Unraveling filamentous algae as a renewable bioresource for advanced moisture-absorbent innovative aquatic fibers

TL;DR

This study explores using filamentous algae to create sustainable, moisture-absorbent fibers for textiles, with Rhizoclonium sp. showing strong potential.

Contribution

The study introduces Rhizoclonium sp. as a novel, renewable source for bio-based textile fibers with superior moisture absorption.

Findings

Rhizoclonium sp. achieved a high biomass yield of 1.04 g dry weight L−1 after 21 days.

Optimized cultivation increased biomass productivity by 8.6% and improved fiber flexibility.

Rhizoclonium sp. fibers showed 12% moisture regain, outperforming cotton and lyocell.

Abstract

Filamentous algae, characterized by high cellulose content and absence of lignin, present a promising sustainable alternative to conventional plant and synthetic fibers. The present study systematically evaluated the suitability of freshwater filamentous algae as a new resource for textile fibers, targeting applications in moisture-absorbent textiles. Among twelve strains screened, the isolate Rhizoclonium sp. emerged as the most promising candidate due to its high biomass yield (1.04 g dry weight L− 1) after 21 days of cultivation. In addition, it showed superior visible fiber flexibility following air-drying, an essential prerequisite for textile processing. Cultivation conditions were optimized (using WHM medium, pH 8, and thiamin supplementation) to maximize fiber quality, resulting in 8.6% increase in biomass productivity. Biochemical profiling of the optimized biomass revealed a significant enhancement of total carbohydrates (+ 18.0%), alongside reductions in protein (-18.4%) and ash content (-14.9%), supporting improved fiber durability and flexibility. Comparative FTIR analysis showed a strong cellulose signature and marked similarity to cotton, while also revealing high native starch content, further supporting their applicability as bio-based binders in nonwoven products. Functional characterization demonstrated that optimized Rhizoclonium sp. fibers exhibited exceptional moisture regain (~ 12%), surpassing conventional fibers such as cotton and lyocell. Overall, this study establishes native Rhizoclonium sp. as a highly versatile and renewable bioresource for innovative aquatic fibers, underpinning the development of an environmentally responsible algae-derived textile value chain.

The online version contains supplementary material available at 10.1186/s40643-026-01028-1.

Figures

Morphological and molecular characterization of MZCH #10606 using light microscopy, fluorescent microscopy with DAPI staining (B), transmission electron microscopy (C, D). The phylogenetic tree is based on ITS (ITS1 + 5.8 S + ITS2) sequences (E). The evolutionary history was inferred by using the Maximum Likelihood method and Tamura-Nei model (Tamura and Nei [1993](#CR66)). The bootstrap consensus tree inferred from 1000 replicates is taken to represent the evolutionary position of MZCH #10606, analyzed using MEGA11 (Tamura et al. [2021](#CR67))

Biomass yield of *Rhizoclonium* sp. #10606 in comparison with other filamentous algae grown under the same conditions (Rahaman et al. [2025](#CR55)) after 21 days of growth in WHM, which included *O. foveolatum* #10602, *O. angustistomum* #10604, *K. nitens* #10199, *H. dissilens* #737, *Zygnema* sp. #769, *Z. circumcarinatum* #10230, *Spirogyra* sp. #771, *Spirogyra* sp. #779, *S. pratensis* #10213, *G. neglecta* #478, *M. calospora* #580

Comparison of different cellulosic textile fibers including cotton (A), hemp (B), and lyocell (C) with those from *Rhizoclonium* sp. (D). The top row displays natural fibers, while lower row shows the corresponding SEM images

Biomass productivity of *Rhizoclonium* sp. cultivated for 21 days in various growth media (A), varied concentrations of WHM stocks (B), different vitamin supplementations (C), and different initial pH values (D). I, II, III, IV, V, VI, VII, and VIII represent specific components from WHM which are CaCl_2_.2H_2_O, MgSO_4_.7H_2_O, NaNO_3_, NaHCO_3_, K_2_HPO_4_, micronutrients, vitamins, and HEPES, respectively. Ti, Bi, and Cy represent thiamin (vitamin B1), biotin (vitamin H), and cyanocobalamin (vitamin B12), respectively. Columns with the same letter showed insignificant differences using Tuke

