Light-activated Polymer Research Articles

Peri-operative outcomes of IlluminOss fixation for pelvic metastatic bone disease

BackgroundPelvic metastatic bone disease (MBD) leads to significant pain and functional impairment. Managing these lesions through an open approach involves invasive procedures linked to potential morbidity and complications. The IlluminOss system, a UV light-activated polymer implant, has shown efficacy and safety in managing various fractures. This study evaluates the effectiveness of IlluminOss photodynamic bone stabilization system (PBSS) in pelvic MBD. MethodsA retrospective cohort review was conducted, including all patients treated with the PBSS system for MBD of the pelvis and acetabulum. ResultsFifteen patients were included with a mean follow-up of 4.97 months (SD 3.05). In the thirteen patients treated with the IlluminOss without concurrent total hip arthroplasty, the mean operative time was 170.4 min (SD 90.6). The mean estimated blood loss was 52.3 mL (SD 73.7). No patients required transfusions. The mean visual analog scale (VAS) pain score at the latest follow-up was 2.29, significantly lower than the preoperative score of 9.07 (p < 0.001). Thirteen patients (92.9 %) had improved functional status at the latest follow-up. ConclusionPBSS offers similar operative times, reduced blood loss, and decreased need for transfusions compared to open pelvic fixation methods. It also demonstrates significant pain reduction and improved functional outcomes without increased complications.

Biomechanical Evaluation of an Atraumatic Polymer-assisted Peripheral Nerve Repair System Compared with Conventional Neurorrhaphy Techniques.

Microsuturing, the gold standard for peripheral nerve repair, can create tension and damage at the repair site, potentially impacting regeneration and causing neuroma formation. A sutureless and atraumatic polymer-assisted system was developed to address this challenge and support peripheral nerve repair. The system is based on a biocompatible and biodegradable biosynthetic polymer and consists of a coaptation chamber and a light-activated polymer for securing to the nerve. In this study, we compare the system's biomechanical performance and mechanism of action to microsutures and fibrin repairs. The system's fixation force was compared with microsutures and fibrin glue, and evaluated across various nerve diameters through tensile testing. Tension and tissue morphology at the repair site were assessed using finite element modeling and scanning electron microscopy. The fixation force of the polymer-assisted repair was equivalent to microsutures and superior to fibrin glue. This force increased linearly with nerve diameter, highlighting the correlation between polymer surface contact area and performance. Finite element modeling analysis showed stress concentration at the repair site for microsuture repairs, whereas the polymer-assisted repair dissipated stress along the nerve, away from the repair site. Morphological analysis revealed nerve alignment with no tissue trauma for the polymer-assisted repair, unlike microsutures. The mechanical performance of the polymer-assisted coaptation system is suitable for peripheral nerve repair. The achieved fixation forces are equivalent to those of microsutures and superior to fibrin glue, minimizing stress concentration at the repair site and avoiding trauma to the severed nerve ends.

A light-activated polymer with excellent serum tolerance for intracellular protein delivery.

The design of efficient materials for intracellular protein delivery has attracted great interest in recent years; however, most current materials for this purpose are limited by poor serum stability due to the early release of cargoes triggered by abundant serum proteins. Here, we propose a light-activated crosslinking (LAC) strategy to prepare efficient polymers with excellent serum tolerance for intracellular protein delivery. A cationic dendrimer engineered with photoactivatable O-nitrobenzene moieties co-assembles with cargo proteins via ionic interactions, followed by light activation to yield aldehyde groups on the dendrimer and the formation of imine bonds with cargo proteins. The light-activated complexes show high stability in buffer and serum solutions, but dis-assemble under low pH conditions. As a result, the polymer successfully delivers cargo proteins green fluorescent protein and β-galactosidase into cells with maintained bioactivity even in the presence of 50% serum. The LAC strategy proposed in this study provides a new insight to improve the serum stability of polymers for intracellular protein delivery.

