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Open Access Publications from the University of California

Scholarly Works (18 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2023)

The promise of π-conjugated (semiconducting) polymers is to combine the electronic functionality of semiconductors with the processability and mechanical robustness of plastics. However, most research done on the mechanical properties of polymeric semiconductors (e.g., for organic photovoltaics, thin-film transistors, wearable sensors) has had the underlying goal of increasing the “stretchability”: the deformability and softness. Yet, softness is the wrong characteristic for many applications envisioned for organic semiconductors, including electronic interconnects, conductive paints and coatings, conductive adhesives, touch screens and displays, electronic textiles and fabrics, chemical sensors, and distributed sources of solar energy at risk of damage by indentation, scratching, and abrasion. For example, for organic photovoltaics, solar cells that can be integrated into surfaces already modified by human artifacts (e.g., rooftops, roads, and painted outdoor surfaces) comprise a greater potential source of renewable energy than the niche uses envisioned for portable and wearable solar cells. As such, a focus on modulus and ultimate extensibility—properties characteristic of “stretchability”—at the expense of mechanical robustness (e.g., strength, toughness, elasticity, and adhesion)—leaves many potentially lucrative applications on the table. Thus, the mechanical performance of a semiconducting polymer film must be tailored to the mechanical requirements for the device in which it is incorporated. Likewise, a semiconducting polymer film must also serve a structural role, as a glue that holds the device stack together; it must have sufficient cohesive and adhesive energy to retain electronic function of the device even when deformed. As such, the polymeric semiconductor also must function as an adhesive, despite this not being the primary function. This dissertation discusses two methods for controlling the mechanical properties of semiconducting polymer films that are common to conventional polymers, yet rarely applied to conjugated polymers. The first is the processing of the polymer film using continuous deposition methods common for industrial manufacturing of plastic materials. The second is the use of a crosslinker to introduce covalent bonds between polymer chains (common for commercial rubbers and elastomers). Finally, this dissertation discusses how changes to the side chain length of a model conjugated polymer affect the adhesive function of the polymer film.

    Cover page: Beyond Stretchability: The Mechanical Properties of Semiconducting Polymers
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2019)
    Endobronchial ultrasound (EBUS) and transbronchial needle aspiration (TBNA) have changed the landscape of pulmonology. Mediastinal structures beyond the confines of airway walls are visualized in real-time with EBUS, leading to improved accuracy of tissue sampling and diagnostic yield. With the development of various needle sizes ranging from 25-G to 19-G, the sampling of lymph nodes is becoming easier and more commonplace. Yet, certain conditions such as sarcoidosis and lymphoma may still be difficult to diagnose via EBUS-TBNA. Furthermore, in the age of targeted therapy, there are more demands on EBUS-TBNA samples for molecular marker testing and next-generation sequencing. Here, we present a complementary methodology, EBUS-guided intranodal forceps biopsy (EBUS-IFB), for tissue acquisition that may help address these deficiencies. Specifically, we aim to propose indications, contraindications, outline approaches in performing IFB, and provide an overview of the data for this complementary technique.
      Cover page: Endobronchial ultrasound-guided intranodal forceps biopsy (EBUS-IFB)—technical review
      • Article
      • Peer Reviewed
      Dermatology Online Journal, Volume 19, Issue 2 (2013)
        Creative Commons 'BY-NC-ND' version 4.0 license
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2021)
        PURPOSE: Lebers hereditary optic neuropathy (LHON) is the most common mtDNA optic neuropathy. It most frequently causes dense bilateral central scotomas that are often characterized in clinical studies by Humphrey visual field testing (HVF) using a stimulus size III. This provides numerical quantification of the visual field defect using the mean deviation. However, this size III testing strategy has limitations. We used stimulus size V to monitor these patients and evaluated intertest variability and dynamic range to determine the testing reliability and reproducibility. METHODS: This was a longitudinal retrospective cohort study comparing Stimulus III and Stimulus V HVF of 62 LHON patients who had reached the plateau stage of the disease. The intertest variability and mean defect were calculated for both stimulus sizes for 38 patients. The mean defect for stimulus size V was calculated using an algorithm developed by the University of Iowa Visual Field Reading Center. RESULTS: Stimulus size V HVFs had lower inter-test variability as measured by mean defect standard deviation (Z = 169, P < 0.01). The floor effect seen with Stimulus III HVF in LHON, was less pronounced with Stimulus V HVF. The correlation of stimulus size III and V mean defect was strong (r = 0.90, P < 0.01), and a mathematical model was constructed to calculate the Stimulus size V mean defect from the Stimulus size III results (MDstimV = 0.988 x MDStimIII + 1.35, R2 = 0.82 P < 0.01). CONCLUSIONS: Stimulus size V HVF had lower intertest variability and a better dynamic range than Stimulus size III HVF in LHON patients. This makes the stimulus V HVF a more reliable metric to follow LHON patients especially in clinical trials. The mathematical model presented can be used to generate a Stimulus V equivalent mean defect from Stimulus III HVFs. TRANSLATIONAL RELEVANCE: Using Stimulus V HVF in LHON patients increases its ability to detect and quantify a response to treatment, making it a useful metric for future LHON clinical trials and the clinical setting.
          Cover page: Benefit of Stimulus Size V Perimetry for Patients With a Dense Central Scotoma From Lebers Hereditary Optic Neuropathy.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2023)
          Traumatic brain injury (TBI) affects millions of people each year and, in many cases, results in long-term disabilities. Once a TBI has occurred, there is a significant breakdown of the blood-brain barrier resulting in increased vascular permeability and progression of the injury. In this study, the use of an infusible extracellular matrix-derived biomaterial (iECM) for its ability to reduce vascular permeability and modulate gene expression in the injured brain is investigated. First, the pharmacokinetics of iECM administration in a mouse model of TBI is characterized, and the robust accumulation of iECM at the site of injury is demonstrated. Next, it is shown that iECM administration after injury can reduce the extravasation of molecules into the brain, and in vitro, iECM increases trans-endothelial electrical resistance across a monolayer of TNFα-stimulated endothelial cells. In gene expression analysis of brain tissue, iECM induces changes that are indicative of downregulation of the proinflammatory response 1-day post-injury/treatment and neuroprotection at 5 days post-injury/treatment. Therefore, iECM shows potential as a treatment for TBI.
            Cover page: Infusible Extracellular Matrix Biomaterial Promotes Vascular Integrity and Modulates the Inflammatory Response in Acute Traumatic Brain Injury.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2018)