Morphology as recorded by SEM (upper panel) and FTIR spectra (lower panel) of *Rhizoclonium* sp. cultivated for 21 days under control and optimized conditions

Full text

Introduction

The combined challenges of rising environmental concerns and the urgent demand for sustainable solutions have placed the search for new bioresources at the center of many scientific explorations. In textile industry, environmental concerns are connected to traditional materials such as cotton and synthetic polymers and, therefore, sustainable eco-friendly alternative textile fibers gain increasing attention. Cotton cultivation requires extensive land, water and pesticide use, while synthetic fibers like polyester and nylon are derived from non-renewable petrochemicals and contribute significantly to microplastic pollution. These challenges highlight the urgent need to explore alternative, renewable sources for textile fiber production. In recent years, plant-based fibers such as hemp, flax and bamboo are being re-evaluated due to their lower environmental footprint compared to cotton (Ahmed et al. 2025). Similarly, regenerated fibers from cellulose, such as lyocell and modal, are gaining popularity for their biodegradability and efficient production processes. Beyond terrestrial resources, innovative research has turned toward microbial and algal systems, where algae-derived cellulose showed promising potential as novel renewable fiber sources. Given the rising concerns related to the environmental impact of textile production and growing global consumption, interest in bio-based textile solutions, such as fibers, dyes and natural colors derived from microalgae and filamentous algae has risen (Blanckart et al. 2025). Specifically, filamentous green algae have high cellulose content without lignin, making them a promising alternative for fiber-based products (Chao et al. 1999). Algal-based materials can be used in various applications beyond textiles, including bio-based packaging materials, insulating construction materials, components of biodegradable composites and in the development of novel medical products like wound dressings or tissue engineering scaffolds (Chao et al. 1999; Zhong et al. 2021).

Existing examples of algae-based fibers include nanofibrils derived from cellulose extracted from Cladophora glomerata (Xiang et al. 2016) and Chaetomorpha antennia (Bhutiya et al. 2018). In addition, regenerated chemical fibers such as SeaCell™ are currently produced from brown algae, which are ground into powder and incorporated as particles into a cellulose spinning mass (Kim et al. 2022). However, there is still no application in which native algal filaments can be directly processed and converted into textiles using established mechanical methods without chemical breakdown or pulverization. In this context, filamentous algae hold considerable potential as novel aquatic fibers for renewable and sustainable textile production. Unlike powdered or chemically processed algae, filamentous algae provide naturally elongated structures that could, in principle, be spun and woven using conventional textile machinery. Their naturally elongated structures are widely varied based on the species (Rahaman et al. 2025), making them particularly suitable for textile applications, opening the door to a new class of sustainable fabrics with reduced environmental footprint.

From an environmental perspective, algae cultivation offers several environmental advantages. In addition to the possible cultivation on wastewater or seawater (Han et al. 2025; Ebaid et al. 2025), they do not require arable land and can grow independently of seasonal cycles. Moreover, algal cultivation eliminates the need for harmful pesticides and fertilizers, and helps to mitigate pollution associated with petrochemical-based synthetic fibers. In contrast, the latter (such as polyester), currently dominating the textile industry, contribute substantially to greenhouse gas emissions and microplastic pollution, releasing over 720,000 plastic particles per gram during washing (Cai et al. 2020), which can ultimately enter the food chain resulting in many negative consequences (Abomohra and Hanelt 2022).

