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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2021)

Soft robotics is a promising field that can solve several limitations of traditional rigid robotics. These systems are composed of soft and flexible materials to achieve high degrees-of-freedom and compliance with their surroundings. An important part of soft robotics is developing methods to actuate the soft structures. A popular method involves inflating soft hollow structures with a pneumatic pump that can achieve rapid and precise actuation. However, the structure must be tethered to a heavy and rigid pump, which limits its application. An alternative method vaporizes embedded liquid to inflate the structure instead. The simplest and widely used design to vaporize such liquid is by installing a heating element near the liquid. Heating the system beyond the boiling point rapidly boils the liquid and deforms the structure. The small amount of liquid and heater makes it easier to be packaged into a portable device. Nevertheless, this technique possesses several limitations that must be improved to be practical. This dissertation addresses these limitations and introduces methods that can advance the field for future robotics. Chapter 2 describes how actuation through vaporization can be affected by the environment and introduces a system that consists of double-layered walls and a thermoelectric device. Chapter 3 aims to implement ultrasonic waves that propagate through materials, which enables a system with detachable parts. Chapter 4 utilizes vibrating mesh atomization to drastically improve the slow actuation speed by evaporating small droplets with large surface areas. Last, chapter 5 introduces a method that can potentially remove electrical components by combining ultrasonics with shape optimization. These studies show that soft actuation through vaporization has significant room for improvement and can potentially replace commercial actuation methods with further optimization.

    Cover page: The Development of Soft Actuation and Selective Control Methods through Vaporization
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2024)
    BACKGROUND: Although early discharge after colectomy has garnered significant interest, contemporary, large-scale analyses are lacking. OBJECTIVE: The present study utilized a national cohort of patients undergoing colectomy to examine costs and readmissions following early discharge. METHODS: All adults undergoing elective colectomy for primary colon cancer were identified in the 2016-2019 Nationwide Readmissions Database. Patients with perioperative complications or prolonged length of stay (>8 days) were excluded to enhance cohort homogeneity. Patients discharged by postoperative day 3 were classified as Early, and others as Routine. Entropy balancing and multivariable regression were used to assess the risk-adjusted association of early discharge with costs and non-elective readmissions. Importantly, we compared 90-day stroke rates to examine whether our results were influenced by preferential early discharge of healthier patients. RESULTS: Of an estimated 153,996 patients, 45.5% comprised the Early cohort. Compared to Routine, the Early cohort was younger and more commonly male. Patients in the Early group more commonly underwent left-sided colectomy and laparoscopic operations. Following multivariable adjustment, expedited discharge was associated with a $4,500 reduction in costs as well as lower 30-day (adjusted odds ratio [AOR] 0.74, p<0.001) and 90-day non-elective readmissions (AOR 0.74, p<0.001). However, among those readmitted within 90 days, Early patients were more commonly readmitted for gastrointestinal conditions (45.8 vs 36.4%, p<0.001). Importantly, both cohorts had comparable 90-day stroke rates (2.2 vs 2.1%, p = 0.80). CONCLUSIONS: The present work represents the largest analysis of early discharge following colectomy for cancer and supports its relative safety and cost-effectiveness.
      Cover page: Early discharge following colectomy for colon cancer: A national perspective.
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2024)
      BACKGROUND: Multiagent neoadjuvant chemotherapy (NAT) has been linked with improved survival for locally advanced (LA) or borderline resectable (BR) pancreatic ductal adenocarcinoma (PDAC). However, the existence of disparities in its utilization remains to be elucidated. METHODS: All adults with PDAC were tabulated from the 2011-2017 Nationwide Cancer Database. Tumor vascular involvement was determined using the clinical T stage and CS_EXTENSION variables. The significance of temporal trends was calculated using Cuzicks non-parametric test. A Cox proportional hazard model was used to assess the impact of NAT utilization on hazard of two-year mortality. A logistic regression model was developed to determine factors associated with receipt of NAT. RESULTS: Of 3811 patients meeting inclusion criteria, 50.8 % received NAT. NAT utilization significantly increased over the study period, from 31.7 % in 2011 to 81.1 % in 2017 (p < 0.001). NAT was associated with significantly reduced two-year mortality (Hazards Ratio 0.34, 95 % Confidence Interval [CI] 0.18-0.67).After adjustment, younger (Adjusted Odds Ratio [AOR] 0.97/year, CI 0.96-0.98) and Black (AOR 0.65, CI 0.48-0.89; ref: White) patients demonstrated reduced odds of NAT. Furthermore, patients with Medicare (AOR 0.73, CI 0.59-0.90; ref: Private) or Medicaid insurance (AOR 0.67, CI 0.46-0.97; ref: Private) had lower odds of NAT, as did those treated at non-academic institutions (Community: AOR 0.42, CI 0.35-0.52, Integrated: 0.68, CI 0.54-0.85) or in the lowest education quartile (AOR 0.52, CI 0.29-0.95; ref: Highest). CONCLUSIONS: We identified increasing utilization of NAT for BR/LA pancreatic adenocarcinoma. Despite being linked with significantly reduced two-year mortality, socioeconomic disparities affect odds of NAT.
        Cover page: Disparities in neoadjuvant chemotherapy for pancreatic adenocarcinoma with vascular involvement.
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2024)
        BACKGROUND: Disparities in colorectal cancer screening have been documented among people with intellectual and developmental disabilities (IDD). However, surgical outcomes in this population have yet to be studied. The present work aimed to evaluate the association of IDD with outcomes following colorectal cancer resection. METHODS: All adults undergoing resection for colorectal cancer in the 2011-2020 National Inpatient Sample were identified. Multivariable linear and logistic regression models were developed to examine the association of IDD with risk factors as well as outcomes including mortality, complications, costs, length of stay (LOS), and non-home discharge. The study is limited by its retrospective nature and did not capture disease staging or time of diagnosis. RESULTS: Among 722,736 patients undergoing colorectal cancer resection, 2,846 (0.39%) had IDD. Compared to patients without IDD, IDD patients were younger and had a higher burden of comorbidities. IDD status was associated with increased odds of non-elective admission (AOR 1.40 [95% CI 1.14-1.73]) and decreased odds of treatment at high-volume centers (AOR 0.64 [95% CI 0.51-0.81]). Furthermore, IDD patients experienced significantly greater LOS (9 vs 6 days, p<0.001) and hospitalization costs ($23,500 vs $19,800, p<0.001) relative to neurotypical patients. Upon risk adjustment, IDD was significantly associated with 2-fold increased odds of mortality (AOR 2.34 [95% CI 1.48-3.71]), 1.4-fold increase in complications (AOR 1.41 [95% CI 1.15-1.74]), and 6.8-fold increase in non-home discharge (AOR 6.83 [95% CI 5.46-8.56]). CONCLUSIONS: IDD patients undergoing colorectal cancer resection experience increased likelihood of non-elective admission, adverse clinical outcomes, and resource use. Our findings highlight the need for more accessible screening and patient-centered interventions to improve quality of surgical care for this at-risk population.
          Cover page: Disparities in outcomes of colorectal cancer surgery among adults with intellectual and developmental disabilities.
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2024)
          BACKGROUND: Primary care physicians (PCP) play a key role in offering colorectal cancer (CRC) screenings, particularly amongst underserved populations. Given potential delays in or omission of CRC screening in the absence of a PCP, we aimed to determine stage of CRC at diagnosis in an underserved population. METHODS: A retrospective chart review was conducted at two Los Angeles County safety-net hospitals. Inclusion criteria were a CRC diagnosis between 2018 and 2021 and age between 50 and 75 years at diagnosis time. The primary outcome was the cancer stage at diagnosis. RESULTS: A total of 373 patients were included, of those, 52.5 % had a PCP. Compared to others, PCP was similar in age, racial composition, and primary spoken language (Table 1). Of patients with a PCP, 52.0% were diagnosed by screening. After screening, the most common indication for colonoscopy were blood per rectum (24.9 %) and imaging findings (18.0 %). Patients with a PCP had a significantly lower rate of late stage CRC than those without a PCP (42.4 % vs. 68.0 %, p < 0.001). After adjustment, having a PCP was associated with significantly reduced odds of late stage CRC (Adjusted Odds Ratio 0.83, 95 % Confidence Interval [0.68-1.04]). Having a PCP was not associated with any adjusted increase in number of adenomas or tumor size. CONCLUSIONS: Patients with a PCP, irrespective of undergoing screening, were diagnosed at earlier CRC stages. This underlines the crucial role of PCPs in CRC and diagnosis, reinforcing the need for their active involvement in these processes.
            Cover page: Engaging primary care physicians is critical in the screening and diagnosis of colorectal cancer at safety-net hospital systems.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2023)

