Release Burst Research Articles

Protein encapsulation in polymeric microneedles by photolithography

Recent interest in biocompatible polymeric microneedles for the delivery of biomolecules has propelled considerable interest in fabrication of microneedles. It is important that the fabrication process is feasible for drug encapsulation and compatible with the stability of the drug in question. Moreover, drug encapsulation may offer the advantage of higher drug loading compared with other technologies, such as drug coating. In this study, we encapsulated a model protein drug, namely, bovine serum albumin, in polymeric microneedles by photolithography. Drug distribution within the microneedle array was found to be uniform. The encapsulated protein retained its primary, secondary, and tertiary structural characteristics. In vitro release of the encapsulated protein showed that almost all of the drug was released into phosphate buffered saline within 6 hours. The in vitro permeation profile of encapsulated bovine serum albumin through rat skin was also tested and shown to resemble the in vitro release profile, with an initial release burst followed by a slow release phase. The cytotoxicity of the microneedles without bovine serum albumin was tested in three different cell lines. High cell viabilities were observed, demonstrating the innocuous nature of the microneedles. The microneedle array can potentially serve as a useful drug carrier for proteins, peptides, and vaccines.

Time to pull out the stops: Spirantization in Pacific Northwestern English.

Anecdotal evidence suggests that English speakers in North America are spirantizing stops. Spirantization is a consonant lenition process active in many languages, but has traditionally been assumed not to be active in English, except as a lexical or affixal process. This study is an investigation into the spirantization of stops using recordings of eight age/sex matched dyads (n=16) from a small corpus of Pacific Northwestern English speech. Representative monologues were extracted for each speaker and analyzed acoustically. Alveolars and voiceless aspirated stops were excluded from analysis as alveolar stops have a large number of allophones, and aspiration may block spirantization. The resulting tokens were rated for the absence of a stop burst, the presence of frication noise, and the presence of formant structure. Scores for each factor were then used to create a coarse‐grained spirantization score for each token, with lack of a release burst, and presence of frication or formants indicating incomplete closure. Preliminary results from four speakers (88 tokens total) show that spirantization is indeed occurring: 44% of the tokens were spirantized. Additionally, it appears that velars are much more likely to spirantize than bilabials: 77% of velars spirantized compared to 26% of bilabials.

Experience, representations and the production of second language allophones

In this study we examined the effect of language experience on the production of second language (L2) allophones. We analysed production data of the Spanish stop—approximant alternation (b d g ~ β ð ) from Low Intermediate and High Intermediate level native English/Spanish L2 speakers and five native Mexican Spanish speakers. This allophonic alternation is conditioned primarily by position in the word and lexical stress. We examined the use of two cues to the alternation — consonant intensity and the presence of a release burst — and analysed how these cues varied in participants’ productions in distinct contexts. Results show that the use of these cues differs with experience; that is, learners with greater language experience exhibit cue use that is closer to the native speakers’ cue use. Results further suggest that Low Intermediate learners may be using a basic rule for producing the alternation, but that over time shift to a more nuanced production pattern. These results indicate that more experienced learners’ ability to use these phonetic cues in a native-like fashion emerges over the course of allophone acquisition.

PEGylated TNF-related apoptosis-inducing ligand (TRAIL)-loaded sustained release PLGA microspheres for enhanced stability and antitumor activity

