Solution Properties and Self-Assembling of Cationic Diblock Copolymers

Solution properties and self-assembling of three polycations have been studied. The main emphasis was on poly((vinylbenzyl) trimethylammonium triflate) (PVBTMA-OTf), synthesized via RAFT polymerization. The PVBTMA-OTf is soluble in water, however, the presence of triflate ions turned it thermoresponsive. Both PVBTMA-OTf and its counterpart with a chloride counterion (PVBTMAC) underwent an UCST type phase transition in aqueous triflate solutions. With increasing the molar mass the cloud point shifted to higher temperatures. The behavior was different in two less hydrophobic polycations, poly((2-(methacryloyloxy)ethyl) trimethylammonium chloride) (PMOTAC) and poly (3-(acrylamidopropyl)trimethylammonium chloride) (PAMPTMAC). Higher amounts of hydrophobic ions were needed to induce the UCST behavior. Diblock copolymers comprised of a poly(ethylene glycol) (PEG) block and PVBTMA-OTf with different block lengths were synthesized via controlled RAFT polymerizations. The block copolymers underwent stepwise phase separation when the polycation blocks were kept short. During cooling, the polymers first phase separated below cloud point temperature (TcU), but solutions became clear (at TcL) upon further cooling. The stepwise phase separation was dependent on the LiOTf concentration and molar mass of the polymers. The copolymers with longer cationic blocks phase separated in a single step similarly to the phase separation of the homopolymer PVBTMA-OTf. The block copolymers formed core-shell particles below TcL. Copolymers with short cationic blocks built up PEG-stabilized particles, however, when the positively charged blocks were long, PEG was buried inside the particles. Due to the complex interactions between two blocks and as well as the interactions mediated by the counterions, the segregation of the blocks is difficult. As a result, with increasing the cationic block length the copolymers phase separated into complex aggregates. Styrenic polycations PVBTMAC were chain extended with diacetone acrylamide (DAAM) via RAFT in aqueous solutions. Only spherical particles were obtained in pure water. However, by increasing the ionic ratio [NaCl]/[Cp] (where [Cp] is the concentration of cationic repeating unit), the particle morphology changed from spheres to fused aggregates or worms, even to vesicles when short styrenic macroCTAs were used. The final morphology depended on the second block length and the solids content. Copolymers with either long styrenic stabilizers or with other macroCTAs, PMOTAC and PAMPTMAC formed spheres, cloudberries, or raspberries with increasing the salt concentration or the solids content. Cationic particles from PVBTMAC prepared in salt-free dispersions phase separated in aqueous triflate solutions at a critical temperature. In some cases, the phase separation occurred in two steps. When the PISA reactions were conducted in triflate solutions, fused spheres were obtained. Increasing the solids content, particle morphologies evolved to vesicles with small lumens. The particles prepared at 70° C in aqueous LiOTf changed from spheres or fused spheres to wormlike networks/ fused aggregates when cooled to room temperature. On the other hand, the morphologies of the particles prepared with PMOTAC or PAMPTMAC macroCTAs were not affected by triflate ions. To sum up, this work presents the use of triflate ions to induce thermoresponsive behavior in polycations and their diblock copolymers. Covalent linkage of hydrophilic PEG blocks to the responsive polycation PVBTMA-OTf enhances the stability of the particles, and the behavior is dependent on molar mass and LiOTf concentration. Using styrenic polycations as sole steric stabilizers in PISA, a full morphological window of particles can be obtained simply by adjusting the ionic strength. The particles made with styrene based cationic stabilizers also show UCST behavior. This study demonstrates the use of triflate ions in PISA to induce order-order or morphological