            Background

            Despite the known advantages of minimally invasive surgery (MIS) for diverticular disease, the impact of conversions to open (CtO) colectomy remains understudied. The present study used a nationally representative database to characterize risk factors and outcomes associated with CtO in patients with diverticular disease.

            Methods

            All elective adult hospitalizations entailing colectomy for diverticulitis were identified in the 2017-2019 Nationwide Readmissions Database. Annual institutional caseloads of MIS and open colectomy were independently tabulated. Restricted cubic splines were utilized to non-linearly estimate the risk-adjusted association between hospital volumes and CtO. Additional regression models were developed to evaluate the association of CtO with outcomes of interest.

            Results

            Of an estimated 110,281 patients with diverticulitis who met study criteria, 39.3% underwent planned open colectomy, 53.3% completed MIS, and 7.4% had a CtO. Following adjustment, an inverse relationship between hospital MIS volume and risk of CtO was observed. In contrast, increasing hospital open volume was positively associated with greater risk of CtO. On multivariable analysis, CtO was associated with lower odds of mortality (AOR 0.3, p = 0.001) when compared to open approach, and similar risk of mortality when compared to completed MIS (AOR 0.7, p = 0.436).

            Conclusion

            In the present study, institutional MIS volume exhibited inverse correlation with adjusted rates of CtO, independent of open colectomy volume. CtO was associated with decreased rates of mortality compared to planned open approach but equivalence risk relative to completed MIS. Our findings highlight the importance of MIS experience and suggest that MIS may be safely pursued as the initial surgical approach among diverticulitis patients.
              Cover page: Association of hospital volume with conversion to open from minimally invasive colectomy in patients with diverticulitis: A national analysis
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