The purpose of this work was to develop an effective PEGylated TNF-related apoptosis-inducing ligand (PEG-TRAIL) delivery system for antitumor therapy based on local injection to tumor sites that has a sustained effect without protein aggregation or an initial release burst. The authors designed poly (lactic-co-glycolic) acid (PLGA) microspheres that deliver PEG-TRAIL locally and continuously at tumor sites with sustained biological activity and compared its performance with that of TRAIL microspheres. TRAIL or PEG-TRAIL was microencapsulated into PLGA microspheres using a double-emulsion solvent extraction method. Prepared TRAIL and PEG-TRAIL microspheres showed entirely spherical, smooth surfaces. However, PEG-TRAIL microspheres exhibited a 2.07-fold higher encapsulation efficiency than TRAIL microspheres, and exhibited a tri-phasic in vitro release profile with a lower initial burst (15.8%) than TRAIL microspheres (42.7%). Furthermore, released PEG-TRAIL showed a continued ability to induce apoptosis over 14 days. In vivo pharmacokinetic studies also demonstrated that PEG-TRAIL microspheres had a sustained release profile (18 days), and that the steady-state concentration of PEG-TRAIL in rat plasma was reached at day 3 and maintained until day 15; its steady-state concentration in rat plasma changed from 1444.3 ± 338.4 to 2697.7 ± 419.7 pg/ml. However, TRAIL microspheres were released out within 2 days after administration. Finally, in vivo antitumor tests revealed that tumor growths were significantly more inhibited by a single dose of PEG-TRAIL microspheres than TRAIL microspheres when delivered at 300 μg of TRAIL/mouse. Tumors taken from mouse treated with PEG-TRAIL microspheres showed 78.3% tumor suppression at 24 days, and this was 3.02-fold higher than that observed for TRAIL microspheres (25.9% tumor inhibition). Furthermore, these improved pharmaceutical characteristics of PEG-TRAIL microspheres resulted in superior therapeutic effects without detectable side effects. These findings strongly suggest that PEG-TRAIL microspheres offer a new therapeutic strategy for the treatment of cancers.

Identification of the place of articulation of trilingual postvocalic nasals and stops by native speakers of American English, Korean and Japanese.

Native speakers of American English and Korean produced postvocalic nasals and stops in /CVC/ frames in which the syllable final segment was a consonant with airstream blocking, and native speakers of Japanese produced more nasal /N/ and obstruent /Q/ in /CVNCV/ and /CVQCV/ frames. In Japanese stimuli, the consonant after the nasal or the obstruent was always a stop. Their utterances were recorded and edited to be used as stimuli for the experiment. The release burst of the English stimuli and the second syllable of Japanese stimuli were deleted. Native speakers of these three languages were recruited as listeners. They identified the place of articulation of the syllable‐final nasals and stops of the three languages. As predicted, Japanese listeners performed most poorly because there are no phonemic contrasts between postvocalic nasals or stops in Japanese. Korean listeners outperformed the other two groups of listeners in identifying the place of articulation. Postvocalic stops in Korean are not released, so the Korean listeners may not depend on the release burst to identify the place of articulation of a syllable final stop. However, they made more voicing errors than American listeners probably because voiced stops in Korean cannot occur in a postvocalic position.

Vocal Attractiveness Increases by Averaging

Vocal attractiveness has a profound influence on listeners-a bias known as the "what sounds beautiful is good" vocal attractiveness stereotype [1]-with tangible impact on a voice owner's success at mating, job applications, and/or elections. The prevailing view holds that attractive voices are those that signal desirable attributes in a potential mate [2-4]-e.g., lower pitch in male voices. However, this account does not explain our preferences in more general social contexts in which voices of both genders are evaluated. Here we show that averaging voices via auditory morphing [5] results in more attractive voices, irrespective of the speaker's or listener's gender. Moreover, we show that this phenomenon is largely explained by two independent by-products of averaging: a smoother voice texture (reduced aperiodicities) and a greater similarity in pitch and timbre with the average of all voices (reduced "distance to mean"). These results provide the first evidence for a phenomenon of vocal attractiveness increases by averaging, analogous to a well-established effect of facial averaging [6, 7]. They highlight prototype-based coding [8] as a central feature of voice perception, emphasizing the similarity in the mechanisms of face and voice perception.

Perception of Japanese mora nasal /N/ and mora obstruent /Q/ by native Japanese, English, and Thai speakers.

