Biomechanical evaluation of novel intra- and extramedullary assembly fixation for proximal humerus fractures in the elderly.

Purpose: A novel intra- and extramedullary assembly fixation method was introduced, which achieved good clinical results in complex proximal humeral fractures; however, evidence of its comparability with traditional fixation is lacking. This biomechanical study aimed to compare it with traditional fixation devices in osteoporotic proximal humeral fractures. Methods: Three-part proximal humeral fractures with osteopenia were created on 12 pairs of fresh frozen humerus specimens and allocated to three groups: 1) lateral locking plate, 2) intramedullary nail, and 3) intra- and extramedullary assembly fixation. The specimens were loaded to simulate the force at 25° abduction. Thereafter, an axial stiffness test and a compound cyclic load to failure test were applied. Structural stiffness, number of cycles loaded to failure, and relative displacement values at predetermined measurement points were recorded using a testing machine and a synchronized 3D video tracking system. Results: In terms of initial stiffness and the number of cycles loaded to failure, the intra- and extramedullary assembly fixation group showed notable improvements compared to the other groups (p <0.017). The mean relative displacement value of measurement points in the intra- and extramedullary assembly fixation group was smaller than that in the other two groups. However, there was no significant difference until 10,000 cycles. The mean relative displacement of the intramedullary nail group (3.136 mm) exceeded 3 mm at 7,500 cycles of loading. Conclusion: In this test model, axial fixation can provide better mechanical stability than non-axial fixation. The intra- and extramedullary assembly fixation is better able to prevent the varus collapse for elderly proximal humeral fractures with posteromedial comminution.

Leveraging a smartphone to perform time-gated luminescence measurements.

Empowered by advanced on-board sensors, high-performance optics packages and ever-increasing computational power, smartphones have democratized data generation, collection, and analysis. Building on this capacity, many platforms have been developed to enable its use as an optical sensing platform for colorimetric and fluorescence measurements. In this paper, we report the ability to enable a smartphone to perform laboratory quality time-resolved analysis of luminescent samples via the exploitation of the rolling shutter mechanism of the native CMOS imager. We achieve this by leveraging the smartphone's standard image capture applications, commercially available image analysis software, and housing the device within a UV-LED containing case. These low-cost modifications enable us to demonstrate the smartphone's analytical potential by performing tasks ranging from authentication and encryption to the interrogation of packaging, compounds, and physical phenomena. This approach underscores the power of repurposing existing technologies to extend the reach and inclusivity of scientific exploration, opening new avenues for data collection and analysis.

[Early effectiveness of computer navigation system-assisted transiliac-transsacral screws placement for posterior pelvic ring injuries].

Objective: To investigate the early effectiveness of transiliac-transsacral screws internal fixation assisted by augmented reality navigation system HoloSight (hereinafter referred to as "computer navigation system") in the treatment of posterior pelvic ring injuries. Methods: A retrospective analysis was made in the 41 patients with posterior pelvic ring injuries who had been treated surgically with transiliac-transsacral screws between June 2022 and June 2023. The patients were divided into navigation group (18 cases, using computer navigation system to assist screw implantation) and freehand group (23 cases, using C-arm X-ray fluoroscopy to guide screw implantation) according to the different methods of transiliac-transsacral screws placement. There was no significant difference in gender, age, body mass index, causes of injuries, Tile classification of pelvic fracture, days from injury to operation, usage of unlocking closed reduction technique between the two groups ( P>0.05). The time of screw implantation, the fluoroscopy times, the guide wire adjustment times of each screw, and the incidence of complications were recorded and compared between the two groups. The position of the transiliac-transsacral screw was scanned by CT within 2 days after operation, and the position of the screw was classified according to Gras standard. Results: The operation was successfully completed in both groups. The time of screw implantation, the fluoroscopy times, and the guide wire adjustment times of each screw in the navigation group were significantly less than those in the freehand group ( P<0.05). There were 2 cases of incision infection in the freehand group, and the incision healed by first intention after active dressing change; there was no screw-related complication in the navigation group during operation and early period after operation; the difference in incidence of complications between the two groups (8.7% vs. 0) was not significant ( P=0.495). According to the Gras standard, the screw position of the navigation group was significantly better than that of the freehand group ( P<0.05). Conclusion: Compared with the traditional freehand method, the computer navigation system assisted transiliac-transsacral screws internal fixation in the treatment of posterior pelvic ring injuries has advantages of improving the accuracy of screw implantation and reducing radiation damage and the time of screw implantation.

