Hydrogel Foams Research Articles

Hemostatic kaolin-polyurethane foam composites for multifunctional wound dressing applications

There are numerous challenges associated with the acute care of traumatic limb injuries in forward military settings. A lack of immediate medical facilities necessitates that the wound dressing perform multiple tasks including exudate control, infection prevention, and physical protection of the wound for extended periods of time. Here, kaolin was incorporated into recently developed robust polyurethane (PU) hydrogel foams at 1–10wt% in an effort to impart hemostatic character. ATR-IR and gel fraction analysis demonstrated that the facile, one-pot synthesis of the PU hydrogel was unaffected by kaolin loading, as well as the use of a non-toxic catalyst, which significantly improved cytocompatibility of the materials. Kaolin was generally well dispersed throughout the PU matrix, though higher loadings exhibited minor evidence of aggregation. Kaolin-PU composites exhibited burst release of ciprofloxacin over 2h, the initial release rates of which increased with kaolin loading. Kaolin loading imparted excellent hemostatic character to the PU foams at relatively low loading levels (5wt%). This work demonstrates the simple and inexpensive synthesis of robust, hemostatic, and absorptive kaolin-PU foams that have promising potential as multifunctional wound dressing materials.

Multi‐Functional Polyurethane Hydrogel Foams with Tunable Mechanical Properties for Wound Dressing Applications

Polyurethane hydrogel foams synthesized through a facile one‐pot, solvent‐free process are described. The roles of polyethylene glycol (PEG) molecular weight, crosslinking density, and foam stabilizer concentration on polymer properties are evaluated for potential applications as wound dressing materials. Material characterization and wound dressing relevant performance evaluations are performed to understand effects of individual components and identify promising formulations. Surprisingly for a solvent‐free reaction, complete polymerization is confirmed by IR and gel fraction analyses. Foam stabilizing agent loading increases mechanical properties including Young's modulus, extensibility, and toughness while decreasing pore size and drug release rate. Mechanical properties are also dependent on the crystalline melting temperature of the PEG diol. Utilizing caffeine as a drug surrogate, high performance liquid chromatography (HPLC) drug‐release analysis identifies that polyurethane hydrogel foams exhibit initial burst release kinetics followed by sustained release over 24 h. Antibiotic compatibility and release is demonstrated for all formulations by zone of inhibition testing against gram‐positive and negative bacteria. image

Development of bioactive hydrogel foams to accelerate healing of chronic wounds

Development of bioactive hydrogel foams to accelerate healing of chronic wounds

Generation of porous solids with well-controlled morphologies by combining foaming and flow chemistry on a Lab-on-a-Chip

We review here how millifluidic techniques can be used to construct versatile Labs-on-a-Chip, in which on-chip bubble generation and flow chemistry are efficiently combined to generate porous solids with highly monodisperse and ordered pore structures. With this approach, a liquid foam with well-controlled structural and chemical properties is first generated, which is then solidified in situ. We discuss here the interplay of various important processing parameters. In particular, we demonstrate that solidification time and foam life time need to be matched wisely in order to control precisely the properties of the final porous material. We also discuss a simple and inexpensive route to the manufacture of chemically and pressure-resistant, millifluidic Labs-on-a-Chip via the machining and hot-pressing of Cyclic Olefin Copolymers. We illustrate our review using the example of the generation of two types of hydrogel foams (synthetic acrylamide-based and biopolymer chitosan-based) and of particle foams, which may be used as green bodies for the manufacture of porous ceramics. The newly designed materials can be used to investigate fundamental questions of the structure–property relationship of porous solid.

Microstructural analysis of foam by use of NMR R 2 dispersion

The spin–spin relaxation rate R 2 (=1/T 2) in hydrogel foams measured by use of a multiple spin echo sequence is found to be dependent on the echo time spacing. This property, referred to as R 2-dispersion, originates to a large extent from molecular self-diffusion of water within internal field gradients that result from magnetic susceptibility differences between the gel and air phase. Another contribution to the R 2 relaxation rate is surface relaxation. Numerical simulations are performed to investigate the relation between the foam microstructure (the mean air bubble radius and standard deviation of the air bubble radius) and foam composition properties (such as magnetic susceptibilities, diffusion coefficient and surface relaxivity) at one hand and the R 2-dispersion at the other hand. The simulated R 2-dispersions of gel foam are in agreement with the measured R 2-dispersions. By correlating the R 2-dispersion parameters and simulated microstructure properties a semi-empirical relationship is obtained that enables the mean air bubble size to be derived from measured R 2-dispersion curves. The R 2-derived mean air bubble size of a hydrogel foam is in agreement with the bubble size measured with X-ray micro-CT. This illustrates the feasibility of using 1H R 2-dispersion measurements to determine the size of air bubbles in hydrogel foams and of alveoli in lung tissue.

Dynamics of fibrovascular tissue ingrowth in hydrogel foams

We have investigated and quantified the degree of fibrovascular tissue ingrowth in cylindrical poly(vinyl alcohol) (PVA) foams of 12.5 mm diameter, 5 mm thickness, and 71% porosity implanted in the mesentery of rats over a period of 25 days. Fibrovascular tissue penetrated the center of PVA foams 5 days postimplantation yet the void fraction available for cell seeding was 55% and the volume average pore diameter was 190 (±39) μm. By 10 days postimplantation the void fraction had decreased to 32% and the volume average pore diameter was 121 (±20) μm. As time elapsed fibrovascular tissue continued to expand and fill the remaining pore space. At 15 days postimplantation the void space was impractical for cell seeding and continued to decrease through the remainder of the study. Our data suggest that hydrogel foams with a polydispersed pore morphology can be prevascularized with adequate space for cell seeding as the volume of tissue penetrating the foam is limited by the smaller pores in the foam structure; however, available void space for cell seeding decreases with time.

Dynamics of fibrovascular tissue ingrowth in hydrogel foams.

We have investigated and quantified the degree of fibrovascular tissue ingrowth in cylindrical poly(vinyl alcohol) (PVA) foams of 12.5 mm diameter, 5 mm thickness, and 71% porosity implanted in the mesentery of rats over a period of 25 days. Fibrovascular tissue penetrated the center of PVA foams 5 days postimplantation yet the void fraction available for cell seeding was 55% and the volume average pore diameter was 190 (+/- 39) microns. By 10 days postimplantation the void fraction had decreased to 32% and the volume average pore diameter was 121 (+/- 20) microns. As time elapsed fibrovascular tissue continued to expand and fill the remaining pore space. At 15 days postimplantation the void space was impractical for cell seeding and continued to decrease through the remainder of the study. Our data suggest that hydrogel foams with a polydispersed pore morphology can be prevascularized with adequate space for cell seeding as the volume of tissue penetrating the foam is limited by the smaller pores in the foam structure; however, available void space for cell seeding decreases with time.