Hip contact force pathways in total hip replacement differ between patients and activities of daily living.

One of the main causes of implant failure and revision surgery in total hip replacement (THR) is aseptic loosening often caused by the accumulation of wear debris arising between the contact surfaces of the acetabular cup and femoral head during activities of daily living (ADL's). However, limited information is available regarding the contact force pathways between these two surfaces during specific ADL's. In this study, through musculoskeletal modelling, we aimed to estimate the orientation of the hip contact force pathway on the acetabular cup. One hundred and thirty-two THR patients underwent motion capture analysis whilst undertaking locomotor and non-locomotor ADL's. Musculoskeletal simulations were performed to calculate contact force pathways using inverse dynamics analysis. We then qualitatively compared differences in the contact force pathways between patients and between ADL's. Walking resulted in a typical figure-of-eight pattern, with the peak contact forces occurring in the superior-anterior area of the cup. The non-locomotive activities such as stand up, sit down and squat had a more linear shape, spanning across the superior-posterior quarter of the cup. Our results showed a large inter-patient variability in the shape and location of the contact force pathway. There is a distinct difference in the location and shape of the pathway between locomotor and non-locomotor activities and this could result in different wear accumulations. These results could enhance our understanding why revision rates vary across the population and could inform the development of personalised implant design.

Walking in a controlled ankle motion (CAM) boot: In-boot measurement of joint kinematics and kinetics.

Research investigating ankle function during walking in a controlled ankle motion (CAM) boot has either placed markers on the outside of the boot or made major alterations to the structure of the CAM boot to uncover key landmarks. The aim of this study was to quantify joint kinematics and kinetics using "in-boot" skin markers whilst making only minimal structural alterations. Seventeen healthy participants walked at their preferred walking speed in two conditions: (1) in standard athletic trainers (ASICS patriot 8, ASICS Oceania Pty Ltd, USA), and (2) using a hard-cased CAM boot (Rebound® Air Walker, Össur, Iceland) fitted on the right foot. Kinematic measurements revealed that CAM boots restrict sagittal plane ankle range of motion to less than 5°, and to ∼3° in the frontal plane, which is a reduction of 85% and 73% compared to standard footwear, respectively (p < 0.001). This ankle restriction resulted in a reduction of ankle joint total limb work contribution from 38 ± 5% in normal footwear to 13 ± 4% in the CAM boot (p < 0.001). This study suggests that CAM boots do restrict the ankle joint's ability to effectively perform work during walking, which leads to compensatory mechanisms at the ipsilateral and contralateral hip and knee joints. Our findings align with previous research that employed "on-boot" kinematic measurements, so we conclude that in-boot approaches do not offer any benefit to the researcher and instead, on-boot measurements are suitable.

Biomechanical effectiveness of controlled ankle motion boots: A systematic review and narrative synthesis.

INTRODUCTION: Controlled ankle motion (CAM) boots are a below-knee orthotic device prescribed for the management of foot and ankle injuries to reduce ankle range of motion (RoM) and offload the foot and ankle whilst allowing continued ambulation during recovery. There is a lack of clarity within the current literature surrounding the biomechanical understanding and effectiveness of CAM boots. AIMS: To summarise the biomechanical effects of CAM boot wear as an orthotic for restricting ankle RoM and offloading the foot. METHODS: A systematic literature review was conducted in accordance with the PRISMA 2020 guidelines. All papers were independently screened by two authors for inclusion. Methodological quality was appraised using Joanna Briggs Critical Appraisal checklists. A narrative synthesis of all eligible papers was produced. RESULTS: Thirteen studies involving 197 participants (113 male and 84 female) were included. All studies were quasi-randomised and employed a within-study design, of which 12 studies included a control group and a range of CAM boots were investigated. CAM boots can be seen to restrict ankle RoM, however, neighboring joints such as the knee and hip do have kinetic and kinematic compensatory alterations. Plantar pressure of the forefoot is effectively redistributed to the hindfoot by CAM boots. CONCLUSION: The compensatory mechanisms at the hip and knee joint during CAM boot wear could explain the secondary site pain often reported in patients, specifically at the ipsilateral knee and contralateral hip. Although CAM boots can be used to restrict ankle motion, this review has highlighted a lack of in-boot kinematic analyses during CAM boot use, where tracking markers are placed on the anatomical structure rather than on the boot, or through video fluoroscopy, urging the need for a more robust methodological approach to achieve this. There is a need for studies to assess the biomechanical alterations caused by CAM boots in populations living with foot and ankle pathologies. Future research, adopting a longitudinal study design, is required to fully understand the effectiveness of CAM boots for rehabilitation.