Exploiting Dynamic Vector-Level Operations and a 2D-Enhanced Logistic Modular Map for Efficient Chaotic Image Encryption.

Over the past few years, chaotic image encryption has gained extensive attention. Nevertheless, the current studies on chaotic image encryption still possess certain constraints. To break these constraints, we initially created a two-dimensional enhanced logistic modular map (2D-ELMM) and subsequently devised a chaotic image encryption scheme based on vector-level operations and 2D-ELMM (CIES-DVEM). In contrast to some recent schemes, CIES-DVEM features remarkable advantages in several aspects. Firstly, 2D-ELMM is not only simpler in structure, but its chaotic performance is also significantly better than that of some newly reported chaotic maps. Secondly, the key stream generation process of CIES-DVEM is more practical, and there is no need to replace the secret key or recreate the chaotic sequence when handling different images. Thirdly, the encryption process of CIES-DVEM is dynamic and closely related to plaintext images, enabling it to withstand various attacks more effectively. Finally, CIES-DVEM incorporates lots of vector-level operations, resulting in a highly efficient encryption process. Numerous experiments and analyses indicate that CIES-DVEM not only boasts highly significant advantages in terms of encryption efficiency, but it also surpasses many recent encryption schemes in practicality and security.

Age-Related changes in the morphological features of medial column of the proximal humerus in the Chinese population.

Background: Age-related changes in the medial column (MC) of the proximal humerus have a major impact on fracture management; however, the changes in the morphological features remain unclear. This study aimed to investigate the age-related changes in the morphological features of MC and present the morphological grading. Methods: One hundred computed tomography (CT) images of the proximal humerus of 100 individuals (19-95 years) were retrospectively obtained. The individuals were categorized into five age groups to quantify the differences among different ages; the youngest group (18-44 years) served as the baseline group. Parameters of the morphological features were measured on CT images with multiplanar reconstruction based on an explicit definition of MC, including length, thickness, width, oblique thickness (DSM), humeral head diameter (DHM), and ratio (RSM) of DSM to DHM. The morphological grading of MC was presented based on the value of RSM deviating different standard deviations (SD) from the mean value in the baseline group. Results: Significant negative correlations were observed between age and the morphological parameters of MC (r ranged from -0.875 to -0.926; all P < 0.05), excluding DHM (r = 0.081, P = 0.422). Significant differences in the values of morphological feature parameters were detected among the five age groups (all P < 0.001). The highest mean values of morphological feature parameters were observed in the youngest group (18-44 years), which decreased gradually with increasing age until the lowest mean values were observed in the oldest group (≥90 years) (all P < 0.05). The morphological features of MC were categorized into three grades based on the value of RSM deviating 1.5 SD or 3 SD from the mean value in the baseline group. Conclusion: Our study shows that the parameter values of morphological features of MC decreased with increasing age. The morphological features of MC could be categorized into three grades. Our findings may provide a more comprehensive insight into age-related changes in the morphological features of MC that facilitate risk stratification and optimize the management of proximal humeral fractures.

[Effectiveness of three-dimensional visible technique without fluoroscopy versus two-dimensional fluoroscopy in reduction of unstable pelvic fractures].

