Rejuvenation Effects Research Articles

Reversing relaxation-induced embrittlement by high-temperature thermal cyclic annealing in Zr-based metallic glass

Annealing usually induces structural relaxation and reduction of liquid-like regions, leading to embrittlement in bulk metallic glasses (BMGs). Here, we find that the short-term high-temperature thermal cycling (HTC) annealed Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) BMG shows an improved plasticity without sacrificing their yield strength. And only relaxation behavior with increased hardness is observed after HTC, which is different from the rejuvenation effect usually observed in cryogenic thermal cycling (CTC). We revealed that this embrittlement reversal is attributed to enhanced fluctuations of full width at half maximum (FWHM) of the hardness’ distribution at micrometer and larger scales induced by short-term HTC. The enhanced fluctuations of mechanical heterogeneities across the diameter on a cross-section of the short-term HTC sample may increase the number and decrease the size of shear transformation zones (STZs) activated at high stress and promote the deflection of shear bands (SBs) during their propagation to form multiple SBs. The enhanced plasticity after HTC induced relaxation contradicts the common sense that relaxation accompanying with annihilation of free volume or liquid-like region usually causes embrittlement. Present results indicate that short-term HTC could be a powerful mean to tune the mechanical performance, shedding new lights on the interplay among relaxation, mechanical/structural heterogeneity, and plasticity of MGs.

Regeneration Effect of a New Bio-Based Warm-Mix Rejuvenator on Performance and Micro-Morphology of Aged Asphalt.

The use of warm-mix recycling technology can reduce the mixing temperature and the secondary aging of binders in reclaimed asphalt pavement (RAP), which is one of the effective ways to recycle high-content RAP. In this study, the penetration, softening point, ductility, and viscosity were used to characterize the conventional physical properties of aged asphalt after regenerating, while a dynamic shear rheometer (DSR), force ductility tester (FDT), and atomic force microscope (AFM) were used to evaluate the rheological performance and micro-morphology of aged asphalt incorporating a new bio-based warm-mix rejuvenator (BWR) and a commercial warm-mix rejuvenator (ZJ-WR). The regeneration mechanism of warm-mix rejuvenators on aged asphalt was analyzed by Fourier transform infrared spectroscopy (FTIR). The results show that the new bio-based warm-mix rejuvenator can restore the conventional physical properties, low-temperature performance, and micro-morphology of aged asphalt with an appropriate dosage, but it has a negative effect on high-temperature performance. In comparison with 2D area parameters, 3D roughness parameters were more accurate in evaluating the variation in micro-morphology of aged asphalt after regeneration. The FTIR analysis results indicate that both the new bio-based warm-mix rejuvenator and the commercial warm-mix rejuvenator regenerate aged asphalt by physical action, and AS=O and AC-H values are more reasonable than the AC=O value for the restoration evaluation of aged asphalt. And the new bio-based warm-mix rejuvenator has a better regeneration effect on the performance and micro-morphology of aged asphalt than the commercial warm-mix rejuvenator.

Facial Skin Rejuvenation Using Poly- dl -Lactic Acid Injected With a Laser-Generated Needle-Free Microjet Injector.

A laser-induced needle-free microjet injector was developed for rapid, high-speed drug delivery of microliters into the skin. This study evaluated the clinical rejuvenation effect of repeated dermal injections of the collagen simulator poly- dl -lactic acid (PDLA) using a laser-induced needle-free microjet injector. Five PDLA injection sessions using a laser-induced needle-free microjet injector were conducted in patients concerned about aging skin. Facial uplifting, darkness, redness, roughness, pore size, subjective satisfaction, and side effects were evaluated before each session and 4 weeks after treatment completion. Histological evaluation was also performed with immunohistochemical staining of collagen and elastic fibers. The clinical results of 27 female patients were evaluated. The treatment resulted in a noticeable skin surface uplifting (0.711 ± 0.42 mm) and significant improvements in darkness ( p = .013), redness ( p = .009), and roughness ( p = .036), with no significant difference in the pore size ( p = .770). Patients were reported being satisfied with the overall therapeutic effects, despite mild and tolerable adverse effects. Histological findings revealed growth and thickening of collagen and elastic fibers, with marked increase in collagen I and III levels. Repeated dermal injections of PDLA using a laser-induced microjet injector offer excellent drug delivery, achieving high efficacy in skin rejuvenation, patient satisfaction, and safety.

Single-nucleus transcriptomics uncovers a geroprotective role of YAP in primate gingival aging.

