Novel Light-Responsive Biocompatible Hydrogels Produced by Initiated Chemical Vapor Deposition

Abstract

A novel multiresponsive hydrogel has been synthesized by initiated chemical vapor deposition (iCVD). Hydrogels are known for their dynamic swelling response to aqueous environments. A chemical functionalization of the hydrogel surface was performed to add other stimuli-responsive functionalities and obtain a smart material that responds to two stimuli: light irradiation and exposure to aqueous environment. Modifying the hydrogel surface with solution-based methods is often problematic because of the damages caused by the permeation of solvents in the hydrogel. This issue is completely bypassed by the use of solvent-free techniques. Cross-linked polymers of 2-hydroxyethyl methacrylate (HEMA) were functionalized with azobenzene groups, as confirmed by IR spectroscopy and X-ray photoelectron spectroscopy (XPS). Through photoisomerization of the azobenzene, the polarity within the hydrogel is modified and as a consequence the affinity to water. Light irradiation modifies the degree of swelling within thin hydrogel films from 13% before exposure to UV light to 25% after exposure. The possibility of controlling the degree and rate of swelling by light irradiation was never reported before on these time scales and can have exceptional implications for light-induced drug delivery or light-controlled microfluidic systems. The light-responsive hydrogels showed also biocompatibility, which makes them suitable for a great variety of applications as biomaterials.

Strategies for Drug Encapsulation and Controlled Delivery Based on Vapor‐Phase Deposited Thin Films

“…Drug delivery, targeted to a specific body location and/or in time, is an interesting feature of the new generation biomedical devices and it can be achieved through the use of “smart” formulation embedded in tunable polymer shells that hinder the drug release until a proper stimulus is detected . Stimuli‐responsive polymers serve this purpose very well: they undergo changes in thickness, mesh size and/or surface energy depending on the external stimuli, like temperature, pH, and light . Summarizing the previous paragraphs, the deposition of this kind of polymers from the vapor phase can have several advantages: (i) the absolute lack of solvents or high temperature allows easy drug encapsulation, without inducing damages that would harm the formulation or components therein and later the therapeutic effects; (ii) the absence of plasticizers, leachable, and surfactants eliminates the health considerations associated with these components; (iii) the possibility to reproduce interesting geometries by conformally coating the tridimensional features of a substrate; (iv) the easy tunability of the film and surface properties.…”

“…When the API is homogenously dispersed inside a suitable host, made from materials such as cellulose or lipids, the tortuosity of the matrix determines the drug release kinetics. Hydrogel drug formulations are similar to matrix systems as they are usually loaded with the API, but the drug release mechanism depends on swelling of the polymeric material and, thus, it is governed by the matrix mesh size. Furthermore, a reservoir‐drug formulation is usually comprised of a core‐shell structure.…”

“…Biodegradable polymers prevent problems of material accumulation, given that the degenerated polymer fragments are harmless. In‐vitro tests demonstrate that, in fact, the cytotoxic impact of most polymeric layers is very low or even absent . While such tests are limited in estimating the behavior in an extended in‐vivo environment where numerous biological and chemical mechanisms are additionally involved, the initial studies are very promising.…”

Polyhistidine‐Based Metal Coordination Hydrogels with Physiologically Relevant pH Responsiveness and Enhanced Stability through a Novel Synthesis

“…Stimuli‐responsive hydrogels have received intense attention in fields range from tissue engineering to drug delivery for their switchable gel‐sol or other gel volume phase transitions upon the application of stimuli such as light, temperature, pH, redox, etc . Distinct from the stimuli provided by external sources, the physiological microenvironment also provides site‐specific chemical or biological conditions such as pH, glucose, and bioactive molecules .…”

Smart Materials for Biomedical Applications: The Usefulness of Shape-Memory Polymers

“…Similarly, Hearon et al [12] employed a laser actuated SMP microgripper where the stimulus is UV light with polyurethane (PU). Unger et al [81] developed the biocompatible hydrogels that can open the new fields of applications such as biotechnology, light-controlled cell growth or light-controlled drug delivery. These hydrogels are known for their dynamic response to swelling.…”