Objective: To compare the reduction qualities of three-dimensional visible technique without fluoroscopy and two-dimensional fluoroscopy for unstable pelvic fractures during operations. Methods: The clinical data of 40 patients with unstable pelvic fractures, who met the selection criteria in three clinical centers between June 2021 and September 2022, were retrospectively analyzed. According to the reduction methods, the patients were divided into two groups. Twenty patients in trial group were treated with unlocking closed reduction system combined with three-dimensional visible technique without fluoroscopy; 20 patients in control group with unlocking closed reduction system under two-dimensional fluoroscopy. There was no significant difference in the gender, age, injury mechanism, Tile type of fracture, Injury Severity Score (ISS), and the time between injury to operation between the two groups ( P>0.05). The qualities of fracture reduction according to the Matta criteria, operative time, intraoperative blood loss, fracture reduction time, times of fluoroscopy, and System Usability Scale (SUS) score were recorded and compared. Results: All operations were successfully completed in both groups. According to the Matta criteria, the qualities of fracture reduction were rated as excellent in 19 patients (95%) in trial group, which was better than that in the control group (13 cases, 65%), with a significant difference ( χ 2=3.906, P=0.048). The operative time and intraoperative blood loss had no significant differences between the two groups ( P>0.05). The fracture reduction time and times of fluoroscopy were significantly less in trial group than in control group ( P<0.05), and SUS score in trial group was significantly higher in trial group than in control group ( P<0.05). Conclusion: Compared to using unlocking closed reduction system under two-dimensional fluoroscopy, three-dimensional visible technique without fluoroscopy can significantly improve the reduction quality of unstable pelvic fractures without prolonging the operative time, and is valuable to reduce iatrogenic radiation exposure for patients and medical workers.

How to improve the biomechanical stability of endosteal augmentation for proximal humerus fracture with osteopenia? A cadaveric study.

BACKGROUND: Endosteal augmentation enhances the stability of osteoporotic proximal humeral fracture fixation, but the optimal configuration is unknown. The purpose of this study was to compare the biomechanical properties of different lengths of fibula with or without calcar screw in osteoporotic proximal humeral fracture. METHODS: Three-part proximal humeral fractures with osteopenia were created on 20 pairs of fresh-frozen humeri specimens and allocated to four groups: (1) locking plate with a 6-cm fibular strut allograft, (2) locking plate with a 6-cm fibular strut allograft and additional calcar screws, (3) locking plate with a 12-cm fibular strut allograft，and (4) locking plate with a 12-cm fibular strut allograft and additional calcar screws. Specimens were loaded to simulate the force at 25° abduction. Thereafter, an axial stiffness test and a compound cyclic load to failure test were applied. Structural stiffness, number of cycles loaded to failure and relative displacement values for 5000 cycles at predetermined measurement points were recorded using a testing machine and a synchronized 3D video tracking system. FINDINGS: In terms of initial stiffness, number of cycles loaded to failure, and relative displacement values, the groups with 12-cm fibular strut showed obvious improvement compared to the groups with 6-cm fibular strut irrespective of the influence of calcar screw implementation. Further, the groups implemented with calcar screws also showed promising biomechanical stability irrespective of fibular length. INTERPRETATION: Lateral locking plate with longer endosteal fibular augmentation and calcar screw can significantly improve biomechanical stability for elderly proximal humeral fractures with posteromedial comminution.

Treatment of elderly comminuted proximal humeral fracture using endosteal anatomical support system: A case report.

INTRODUCTION: Intramedullary anatomical medial strut with allograft bone (IAMSAB), which accommodates the shape of the proximal humeral cavity and provides rotational stability and direct support to the medial column, was successfully introduced to augment Lateral locking plate (LLP) in the treatment of elderly comminuted proximal humeral fractures. Based on the LLP-IAMSAB construct, a newly titanium endosteal anatomical support system (EASS) was developed. CASE PRESENTATION: Reported here is a single case of a highly comminuted proximal humeral fracture. The fractures were treated with EASS. The patient's fracture healed properly. The 24-month follow-up demonstrated no pain and a good functional outcome, with no signs of reduction loss, absorption of greater tuberosity, varus displacement and avascular necrosis of humeral head. CLINICAL DISCUSSION: The newly developed EASS had several special considerations contributing to satisfactory surgical outcome. The flat plane construct of the proximal end of the EASS directly support humeral head to prevent varus displacement of the humeral head, instead of the purchase between the screw thread and the cancellous bone inside the humeral head in the nail or plate fixation. Medial anatomical shape of proximal end helps to reduce medial cortex reduction. Greater tuberosity support block with rotator cuff suture fixation might promote greater tuberosity healing and prevent its absorption. However, there is no similar construct in the nail or plate fixation. CONCLUSION: The newly developed endosteal anatomical support system might be a promising option in the treatment of elderly comminuted proximal humeral fractures. Although the effectiveness of this system requires additional evaluation upon more patients being treated with this surgical method, the newly developed EASS may serve as a humeral head-preserving method for elderly patients with comminuted proximal humeral fractures.