transitions.Työssä on tutkittu kolmen polykationin liuosominaisuuksia ja itsejärjestymistä. Päähuomio oli poly((vinyylibentsyyli)trimetyyliammoniumtriflaatissa) (PVBTMA-OTf), joka oli valmistettu RAFT-polymeroinnilla. PVBTMA-OTf on vesiliukoinen, mutta triflaatti-ionit tekivät siitä lämpöherkän. Sekä PVBTMA-OTf, että saman polykationin kloridi (PVBTMAC) faasierottuivat (UCST) triflaatin vesiliuoksissa. Moolimassan kasvaessa samepiste siirtyi korkeampiin lämpötiloihin. Kaksi vähemmän hydrofobista polykationia, poly(2-(metakroyylioksi)etyylitrimetyyliammoniumkloridi) (PMOTAC) ja poly(3-(akryyliamidopropyyli)trimetyyliammoniukmkloridi) (PAMPTMAC) käyttäytyivät käyttäytyivät eri tavalla. UCST:n indusoimiseksi tarvittiin suuremmat määrät hydrofobisia ioneja. Kontrolloidulla RAFT-polymeroinnilla syntetisoitiin diblokkikopolymeereja poly(etyleeniglykolista) (PEG) ja eripituisista PVBTMA-OTf-blokeista. Kun polykationiblokit olivat lyhyitä, polymeerien faasierottuminen tapahtui vaiheittain. Jäähdytettäessä polymeerit ensin faasierottuivat samepisteen (TcU) alapuolella, mutta edelleen jäähdytettäessä liuokset kirkastuivat lämpötilassa TcL. Vaiheittainen faasierottuminen riippui IlOTF-konsentraatiosta ja polymeerien moolimassasta. Polymeerit, joissa oli pitkä polykationiblokki, erottuivat yhdessä vaiheessa, kuten homopolymeeri PVBTMA-OTf. Blokkikopolymeerit muodostivat ydin-kuori-partikkeleita TcL:n alapuolella. Ne polymeerit, joissa kationinen blokki oli lyhyt, muodostivat PEG:n stabiloimia partikkeleita, mutta jos kationinen blokki oli pitkä, PEG-blokit hautautuivat partikkelien sisään. Johtuen blokkien välisistä monimutkaisista vuorovaikutuksista, sekä vastaionien välittämistä vuorovaikutuksista, kahden blokin erottuminen erillisiksi faaseiksi on vaikeaa. Tästä johtuen kationisen blokin pidentäminen johti monimutkaisten aggregaattien muodostumineen faasierottumisen yhteydessä. Styreenipohjaisia PVBTMAC-polykationeja pidennettiin vedessä RAFT-tekniikalla diasetoniakryyliamidilla (DAAM). Puhtaassa vedessä muodostui vain pyöreitä partikkeleita. Ionisuhdetta [NaCl]/[Cp] kasvatettaessa partikkelien morfologia muuttui palloista fuusioituneiksi aggregaateiksi tai madoiksi, jopa vesikkeleiksi jos styreenipohjainen makroketjunsiirtäjä oli lyhyt. Lopullinen morfologia riippui kasvavan ketjun pituudesta ja kiintoainepitoisuudesta. Kopolymeerit, joissa oli käytetty pitkää styreenipohjaista stabilisaattoria tai muita ketjunsiirtäjiä PMOTAC ja PAMPTMAC, muodostivat suolakonsentraation tai kiintoainepitoisuuden kasvaessa palloja, lakkoja tai vadelmia. Kationiset partikkelit, jotka oli valmistettu suolattomissa dispersioissa käyttäen PVBTMAC:a faasierottuivat kriittisessä lämpötilassa triflaatin vesiliuoksissa. Joissain tapauksissa faasierottuminen tapahtui kahdessa vaiheessa. Kun PISA-reaktiot oli suoritettu triflaattiliuoksissa, tuloksena oli toisiinsa takertuneita palloja. Kiintoainepitoisuutta nostettaessa muodostui vesikkeleitä, joiden sisällä oleva aukko oli pieni. Kun LiOTF:n vesiliuoksissa 70 °C:ssa valmistetut partikkelit jäähdytettiin huoneenlämpöön, pallot tai toisiinsa takertuneet pallot muodostivat käärmemäisiä verkkoja/fuusioituneita aggregaatteja. Toisaalta, triflaatti-ionit eivät vaikuttaneet niiden partikkeleiden morfologiaan, jotka oli valmistettu käyttäen PMOTAC:a tai PAMPTMAC:a ketjunsiirtäjänä. Yhteenvetona voidaan todeta, että tässä työssä selvitettiin, kuinka polykationit ja niiden blokkikopolymeerit voidaan muuttaa lämpöherkiksi triflaatti-ioneilla. Hydrofiilisen PEGin kovalenttinen kiinnittäminen lämpöherkkään PVBTMA-OTf:in parantaa polymeeripartikkelien stabiilisuutta, ja partikkelien ominaisuudet riippuvat ketjun moolimassasta LiOTf:n konsentraatiosta. Kun käytetään styreenipohjaisia polykationeja ainoana steerisenä stabilisaattorina PISA-reaktiossa, kaikki mahdolliset partikkelimorfologiat on mahdollista saavuttaa yksinkertaisesti ionivahvuutta säätämällä. Työssä osoitettiin, kuinka käyttämällä triflaatti-ioneja PISA-reaktioissa voidaan indusoida järjestyksen tai morfologian muutoksia.

