Combined, Independent Small Molecule Release and Shape Memory via Nanogel-Coated Thiourethane Polymer Networks

Influence of Isocyanate Structure on Recyclable Shape Memory Poly(thiourethane)

In this study, poly(thiourethane) (PTU) with different structures is synthesized by click chemistry from trimethylolpropane tris(3-mercaptopropionate) (S3) and different diisocyanates (hexamethylene diisocyanate, HDI, isophorone diisocyanate, IPDI and toluene diisocyanate, TDI). Quantitative analysis of the FTIR spectra reveals that the reaction rates between TDI and S3 are the most rapid, resulting from the combined influence of conjugation and spatial site hindrance. Moreover, the homogeneous cross-linked network of the synthesized PTUs facilitates better manageability of the shape memory effect. All three PTUs exhibit excellent shape memory properties (R_r and R_f are over 90%), and an increase in chain rigidity is observed to negatively impact the shape recovery rate and fix rate. Moreover, all three PTUs exhibit satisfactory reprocessability performance, and an increase in chain rigidity is accompanied by a greater decrease in shape memory and a smaller decrease in mechanical performance for recycled PTUs. Contact angle (<90°) and in vitro degradation results (13%/month for HDI-based PTU, 7.5%/month for IPDI-based PTU, and 8.5%/month for TDI-based PTU) indicate that PTUs can be used as long-term or medium-term biodegradable materials. The synthesized PTUs have a high potential for applications in smart response scenarios requiring specific glass transition temperatures, such as artificial muscles, soft robots, and sensors.

Photoinduced synthesis of fluorescent hydrogels without fluorescent monomers

A fluorescent monomer-free one-step strategy is developed for the synthesis of fluorescent acrylamide gels, using inexpensive and commercially available rhodamine B as the hydrogen donor in type II photoinitiation system....

Heating/Solvent Responsive Shape-Memory Polymers for Implant Biomedical Devices in Minimally Invasive Surgery: Current Status and Challenge

This review is about the fundamentals and practical issues in applying both heating and solvent responsive shape memory polymers (SMPs) for implant biomedical devices via minimally invasive surgery. After revealing the general requirements in the design of biomedical devices based on SMPs and the fundamentals for the shape-memory effect in SMPs, the underlying mechanisms, characterization methods, and several representative biomedical applications, including vascular stents, tissue scaffolds, occlusion devices, drug delivery systems, and the current R&D status of them, are discussed. The new opportunities arising from emerging technologies, such as 3D printing, and new materials, such as vitrimer, are also highlighted. Finally, the major challenge that limits the practical clinical applications of SMPs at present is addressed.

Step-growth Production of Nanogels for Use as Macromers with Dimethacrylate Monomers

A series of functional nanogels were synthesized by a step-growth mechanism that involved diisocyanate addition to a modest stoichiometric excess of multi-thiols. Nanogels with sizes less than 10 nm were obtained as room temperature liquids with residual thiol groups used to attach methacrylate functionality. Depending on nanogel structure, bulk nanogel properties varied widely, as did the properties of the nanogel-derived and nanogel-modified polymers. Photopolymerization of the reactive nanogels in combination with a dimethacrylate monomer showed dramatically enhanced reaction rate and conversion compared with the dimethacrylate homopolymer. Polymerization shrinkage/ stress as well as mechanical properties of the polymer networks were controlled by changing the ratio of nanogels and dimethacrylate monomers used in formulations. Thus, this study shows the potential of step-growth nanogels for beneficial changes in resin reactivity and application-based performance.

Porous Poly(ε-caprolactone)-Poly(l-lactic acid) Semi-Interpenetrating Networks as Superior, Defect-Specific Scaffolds with Potential for Cranial Bone Defect Repair

The treatment of irregular cranial bone defects is currently limited due to the graft resorption that can occur when an ill-fitting interface exists between an autograft and the surrounding tissue. A tissue engineering scaffold able to achieve defect-specific geometries could improve healing. This work reports a macroporous, shape memory polymer (SMP) scaffold composed of a semi-interpenetrating network (semi-IPN) of thermoplastic poly(l-lactic acid) (PLLA) within cross-linked poly(ε-caprolactone) diacrylate (PCL-DA) that is capable of conformal fit within a defect. The macroporous scaffolds were fabricated using a fused salt template and were also found to have superior, highly controlled properties needed for regeneration. Specifically, the scaffolds displayed interconnected pores, improved rigidity, and controlled, accelerated degradation. Although slow degradation rates of scaffolds can limit healing, the unique degradation behavior observed could prove promising. Thus, the described SMP semi-IPN scaffolds overcome two of the largest limitations in bone tissue engineering: defect "fit" and tailored degradation.

Thiol-functionalized nanogels as reactive plasticizers for crosslinked polymer networks

Significant efforts have been expended to mitigate plasticizer migration from crosslinked methacrylic and poly(vinyl chloride) polymer networks by synthesizing reactive plasticizers that can blend homogenously within the networks to reduce polymer property change, acute toxicity and downstream environmental effects of plasticizer migration with limited and varying amount of success. We hypothesized that appropriate thiol-functionalized nanogels synthesized using the same monomers as the parent network to generate highly compact, crosslinked structures will form thermally stable, homogenous networks and perform as optimal reactive plasticizers. Nanogels were synthesized via a thiol-Michael addition solution polymerization and incorporated at different mass ratios within a polyethylene glycol 400 urethane dimethacrylic monomer to form photo-crosslinked networks. While maintaining the inherent hydrolytic stability, thermal stability and biocompatibility of the parent matrix at ~99% acrylic group conversion, the PEG400 urethane dimethacrylic -nanogel networks retained optical clarity with >90% visible light transmission at 20wt% nanogel concentration within the matrix. The addition of the nanogels also enhanced the elongation of the parent matrix by up to 320%, while a 37°C reduction in glass transition temperature (∆T_g) and ≥50% reduction in modulus was observed. A 52% reduction in the shrinkage stress of the material was also noted. The results indicate that the application of thiol-functionalized nanogels as plasticizers to alter the bulk properties of the parent matrix while mitigating plasticizer migration by covalently crosslinking the nanogels within the polymer matrix provides a simple yet efficient technique to generate network-specific plasticizers with the ability to alter targeted properties within polymers.

Is biopolymer hair a multi-responsive smart material?

A twin-netpoint-switch structure model for animal hair has been proposed for interpreting different shape memory abilities when exposure on different external stimuli, where a twin-netpoint/single-switch structure is for the stimulus of water, heat and UV-light, and a single-netpoint/twin-switch structure is for the stimulus of redox agent.

Water dispersible siloxane nanogels: a novel technique to control surface characteristics and drug release kinetics

Amphiphilic, water-dispersible, crosslinked siloxane nanogels were synthesized and applied as optically clear, functional coatings on the surface of lens substrates to demonstrate the feasibility of siloxane-nanogels to generate covalently tethered coatings and modify the surface properties of intraocular lens substrates.