Updated ACVIM consensus statement on equine herpesvirus-1.

Equine herpesvirus-1 (EHV-1) is a highly prevalent and frequently pathogenic infection of equids. The most serious clinical consequences of infection are abortion and equine herpesvirus myeloencephalopathy (EHM). The previous consensus statement was published in 2009 and considered pathogenesis, strain variation, epidemiology, diagnostic testing, vaccination, outbreak prevention and control, and treatment. A recent survey of American College of Veterinary Internal Medicine large animal diplomates identified the need for a revision to this original consensus statement. This updated consensus statement is underpinned by 4 systematic reviews that addressed key questions concerning vaccination, pharmaceutical treatment, pathogenesis, and diagnostic testing. Evidence for successful vaccination against, or effective treatment of EHV-1 infection was limited, and improvements in experimental design and reporting of results are needed in future studies of this important disease. This consensus statement also updates the topics considered previously in 2009.

Pharmacologic interventions for the treatment of equine herpesvirus-1 in domesticated horses: A systematic review.

BACKGROUND: Equine herpes virus type 1 (EHV-1) infection in horses is associated with upper respiratory disease, neurological disease, abortions, and neonatal death. REVIEW QUESTION: Does pharmacological therapy decrease either the incidence or severity of disease or infection caused by EHV-1 in domesticated horses? METHODS: A systematic review was preformed searching AGRICOLA, CAB Abstracts, Cochrane, PubMed, Web of Science, and WHO Global Health Index Medicus Regional Databases to identify articles published before February 15, 2021. Selection criteria were original research reports published in peer reviewed journals, and studies investigating in vivo use of therapeutic agents for prevention or treatment of EHV-1 in horses. Outcomes assessed included measures related to clinical outcomes that reflect symptomatic EHV-1 infection or virus infection. We evaluated risk of bias and performed a GRADE evaluation of the quality of evidence for interventions. RESULTS: A total of 7009 unique studies were identified, of which 9 met the inclusion criteria. Two studies evaluated valacyclovir or small interfering RNAs, and single studies evaluated the use of a Parapoxvirus ovis-based immunomodulator, human alpha interferon, an herbal supplement, a cytosine analog, and heparin. The level of evidence ranged between randomized controlled studies and observational trials. The risk of bias was moderate to high and sample sizes were small. Most studies reported either no benefit or minimal efficacy of the intervention tested. CONCLUSIONS AND CLINICAL IMPORTANCE: Our review indicates minimal or limited benefit either as a prophylactic or post-exposure treatment for any of the studied interventions in the mitigation of EHV-1-associated disease outcome.

Dynamic Acetabular Cup Orientation during Gait: A Study of Fast- and Slow-Walking Total Hip Replacement Patients.

The dynamic orientation of total hip replacement acetabular cups during walking may vary substantially from their assumed position at surgical implantation and may vary between individuals. The scale of this effect is of interest for both pre-clinical device testing and for pre-operative surgical planning. This work aimed to evaluate (1) patient variation in dynamic cup orientation; (2) whether walking speed was a candidate proxy measure for the dynamic cup orientation; and (3) the relationships between dynamic cup orientation angles and planar pelvic angles. Pelvic movement data for patients with fast (20 patients) and slow (19 patients) self-selected walking speeds were used to calculate acetabular cup inclination and version angles through gait. For aim 1, the range and extremes of acetabular cup orientation angles were analysed for all patients. A large patient-to-patient variation was found in the ranges of both inclination angle (1° to 11°) and version angle (4° to 18°). The version angle was typically retroverted in comparison to the implantation position (greatest deviation 27°). This orientation is substantially different to the static, 0° version, simplifying assumptions in pre-clinical 'edge loading' testing. For aim 2, the cup orientation angles were compared between the fast- and slow-walking groups using statistical parametric mapping. The only significant differences observed were for cup version angle, during ~12% of the gait cycle before toe-off (p < 0.05). Therefore, self-selected walking speed, in isolation, is not a sufficient proxy measure for dynamic acetabular orientation. For aim 3, correlations were recorded between the acetabular cup orientation angles and the planar pelvic angles. The cup inclination angle during gait was strongly correlated (Spearman's coefficient -1) with pelvic obliquity alone, indicating that simple planar assessment could be used to anticipate inclination angle range. The cup version angle was correlated with both pelvic rotation and tilt (Spearman's coefficient 0.8-1), indicating that cup version cannot be predicted directly from any single pelvic movement. This complexity, along with the interaction between inclination angle and range of version angle, supports the use of computational tools to aid clinical understanding.