Aging has a profound impact on the gingiva and significantly increases its susceptibility to periodontitis, a worldwide prevalent inflammatory disease. However, a systematic characterization and comprehensive understanding of the regulatory mechanism underlying gingival aging is still lacking. Here, we systematically dissected the phenotypic characteristics of gingiva during aging in primates and constructed the first single-nucleus transcriptomic landscape of gingival aging, by which a panel of cell type-specific signatures were elucidated. Epithelial cells were identified as the most affected cell types by aging in the gingiva. Further analyses pinpointed the crucial role of YAP in epithelial self-renew and homeostasis, which declined during aging in epithelial cells, especially in basal cells. The decline of YAP activity during aging was confirmed in the human gingival tissues, and downregulation of YAP in human primary gingival keratinocytes recapitulated the major phenotypic defects observed in the aged primate gingiva while overexpression of YAP showed rejuvenation effects. Our work provides an in-depth understanding of gingival aging and serves as a rich resource for developing novel strategies to combat aging-associated gingival diseases, with the ultimate goal of advancing periodontal health and promoting healthy aging.

Phenomenological modeling of aging and rejuvenation on asphalt binder fatigue characteristics

Recycling agents (RAs) have been explored as additives to enhance the properties of recycled asphalt binders. Despite extensive research on RAs, a critical knowledge gap exists regarding their impact on fatigue cracking of asphalt binders, especially considering the aging processes. This study aims to comprehensively investigate the effects of recycling agents on the fatigue properties of asphalt binders, with a specific focus on the influence of aging and rejuvenation. The current Linear Amplitude Sweep (LAS) test analysis procedure is utilized to assess the fatigue properties, and the efficacy of existing LAS test-based indices is evaluated. Furthermore, a novel index based on the simplified viscoelastic continuum damage (S-VECD) theory framework is proposed to monitor changes in fatigue properties with aging and rejuvenation. A total of 26 recycled binder blends are studied and the results demonstrate that the proposed index consistently tracks the effects of aging and rejuvenation in recycled binder blends containing recycling agents. Additionally, cross-scale assessments are conducted by correlating the proposed index with mixture performance, specifically the Indirect Tensile-Cracking Test parameter (CTindex). The findings indicate that the proposed index exhibits a correlation with the CTindex after 1-day Long Term Aging testing and effectively captures the aging sensitivity across different scales.

Effects of rejuvenators and aging conditions on the properties of blended bitumen and the cracking behavior of hot asphalt mixtures with a high RAP content

The utilization of Reclaimed Asphalt Pavement (RAP) in asphalt pavement has obtained global popularity because of its cost-efficiency, technical advantages, and positive environmental influence. However, incorporating RAP requires careful consideration of cracking resistance because of the existence of age hardening of bitumen in RAP. For the mixtures containing high RAP contents, rejuvenators are often applied to enhance the performances of aged bitumen and the cracking of mixtures. This research aims to evaluate the effects of different rejuvenators on the rheological properties of bitumen and the cracking resistance of the mixture under short and long-term aging conditions. To achieve this goal, three rejuvenators - namely, RA1 (petroleum-based), RA2 (waste vegetable oil-based), and RA3 (modified soybean oil-based) were evaluated at contents of 0%, 4%, 12%, and 20%, respectively. The dynamic shear rheometer (DSR) test results show that, under unaged and rolling thin-film oven (RTFO) aging conditions, blended bitumen with RA1 and RA3 have higher G*/sinδ than RA2. Conversely, under pressure aging vessel (PAV) aging conditions, blended bitumen with RA1 and RA3 has lower G*sinδ than that with RA2. Regarding the cracking resistance, the indirect tension asphalt cracking test results show that, under short-term oven aging (STOA) conditions, the mixture using RA2 and RA3 has a higher cracking tolerance index (CTIndex) than the one with RA1. However, under long-term oven aging (LTOA) conditions, the mixture using RA1 has the highest CTIndex value. In addition, the high correlations between G*sinδ with CTIndex and post-peak slope (|m75|) and between the CTIndex and |m75| are observed.