Japanese mora nasal /N/ and more obstruent /Q/ are produced at different places of articulation, being homorganic with the following consonant. Four native speakers of Japanese produced /N/ and /Q/ in /CVNCV/ and /CVQCV/ contexts, where the consonant after /N/ and /Q/ is always a stop. Their utterances were recorded and digitized. The word final /CV/ was edited out, and the stimuli with the structure of /CVN/ and /CVQ/ were created. Twelve native speakers of Japanese, American English, and Thai were recruited as listeners. The listeners were told to identify the syllable‐final nasal (/m/, /n/ or /ŋ/, and the missing stop (/p/, /t/, /k/, /b/, /d/, or /g/). Generally, the Thai listeners outperformed the other two groups of listeners, and the Japanese listeners performed most poorly. The Thai listeners good performance may be partly explained by the fact that in Thai postvocalic stops are normally unreleased, and the Thai listeners were less dependent on the release burst to identify the place of articulation of a postvocalic stop. The Thai listeners tended to identify voiced stops as voiceless stops of the same place of articulation. This may be because voiced stops cannot occur postvocalically in Thai.

Voicing and devoicing in similar German and English word pairs by native speakers of German

A number of languages manifest a pattern of word-final obstruent devoicing, i.e., words ending with underlying voiced obstruents are pronounced so as to be (largely) indistinguishable from words ending with final voiceless obstruents. One question regarding this tendency to devoice voiced obstruent targets is what occurs when native speakers of such a language learn a second language that has a word-final obstruent voicing contrast. For example, do German speakers neutralize voicing contrasts in English as they tend to do in German, or can they learn to produce voiced obstruents in Englis, despite devoicing them in German? To examine this issue, ten native speakers of German produced various phonologically-similar minimal pairs in German and English (e.g., English: Lied/light; German: Leid/leit). Acoustic measurements were made of their productions in both languages, viz., vowel duration preceding final consonants, final consonant duration, duration of voicing during final consonants, and final release burst duration; their English productions were also compared to those of native English speakers. The native German speakers tended to neutralize the voicing distinction to a greater extent when producing German words versus phonologically-similar English words, but they typically did not produce as much of a contrast in English as native English speakers.

How myosin VI coordinates its heads during processive movement

A processive molecular motor must coordinate the enzymatic state of its two catalytic domains in order to prevent premature detachment from its track. For myosin V, internal strain produced when both heads of are attached to an actin track prevents completion of the lever arm swing of the lead head and blocks ADP release. However, this mechanism cannot work for myosin VI, since its lever arm positions are reversed. Here, we demonstrate that myosin VI gating is achieved instead by blocking ATP binding to the lead head once it has released its ADP. The structural basis for this unique gating mechanism involves an insert near the nucleotide binding pocket that is found only in class VI myosin. Reverse strain greatly favors binding of ADP to the lead head, which makes it possible for myosin VI to function as a processive transporter as well as an actin-based anchor. While this mechanism is unlike that of any other myosin superfamily member, it bears remarkable similarities to that of another processive motor from a different superfamily--kinesin I.

Individual differences in the production and perception of the voicing contrast by native and non-native speakers of English

Investigations of acoustic characteristics of speech production and their perceptual correlates often determine that various common patterns are observed among groups of talkers/listeners. It is also sometimes reported that a certain amount of noise occurred in the data, i.e., that not all subjects fit general patterns that were observed. While individuals who do not demonstrate typical patterns are often viewed as outliers, subjects who represent exceptions also provide important information. The present study reports findings obtained from 15 native speakers of English and 15 non-native (native Mandarin) speakers of English who were recorded producing several final-position voiced/voiceless CVC word pairs and who also made voicing judgments about voiced/voiceless cognates produced by other native English and native Mandarin speakers. All native subjects in the present study produced multiple acoustic cues in making voicing distinctions (e.g., vowel duration, final stop closure duration, voicing during final stop occlusion, release burst); however, not all subjects used all these acoustic cues or the same combinations of cues in their voicing contrasts. Only about half the native Mandarin speakers used multiple acoustic cues in attempting to produce a voicing contrast. Various group trends, as well as subgroup variations, in production and perception will be discussed.