Acute biomechanical responses to wearing a controlled ankle motion (CAM) Walker boot during walking.

BACKGROUND: Controlled ankle motion (CAM) boots are often prescribed during the rehabilitation of lower limb injuries and pathologies to reduce foot and ankle movement and loading whilst allowing the patient to maintain normal daily function. RESEARCH QUESTION: The aim of this study was to quantify the compensatory biomechanical mechanisms undergone by the ipsilateral hip and knee joints during walking. In addition, the compensatory mechanisms displayed by the contralateral limb were also considered. METHODS: Twelve healthy participants walked on an instrumented treadmill at their preferred walking speed. They underwent kinematic and kinetic analysis during four footwear conditions: normal shoes (NORM), a Malleo Immobil Air Walker on the right leg (OTTO), a Rebound® Air Walker on the right leg with (EVEN) and without (OSS) an Evenup Shoelift™ on the contralateral leg. RESULTS: CAM boot wear increased the relative joint contribution to total mechanical work from the ipsilateral hip and knee joints (p < 0.05), which was characterised by increased hip and knee abduction during the swing phase of the gait cycle. EVEN increased the absolute work done and relative contribution of the contralateral limb. CAM boot wear reduced walking speed (p < 0.05), which was partially compensated for during EVEN. SIGNIFICANCE: The increased hip abduction in the ipsilateral leg was likely caused by the increase in effective leg length and limb mass, which could lead to secondary site complications following prolonged CAM boot wear. Although prescribing an even-up walker partially mitigates these compensatory mechanisms, adverse effects to contralateral limb kinematics and kinetics (e.g., elevated knee joint work) should be considered.

Viremia and nasal shedding for the diagnosis of equine herpesvirus-1 infection in domesticated horses.

BACKGROUND: Equine herpesvirus type 1 (EHV-1) infection is associated with upper respiratory disease, EHM, abortions, and neonatal death. RESEARCH QUESTIONS: Are nasal secretions a more sensitive biological sample compared to blood for the detection of EHV-1 infection? How long is EHV-1 detectable after primary infection by PCR? METHODS: MedLine and Web of Science searches identified original peer-reviewed reports evaluating nasal shedding and viremia using virus isolation methods or PCR published in English before October 9, 2023. RESULTS: Sixty experimental and 20 observational studies met inclusion criteria. EHV-1 detection frequency by qPCR in nasal secretions and blood from naturally-infected horses with fever and respiratory signs were 15% and 9%, respectively; qPCR detection rates in nasal secretions and blood from horses with suspected EHM were 94% and 70%, respectively. In experimental studies the sensitivity of qPCR matched or exceeded that seen for virus isolation from either nasal secretions or blood. Detection of nasal shedding typically occurred within 2 days after EHV-1 inoculation with a detection period of 3 to 7 days. Viremia lasted 2 to 7 days and was usually detected ≥1 days after positive identification of EHV-1 in nasal secretions. Nasal shedding and viremia decreased over time and remained detectable in some horses for several weeks after inoculation. CONCLUSIONS AND CLINICAL IMPORTANCE: Under experimental conditions, blood and nasal secretions have similar sensitivity for the detection of EHV-1 when horses are sampled on multiple consecutive days. In contrast, in observational studies detection of EHV-1 in nasal secretions was consistently more successful.

Relationship between equine herpesvirus-1 viremia and abortion or equine herpesvirus myeloencephalopathy in domesticated horses: A systematic review.

BACKGROUND: Equine herpes virus type 1 (EHV-1) infection in horses is associated with upper respiratory disease, neurological disease, abortions, and neonatal death. OBJECTIVE: To determine if there is an association between the level and duration of EHV-1 viremia and either abortion or equine herpesvirus myeloencephalopathy (EHM) in domesticated horses? METHODS: A systematic review was performed searching numerous databases to identify peer reviewed reports that evaluated viremia and EHM, or viremia and abortion published before January 19, 2021. Randomized controlled trials and observational studies were assessed for risk of bias or publication quality. RESULTS: A total of 189 unique studies were identified, of which 34 met the inclusion criteria. Thirty studies evaluated viremia and neurologic outcomes including 4 observational studies. Eight experimental studies examined viremia and abortion, which used the Ab4 and OH03 virus strains or recombinant Ab4 derivatives. Incidence rates for both EHM and abortion in experimental studies varied among the studies as did the level of evidence. Viremia was generally detectable before the onset of either EHM or abortion. Risk of bias was generally low to moderate, sample sizes were small, and multiple studies reported negative outcome data. CONCLUSIONS AND CLINICAL IMPORTANCE: The results of this study support that viremia is regularly present before EHM or abortion occurs. However, no inferences could be made about the relationship between the occurrence of either neurological signs or abortion and the magnitude or duration of viremia.