Owing to the unique morphology and biochemical composition of filamentous algae, they could provide a sustainable alternative to both cotton and synthetic fibers, offering renewable, biodegradable, and functional materials for textiles. Despite their promising structure and properties, along with their potential to produce value-added compounds, filamentous algae are largely underexplored and underutilized across industries. While considerable research has focused on microalgae- and seaweeds-derived products or chemically processed algae fibers, there is a notable lack of studies investigating the direct use of native macroscopic filamentous algae as textile raw materials. This gap is particularly significant given the environmental and sustainability challenges posed by conventional textile fibers. Therefore, this study focuses on screening freshwater filamentous algae as a potential source of sustainable textile fibers. The study aimed to identify promising algal strains based on key fiber attributes, including cell size, mechanical strength, flexibility, and chemical composition. Cultivation conditions were optimized to maximize biomass yield while enhancing fiber quality and relevant biochemical properties. In addition, possible application of these fibers to produce yarns, knitted fabrics, and nonwovens was evaluated through a comprehensive analysis of their mechanical, hygroscopic, and processing characteristics. By bridging algal biotechnology with textile engineering, this work seeks to establish the foundation for the development of fully algae-based innovative aquatic textile fibers.

Materials and methods

Algae strains and identification

In addition to 11 freshwater filamentous algae provided by the Microalgae and Zygnematophyceae Collection Hamburg (MZCH) (Rahaman et al. 2025), the filamentous alga MZCH #10606 was isolated from an aquarium in Mönchengladbach, Germany. Cultures were maintained in liquid Woods Hole Medium (WHM) as recommended by the culture collection (MZCH 2016), with subcultures performed every 4–5 weeks to ensure continued growth and viability. Algae were incubated under light conditions and aeration as described later. Identification of strain MZCH #10606 was carried out using imaging techniques, including light microscopy and fluorescence microscopy, as well as molecular methods as described in the following sections.

Microscopy and fluorescence imaging

The length and width of vegetative algal cells were measured using ImageJ integrated to the light microscopy (Zeiss Axio Imager. A1, Carl Zeiss Microscopy, Germany). The nuclei of strain MZCH #10606 were stained with 4′,6-diamidino-2-phenylindole (DAPI, CAS D1306) following Thermo Fisher standard protocol for fluorescence imaging. Briefly, a 300 nM DAPI staining solution was prepared in phosphate-buffered saline (PBS). For live-cell staining, algal filaments were washed 3 times with PBS to remove residual culture medium and impurities, then cells were covered with an adequate amount of DAPI solution. The samples were incubated 5 min in the dark, then DAPI solution was removed by washing 3 times with PBS. DAPI fluorescence was excited at 358 nm and emission was recorded at 461 nm using AxioImager A2 epifluorescence microscope (Carl Zeiss Microscopy, Germany).

Cell wall ultrastructure of the strain MZCH #10606 was also examined using transmission electron microscopy (TEM) as described by Hess et al. (2022). Samples were imaged with a dual speed CCD camera (Zeiss EM 906 Tröndle Restlichtverstärkersysteme, TRS) equipped with software Image SP-Professional + Panorama (MIA).

DNA extraction and sequencing

DNA extraction was conducted as previously described (D’Souza et al. 2025). The primer pair used for amplifying the entire ITS rDNA was A1 (5’-ATGCTTAAGTTCAGCGGGTAG-3 ‘) and S1 (5’-GAACCTGCGGAAGGATCA-3’). In brief, cyclic phase consisted of denaturation step at 94°C for 5 min, then 32 cycles of denaturation at 94°C for 50 sec, annealing at 52°C for 1 min and extension at 72°C for 90 sec, ending in an extension phase of 10 min at 72°C. The 646 bp amplicon was purified using the NucleoSpin PCR cleaning Kit (REF 740609.50, Macherey-Nagel, Germany), and sequencing was carried out by GENEWIZ Germany GmbH.

Algae cultivation and optimization

The studied algae were cultivated in the selected medium using 500 mL laboratory Schott bottles. An algal biomass of ca. 0.4 g fresh weight was used for inoculation. Cultures were incubated in a growth chamber (Percival, SE41-P4, CLF Plant Climatics GmbH) for a duration of 21 days. The cultures were maintained under continuous aeration (~ 0.2 volume air per volume liquid per minute, vvm) at a temperature of 25 °C and light conditions of 16:8-hour light-dark cycle at average light intensity of 240 µmol photons m^-2^ s^-1^. Algae were harvested by filtration through 100 μm pore size plankton net and dried by lyophilization (VaCo 5, Zirbus Technology, Germany). The biomass yield was measured gravimetrically as dry weight (g L^-1^), and biomass productivity (BP) was calculated according to Eq. 1;