Multiscale optimization on polymer-based rejuvenators for the efficient recycling of aged high-viscosity modified asphalt: Molecular dynamics simulation and experimental analysis

With the depletion of fossil fuels, the advancement of efficient pavement recycling technology has garnered widespread attention, which contributes to the promotion of sustainable economic and environmental development. The polymers in polymer-based composite rejuvenators (PBCRs) are the key to restoring the performance of aged high-viscosity modified asphalt (HVMA). To optimize the polymers in PBCRs, this study investigates the rejuvenation effect and interface diffusion mechanism of various PBCRs using molecular dynamics simulation and experimental analysis. First, four PBCRs with different polymer components were designed, and their impact on the performance of weather-aged HVMA were examined using the rheological test, low-temperature force ductility test, crack resistance test, and aging resistance test. Subsequently, the rejuvenation effects of four PBCRs were ranked using the comprehensive performance radar chart. Finally, molecular models and layer models of weather-aged HVMA and four PBCRs were constructed, and the diffusion fusion process and interaction mechanism were analyzed using the molecular dynamics simulation. The findings indicate that PBCRs can rebuild the polymer network structure, partially restore the rheology, elastic recovery, and low-temperature ductility of aged HVMA. Additionally, PBCRs significantly reduce the crack potential of aged HVMA and ensure satisfactory aging resistance. Molecular dynamics simulation shows that due to the differences in their molecular structures, the diffusion ability of PBCRs is ranked as follows: crumb rubber rejuvenator (CR + R) > SBR rejuvenator (SBR + R) > SBS rejuvenator (SBS + R) > HVM rejuvenator (HVM + R). In summary, SBS + R proves most effective in regulating asphalt components and rebuilding the polymer network structure, but its interfacial diffusion ability is inferior to CR + R and SBR + R. CR + R has the highest diffusion coefficient, but its rejuvenation effect is not ideal. HVM + R is slightly less effective at rejuvenation than SBS + R, but has the worst diffusion capacity. The rejuvenation effect and diffusion ability of SBR + R are both not ideal. This study has significant implications for optimizing the polymers in PBCRs and promoting the efficient rejuvenation and eco-friendly sustainable development of HVMA.

Deciphering non-elastic deformation in amorphous alloy: Simultaneous aging-induced ordering and rejuvenation-induced disordering

The mechanical and physical properties of amorphous alloys depend on their time, temperature, and stress history. Due to their out-of-thermodynamic-equilibrium nature, describing the nonelastic deformation while considering the evolution of the structural state poses a significant challenge. We address this challenge by incorporating a parameter for structural state changes into a conventional deformation theory. This allows us to account for aging-induced ordering and deformation-induced disordering in the description of the mechanical deformation. In the apparent elastic regime (small strain), aging dominates while disorder caused by deformation can be disregarded. In this context, we have also made modifications to the widely used stretched exponential function, incorporating in-situ aging during deformation. This modification successfully describes the stress relaxation behavior under small deformation conditions and provides insights into parameter evolution in this process. Under large deformation conditions, both aging and deformation induced rejuvenation effects on the structural state must be considered simultaneously. By analyzing the evolution of defect concentration during this process, we describe relevant experimental results within the framework of the free volume theory, effectively separating the contributions of aging and rejuvenation to the structural state during the deformation process.

Anatomy, ploidy level, and essential oil composition of <i>Hyssopus officinalis</i> ʻNikitskiy Beliyʼ <i>in vitro</i> and <i>ex situ</i>

Background. Clonal micropropagation is a biotechnological method for plant multiplication. The existing data on the structure of organs in vitro, genetic stability, and essential oil composition are limited for Hyssopus officinalis L., so this study was aimead at investigating these aspects under a short period of in vitro culturing.Materials and methods. Plants of Hyssopus officinalis ʻNikitskiy Beliyʼ cultivated ex situ, in vitro and ex vitro were analyzed. Conventional methods were applied to study plant anatomy, ploidy level, and relative DNA content, as well as to extract and analyze essential oil. Statistical analysis was performed using the Past 4.03 software.Results. According to the results obtained, with 6-BAP introduced into MS nutrient medium in optimal concentrations (0.3– 0.5 mg/L), the general in vitro structure of leaf blades in the developed microshoots was similar to those in ex situ plants, while the qualitative and quantitative changes observed were induced by the effect of specific culturing conditions and plant rejuvenation. The analysis of the ploidy level and relative DNA content in the nuclei isolated from the leaf tissue cells of the microshoots ex vitro after adaptation revealed no changes compared to the ex situ leaf parameters. The mass fraction of essential oil and its component composition in the mother plants and ex vitro regenerants were similar.Conclusion. Cultivation of Hyssopus officinalis ʻNikitskiy Beliyʼ microshoots on MS nutrient medium with 6-BAP optimal concentrations promotes morphogenesis without significant deviations in the ploidy level, relative DNA content, essential oil yield, or its component composition. The developed protocol for clonal micropropagation of Hyssopus officinalis ʻNikitskiy Beliyʼ provides clones identical to the ex situ plants.

