzothiazole heterocycles and a trimethine bridge were found to bind to a parallel-stranded DNA guanine quadruplex based on the MYC oncogene promoter sequence with high nanomolar affinity and 1:1 stoichiometry. The dyes exhibited substantial fluorescence enhancements upon binding. In the presence of homologous guanine-rich peptide nucleic acid oligomers, PNA-DNA heteroquadruplexes were formed. The dyes retained their ability to bind to the heteroquadruplexes at low micromolar concentrations and with varying fluorescence enhancements, although indeterminate stoichiometries preclude quantitative comparison of the affinities with the DNA homoquadruplex precursor. The difference in fluorescence enhancement between DNA homoquadruplex and PNA-DNA heteroquadruplex allows the dyes to be used as fluorogenic indicators of hybridization in a facile method for determining PNA-DNA stoichiometry.