            Importance

            Recent increases in US opioid-related deaths underscore the need to understand drivers of fatal overdose. The initial prescription of opioids represents a critical juncture because it increases the risk of future opioid use disorder and is preventable.

            Objective

            To examine new opioid prescribing patterns in US patients at increased risk of overdose from benzodiazepine use.

            Design, setting, and participants

            This study used publicly available data from the National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care Survey from January 1, 2005, through December 31, 2015, to identify adults 20 years or older receiving new opioid prescriptions and concurrently using a benzodiazepine.

            Main outcomes and measures

            Population-based rates of new opioid prescriptions stratified by use of benzodiazepines.

            Results

            This study analyzed 13 146 visits, representing 214 million visits nationally, with a new opioid prescription. Rates of new opioid prescriptions among adults using a benzodiazepine increased from 189 to 351 per 1000 persons between 2005 and 2010 (rate difference, 162; 95% CI, 29-295; P = .02) and decreased to 172 per 1000 persons by 2015 (rate difference, -179; 95% CI, -310 to -48; P = .008). New opioid prescriptions in the general population not using benzodiazepines increased nonsignificantly from 78 to 93 per 1000 US persons between 2005 and 2010 (rate difference, 15; 95% CI, -3 to 33; P = .10) and decreased nonsignificantly to 79 per 1000 persons by 2015 (rate difference, -14; 95% CI, -38 to 11; P = .28). The likelihood of receiving a new opioid prescription during an ambulatory visit remained higher for patients concurrently using benzodiazepines compared with the general population after adjusting for demographic characteristics, comorbidities, and diagnoses associated with pain (adjusted relative risk, 1.83; 95% CI, 1.56-2.15; P < .001). Naloxone was coprescribed in less than 1% of visits when a patient concurrently used a benzodiazepine.