\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$BP\text{}\left(g{\text{}L}^{\mathrm{-}1}{\text{}d}^{\mathrm{-}1}\right)\mathrm{=}\left({W}_{f}\mathrm{-}{W}_{i}\right)\times{\left({t}_{f}\mathrm{-}{t}_{i}\right)}^{\mathrm{-}1}$$\end{document}

where Wi represents the equivalent biomass yield as dry weight (g L^-1^) at the inoculation time (ti), and Wf represents the biomass yield at the harvest time (tf). The dried algae were finely pulverized as previously described (Rahaman et al. 2025) and stored under dry conditions until further use.

To enhance the biomass yield, growth conditions were optimized by evaluating various media including WHM (Nichols 1973), WH (Nichols 1973), BG-11 (Stanier et al. 1971), modified MG (Stanier et al. 1971), modified C (Stanier et al. 1971), KC (Kessler and Czygan 1970), and Flory (Abomohra et al. 2013). Furthermore, the composition of the most promising medium, along with pH and vitamin mixture, was optimized. The growth performance and characteristics of the algal fibers cultivated in the standard medium (control) and under optimized conditions were then compared. In addition, fiber morphology of all studied algae was examined by scanning electron microscopy (SEM) using a TM4000Plus Tabletop microscope (Hitachi, Tokio, Japan) after air-drying.

FTIR and biochemical composition

The infrared spectra from the twelve studied algae were examined through Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR, Shimadzu, Japan). The resulting spectra were compared against a comprehensive library (LabSolutions IR) containing approximately 12,000 reference spectra, including starch, cellulose, and cotton. Each algal spectrum was queried against the library, yielding the top 20 matches ranked by similarity score, ranging from 0 to 1000. This scoring system enabled an assessment of how closely each algal spectrum to starch, microfibril cellulose, and cotton, providing insights into the potential fiber properties of the studied strains. In addition, biomass composition including total carbohydrates, proteins, lipids, and ash were measured as described previously (Rahaman et al. 2025).

Microscopic analysis

The morphology of algae fibers was investigated using a TM4000Plus Tabletop scanning electron microscope (Hitachi, Tokyo, Japan). Briefly, air-dried samples were mounted directly onto the sample holder and observed under microscope. Images were acquired at an accelerating voltage of 15 kV and a magnification of 100×, with working distance of 10.9 mm. The samples were analyzed under vacuum of 50 Pa using a mixed signal mode for imaging.

Physical properties of algae fibers

The tenacity (cN tex^-1^), elongation (Emax, %), and linear density (dtex) of the algal fibers were measured using a Favimat^+^ single-fiber testing device (Textechno H. Stein GmbH & Co. KG, Germany). Measurements were conducted on the individual fibers under both dry and wet conditions. For the dry tests, fibers were conditioned in a standard atmosphere (20°C, 65% relative humidity), and subsequently tested under these conditions. For the wet tests, individual fibers were immersed in water for 5 s, allowed to drip for 10 s, then measured immediately. All measurements were carried out at a 210 cN load cell, a gauge length of 10.0 mm, and a test speed of 2.0 mm min^-1^. A pretension of 0.5 cN tex^-1^ was applied, and the force threshold for the measurement was set at 0.10%, with a specified force drop of 90.0%. For calculations, the linear density of fibers was assumed to be a nominal value of 2.80 dtex. Results were recorded as load-extension curves from which the load data were converted into tenacity. The elongation percentage of fibers was also determined to enable accurate comparisons across samples.