Polycation-PEG Block Copolymer Undergoes Stepwise Phase Separation in Aqueous Triflate Solution

A block copolymer poly(ethylene glycol)-b-poly(vinylbenzyltrimethylammonium triflate), PEG-PVBTMA-OTf, and a homopolymer PVBTMA-OTf were synthesized through RAFT reactions. The polymers were studied in aqueous triflate solutions with varying temperatures, changing also the polymer and salt concentrations. The hydrophobic triflate anion turns polycations thermoresponsive, and they show an UCST. In the block copolymer, the interaction between the PEG and the cationic block makes the phase separation occur in distinct steps. Upon cooling, transparent solutions first turn turbid and then partially clear at T-cL. The T-cL is not observed in a mixed solution of PVBTMA-OTf and PEG macro-CTA. By considering the interplay between ionic, hydrogen bonding, and hydrophobic interactions, an overall picture of the complex phase separation processes is suggested.Peer reviewe

Molecular Mass Affects the Phase Separation of Aqueous PEG-Polycation Block Copolymer

Mechanisms of the phase separation and remixing of cationic PEG-containing block copolymers have been investigated in aqueous lithium triflate solutions. The polycation was poly(vinylbenzyl trimethylammonium triflate). We have previously reported on one such block copolymer, which upon cooling of a hot clear solution first underwent phase separation into a turbid colloid and, later, partially cleared again with further cooling. To better understand the balance of various interactions in the solutions/dispersions, a series of polymers with varying DP of the cationic block was synthesized. From one of the polymers, the alkyl end group (a fragment of the chain transfer agent) was removed. The length of the cationic block affected critically the behavior, but the hydrophobic end group had a minimal effect. Polymers with a short cationic block turn cloudy and partially clear again during a temperature decrease, whereas those with a long cationic block phase separate and slowly precipitate and remix only when heated. Phase separation takes place via particle formation, and we suggest different mechanisms for colloidal stabilization of particles composed of short or long chains.Peer reviewe

Thermoresponsive Polycation-Stabilized Nanoparticles through PISA. Control of Particle Morphology with a Salt

Poly [(vinylbenzyl) trimethylammonium chloride] (PVBTMAC) has been used as a stabilizer in the polymerization-induced self-assembly polymerizations of diacetone acrylamide (DAAM). A whole spectrum of particle morphologies was obtained simply by adjusting the ionic strength of the reaction mixtures; no dilution of the cationic charges with noncharged comonomers or with noncharged polymers was needed. In addition to the ionic strength, the effects of solid content and the length of the PDAAM block on the morphologies of the particles were studied in detail. The experiments are a continuation to previous studies on solution properties of PVBTMAC. It has been shown earlier that the solubility of the polycation may be tuned with counterions. Hydrophobic triflate ions induce an upper critical solution temperature behavior. In the present case, the chains bound to hydrophobic cores of the particles show either a one-step phase separation in aqueous triflate solutions or under certain conditions, a two-step transition. The step-wise transition is typical for responsive polymers with limited mobility.Peer reviewe

Anxiety and Stress among Dental Patients During the COVID-19 Pandemic

Aim or Purpose: COVID-19 pandemic posed a significant burden to several countries across the globe on the health, social, and economic fronts. There has been a transformation in people's behavior during the pandemic in light of the fear of infection and the uncertainty associated with the disease. The aim of this study was to ascertain the anxiety and stress among dental patients during the COVID-19 pandemic. Materials and Methods: This cross-sectional study was conducted among 1421 patients attending the outpatient department of a tertiary dental institution in the state of Andhra Pradesh. A self-administered questionnaire was used for data collection which was made available in both English and Telugu. Descriptive statistics and chi square tests were done to analyze the study data. Results: Subjects with no previous history of COVID-19 infection were found to be more anxious and stressful about COVID-19 compared to their counterparts. Fear of making family members vulnerable and the uncertainty of the prognosis in case of COVID-19 were the major reasons for anxiety and stress. The study subjects believed that seeking dental care during the pandemic is a risk factor for acquiring COVID-19. Most of the study subjects sought emergency care. Conclusions: The oral health fraternity needs to advertise the precautions being taken to curtail the possibility of transmission of infection in dental settings. Also, there is a necessity that the profession introspects the basic requirements of setting up an oral health care facility, especially by integrating the lessons learnt in the pandemic