Augmented Stability in Leaving Original Internal Fixation with Multidimensional Cross Locking Plate through Mini-Open Femoral Anterior Approach for Aseptic Femoral Shaft Nonunion: A Retrospective Cohort Study.

OBJECTIVE: Aseptic femoral shaft nonunion constitutes approximately 1%-10% of all femoral shaft fractures treated with intramedullary nail (IMN) fixation, possibly attributable to the lack of anti-rotational stability. Although a lateral locking plate (LP) with retainment of original IMN has shown the most success, lateral LP inflicts significant surgical trauma on patients. Therefore, the Multidimensional Cross Locking Plate (MDC-LP) was designed based on a mini-open femoral anterior approach. We aim to report and compare the technical aspects and clinical outcomes of using anterior MDC-LP or lateral LP with retention of original IMN for the treatment of aseptic femoral shaft nonunion. METHODS: In this single center retrospective cohort study, records of 49 patients who had undergone revision of femoral shaft aseptic nonunion with anterior MDC-LP or lateral LP while retaining the original IMN from January 2015 to October 2019 were retrospectively reviewed. Information on patients' demographics, clinical data, and surgical outcomes were gathered and analyzed. X-ray and CT scans were used for bone union evaluation and the lower extremity functional scale (LEFS) was used for follow-up functional evaluation. For quantitative data, the Student's t-test was used if the data were normally distributed. The Mann-Whitney U-test was used for non-normally distributed data. For qualitative data, the Chi-square test was used for comparisons. RESULTS: Twenty-seven patients were treated with anterior MDC-LP, and 22 patients were treated with lateral LP. There are no significant differences in age, sex, BMI, time since initial femoral shaft fracture, initial fracture type (close/open), nonunion type, or nonunion location between patients' group. Among patients treated with anterior MDC-LP, an average of 2-months advantage in time to union was observed (4.09 months vs. 6.8 months in the lateral LP group: P = 0.000), smaller incision was required for MDC-LP installment (7.7 cm vs 17.1 cm in lateral LP group: P = 0.000). CONCLUSIONS: For the treatment of aseptic femoral shaft nonunion with retainment of original IMN, anterior MDC-LP via mini-open femoral anterior approach described in this study is a better option than lateral LP for achieving faster bone union and satisfactory functional outcome with less surgical trauma.

Comparative study of temperature effects on white sandstone and rockburst-like materials.

Rockburst physical model test, as one of the important means to study deep tunnel engineering, reflects the main influencing factors of rockburst into the model test through similar theory, so as to reveal the formation mechanism, influencing factors and evolution law of different types of rockburst in deep tunnels. In order to study the mechanical properties of white sandstone in deeply buried tunnels at high ground temperatures, materials suitable for conducting rockburst physical and mechanical tests were developed on the basis of the Daqian Shi Ling tunnel project, and similar material ratios were preferentially selected on the basis of white sandstone. Judged by the rock burst propensity, similar materials with low strength and high brittle characteristics, can better simulate the characteristics of white sandstone, and all show a strong propensity to rock burst, is the ideal rock burst similar materials. Uniaxial compressive tests were conducted on similar materials and the original rock at different temperatures, and comparative analysis was performed. Through the study of stress, displacement and modulus of elasticity, it was concluded that the compressive strength of similar materials gradually increased with temperature in the range of 20-100°C, and the vertical displacement at peak strength decreased with increasing temperature. The damage forms of white sandstone and similar materials at different temperatures were comparatively analyzed, and it was obtained that the damage forms of white sandstone and similar materials were basically the same, with a few specimens showing tensile and shear damage, and most specimens showing the form of combined tensile and shear damage. The study of rock burst similar materials and the development of the failure characteristics of rock burst under the action of thermal coupling are of great significance to the mechanism of rock burst generation and prediction.