Moisture regain analysis

To determine moisture regain, samples were initially conditioned for 24 h in a standard atmosphere (20°C, 65% relative humidity) in accordance with DIN EN ISO 139. After conditioning, the samples were weighed to obtain the conditioned weight (Wc). They were then oven dried at 100 °C until constant weight. To prevent moisture re-absorption during cooling, the dried samples were stored in a desiccator before being weighed to determine the dry weight (Wd). The moisture regain (MR) was calculated using Eq. 2;

\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$MR\left({\%}\right) = \frac{{W}_{c}-{W}_{d}}{{W}_{d}}\times 100$$\end{document}

Statistical analysis

All experiments were performed in three biological replicates and results are expressed as the mean ± standard deviation (SD). Statistical analysis was conducted using ANOVA in SPSS (IBM, version 30), followed by LSD or Tukey test with a significance threshold set at a 95% confidence level.

Results and discussion

Identification of the new isolate

Morphological examination of the strain MZCH #10606 showed unbranched, filamentous structure composed of elongated cylindrical cells (Fig. 1A). The average cell dimensions were 51.21 ± 2.76 μm in length and 21.28 ± 0.86 μm in width (n = 10). Each cell contained a single, large, net-shape chloroplast along the cell wall. Fluorescent microscopy following DAPI staining showed nuclei as bright distinct spots (Fig. 1B). Each cell displayed multiple distinct nuclei, suggesting the organism as a member of the genus Rhizoclonium (Chlorophyta, Ulvaceae, Cladophoraceae) (Ichihara et al. 2013).

Fig. 1. Morphological and molecular characterization of MZCH #10606 using light microscopy, fluorescent microscopy with DAPI staining (B), transmission electron microscopy (C, D). The phylogenetic tree is based on ITS (ITS1 + 5.8 S + ITS2) sequences (E). The evolutionary history was inferred by using the Maximum Likelihood method and Tamura-Nei model (Tamura and Nei 1993). The bootstrap consensus tree inferred from 1000 replicates is taken to represent the evolutionary position of MZCH #10606, analyzed using MEGA11 (Tamura et al. 2021)

TEM examination of filaments cross sections (Fig. 1C-D) revealed cylindrical structure, with a multilayered and highly structured cell wall having a total thickness of 3.59 μm. The outer layer of the cell wall appeared compact, consisting of primarily non-fibrillar material. The inner layer was the most distinctive, consisting of eight sub-layers with alternating bright and dark bands. The banding pattern suggests differences in the orientation of cellulose microfibrils or variations in the packing of cell wall components (Fujino and Itoh 1994). The arrangement of these parallel lamellae within the multilayer structure forms a strong, plywood-like architecture that provides mechanical strength to the cell wall (Spain and Funk 2022). Such a cell wall complexity can provide mechanical strength, protection, and resilience to environmental stresses while maintaining essential cellular functions (Fujino and Itoh 1994; Cosgrove 2005). Furthermore, ITS sequencing followed by BLAST and phylogenetic analysis (Fig. 1E) placed the isolate in the genus of Rhizoclonium (bp identity of 93.6% with the closest Rhizoclonium relative). The sequence coverage in the available databases did not allow to attribute a species name and, therefore, the isolate was deposited as Rhizoclonium sp. at MZCH under strain number #10606.

Algae screening

Biomass yield and air-drying

The development of sustainable textile aquatic fibers from freshwater filamentous algae is an innovative approach that was evaluated for the first time in the present study. To identify an appropriate filamentous alga for large-scale production in textile application, an initial screening was performed by comparing the newly isolated strain Rhizoclonium sp. with those evaluated in a recent study (Rahaman et al. 2025). In the previous study, 91 filamentous algal strains from MZCH were screened. Eleven algal strains were selected based on their growth and cell dimensions, where biomass yield (dry weight, dw) after 21 days of cultivation ranged from 0.13 to 0.70 g L^−1^ (Rahaman et al. 2025). In the present study, Rhizoclonium sp. grown under the same conditions achieved a higher biomass yield of 1.04 g dw L^−1^, which is 48.6% higher than the best-performing strain, Oedogonium foveolatum, in the previous study (Fig. 2). To date, no commercial photobioreactor is available for filamentous freshwater algae, especially Rhizoclonium sp. Although the present study was conducted at a laboratory scale, pilot-scale biomass productivity can be estimated from the obtained results. Assuming that approximately two-thirds of the surface area effectively contributes to biomass production, and based on the biomass productivity achieved in the present bottle cultures, an average areal productivity of approximately 29.8 kg ha^−1^ day^−1^ can be estimated. Under an operational regime of 12 cultivation cycles per year, this corresponds to a potential annual yield of 7.5 t ha^−1^ year^−1^. While these values represent theoretical estimates, they demonstrate that Rhizoclonium sp. could reach biomass productivities comparable to other industrial algal systems and provide a realistic foundation for future pilot-scale validation.