Nicotine Dependence Among Smokers Using Fagerstrom Nicotine Dependence Test

Aim or Purpose: While formulating tobacco cessation strategies, it is important that the dependence of tobacco among the target population be established. More often, dependence is an ignored concept while drafting directives, while prevalence of the habit is prioritized. The aim of this study was to assess nicotine dependence among cigarette smokers attending a tertiary oral health care fracility. Materials and Methods: This cross-sectional study was conducted on 203 cigarette smokers attending the outpatient department of a tertiary oral health care facility in Andhra Pradesh, India. Fagerström Test for Nicotine Dependence (FTND) was used to assess nicotine dependence. Kruskal Wallis ANOVA and Chi-square tests were done to analyze the study data. Results: The mean nicotine dependence score among the study population was 4.68±1.93. Elder age groups and subjects belonging to lower socioeconomic strata demonstrated significantly higher mean FTND scores. Most of the study subjects reported smoking at least 10 cigarettes per day. Conclusions: Moderate tobacco dependence was observed among the study subjects. Identification of elder age groups and people from lower socioeconomic strata as distinct groups for tobacco cessation strategies is extremely important as the one-size fits all concept may not work for people with obvious disparities in dependence

Aloe vera gel in chronic periodontitis: a clinico-microbiological study

Aim or Purpose: Chronic periodontitis is one of the most common oral health problems which has a significant negative influence on the quality of life, in general, and oral health related quality of life, in particular. The aim of this study is to evaluate the effectiveness of Aloe vera gel in the treatment of chronic periodontitis. Materials and Methods: This split-mouth randomized controlled trial was done among 20 subjects with chronic periodontitis in the age range of 20 and 55 years. Ethical clearance was obtained from the institutional ethics committee. Plaque index, gingival bleeding index, probing pocket depths, and clinical attachment levels, mean log counts of Porphyromonas gingivalis were recorded at baseline and 3 months. Wilcoxon signed rank tests were done to analyze the trial data. Results: The mean change in the plaque index scores for the test and control sites were 0.73±0.35 and 0.33±0.46, respectively. There was a significant difference in the proportion of gingival bleeding between the test and control sites at the 3 months follow-up. The mean PPD and CAL scores, mean log CFU of Porphyromonas gingivalis were significantly lesser for the test sites at the 3 months follow-up. Conclusions: Aloe vera gel as a local drug delivery agent has been found to be effective in the management of chronic periodontitis. It is important that insights from alternative medicine be carefully considered to advance the treatment modalities in dentistry while being cost-effective

Impact of Sense of Coherence on Oral Health

Aim or Purpose: Sense of Coherence (SOC) is a logical factor that enables people to cope with stressors and successfully improve health. Oral health has an impact on general health and Quality of Life. This study was undertaken with the aim to assess the impact of SOC with Oral Hygiene, dental caries and periodontal status among young adults. Materials and Methods: The study was conducted among 500 young adults of age group 19 to 23 years selected using cluster random sampling. SOC data were collected using 13 item standardized versions of SOC scale proposed by Antonovsky. Oral hygiene status was assessed using Oral Hygiene Index- Simplified(OHI-S) b, Dental caries was assessed using WHO criteria Decayed Missing Filled Treatment (DMFT) index and Periodontal status was estimated using the Community Periodontal Index (CPI). Analysis was done using Median test and Pearson correlation to compare SOC scores with dental parameters. Level of significance was set at 0.05. Results: SOC scores ranged from a minimum of 22 to a maximum of 81. The mean SOC score is 52.8 ± 7.6. There was no significant association between SOC and OHI(S), and mean DMFT. CPI and LOA (Loss of Attachment) were found to be significantly associated with SOC. The correlation test confirms that there is a significant weak correlation (R= -0.094; p<0.05) between CPI and SOC, i.e., as SOC score increases, CPI score decreases. However, Correlation value is not significant in LOA vs SOC. Conclusions: This concept can be used to modify the oral health care behaviors to improve quality of life