Vaccination for the prevention of equine herpesvirus-1 disease in domesticated horses: A systematic review and meta-analysis.

BACKGROUND: Equine herpes virus type 1 (EHV-1) infection in horses is associated with respiratory and neurologic disease, abortion, and neonatal death. HYPOTHESIS: Vaccines decrease the occurrence of clinical disease in EHV-1-infected horses. METHODS: A systematic review was performed searching multiple databases to identify relevant studies. Selection criteria were original peer-reviewed research reports that investigated the in vivo use of vaccines for the prevention of disease caused by EHV-1 in domesticated horses. Main outcomes of interest included pyrexia, abortion, neurologic disease, viremia, and nasal shedding. We evaluated risk of bias, conducted exploratory meta-analyses of incidence data for the main outcomes, and performed a GRADE evaluation of the quality of evidence for each vaccine subtype. RESULTS: A total of 1018 unique studies were identified, of which 35 met the inclusion criteria. Experimental studies accounted for 31/35 studies, with the remainder being observational studies. Eight vaccine subclasses were identified including commercial (modified-live, inactivated, mixed) and experimental (modified-live, inactivated, deletion mutant, DNA, recombinant). Risk of bias was generally moderate, often because of underreporting of research methods, and sample sizes were small leading to imprecision in the estimate of the effect size. Several studies reported either no benefit or minimal vaccine efficacy for the primary outcomes of interest. Meta-analyses revealed significant heterogeneity was present, and our confidence in the quality of evidence for most outcomes was low to moderate. CONCLUSIONS AND CLINICAL IMPORTANCE: Our review indicates that commercial and experimental vaccines minimally reduce the incidence of clinical disease associated with EHV-1 infection.

Discrete Hamstring: Quadriceps Strength Ratios Do Not Represent Angle-Specific Ratios in Premier League Soccer Players.

ABSTRACT: Lunn, DE, Nicholson, G, Cooke, M, Crespo, R, Robinson, T, Price, RJ, and Walker, J. Discrete hamstring: quadriceps strength ratios do not represent angle-specific ratios in Premier League soccer players. J Strength Cond Res 37(12): 2417-2422, 2023-This study compared angle-specific hamstring:quadriceps (H:Q) ratios with their discrete counterparts during strength testing in professional male soccer players. Twenty-seven professional English Premier League soccer players were recruited for this study (age: 22 ± 4 years; stature: 1.81 ± 0.08 m; body mass: 74.7 ± 6.5 kg). Isokinetic testing of the knee flexors and extensors was conducted concentrically at two angular velocities (60° and 240°·s -1 ) and eccentrically (for the knee flexors only) at 30°·s -1 . Conventional H:Q ratio was calculated as the ratio between peak joint moment in the flexors and extensors at 60°·s -1 . Functional H:Q ratio was calculated as the peak joint moment in the flexors during the eccentric condition and the extensors at 240°·s -1 . Discrete conventional and functional H:Q ratios were 0.56 ± 0.06 and 1.28 ± 0.22, respectively. The residual differences between discrete values and angle-specific residual values were 13.60 ± 6.56% when normalized to the magnitude of the discrete value. For the functional ratios, the normalized residual was 21.72 ± 5.61%. Therefore, neither discrete ratio was representative of angle-specific ratios, although the conventional ratio had lower error overall. Therefore, practitioners should consider H:Q ratio throughout the full isokinetic range of motion, not just the discrete ratio calculated from peak joint moments, when designing and implementing training programs or monitoring injury risk, recovery from injury, and readiness to return to play.

Multi-responsive hydrogel structures from patterned droplet networks.