            Conclusions and relevance

            In 2010, new opioid prescriptions for US adults stopped increasing and began to decrease among higher-risk patients who used benzodiazepines. These patterns suggest that the recent increase in opioid-related deaths may be associated with factors other than physicians writing new opioid prescriptions. Nevertheless, prescribing among higher-risk patients still occurred at rates higher than rates in the general population, representing an important opportunity to improve quality of care for patients experiencing pain.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2022)
              The conductive polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is ubiquitous in research dealing with organic electronic devices (e.g., solar cells, wearable and implantable sensors, and electrochemical transistors). In many bioelectronic applications, the applicability of commercially available formulations of PEDOT:PSS (e.g., Clevios) is limited by its poor mechanical properties. Additives can be used to increase the compliance but pose a risk of leaching, which can result in device failure and increased toxicity (in biological settings). Thus, to increase the mechanical compliance of PEDOT:PSS without additives, we synthesized a library of intrinsically stretchable block copolymers. In particular, controlled radical polymerization using a reversible addition-fragmentation transfer process was used to generate block copolymers consisting of a block of PSS (of fixed length) appended to varying blocks of poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA). These block copolymers (PSS(1)-b-PPEGMEA(x), where x ranges from 1 to 6) were used as scaffolds for oxidative polymerization of PEDOT. By increasing the lengths of the PPEGMEA segments on the PEDOT:[PSS(1)-b-PPEGMEA(1-6)] block copolymers, ("Block-1" to "Block-6"), or by blending these copolymers with PEDOT:PSS, the mechanical and electronic properties of the polymer can be tuned. Our results indicate that the polymer with the longest block of PPEGMEA, Block-6, had the highest fracture strain (75%) and lowest elastic modulus (9.7 MPa), though at the expense of conductivity (0.01 S cm-1). However, blending Block-6 with PEDOT:PSS to compensate for the insulating nature of the PPEGMEA resulted in increased conductivity [2.14 S cm-1 for Blend-6 (2:1)]. Finally, we showed that Block-6 outperforms a commercial formulation of PEDOT:PSS as a dry electrode for surface electromyography due to its favorable mechanical properties and better adhesion to skin.
                Cover page: Intrinsically Stretchable Block Copolymer Based on PEDOT:PSS for Improved Performance in Bioelectronic Applications
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2022)

                Objectives

                Nurse practitioners and physician assistants (NPs/PAs) increasingly practice in emergency departments (EDs), yet limited research has compared their practice patterns with those of physicians.

                Design, setting and participants

                Using nationally representative data from the National Hospital Ambulatory Medical Care Survey (NHAMCS), we analysed ED visits among NPs/PAs and physicians between 1 January 2009 and 31 December 2017. To compare NP/PA and physician utilisation, we estimated propensity score-weighted multivariable regressions adjusted for clinical/sociodemographic variables, including triage acuity score (1=sickest/5=healthiest). Because NPs/PAs may preferentially consult physicians for more complex patients, we performed sensitivity analyses restricting to EDs with >95% of visits including the NP/PA-physician combination.

                Exposures

                NPs/PAs.

                Main outcome measures

                Use of hospitalisations, diagnostic tests, medications, procedures and six low-value services, for example, CT/MRI for uncomplicated headache, based on Choosing Wisely and other practice guidelines.

                Results

                Before propensity weighting, we studied visits to 12 410 NPs/PAs-alone, 21 560 to the NP/PA-physician combination and 143 687 to physicians-alone who saw patients with increasing age (41, 45 and 47 years, p<0.001) and worsening triage acuity scores (3.03, 2.85 and 2.67, p<0.001), respectively. After weighting, NPs/PAs-alone used fewer medications (2.62 vs 2.80, p=0.002), diagnostic tests (3.77 vs 4.66, p<0.001), procedures (0.67 vs 0.77, p<0.001), hospitalisations (OR 0.35 (95% CI 0.26 to 0.46)) and low-value CT/MRI studies (OR 0.65 (95% CI 0.53 to 0.80)) than physicians. Contrastingly, the NP/PA-physician combination used more medications (3.08 vs 2.80, p<0.001), diagnostic tests (5.07 vs 4.66, p<0.001), procedures (0.86 vs 0.77, p<0.001), hospitalisations OR 1.33 (95% CI 1.17 to 1.51) and low-value CT/MRI studies (OR 1.23 (95% CI 1.07 to 1.43)) than physicians-results were similar among EDs with >95% of NP/PA visits including the NP/PA-physician combination.

                Conclusions and relevance

                While U.S. NPs/PAs-alone used less care and low-value advanced diagnostic imaging, the NP/PA-physician combination used more care and low-value advanced diagnostic imaging than physicians alone. Findings were reproduced among EDs where nearly all NP/PA visits were collaborative with physicians, suggesting that NPs/PAs seeing more complex patients used more services than physicians alone, but the converse might be true for more straightforward patients.
                  Cover page: US emergency care patterns among nurse practitioners and physician assistants compared with physicians: a cross-sectional analysis
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2023)
                    Cover page: External Measurement of Swallowed Volume During Exercise Enabled by Stretchable Derivatives of PEDOT:PSS, Graphene, Metallic Nanoparticles, and Machine Learning
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2016)
                    In this paper, the authors describe an online tool with which to convert and thus quantify count finger measurements of visual acuity into Snellen equivalents. It is hoped that this tool allows for the re-interpretation of retrospectively collected data that provide visual acuity in terms of qualitative count finger measurements.
                      Cover page: Correcting Finger Counting to Snellen Acuity
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