Technique and clinical results of a new intramedullary support nail and plate system for fixation of 3- or 4- part proximal humeral fractures in older adults.

BACKGROUND: Internal fixation of complex proximal humeral fractures (PHF) with osteoporosis is associated with a high incidence of complications. This study introduces the technique and clinical results of a novel intramedullary support nail and plate system (ISNPs) for the internal fixation of 3- or 4- part PHF in older adults. The ISNPs combines the concept of intramedullary support and dynamic fixation into a locking plate fixation system that can be applied using a minimally invasive surgical approach. METHODS: A total of 46 consecutive patients diagnosed with 3- or 4-part PHF that met the criteria were included in this study, including 18 in the ISNPs group and 28 in the conventional locking plate (LP) group. Clinical results, including operative time, intraoperative bleeding, reduction quality, subjective outcome ratings, and complications, were compared between the two groups. Functional outcomes were evaluated using the Constant score and disability of the arm, shoulder, and hand (DASH) questionnaire at 1-year follow-up. RESULTS: There were no significant differences in age, sex, local bone quality, Neer-fracture type, and follow-up time between the ISNPs and LP groups. For clinical analysis, there were no significant differences in intraoperative bleeding and operation time between the ISNPs and LP groups. Significant differences were observed in the percentage of the malreduced cases, Constant and DASH score analysis, and the patients' subjective evaluation ('excellent' and 'good' %) between the two groups. CONCLUSION: The ISNPs technique proposed in this study provides a novel hybrid internal fixation model for complex PHF with osteoporosis. The clinical results at 1-year follow-up confirmed the advantage of applying it to 3- or 4- part PHF in older patients. Further studies are required to optimize its design and explore its optimal indications.

matExplorer: Visual Exploration on Predicting Ionic Conductivity for Solid-state Electrolytes.

Lithium ion batteries (LIBs) are widely used as important energy sources for mobile phones, electric vehicles, and drones. Experts have attempted to replace liquid electrolytes with solid electrolytes that have wider electrochemical window and higher stability due to the potential safety risks, such as electrolyte leakage, flammable solvents, poor thermal stability, and many side reactions caused by liquid electrolytes. However, finding suitable alternative materials using traditional approaches is very difficult due to the incredibly high cost in searching. Machine learning (ML)-based methods are currently introduced and used for material prediction. However, learning tools designed for domain experts to conduct intuitive performance comparison and analysis of ML models are rare. In this case, we propose an interactive visualization system for experts to select suitable ML models and understand and explore the predication results comprehensively. Our system uses a multifaceted visualization scheme designed to support analysis from various perspectives, such as feature distribution, data similarity, model performance, and result presentation. Case studies with actual lab experiments have been conducted by the experts, and the final results confirmed the effectiveness and helpfulness of our system.

Achieve Closed Reduction of Irreducible, Unilateral Vertically Displaced Pelvic Ring Disruption with an Unlocking Closed Reduction Technique.