Responsive hydrogels that undergo controlled shape changes in response to a range of stimuli are of interest for microscale soft robotic and biomedical devices. However, these applications require fabrication methods capable of preparing complex, heterogeneous materials. Here we report a new approach for making patterned, multi-material and multi-responsive hydrogels, on a micrometre to millimetre scale. Nanolitre aqueous pre-gel droplets were connected through lipid bilayers in predetermined architectures and photopolymerized to yield continuous hydrogel structures. By using this droplet network technology to pattern domains containing temperature-responsive or non-responsive hydrogels, structures that undergo reversible curling were produced. Through patterning of gold nanoparticle-containing domains into the hydrogels, light-activated shape change was achieved, while domains bearing magnetic particles allowed movement of the structures in a magnetic field. To highlight our technique, we generated a multi-responsive hydrogel that, at one temperature, could be moved through a constriction under a magnetic field and, at a second temperature, could grip and transport a cargo.

Current Preclinical Testing of New Hip Arthroplasty Technologies Does Not Reflect Real-World Loadings: Capturing Patient-Specific and Activity-Related Variation in Hip Contact Forces.

BACKGROUND: Total hip arthroplasty (THA) implants are routinely tested for their tribological performance through regulatory preclinical wear testing (eg, ISO-14242). The standardized loading conditions defined in these tests consist of simplified waveforms, which do not specifically represent in vivo loads in different groups of patients. The aim of this study is to investigate, through musculoskeletal modeling, patient-specific and activity-related variation in hip contact forces (HCFs) in a large cohort of THA patients during common activities of daily living (ADLs). METHODS: A total of 132 THA patients participated in a motion-capture analysis while performing different ADLs, including walk, fast walk, stair ascent, and descent (locomotor); sit to stand, stand to sit, squat, and lunge (nonlocomotor). HCFs were then calculated using the AnyBody Modeling System and qualitatively compared across all activities. The influence of gender on HCFs was analyzed through statistical parametric mapping analysis. RESULTS: Systematic differences were found in HCF magnitudes and individual components in both locomotor and nonlocomotor ADLs. The qualitative analysis of the ADLs revealed a large range and a large variability in forces experienced at the hip during different activities. Significant differences in the 3-dimensional loading patterns were observed between males and females across most activities. CONCLUSION: THA patients present a large variability in the forces experienced at the hip joint during their daily life. The interpatient variation might partially explain the heterogeneity observed in implant survival rates. A more extensive preclinical implant testing standard under clinically relevant loading conditions has been advocated to better predict and avoid clinical wear problems.

Hip kinematics and kinetics in total hip replacement patients stratified by age and functional capacity.

To examine functional differences in total hip replacement patients (THR) when stratified either by age or by functional ability as defined by self-selected walking speed. THR patients and a control group underwent three-dimensional motion analysis under self-selected normal and fast walking conditions. Patients were stratified into five age groups for comparison with existing literature. The THR cohort was also stratified into three functional groups determined by their self-selected gait speed (low function <1SD of total cohort's mean walking speed; high function >1SD; normal function within 1SD). Hip kinematics, ground reaction forces, joint moments and joint powers in all three planes (x-y-z) were analysed. 137 THR and 27 healthy control patients participated. When stratified by age, during normal walking the youngest two age groups walked quicker than the oldest two groups (p < 0.0001) but between-group differences were not consistent across age strata. The differences were diminished under the fast walking condition. When stratified by function, under normal walking conditions, the low function and normal function THR groups had a reduced extension angle (mean = 1.75°, SD = ±7.75, 1.26°â€¯±â€¯7.42, respectively) compared to the control group (-6.07°â€¯±â€¯6.43; p < 0.0001). The low function group had a reduced sagittal plane hip power (0.75 W/kg ±â€¯0.24), reduced flexor (0.60 Nm/kg ±â€¯0.85) and extensor moment (0.51 Nm/kg ±â€¯0.17) compared to controls (p < 0.0001). These differences persisted under the fast walking condition. There were systematic differences between patients when stratified by function, in both walking conditions. Age-related differences were less systematic. Stratifying by biomechanical factors such as gait speed, rather than age, might be more robust for investigating functional differences.

DNA-Inspired Strand-Exchange for Switchable PMMA-Based Supramolecular Morphologies.

Inspired by nanotechnologies based on DNA strand displacement, herein we demonstrate that synthetic helical strand exchange can be achieved through tuning of poly(methyl methacrylate) (PMMA) triple-helix stereocomplexes. To evaluate the utility and robustness of helical strand exchange, stereoregular PMMA/polyethylene glycol (PEG) block copolymers capable of undergoing crystallization driven self-assembly via stereocomplex formation were prepared. Micelles with spherical or wormlike morphologies were formed by varying the molecular weight composition of the assembling components. Significantly, PMMA strand exchange was demonstrated and utilized to reversibly switch the micelles between different morphologies. This concept of strand exchange with PMMA-based triple-helix stereocomplexes offers new opportunities to program dynamic behaviors of polymeric materials, leading to scalable synthesis of "smart" nanosystems.

