Controlling the release kinetics of substances from polymeric fibers is essential for applications that demand precise transport properties. Traditional melt-spun fibers, where active compounds are embedded within the polymer matrix, often suffer from burst release, limited loading capacity, and diffusion constraints due to the polymer structure. To address these challenges, we introduce melt-spun liquid-core filaments (LiCoFs), a novel fiber platform featuring a polymer sheath encapsulating a substance-filled liquid reservoir that enables sustained substance release [1].
Two application examples are presented. The first example focuses on medical LiCoFs, consisting of a drug-containing liquid core enveloped by poly(ε-caprolactone). Experiments were conducted using fluorescein sodium salt as a model drug, dissolved in various liquid core materials. For some fibers, the liquid was replaced with different drug-containing solutions using a pumping device. Thermal, mechanical, and structural characteristics of LiCoFs were analyzed, and extensive drug diffusion trials were performed to evaluate release kinetics. These drug-loaded LiCoFs pave the way towards a new generation of medical textiles enabling localized drug delivery. The second example explores the effectiveness of LiCoFs containing toxic agents dissolved in liquid cores to kill insects, offering an innovative approach to insect control. By encapsulating active agents within the liquid core, a controlled and sustained release mechanism is achieved, enhancing long-term effectiveness. This application underscores the adaptability of LiCoFs in developing specialized fibers for pest control.

[1] Röthlisberger, M.; S. Dul; P. Meier; G. Giovannini; R. Hufenus; E. Perret, Drug delivery with melt-spun liquid-core fibers. Polymer 2024, 298, 126885. DOI: 10.1016/j.polymer.2024.126885.

Polymerization-Induced Self-Assembly (PISA) is a platform technology that can be used for the synthesis of block copolymer nanoparticles as a concentrated colloidal dispersion with various potential applications, including next-generation Pickering emulsifiers.[1] However, PISA usually involves vinyl monomers, which produce non-degradable environmentally-persistent copolymers. In principle, one solution to this problem involves statistically copolymerizing a cyclic monomer with a vinyl monomer via radical ring-opening copolymerization to introduce (thio)esters into the backbone but such cyclic comonomers require low-yielding multi-step syntheses.[2]
Instead, we have developed reverse sequence PISA, which can be used to prepare sterically-stabilized diblock copolymer nanoparticles directly in aqueous media at up to 40% w/w solids. This involves dissolving a a trithiocarbonate-capped hydrophobic polymeric precursor in a suitable hydrophilic monomer (e.g. N,N’-dimethylacrylamide) and then polymerizing this monomer either in the bulk or in concentrated aqueous solution via RAFT polymerization. At an appropriate intermediate monomer conversion, water is added to the reaction mixture to induce a trithiocarbonate end-group self-assembly of nascent diblock copolymer nanoparticles and the polymerization continues until full conversion is achieved.
Spherical nanoparticles are invariably obtained when using amorphous hydrophobic precursors (e.g. poly(ε-caprolactone) or Jeffamines®).[3,4] However, highly anisotropic diblock copolymer nanoparticles can be prepared by using a semicrystalline poly(L-lactide) precursor, which results in crystallization-driven self-assembly (CDSA).[5] In this case, either rod-like nanoparticles or diamond-like platelets can be obtained, depending on the target diblock copolymer composition. Such nanoparticles are susceptible to hydrolytic degradation of the core-forming aliphatic polyester chains when subjected to either acidic or basic conditions.

Polyesters are gaining increasing attention as biodegradable polymers that play a key role in solving increasingly pressing environmental challenges. Radical ring-opening polymerisation (RROP) of cyclic ketene acetals (CKAs) represents a synthetic strategy to produce fully biodegradable and functional polyesters with a wide range of accessible properties such as semi-crystallinity, hydrophilicity and pH sensitivity. With the introduction of pH-sensitive polyesters from RROP, the unravelling of the branching reaction and the ability to control macroscopic properties by polymer structure, RROP of CKAs has taken a giant step forward.[1]
Being biodegradable means that the chemistry has to be explored in the light of Green Chemistry and one of the main factors is the use of sustainable ways to promote the reaction. Inspired by this notion, UV light was found to accelerate the reaction to unprecedented levels and photochemical action plots showed a wavelength specific acceleration (Fig. 1A).[2, 3] As UV light is non-invasive, this also shows a very good and sustainable way to promote the reaction. In addition, supercritical CO2 was tested as a green solvent because it can be recycled from the atmosphere (Fig. 1B).[4] By adjusting the pressure and temperature of the supercritical substance, we were able to tune critical parameters such as molecular weight via these reaction parameters.
The ability to control and promote the reaction by two different means, supercritical CO2 and UV light, demonstrates the high potential of RROP to develop a whole new array of environmentally friendly polyesters.