Three-Dimensional Bioprinting for Tissue Engineering and Regenerative Medicine in Down Under: 2020 Australian Workshop Summary.

Three-Dimensional Bioprinting for Tissue Engineering and Regenerative Medicine in Down Under: 2020 Australian Workshop Summary.

Light-Activated Polymer-Coated Mesoporous Silica with Azobenzene Moiety for the Controlled Delivery of Guest Molecules.

In this study, we have synthesized a light-activated polymer-coated mesoporous silica nanovalve with poly(trans-4-methacryloyloxyazobenzene-co-methylmethacrylic acid-co-vinyltrimethoxysilane) (PMMV) (MSNs/PMMV) for the controlled delivery of guest molecules. The hydrophobicity of azobenzene varies depending on the structure of each isomer. Typically, trans isomers are hydrophobic due to the aromatic ring, but they become more hydrophilic when they are changed to the cis confirmation. Using this concept, we introduced PMMV as a light active nanovalve on the mesoporous silica. To optimize the coating of the light-activated polymer on mesoporous silica, we investigated the conformational change of PMMV in solutions at various pHs. PMMV has a dot-like morphology in acidic solutions under pH 4, but sheet-like morphology in solutions at pH over 4. We investigated the nanovalve behavior of MSNs/PMMV by introducing propidium iodide (PI) as guest molecules. Time-resolved fluorescence spectroscopy showed the excellent light activity of PMMV for open pores. The new PMMV-coated mesoporous silica could be applied in the smart nanovalve system for the controlled delivery of various guest molecules.

Cantilever beam shape control with light activated polymers using hierarchical particle swarm optimizer

A shape control with light activated polymers (LAPs) is designed in present article. Under ultraviolet light irradiation, the structures of crosslink networks in LAPs alter. Such alterations lead to macroscopical deformation. On this basis, LAPs possess the potential to be actuators. For shape control, so many parameters of actuators could be optimized. A three-layer hierarchical particle swarm optimizer (HPSO) algorithm is proposed to search the appropriate group of LAPs numbers, locations and lengths. Numerical simulations (monotonic function shape control and non-monotonic function shape control) illustrate that HPSO is effective.

Photo-induced bending in a light-activated polymer laminated composite.

Light activated polymers (LAPs) have attracted increasing attention since these materials change their shape and/or behavior in response to light exposure, which serves as an instant, remote and precisely controllable stimulus that enables non-contact control of the material shape and behavior through simple variation in light intensity, wavelength and spatially controlled exposure. These features distinguish LAPs from other active polymers triggered by other stimuli such as heat, electrical field or humidity. Previous examples have resulted in demonstrations in applications such as surface patterning, photo-induced shape memory behavior, and photo-origami. However, in many of these applications, an undesirable limitation has been the requirement to apply and maintain an external load during light irradiation. In this paper, a laminated structure is introduced to provide a pre-programmed stress field, which is then used for photo-induced deformation. This laminated structure is fabricated by bonding a stretched elastomer (NOA65) sheet between two LAP layers. Releasing the elastomer causes contraction and introduces a compressive stress in the LAPs, which are relaxed optically to trigger the desired deformation. A theoretical model is developed to quantitatively examine the laminated composite system, allowing exploration of the design space and optimum design of the laminate.