Incomplete neutralization in Dutch opacity

In Dutch, syllable‐final plosives are devoiced so /bad/ ‘‘bathe’’ is pronounced [bat]. However, despite being resyllabified to syllable‐initial position by a clitic in /bad+er/ ‘‘bathe her,’’ the /d/ is still devoiced: [ba.ter]. This is referred to as phonological opacity because a generalization syllable‐final devoicing is obscured or rendered opaque by another process—resyllabification. In this experiment, the acoustics and perception of this opaque relationship will be investigated. The voice onset time, release burst, and consonant duration of plosives for native Dutch speakers in phrases such as [ba.ter] will be compared to those in a phrase such as [ba.der] ‘‘bather’’ and /prat+er/ ‘‘speaker’’ [pra.ter]. Also, a perception experiment will be conducted testing whether native Dutch speakers are able to distinguish these phones. Based on a similar study of German [R. Port and M. O’Dell, J. Phonetics 13, 455–471 (1985)], it is expected that the [t] in [ba.ter] is not identical to the [t] in [pra.ter]. If, indeed, this is the case, and the [t] in [ba.ter] instead bears some of the acoustic properties of [d] in [ba.der], this would provide a useful set of perceptual cues enabling speakers to observe the devoicing generalization through the opacity.

Controlled release of nerve growth factor from fibrin gel

Nerve growth factor (NGF) is known to promote the axonal regeneration in injured nerve system. Delivery of NGF for a long period in a controlled manner may enhance the regeneration efficacy. In this study, we investigated whether NGF can be released from fibrin gel for a long period in a controlled manner. We also investigated whether sustained delivery of NGF using fibrin gel can enhance the efficacy of NGF in vitro. The addition of heparin to fibrin gel decreased the rate of NGF release from the fibrin gel. As the concentrations of thrombin and fibrinogen in fibrin gel increased, the NGF release rate decreased significantly, and the initial release burst decreased. NGF was released for up to 14 days in vitro. The bioactivity of NGF released from fibrin gel was assessed by morphological changes of pheochromocytoma (PC12) cells cultured in the presence of NGF-containing fibrin gel. NGF released from fibrin gel exhibited significantly higher degrees of PC12 cell viability and differentiation than NGF added in a free form daily into the culture medium. This study demonstrates that fibrin gel can release NGF in a sustained, controlled manner and in a bioactive form.

Variation in Rioplatense Spanish /s/ + stop sequences

This acoustic study of Rioplatense Spanish examines the lenition of syllable-onset, voiced stops after /s/. Four Rioplatense speakers from Buenos Aires participated in an acoustic experiment by reading sentences with the target stop occurring in phrase-initial, word-initial, and word-medial positions in both a conversational and clear speech style. Stop tokens at all three places of articulation were analyzed for the presence of voicing, of a stop-closure interval, and of a release burst. The variable realization of the preceding coda /s/ in all conditions was also transcribed and analyzed, to evaluate co-occurrence patterns in the sequence. The results indicated frequent occurrences of stop spirantization in the conversational style and in phrase-medial positions. Further, variants of /s/ containing only a laryngeal gesture, such as [h], co-occur with spirantized variants of the voiced stops. An articulatory phonology account is presented of the variation in stop realization, as well as of the relationship between the /s/ variant and its following stop. [Work supported by NIH.]

Locus equation encoding of stop place: revisiting the voicing/VOT issue

This study explored the consistency of locus equation slopes to serve as phonetic descriptors of stop place in CV utterances across voiced versus voiceless aspirated stops. Using traditional locus equation measurement sites for F2 onsets, voiceless labial and coronal stops had lower locus equation slopes relative to their voiced counterparts, whereas velars failed to show voicing differences. When locus equations were derived using F2 onsets for voiced stops that were measured closer to the stop release burst, comparable to the protocol for measuring voiceless aspirated stops, the slope differences across voicing were greatly minimized. This methodological factor, rather than an underlying phonetic-based explanation, provides a reasonable account for the observed flatter locus equation slopes of voiceless labial and coronal stops relative to voiced cognates.