OBJECTIVE: To be able to treat irreducible unilateral vertically displaced pelvic ring disruption (UVDPRD) using closed reduction, we introduced a technique named Unlocking Closed Reduction Technique (UCRT) and evaluated its effectiveness with improved pelvic closed reduction system (PCRS). METHODS: A retrospective study was performed in our department. Between January 2014 and December 2017, 43 patients whose UVDPRD were not successfully reduced using transcondylar traction. Subsequently, they were treated with UCRT using improved PCRS. The study included 19 male and 24 female patients, with a mean age at the time of the operation of 46.2 years. During surgery, operation time and blood loss were recorded. Post-surgical reduction quality was evaluated using Matta scoring criteria and patient lower-extremity functional outcome was evaluated using Majeed functional scoring criteria. RESULTS: When used with improved PCRS, UCRT achieved pelvic reduction in all 43 cases of irreducible UVDPRD with postoperative pelvic reduction quality rated excellent and good for 42/43 (97.6%) patients according to the Matta scoring criteria (Matta Score < 10 mm). While no post-surgical complications emerged as the direct result of UCRT in this cohort of patients, 8/37 patients who were treated with subcutaneous supra-acetabular pedicle screw internal fixation (INFIX) for anterior ring fixation developed lateral femoral cutaneous nerve injury but recovered 6 months postoperatively. No revision surgery was performed on any of the recruited patients. All patients' lower-extremity functionality was rated excellent with an average Majeed function score of 94.3 during the last follow-up at an average of 41.6 months postoperatively. CONCLUSION: With excellent surgical and functional outcomes in patients with irreducible UVDPRD, improved PCRS-assisted UCRT proved to be a safe and effective method for the treatment of irreducible UVDPRD.

Finite element analysis of an intramedulary anatomical strut for proximal humeral fractures with disrupted medial column instability: A cohort study.

BACKGROUND: Lateral locking plate (LLP) fixation has gained popularity for the treatment of proximal humeral fractures (PHFs); however, complications can occur due to loss of the medial cortical buttress from fracture comminution. MATERIALS AND METHODS: We designed a novel intramedullary anatomical medial strut with allograft bone (IAMSAB) using MIMICS software to specifically fill the intramedullary canal of the proximal humeral bone. We used finite element analysis to evaluate the biomechanical characteristics of a LLP, LLP-intramedullary fixation system (IFS), LLP-anatomical medial locking plate (AMLP), or the combined application of a LLP and IAMSAB (LLP-IAMSAB) fixation construct in patients with a PHF and an unstable medial column. RESULTS: For axial or rotational loads, under (normal) Nor or osteoporotic (Ost) bone conditions, the LLP-IAMSAB fixation construct was significantly stiffer than the LLP-IFS fixation construct, and displacement at the fracture site after LLP-IAMSAB fixation was significantly less than after LLP or LLP-IFS fixation (P < 0.05). Stiffness of the LLP-IAMSAB and LLP-AMLP fixation constructs and displacement at the fracture site after LLP-IAMSAB and LLP-AMLP fixation were not significantly different. The IFS, AMLP, and IAMSAB shared the load in the LLP and decreased the risk of implant failure. There were no significant differences in von Mises stress and stress distribution after fixation with the LLP-IFS, LLP-AMLP, and LLP-IAMSAB constructs. CONCLUSION: These data suggest that the IAMSAB can provide direct medial support or resistance to rotation and augment the biomechanics of the LLP. The combined application of the IAMSAB and LLP may achieve functional outcomes that are similar to the LLP-AMLP fixation construct.

A bibliometric analysis of exertional heat stroke research in Web of Science.

BACKGROUND: Exertional heat stroke is a fatal condition and remains a health problem. This paper evaluates the publication trend regarding exertional heat stroke research between 1996 and 2015 using a bibliometric method. METHOD: Articles regarding exertional heat stroke research published between 1996 and December 2015 were searched for in the SCI-EXPANDED database of Web of Science. The search results were analyzed with regard to publication year; publication quantity regarding countries/regions, and authors; citation frequency; and journal distribution. CiteSpace (v3.6) was used for a document co-citation visualization analysis. RESULTS: In total, 289 publications on heat stroke were located. After selection, 209 original articles conducted across 28 countries/regions and published in 83 journals were included in the analysis. The USA, Isreal, and France were the most common locations for exertional heat stroke studies. The CiteSpace visualization cluster analysis showed that exertional heat stroke-related mortality and protective measures were constant concerns of research. CONCLUSIONS: Research related to exertional heat stroke has been continuous concerned. USA is still the leading country in this field.