Real-space model for activated processes in rejuvenation and memory behavior of glassy systems.

We offer an alternative real-space description, based purely on activated processes, for the understanding of relaxation dynamics in hierarchical landscapes. To this end, we use the cluster model, a coarse-grained lattice model of a jammed system, to analyze rejuvenation and memory effects during aging after a hard quench. In this model, neighboring particles on a lattice aggregate through local interactions into clusters that fragment with a probability based on their size. Despite the simplicity of the cluster model, it has been shown to reproduce salient observables of the aging dynamics in colloidal systems, such as those accounting for particle mobility and displacements. Here, we probe the model for more complex quench protocols and show that it exhibits rejuvenation and memory effects similar to those attributed to the complex hierarchical structure of a glassy energy landscape.

Investigation of the fracture performance of reclaimed asphalt mixture at the intermediate temperature using multi-parameters

Fracture energy (Gf) and J-integral are two widely used parameters to evaluate the intermediate-temperature fracture performance of hot mix asphalt. Other parameters, such as balanced cracking index (BCI), cracking resistance index (CRI), cracking tolerance index (CTindex) and toughness index (TI), were proposed to characterize the fracture performance subtly. However, these parameters generally could not generate consistent fracture performance. In this study, six indices (Gf, J-integral, BCI, CRI, CTindex and TI) were selected to characterize the intermediate-temperature fracture performance of HMA to address the effects of RAP and rejuvenator on the fracture resistance. The overall fracture performance of all mixtures was evaluated using all these parameters using a scoring method. Pairwise correlation analysis was conducted among the variables. In addition, coefficients of variability (COV) were also measured. The results showed that all facture parameters indicated that a certain amount of RAP could enhance the fracture performance. However, the optimal contents of RAP were inconsistent among different fracture parameters. Rejuvenator could improve the fracture resistance. The fracture score of HMA with 50% RAP was highest, indicating the fracture resistance of HMA with 50% RAP was superior considering all the fracture variables. Pairwise correlation analysis showed that Gf presented poor correlations with all other variables. BCI, CTindex and TI showed large COVs, while Gf, J-integral and CRI showed low COVs.

Direct Correlation among Telomere Length, Cellular Aging, and Rejuvenation Effects of Honey Child Powder

Direct Correlation among Telomere Length, Cellular Aging, and Rejuvenation Effects of Honey Child Powder

Simultaneous Skin Rejuvenation in Patients Undergoing Medical Treatment for Actinic Keratosis and Non-Melanoma Skin Cancer: A Case Series Analysis

This original article presents the findings of a comprehensive case series, shedding light on the efficacy of diverse treatment modalities for managing precancerous and cancerous skin lesions and their remarkable rejuvenation effects on the skin. A particular focus is placed on the promising outcomes achieved through the application of a combination treatment involving 5-Fluorouracil (5-FU) and salicylic acid, which demonstrates enduring and noteworthy results. Furthermore, alternative therapeutic approaches, including 5-FU monotherapy, Methyl aminolevulinate–photodynamic therapy (MAL-PDT), and the combination of Imiquimod therapy with MAL-PDT, exhibit substantial potential for patients seeking non-surgical solutions. These treatments manifest as valuable tools in improving skin texture and mitigating the effects of photodamage. Nevertheless, the intricate interplay between the chosen treatment, the extent of photodamage, and individual patient characteristics, with a particular emphasis on age, necessitates long-term follow-up to gauge treatment outcomes and the likelihood of lesion recurrence. Notably, these treatments are associated with a significant degree of inflammation, igniting curiosity regarding enhanced skin cellular turnover and the potential for a more youthful skin appearance. Our findings accentuate the promise of topical fluorouracil (5-FU) and photodynamic therapy (PDT) in combating photoaging among patients with actinic keratoses. However, a need for further in-depth research is evident to unravel the nuanced relationships between these treatments, the severity of photodamage, and the influence of patient-specific factors. Such comprehensive investigations are instrumental in optimizing patient care and outcomes, offering a holistic approach to managing photodamage within the context of actinic keratoses. This work, when combined with existing literature, provides valuable insights and serves as a catalyst for future research to fully unlock the potential of these treatments, ultimately enhancing the quality of patient care.