Fig. 2. Biomass yield of Rhizoclonium sp. #10606 in comparison with other filamentous algae grown under the same conditions (Rahaman et al. 2025) after 21 days of growth in WHM, which included O. foveolatum #10602, O. angustistomum #10604, K. nitens #10199, H. dissilens #737, Zygnema sp. #769, Z. circumcarinatum #10230, Spirogyra sp. #771, Spirogyra sp. #779, S. pratensis #10213, G. neglecta #478, M. calospora #580

A critical factor for the economic competitiveness of a new fiber raw material is the cost-efficiency of its manufacturing procedure including drying as the first post-harvest process. Since freeze-drying (lyophilization) is an energy intensive and costly method, the suitability of the algal filaments for conventional air-drying as a more cost-effective alternative was evaluated. For this purpose, filaments of the 12 algal strains were air-dried and the resulting material was compared for fiber quality (Supplementary material, Fig. S1). The results showed distinct differences in material behavior after air-drying. While most studied algae became rigid and brittle, Rhizoclonium sp., Oedogonium foveolatum and Oedogonium angustistomum retained their flexibility and developed a fluffy fibrous texture comparable to conventional natural fibers, with Rhizoclonium sp. showing the most favorable characteristics. The observed species-specific differences in fiber flexibility can be attributed to variations in cell wall and extracellular matrix structure. Rhizoclonium sp. belongs to the Cladophoraceae family, which is characterized by a cellulose-rich nanofibrillar cell wall with relatively low amounts of mucilage (Mihranyan 2011; Zhou et al. 2019; Domozych and LoRicco 2023). Upon water removal, this structure preserves the filamentous morphology, resulting in dry filaments that maintain a flexible fibrous texture. In contrast, most Zygnematophytes have thick sticky mucilage layers and comparatively soft primary cell walls. During dehydration, these walls undergo pronounced shrinkage and surface adhesion (Herburger et al. 2019; Domozych and LoRicco 2023; Permann and Holzinger 2024), yielding crust-like residues which render the filaments inflexible after drying. These structural distinctions provide a mechanistic explanation of flexibility and fiber integrity of Rhizoclonium sp. fibers after air-drying. This property is a fundamental prerequisite for textile processing into fibers and yarns (Rahman et al. 2023). Additionally, SEM images corroborated this finding, where fiber structure of Rhizoclonium sp. appeared markedly less fragmented and more cohesive than that of the other studied algae. Considering these fundamental fiber properties, particularly the high flexibility after simple air-drying, these results suggest Rhizoclonium sp. as a promising candidate for further investigation.

FTIR analysis

Previous studies reported that filamentous algae, because of their elongated cell morphology and their cellulosic cell walls, could provide a promising source as textile fibers (Johnson et al. 1996; Rahaman et al. 2025). In addition, filamentous algae offer eco-friendly solutions for carbon capture and storage, owing to their high growth rate, CO_2_-fixation during photosynthetic activity, biocompatibility and favorable physical and mechanical properties (Klemm et al. 2005; Moon et al. 2011; Zhai et al. 2022). In this context, FTIR is a valuable tool for characterizing the chemical composition and functional groups of cellulosic materials, allowing direct comparison with conventional fibers (Otenda et al. 2022). In the present study, all the twelve studied algae showed almost a similar cellulosic peak ranging between 1630 and 880 cm^-1^, including peaks at 1430, 1380, 1365, 1338, 1028 and 890 cm^-1^ (Fig. S2, Supplementary data), associated with stretching and bending vibration of -CH_2_, -CH, -OH and C-O bonds in cellulose (Siddhanta et al. 2011; Xu et al. 2013; Salem and Ismail 2022).