Effects of optical clearing agents on noninvasive blood glucose monitoring with optical coherence tomography: a pilot study.

Recently, the capability of optical coherence tomography (OCT) has been demonstrated for noninvasive blood glucose monitoring. In this work, we investigate the administration of chemical agents onto human skin tissue to increase the transparency of the surface of the skin, as a means of improving the capability of OCT imaging for clinically relevant applications. Eight groups of experiments were proposed, in which different optical clearing agents (OCA) were used. The results indicate that, when properly used, some OCAs perform well in promoting the capability of OCT for noninvasive blood glucose monitoring. Among the four kinds of OCA we used, 50% v/v glycerol solute turns out to be the best enhancer. Compared with the results of the experiments in which no OCA was used, when 50% glycerol was applied onto the human skin topically, the correlation coefficient between the OCT signal slope (OCTSS) and blood glucose concentration (BGC) was improved by 7.1% on average, and the lag time between changes in the OCTSS and BGC was cut by 8 min on average. The results of 10 w/v mannitol were also good, but not as pronounced.

Energy migration in conjugated polymers: the role of molecular structure.

Conjugated polymers undergo facile exciton diffusion. Different molecular structures were examined to study the role of the excited state lifetimes and molecular conformations on energy transfer. There is a clear indication that extended fluorescence lifetimes give enhanced exciton diffusion as determined by fluorescence depolarization measurements. These results are consistent with a strong electronic coupling or Dexter-type energy transfer as the dominating mechanism. The control of polymer conformations in liquid crystal solvents was also examined and it was determined that more planar conformations gave enhanced energy transfer to emissive low band-gap endgroups.

Conjugation enhancement of intramolecular exciton migration in poly(p-phenylene ethynylene)s.

Efficient energy migration in conjugated polymers is critical to their performance in photovoltaic, display, and sensor devices. The ability to precisely control the polymer conformation is a key issue for the experimental investigations and deeper understanding of the nature of this process. We make use of specially designed iptycene-containing poly(p-phenylene ethynylene)s that display chain-extended conformations when dissolved in nematic liquid crystalline solvents. In these solutions, the polymers show a substantial enhancement in the intrachain exciton migration rate, which is attributed to their increased conjugation length and better alignment. The organizational enhancement of the energy transfer efficiency, as determined by site-selective emission from lower energy traps at the polymer termini, is accompanied by a significant increase of the fluorescence quantum yield. The liquid crystalline phase is a necessary requirement for these phenomena to occur, and when the temperature was increased above the nematic-isotropic transition, we observed a dramatic reduction of the energy transfer efficiency and fluorescence quantum yield. The ability to improve the exciton migration efficiency through precise control of the polymer structure with liquid crystalline solutions demonstrates the importance of a polymer's conformation for energy transfer, and provides a way to improve the energy transporting performance of conjugated polymers.

Sensitivity gains in chemosensing by lasing action in organic polymers.

Societal needs for greater security require dramatic improvements in the sensitivity of chemical and biological sensors. To meet this challenge, increasing emphasis in analytical science has been directed towards materials and devices having highly nonlinear characteristics; semiconducting organic polymers (SOPs), with their facile excited state (exciton) transport, are prime examples of amplifying materials. SOPs have also been recognized as promising lasing materials, although the susceptibility of these materials to optical damage has thus far limited applications. Here we report that attenuated lasing in optically pumped SOP thin films displays a sensitivity to vapours of explosives more than 30 times higher than is observed from spontaneous emission. Critical to this achievement was the development of a transducing polymer with high thin-film quantum yield, a high optical damage threshold in ambient atmosphere and a record low lasing threshold. Trace vapours of the explosives 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) introduce non-radiative deactivation pathways that compete with stimulated emission. We demonstrate that the induced cessation of the lasing action, and associated sensitivity enhancement, is most pronounced when films are pumped at intensities near their lasing threshold. The combined gains from amplifying materials and lasing promise to deliver sensors that can detect explosives with unparalleled sensitivity.