BIOLOGICAL AGE REDUCTION AND LIFESPAN EXTENSION UPON YOUTHFUL CIRCULATION EXPOSURE

Abstract We performed extended (3-month) Heterochronic Parabiosis (HPB), followed by a 2-month detachment period of anastomosed pairs. Old detached mice exhibited improved physiological parameters and lived longer than control isochronic mice. HPB drastically reduced the biological age of blood and liver based on epigenetic analyses across several clock models using multiple independent platforms; remarkably, this rejuvenation effect persisted even after 2 months of detachment. Transcriptomic and epigenomic profiles of anastomosed mice showed an intermediate phenotype between old and young, suggesting a global multi-omic rejuvenation effect. In addition, old HPB mice showed gene expression changes opposite to aging, but akin to several lifespan-extending interventions. Altogether, we reveal that long-term Heterochronic Parabiosis can decrease the biological age of mice, in part through long-lasting epigenetic and transcriptome remodeling, culminating in the extension of lifespan and healthspan.

Novel rejuvenators for sustainable recycling of aged SBS modified bitumen: Performance evaluation and reactive mechanism analysis

The performance of aged styrene-butadiene-styrene (SBS) modified bitumen (SMB) is jointly dominated by the aging of bitumen and degradation of SBS crosslinking network structure. Despite some epoxy reactive rejuvenators which can re-crosslink SBS fragments are able to reconstruct the SBS cross-linking network compared with conventional rejuvenator, the performance of aged SMB regenerated by existing epoxy reactive reactants is unbalanced achieving good low temperature performance by sacrificing high temperature performance. In order to further improve the comprehensive road performance of regenerated SMB, a novel reactive rejuvenator was proposed and assessed in this study aiming at effectively improving the high temperature performance of regenerated SMB. The restoration effectiveness of the reactive rejuvenators was evaluated and compared by the physical properties, rheological properties and FTIR of rejuvenated SMB. The physical and rheological experimental results show that 2,2'-[1,3-phenylenebis (oxymethylene)] dioxirane (RDGE) and 1,6-hexanediol diglycidyl ether (HDDGE) are beneficial to high and low temperature performance of regenerated SMB, respectively, and their composite action can complement each other. Compared with N, N-dimthylbenzylamine (BDMA), 3,6,9,12-tetraazatetradecane-1,14-diamine (PEHA) with crosslinking effect can excellently make up for the disadvantages of epoxy rejuvenator, which has better and balanced recovery effect in consideration of both low and high temperature properties of regenerated SMB. The reactive rejuvenator containing PEHA and RDGE can further alleviate high temperature performance loss of regenerated SMB by an appropriate mix ratio. The changes of chemical functional groups of FTIR and fluorescence microscope directly prove that a novel recovery reaction for degraded SBS network structure via the introduction of PEHA (a kind of polybasic primary amines) is conducive to balancing high and low temperature performance of regenerated SMB.

A novel WCO-MDI reactive rejuvenation method for aged SBS modified asphalt toward sustainable asphalt pavements

The sustainable advancement and low-carbon application of asphalt pavement significantly benefit from the reutilization of waste SBS modified asphalt (SBSMA) mixtures. However, the high-efficiency rejuvenation of aged SBSMA (ASBSMA) remains a persistent challenge. In this study, a novel reactive rejuvenator was developed using waste cooking oil (WCO) and methylene diphenylene isocyanate (MDI) to restore asphalt components and reconstruct SBS structures in ASBSMA. Temperature Sweep, Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC) tests were conducted to investigate the rejuvenation effect and mechanism of ASBSMA. The results indicate that the incorporation of WCO restores the low temperature performance of ASBSMA, but adversely affects its high temperature performance. Conversely, the addition of MDI enhances the high temperature performance of ASBSMA, but an excessive dose of MDI has a negative impact on its low temperature performance. Chemical composition analysis shows that the rejuvenation by WCO is a physical dissolution and softening process, while MDI can react with the SBS aged products to produce long chain products with an amide structure and reconstruct the cross-linked structure of SBS. Although the temperature stability of rejuvenated SBSMA is not fully restored to its original state, it shows significant improvement compared with ASBSMA due to the reconstruction of SBS structure. This study effectively clarifies the reactive rejuvenation mechanism of ASBSMA, achieves the synergistic restoration of asphalt components and SBS structure, and contributes to high-efficient recycling of WCO and waste asphalt materials.