Joining and splitting models with Markov melding.

Analysing multiple evidence sources is often feasible only via a modular approach, with separate submodels specified for smaller components of the available evidence. Here we introduce a generic framework that enables fully Bayesian analysis in this setting. We propose a generic method for forming a suitable joint model when joining submodels, and a convenient computational algorithm for fitting this joint model in stages, rather than as a single, monolithic model. The approach also enables splitting of large joint models into smaller submodels, allowing inference for the original joint model to be conducted via our multi-stage algorithm. We motivate and demonstrate our approach through two examples: joining components of an evidence synthesis of A/H1N1 influenza, and splitting a large ecology model.

Refining muscle geometry and wrapping in the TLEM 2 model for improved hip contact force prediction.

Musculoskeletal models represent a powerful tool to gain knowledge on the internal forces acting at the joint level in a non-invasive way. However, these models can present some errors associated with the level of detail in their geometrical representation. For this reason, a thorough validation is necessary to prove the reliability of their predictions. This study documents the development of a generic musculoskeletal model and proposes a working logic and simulation techniques for identifying specific model features in need of refinement; as well as providing a quantitative validation for the prediction of hip contact forces (HCF). The model, implemented in the AnyBody Modeling System and based on the cadaveric dataset TLEM 2.0, was scaled to match the anthropometry of a patient fitted with an instrumented hip implant and to reproduce gait kinematics based on motion capture data. The relative contribution of individual muscle elements to the HCF and joint moments was analyzed to identify critical geometries, which were then compared to muscle magnetic resonance imaging (MRI) scans and, in case of inconsistencies, were modified to better match the volumetric scans. The predicted HCF showed good agreement with the overall trend and timing of the measured HCF from the instrumented prosthesis. The average root mean square error (RMSE), calculated for the total HCF was found to be 0.298*BW. Refining the geometries of the muscles thus identified reduced RMSE on HCF magnitudes by 17% (from 0.359*BW to 0.298*BW) over the whole gait cycle. The detailed study of individual muscle contributions to the HCF succeeded in identifying muscles with incorrect anatomy, which would have been difficult to intuitively identify otherwise. Despite a certain residual over-prediction of the final hip contact forces in the stance phase, a satisfactory level of geometrical accuracy of muscle paths has been achieved with the refinement of this model.

Dimensional Control and Morphological Transformations of Supramolecular Polymeric Nanofibers Based on Cofacially-Stacked Planar Amphiphilic Platinum(II) Complexes.

Square-planar platinum(II) complexes often stack cofacially to yield supramolecular fiber-like structures with interesting photophysical properties. However, control over fiber dimensions and the resulting colloidal stability is limited. We report the self-assembly of amphiphilic Pt(II) complexes with solubilizing ancillary ligands based on polyethylene glycol [PEGn, where n = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, Pt-PEG16, self-assembled to form polydisperse one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led to short seeds which, on addition of further molecularly dissolved Pt-PEG16 complex, underwent elongation in a "living supramolecular polymerization" process to yield relatively uniform fibers of length up to ca. 400 nm. The fiber lengths were dependent on the Pt-PEG16 complex to seed mass ratio in a manner analogous to a living covalent polymerization of molecular monomers. Moreover, the fiber lengths were unchanged in solution after 1 week and were therefore "static" with respect to interfiber exchange processes on this time scale. In contrast, similarly formed near-uniform fibers of Pt-PEG12 exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, Pt-PEG12 fibers partially evolved into 2D platelets. Furthermore, self-assembly of Pt-PEG7 yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (Pt-PEG16), the platelets formed assemblies via the growth of fibers selectively from their short edges. Our studies demonstrate that when interfiber dynamic exchange is suppressed, dimensional control and hierarchical structure formation are possible for supramolecular polymers through the use of kinetically controlled seeded growth methods.

Engineering live cell surfaces with functional polymers via cytocompatible controlled radical polymerization.

The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization), synthetic polymers with narrow polydispersity (Mw/Mn < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain-transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared with conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.

Light-Mediated Atom Transfer Radical Polymerization of Semi-Fluorinated (Meth)acrylates: Facile Access to Functional Materials.

A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (D ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results disclosed herein should create opportunities across a variety of fields that exploit fluorine-containing polymers for tailored bulk, interfacial, and solution properties.