A photoviscoplastic model for photoactivated covalent adaptive networks

Light activated polymers (LAPs) are a class of contemporary materials that when irradiated with light respond with mechanical deformation. Among the different molecular mechanisms of photoactuation, here we study radical induced bond exchange reactions (BERs) that alter macromolecular chains through an addition-fragmentation process where a free chain whose active end group attaches then breaks a network chain. Thus the BER yields a polymer with a covalently adaptable network. When a LAP sample is loaded, the macroscopic consequence of BERs is stress relaxation and plastic deformation. Furthermore, if light penetration through the sample is nonuniform, resulting in nonuniform stress relaxation, the sample will deform after unloading in order to achieve equilibrium. In the past, this light activation mechanism was modeled as a phase evolution process where chain addition-fragmentation process was considered as a phase transformation between stressed phases and newly-born phases that are undeformed and stress free at birth. Such a modeling scheme describes the underlying physics with reasonable fidelity but is computationally expensive. In this paper, we propose a new approach where the BER induced macromolecular network alteration is modeled as a viscoplastic deformation process, based on the observation that stress relaxation due to light irradiation is a time-dependent process similar to that in viscoelastic solids with an irrecoverable deformation after light irradiation. This modeling concept is further translated into a finite deformation photomechanical constitutive model. The rheological representation of this model is a photoviscoplastic element placed in series with a standard linear solid model in viscoelasticity. A two-step iterative implicit scheme is developed for time integration of the two time-dependent elements. We carry out a series of experiments to determine material parameters in our model as well as to validate the performance of the model in complex geometrical and loading configurations. The comparison between the finite element simulations and experiments shows that the model can accurately capture the response of the LAP under a wide range of coupled photo-mechanical loading conditions, such as light induced stress relaxation, creep in tension, and bending. Furthermore, we demonstrate the versatility of the model by simulating a series of examples that exhibit complex three-dimensional, time-dependent photodeformation, including photoorigami, photoforming, and photobulge tests.

Photo-induced deformation of active polymer films: Single spot irradiation

Light-activated polymers can undergo complex deformation in response to the combination of mechanical and optical stimuli. These materials are attractive for remote actuation and sensing applications. However, the behavior of such materials subjected to photomechanical patterning is not well understood. In this paper we consider a polymer that operates by photoactivated stress relaxation; at the molecular level, photoinitiation of residual initiator molecules generate free radicals that break and then reform in-chain functionalities of stretched chains in an elastomeric network, which results in macroscopic stress relaxation. We carry out experiments and finite element calculations that demonstrate the sequence of deformation events culminating in the formation of a buckled spot as a result of biaxially stretching the elastomeric film then irradiating a circular region followed by releasing the mechanical constraint. In order to better understand the photomechanics, we analyze a simpler model problem wherein a linear elastic, stress relaxing disk is subjected to (i) radial extension, (ii) irradiation of a concentric circular region, and (iii) release of the applied displacements in (i), which results in deformation and stress redistribution. In the final step, the deformation may transition from planar to buckling out of the plane depending on system parameters. Companion finite element calculations are performed against which our analytical results are in good agreement. Although not directly comparable, the analytic model qualitatively agrees with the experiments. The results of this work provide a useful foundation from which to explore more interesting behavior of periodically photo-mechanically patterned films and other more challenging actuation problems.

Photomechanics of light-activated polymers

Light-activated polymers are an exciting class of modern materials that respond mechanically when irradiated by light at particular wavelengths. While details of the mechanisms that connect the optical excitation to mechanical behavior are complex and differ from material to material, there is sufficient commonality among them to permit the development of a generalized modeling framework to describe the photomechanics. The features shared by light-activated polymers involve light interacting with the material, which triggers photochemical reactions that alter the structure of the crosslinked polymer network. Many such structural alterations result in an evolution of the polymer network, and subsequent macroscopic deformation. When this process is appropriately executed it can enable a photomechanical shape-memory effect. In this paper, we develop a three-dimensional finite-deformation modeling framework to describe the photomechanical response of light-activated polymer systems. This framework integrates four coupled phenomena that contribute to macroscopic photomechanical behavior: photophysics, photochemistry, chemomechanical coupling, and mechanical deformation. The chemomechanical coupling consists of chemically induced structural alterations of the crosslinked network that result in subsequent deformation. We describe this behavior through a decomposition of the crosslinked network into two components consisting of an original network and a photochemically altered network; both evolve during photomechanical deformation. The modeling framework presented in this paper is sufficiently general that it is applicable to light-activated polymer systems that operate with various mechanisms in each of the four areas. Using this modeling approach, we develop constitutive models for two recently developed light-activated polymer systems [Lendlein, A., Hongyan, J., Junger, O., Langer, R., 2005. Light-induced shape-memory polymers. Nature 434 (7035) 879; Scott, T.F., Schneider, A.D., Cook, W.D., Bowman, C.N., 2005. Photoinduced plasticity in crosslinked polymers. Science 308 (5728) 1615]. For the material developed by Scott and his co-workers we validate our model by measuring and numerically simulating photo-induced stress relaxation and bending deformation and obtain good agreement between measurements and predictions. Finally, we use the model to study the effects of photomechanical parameters (applied strain magnitude, irradiation time and intensity, and photoabsorber concentration) and the behavior of the network evolution rule on the material response.