The efficiency of bio-char as bitumen modifier

Improving the mechanical properties of bitumen is an important goal for road pavements design. For this reason, new compounds are now being sought for testing as bitumen modifiers.In this work, the authors studied the effect that two different chars have on two 50/70 bitumens with different chemical and physical characteristics. A complete morphological, surface and bulk characterization of the two additives was carried out. In addition, rheology, Nuclear Magnetic Resonance (NMR) relaxometry and atomic force microscopy were used to analyze the effect that the two additives exert on the properties of the bitumens. According to the results, the char sample with high porosity could be used as a modifier of mechanical properties, while no rejuvenation effects were observed for either of the two additives tested. In addition, the two additives do not give rise to segregation phenomena.

Structural Relaxation, Rejuvenation and Plasticity of Metallic Glasses: Microscopic Details from Anelastic Relaxation Spectra

The lack of periodicity and long-range order poses significant challenges in explaining and modeling the properties of metallic glasses. Conventional modeling of nonexponential relaxation with stretched exponents leads to inconsistencies and rarely offers information on microscopic properties. Instead, using quasi-static anelastic relaxation, we have obtained relaxation-time spectra over >10 orders of magnitude of time for several metallic glasses. The spectra enable us to examine in microscopic detail the distribution of shear transformation zones and their properties. They reveal an atomically-quantized hierarchy of shear transformation zones, providing insights into the effect of structural relaxation and rejuvenation, the origin of plasticity and the mechanisms of the alpha and beta relaxation.

Evaluating the Short-term Performance of Spray-on Rejuvenators using a Modified Bending Beam Rheometer Test Methodology

Spray-on rejuvenation is a preventive maintenance strategy that highway agencies use to prolong the service life of asphalt pavements. This process involves applying rejuvenators on the surface of asphalt pavement to reverse the stiffening caused by aging. However, with several rejuvenators available on the market, it can be challenging to select specific products without understanding their effects at the mixture level. In this study, 12 different spray-on rejuvenators were applied on two different test sections (each with multiple test cells) at the Minnesota Road Research Facility. To assess the short-term (1–2 months) performance of rejuvenators, bending beam rheometer (BBR) test beams were prepared from the surface of the field-extracted cores, and a creep stiffness test was performed. The creep stiffness was measured at three different temperatures to evaluate the effectiveness of rejuvenators at these temperatures. The BBR test was not used to assess the low-temperature cracking resistance; instead, it was simply used to measure the beams’ linear viscoelastic property (i.e., the creep stiffness). Results indicated that the effect of rejuvenation is more evident at higher temperatures (20°C in this case). Besides, specific unexpected effects of rejuvenator products were observed. One of the test sections included extensive microcracks visible on the surface (presumably because of construction-related issues). Some of the rejuvenators closed these microcracks, leading to a “bridging” effect and increasing the stiffness of the BBR beams. This study provides a reference for evaluating the effect of spray-on treatments at the asphalt mixture level, which can assist roadway agencies in decision-making.

Skin rejuvenation effect of the combined PDLLA and non cross-linked hyaluronic acid: A preliminary study.

Skin aging is characterized by wrinkles, rough skin texture, pigmentation, facial erythema, and telangiectasia through structural and functional changes in the epidermis and dermis. Recently, injectable poly(D, L-lactic acid), a biodegradable polymer, has been used widely for skin rejuvenation. This study aims to assess the efficacy and safety of injectable dermal poly D, L-lactic acid) for skin rejuvenation. A total of 16 patients who desired skin rejuvenation were included. All participants received two or three procedure sessions with a 4 weeks interval between sessions. Clinical and three-dimensional images at baseline, before each procedural session, and follow-up visits were obtained. Therapeutic effects were assessed by evaluating signs of aging skin and overall improvement by dermatologists and patients. Histologic examinations with special stains were performed on the posterior auricular areas of consenting patients at baseline and follow-up visits after injecting poly D L-lactic acid into the postauricular area as in the face. Overall, statistically significant differences were observed in all signs of aging skin, such as fine wrinkles, skin texture, irregular pigmentation, telangiectasia, and facial erythema before and after treatments. Half (50%) of patients responded that there was more than 50% overall improvement. There were no severe adverse events. Histologic examination demonstrated increases in collagen and elastic fibers in the dermis. Results of this preliminary study suggest that injectable dermal poly D, L-lactic acid can significantly affect skin rejuvenation without causing any serious adverse events.