Effects of polymer, organic solvent and mixing strength on integrity of proteins and liposomes encapsulated in polymeric microspheres fabricated by the double emulsion process

The double emulsion process has commonly been applied to encapsulate water-soluble bioactive agents into polymeric microspheres. However, the integrity of many of these agents may be destroyed by the highly energetic procedures such as sonication that are routinely used to produce stable water-in-oil (w/o) emulsion. The aim of this research was to pursue the possibility of replacing the sonication by a mild emulsification procedure such as vortex mixing, with the use of certain materials to help to obtain stable w/o emulsion. The following materials were examined: poly(lactide-co-ethylene glycol) (PELA) as the polymer, ethyl acetate and acetone as the solvents, poly(vinyl alcohol) (PVA) and d-α tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS) as the emulsifiers in w/o emulsion. The experimental results, with human serum albumin (HSA) as the encapsulated agent, showed that, when vortex mixing was used, these materials could significantly improve w/o emulsion stability and help to obtain satisfactory encapsulation effects, i.e. high encapsulation efficiency (EE) and low initial release burst. A delicate structure, i.e. liposomes, which is very sensitive to sonication, was then incorporated into microspheres by the ‘modified double emulsion process’. It was found that the liposomes were intact and the encapsulation effects were good. Therefore, it can be concluded that the modified double emulsion process could be advantageous for the encapsulation of delicate substances.

The stability of locus equation slopes across stop consonant voicing/aspiration

The consistency of locus equation slopes as phonetic descriptors of stop place in CV sequences across voiced and voiceless aspirated stops was explored in the speech of five male speakers of American English and two male speakers of Persian. Using traditional locus equation measurement sites for F2 onsets, voiceless labial and coronal stops had significantly lower locus equation slopes relative to their voiced counterparts, whereas velars failed to show voicing differences. When locus equations were derived using F2 onsets for voiced stops that were measured closer to the stop release burst, comparable to the protocol for measuring voiceless aspirated stops, no significant effects of voicing/aspiration on locus equation slopes were observed. This methodological factor, rather than an underlying phonetic-based explanation, provides a reasonable account for the observed flatter locus equation slopes of voiceless labial and coronal stops relative to voiced cognates reported in previous studies [Molis et al., J. Acoust. Soc. Am. 95, 2925 (1994); O. Engstrand and B. Lindblom, PHONUM 4, 101–104]. [Work supported by NIH.]

The role of air pressure and contact force in shaping obstruent consonant onset

Soft tissues (the tongue or lips) are used to form the narrow oral constriction for turbulence noise generation during the production of obstruent consonants. The displacement of the soft tissue subject to oral pressure buildup is comparable to the vertical dimension of the constriction. The contact force during the closure of stop consonants and affricates provides a pressure load over 5 times larger than the air pressure at the surface in contact. It can influence the time variation of the constriction size at onset in the form of elastic energy stored in the compliant structure forming the constriction. A finite element fluid–structure interaction program has been used to simulate the effect of these external forces during the onset of obstruent consonants. Preliminary results from a 2‐D tongue tip constriction/closure model show that air pressure and contact force can introduce movement on the order of 0.1–0.2 mm during the first tens of milliseconds after release, which is enough to affect the size of the constriction at onset and the nature of release burst. The results of this kind can be used for speech synthesis, guiding the modification of the trajectories of articulators at the consonant onset. [Work supported by NIH.]