Fibers of Rhizoclonium sp. showed the highest similarity score with respect to starch (877), followed by microfibril cellulose (799) and cotton (791) (Fig. 3A). This finding suggests the presence of a significant cellulose backbone. It is noteworthy to mention that the highest similarity score with cotton was recorded with Rhizoclonium sp. (791), followed by both Oedogonium angustistomum and Spirogyra pratensis (790). However, the lowest similarity score for cotton was recorded with Spirogyra sp. #771 (761). Although Oedogonium angustistomum scored the highest microfibrillated similarity with 843, Rhizoclonium sp. also showed a good match of 799, supporting its potential as a cellulosic textile fiber. Given that cotton is a known natural fiber with high tensile strength (Kong et al. 2021), these results suggest that Rhizoclonium sp. would be comparable to textile fibers. As cotton (Gossypium spp.) is the most important fiber crop globally, with annual production of 25 million metric tons (Eleutério et al. 2025), a comparison of the FTIR spectrum of Rhizoclonium sp. with that of cotton is presented in Fig. 3B, highlighting their shared cellulose features. Both samples exhibited a broad band at ~ 3343 cm^−1^ corresponding to O-H stretching vibrations of hydroxyl groups due to moisture content. Cotton sample showed a single peak at ~ 2896 cm^−1^, whereas the algae sample exhibited asymmetric shoulders, indicating the presence of overlapping peaks that may include N-H stretching vibrations in addition to C-H stretching of CH and CH_2_ groups (Tammer 2004). Notably, a distinct peak around 1730 cm^−1^, associated to carbonyl groups (C = O), was recorded in algae but absent in cotton, which is associated with lipids esters. In addition, algae exhibited strong peaks at 1641 and 1550 cm^−1^ corresponding to amide I and amide II, which are indicative of proteins, reflecting the almost pure cellulose composition of cotton. Specifically, the fingerprint region (1200 –900 cm^−1^) revealed that cotton primarily consists of the polysaccharide backbone of cellulose, while algae represented signal corresponding not only to cellulose but also to carbohydrate and other compounds. Overall, Rhizoclonium spectrum closely resembles that of cotton, with only minor differences in peak intensity or sharpness likely due to non-cellulosic components or variations in crystallinity, suggesting that Rhizoclonium fibers have a cellulose composition comparable to conventional cotton and supporting their potential as a renewable cellulose-based textile material. To further enhance the purity and functional quality of cellulosic structure in algae, a biorefinery approach involving the pre-extraction of value-added compounds, such as pigments, proteins, or lipids, is of great importance (Rahaman et al. 2025). This could help maintain the cellulose framework for textile applications while maximizing resource utilization, contributing to a sustainable and zero-waste valorization of Rhizoclonium sp. biomass.

Fig. 3A FTIR similarity score of different studied algae compared to cotton, starch and microfibril cellulose, and B the FTIR spectra of Rhizoclonium sp. compared to cotton

Morphological evaluation

Fiber geometry further plays a critical role in determining haptic characteristics, draping behavior, and the overall aesthetics of the final fabric (Gupta and Kothari 2008). With an unbranched structure and average cell widths of 21 μm, fibers from Rhizoclonium sp. exhibit a structural profile closely resembling conventional fibers (Fig. 4). This dimensional similarity facilitates intimate blending with established textile fibers, such as cotton or lyocell, to engineer yarns with tailored mechanical and functional properties. SEM imaging revealed that dried Rhizoclonium sp. filaments do not possess a smooth cylindrical surface, but rather a collapsed and irregularly folded structure (Fig. 4D). Remarkably, this surface pattern functionally parallels the natural twists or convolutions of cotton fibers, which are essential for spinnability by increasing contact points and friction between fibers (Gupta and Kothari 2008), thereby enhancing fiber cohesion within yarn. It is therefore plausible that the folded surface of Rhizoclonium sp. filaments similarly promotes inter-fiber adhesion, supporting stable yarn formation and positioning these algal fibers as promising candidates for mechanical spinning and textile fabrication.