The antimicrobial properties of light-activated polymers containing methylene blue and gold nanoparticles

We report the formation of polysiloxane polymers containing embedded methylene blue and gold nanoparticles incorporated by a swell-encapsulation-shrink method. These polymers show significant antimicrobial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli with up to a 3.5 log 10 reduction in the viable count when exposed for 5 min to light from a low power 660 n m laser. The bacterial kill is due to the light-induced production of singlet oxygen and other reactive oxygen species by the methylene blue. Interestingly, the presence of 2 n m gold nanoparticles significantly enhanced the ability of the methylene blue to kill bacteria.

Dynamic mechanical analysis of storage modulus development in light-activated polymer matrix composites

Objectives: The goal of this study was to evaluate the potential for using dynamic mechanical analysis of tubular geometry in a three-point flexure fixture for monitoring the storage modulus development of a light-activated polymer matrix composite. Methods: Composite samples were inserted into PTFE tubes and tested in a three-point bend fixture in a dynamic mechanical analyzer (DMA) at 200 Hz with 20 μm amplitude. Samples were light activated for 60 s (385 mW/cm 2 at the composite surface) and storage modulus ( E′) was measured continuously for the seven light-activated composites studied (one microfill, four hybrids and two unfilled resins). Cores of composite were removed from the PTFE sheath after 13.5 min and evaluated with the same parameters in the DMA. A finite element model of the test configuration was created and used to estimate operating parameters for the DMA. Degree of conversion (DC) was measured using micro-Fourier Transform Infrared (FTIR) spectroscopy for the microfilled composite samples and one hybrid 13.5 and 60 min after light activation. Results: The E′ for a generic hybrid and microfilled composite was 13,400±1100 and 5900±200 MPa, respectively, when cured within the tube and then removed and tested in the DMA. DC was 54.6% for the hybrid and 60.6% for the microfill. A linear regression of E′ for the sheath and core vs core alone ( r 2=0.986) indicated a linear scaling of the sheath and core values for E′ enabling a correction for estimated E′ values of the composite core. Significance: This method estimates the storage modulus growth during light-activated polymerization of highly filled dimethacrylates. Although the approach is phenomenological in that quantitative measurements of E′ are not made directly from the DMA, estimates of early polymerization kinetics appear to be validated by three different approaches.

Cure kinetics of light-activated polymers

The purpose of this article is to develop a mathematical model that de- scribes photocure and photopolymerization kinetics. This model is neither wholly phenomenological nor mechanistic, but contains elements of both. We draw an analogy between the classical Avrami approach for first-order phase transformations and the kinetic phenomena that occur during photocuring, and take into account cure inhibition due to a decrease in mobility of the constituents. The result is an explicit algebraic two-parameter expression for the extent of cure versus time. More importantly, the two parameters have physical significance, and to some extent can be predicted a priori. The model is compared to three sets of unrelated data, and excellent agreement is obtained, except for part of the data at the onset of the reactions. Physical insight obtained by comparing our theory with experiments supports the existence of preferred sites for initiating the reaction, and indicates that irradiation is the rate-limiting step in the overall cure process in the limit of small irradiation intensities. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2887-2894, 1998

The loss of residual monomer from denture base polymers coated with an ultraviolet light-activated polymer

The loss of residual monomer from denture base polymers coated with an ultraviolet light-activated polymer