Ibuprofen-loaded ethylcellulose/polystyrene microspheres: An approach to get prolonged drug release with reduced burst effect and low ethylcellulose content

The aim of this study was to develop ethylcellulose microspheres for prolonged drug delivery with reduced burst effect. Ethylcellulose microspheres loaded with ibuprofen were prepared with and without polystyrene, which was used to retard drug release from ethylcellulose microspheres. Ibuprofen-loaded ethylcellulose microspheres with a polystyrene content of 0–25% were prepared by the solvent evaporation technique and characterized by drug loading, infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. The in vitro release studies were performed to study the influence of polystyrene on ibuprofen release from ethylcellulose microspheres. The microspheres showed 28–46% of drug loading and 80–92% of entrapment, depending on polymer/drug ratio. The infrared spectrum and thermogram showed stable character of ibuprofen in the microspheres and revealed an absence of drug polymer interaction. The prepared microspheres were spherical in shape and had a size range of 0.1–4μm. Ethylcellulose/polystyrene micro-spheres showed prolonged drug release and less burst effect when compared to microspheres prepared with ethylcellulose alone. Microspheres prepared with an ethylcellulose/polystyrene ratio of 80:20 gave a required release pattern for oral drug delivery. The presence of polystyrene above this ratio gave release over 24 h. To find out the mechanism of drug release from ethylcellulose/polystyrene microspheres, the data obtained from in vitro release were fitted in various kinetic models. High correlation was obtained in Higuchi and Korsmeyer-Peppas models. The drug release from ethylcellulose/polystyrene microspheres was found to be diffusion controlled.

Release bursts in English word-final stops: A longitudinal study of Korean adults’ and children’s production

Stops at the end of Korean words are always unreleased. The question addressed here was whether Korean adults and children living in the U.S. can learn to release stops at the end of English words. Four groups of 18 native Koreans (NK) who differed according to age (adult versus child) and length of residence in the U.S. (3 vs 5 years at T1) participated. Two native English (NE) groups served as age-matched controls. Production data were collected at two times (T1, T2) separated by one year. English words ending in /t/ and /k/ were then examined in perception experiments (Exp. 1, Exp. 2). NE-speaking judges decided whether the final stop has a release burst or not. Exp. 1 showed that NE talkers released /t/ more often than NK talkers did. The effect of time was also significant. Talkers produced release bursts more often at T2 than at T1. Exp. 2 showed that, unlike Exp. 1, there were significant differences between NK adults and children. While NK children did not differ from NE children, NK adults released the final /k/ much less often than NE adults did. Possible reasons for why the expected children’s advantage was seen for /k/, but not for /t/, will be discussed. [Work supported by NIH.]

Effects of noise and cue enhancement on neural responses to speech in auditory midbrain, thalamus and cortex

Speech perception depends on the auditory system’s ability to extract relevant acoustic features from competing background noise. Despite widespread acknowledgement that noise exacerbates this process, little is known about the neurophysiologic mechanisms underlying the encoding of speech in noise. Moreover, the relative contribution of different brain nuclei to these processes has not been fully established. To address these issues, aggregate neural responses were recorded from within the inferior colliculus, medial geniculate body and over primary auditory cortex of anesthetized guinea pigs to a synthetic vowel–consonant–vowel syllable /ada/ in quiet and in noise. In noise the onset response to the stop consonant /d/ was reduced or eliminated at each level, to the greatest degree in primary auditory cortex. Acoustic cue enhancements characteristic of ‘clear’ speech (lengthening the stop gap duration and increasing the intensity of the release burst) improved the neurophysiologic representation of the consonant at each level, especially at the cortex. Finally, the neural encoding of the vowel segment was evident at subcortical levels only, and was more resistant to noise than encoding of the dynamic portion of the consonant (release burst and formant transition). This experiment sheds light on which speech-sound elements are poorly represented in noise and demonstrates how acoustic modifications to the speech signal can improve neural responses in a normal auditory system. Implications for understanding neurophysiologic auditory signal processing in children with perceptual impairments and the design of efficient perceptual training strategies are also discussed.