Thermo-Mechanical Properties of Semi-Degradable Poly(β-amino ester)-co-Methyl Methacrylate Networks under Simulated Physiological Conditions

A New Design of Poly(N-Isopropylacrylamide) Hydrogels Using Biodegradable Poly(Beta-Aminoester) Crosslinkers as Fertilizer Reservoirs for Agricultural Applications

Poly(N-isopropylacrylamide) (P(NIPAAm)) hydrogels were prepared by free-radical polymerization with biodegradable poly (β-amino ester) (PBAE) crosslinkers at 1 wt% and 3 wt% ratio, and compared with conventional N,N'-methylene bisacrylamide (MBA)-crosslinked hydrogel. The influence of the type, molecular weight, and diacrylate/amine ratio of the crosslinker on the crosslink density, compressive strength, and swelling and biodegradation behavior of the hydrogels was investigated. The hydrogels synthesized with lower molecular weight PBAE crosslinkers showed higher crosslinking degrees and compressive strength and lower swelling ratios. To reveal the controlled release behavior of the fertilizer, KNO₃ was used as the model, and its loading and release behavior from these hydrogels was also examined. The N/T5/1 sample with 1.5/1.0 diacrylate/amine molar ratio and 1 wt% PBAE ratio demonstrated the most controlled release of KNO₃ with 66.9% after 18 days in soil. In addition, the hydrogel with the porosity of 71.65% and crosslinking degree of 2.85 × 10^-5 mol cm^-3 showed a swelling ratio of 69.44 g/g, biodegradation rate of 23.9%, and compressive strength of 1.074 MPa. Thus, it can be concluded that the new designed biodegradable P(NIPAAm) hydrogels can be promising materials as nitrate fertilizer reservoirs and also for controlled fertilizer release in soil media for agricultural applications.

Fabrication of dual stimuli-responsive multicompartmental drug carriers for tumor-selective drug release

There has been increasing attention to the development of multi-stimuli-responsive drug carriers for precisely controlled drug release at target disease areas. In this study, pH- and redox-responsive hybrid drug carriers were fabricated by using both ketal-based acid-cleavable precursors and disulfide-based reducible precursors via stop-flow lithography. pH- and redox-sensitive drug release of the dual stimuli-responsive hybrid particles was confirmed, demonstrating their feasibility for selective and efficient drug release into tumor tissues in acidic and highly reductive environments. It was also found that the drug release rate of the particles was fine-tuned by modulating monomer compositions in the precursor. Importantly, the dual stimuli-responsive hybrid particles exhibited synergistic, controlled drug release in complex stimuli (both pH and redox stimuli) environments. To achieve tumor-selective combination chemotherapy, multicompartmental drug carriers consist of an acid-degradable compartment and a reducible compartment, which can separately encapsulate individual model drugs in each of the compartments. The multicompartmental particles exhibited independent drug release upon exposure to the corresponding stimulus. The dual stimuli-responsive, multicompartmental particles are effective drug carriers for tumor-selective release of a drug cocktail, leading to synergistic combination chemotherapy.

Lysine-derived, pH-sensitive and biodegradable poly(beta-aminoester urethane) networks and their local drug delivery behaviour

In this study, a series of covalently crosslinked, l-lysine based poly(beta-aminoester urethane) (LPBAEU) networks with good biodegradability and pH sensitivity was reported. The effect of hydrophilic/hydrophobic characteristics and diacrylate/amine molar ratio on the structure, swelling and degradation behaviour of the networks was investigated. The water transport mechanism and dynamic swelling behavior of the LPBAEU networks were strongly affected by medium pH, and swelling amounts up to 252.2% and 148.7% were observed at pH 5.6 and pH 7.4, respectively. It was found that water diffusion within the networks followed a non-Fickian mechanism. The LPBAEU network with the highest diacrylate/amine molar ratio exhibited the highest tensile strength and Young's modulus. In vitro mass losses of networks showed that the degradation rate of LPBAEU networks can be adjusted from 4 to 14 days. LPBAEU networks also supported loading of doxycycline hyclate (DH) and in vitro release studies demonstrated that release of DH from the networks was substantially hindered in the neutral pH environment, with 20.9-56.2% DH release, whereas DH release was accelerated under mild acidic conditions, with a release percentage of 36.6-99.6%. The release data were fitted to different mathematical models and the obtained results confirmed that these networks released DH in a non-Fickian mechanism. The results of this research support the idea that pH-responsive LPBAEU networks may find potential applications in local drug delivery.

Semi-degradable poly(β-amino ester) networks with temporally controlled enhancement of mechanical properties

Biodegradable polymers are clinically used in numerous biomedical applications, and classically show a loss of mechanical properties within weeks of implantation. This work demonstrates a new class of semi-degradable polymers that show an increase in mechanical properties through degradation via a controlled shift in a thermal transition. Semi-degradable polymer networks, poly(β-amino ester)-co-methyl methacrylate, were formed from a low glass transition temperature crosslinker, poly(β-amino ester), and high glass transition temperature monomer, methyl methacrylate, which degraded in a manner dependent upon the crosslinker chemical structure. In vitro and in vivo degradation revealed changes in mechanical behavior due to the degradation of the crosslinker from the polymer network. This novel polymer system demonstrates a strategy to temporally control the mechanical behavior of polymers and to enhance the initial performance of smart biomedical devices.