Fig. 4. Comparison of different cellulosic textile fibers including cotton (A), hemp (B), and lyocell (C) with those from Rhizoclonium sp. (D). The top row displays natural fibers, while lower row shows the corresponding SEM images

Growth optimization of Rhizoclonium sp.

Growth media selection

The selection of a growth medium for algae cultivation depends on the intended use of the biomass and its derivative products. In general, nitrogen is an important element for algal growth, and nitrogen availability has an impact on cellular lipid production. For instance, nitrogen starvation in the growth medium reduced the biomass productivity (Chu et al. 2014), but enhanced lipid accumulation in filamentous algae such as Hormidium sp. and Oedogonium nodulosum (Zhang et al. 2016). Phosphorus is another key macronutrient which plays a crucial role in the biosynthesis of nucleic acids, phospholipids, and ATP (Solovchenko et al. 2016). Thus, the availability of both nitrogen and phosphorus, as well as other nutrients, must be carefully managed to optimize the overall algal growth, biomass productivity, and the accumulation of valuable biochemicals. In the present study, Rhizoclonium sp. was cultivated in seven different growth media, along with tap water (Fig. 5A). In different tested media, the three major elements including carbon, nitrogen, and phosphorus present in different forms and concentrations (Table S1, Supplementary data). Magnesium sulphate, sodium EDTA, and B-vitamins (B1, B7, B12) are common nutrients across multiple media. In contrast, several compounds are unique to specific media, such as HEPES buffer (WHM and MG), reflecting medium-specific customizations. For instance, Flory has minimal composition whereas WHM and KC have more diverse chemical composition. Among different tested media, Rhizoclonium sp. showed the highest significant biomass productivity in WHM and BG-11 (45.45 and 45.53 mg dw L^-1^ d^-1^, respectively). On the other hand, lower biomass production was observed in WH, MG, and C (Fig. 5A). Despite previous studies confirming the potential of Flory medium for microalgal growth (Abomohra et al. 2013, 2014), no growth was observed in Flory medium in the present study. This finding suggests that the standard formulation of Flory medium may lack essential components such as specific micronutrients, vitamins, or pH buffering agents required for the growth of Rhizoclonium sp. Despite insignificant difference in biomass productivity in WHM and BG-11, WHM was selected for further research as it was the medium originally used to establish the Rhizoclonium sp. reference culture.

Fig. 5. Biomass productivity of Rhizoclonium sp. cultivated for 21 days in various growth media (A), varied concentrations of WHM stocks (B), different vitamin supplementations (C), and different initial pH values (D). I, II, III, IV, V, VI, VII, and VIII represent specific components from WHM which are CaCl_2_.2H_2_O, MgSO_4_.7H_2_O, NaNO_3_, NaHCO_3_, K_2_HPO_4_, micronutrients, vitamins, and HEPES, respectively. Ti, Bi, and Cy represent thiamin (vitamin B1), biotin (vitamin H), and cyanocobalamin (vitamin B12), respectively. Columns with the same letter showed insignificant differences using Tukey test (at P ≤ 0.05)

Macro- and micronutrients

To ensure the economic competitiveness, the development of sustainable bioprocesses that optimize algal biomass productivity while minimizing nutrient inputs is crucial (Brennan and Owende 2010). In the present study, the growth-limiting factors of Rhizoclonium sp. were examined by comparing the growth in standard WHM medium, 2× or 3× concentrated WHM medium as well as 2× of specific WHM components including CaCl_2_, MgSO_4_, NaNO_3_, NaHCO_3_, K_2_HPO_4_, micronutrients, vitamins, and HEPES (Fig. 5B). This approach allows identification of specific macronutrient or micronutrient limitations that constrain growth and metabolite accumulation, providing insights for designing more efficient cultivation strategies. Results showed that standard WHM is an optimal growth medium, which yielded the highest biomass productivity of 50.67 mg dw L^-1^ d^-1^, followed by 48.37 and 47.99 mg dw L^-1^ d^-1^ using double concentration of MgSO_4_ and CaCl_2_, respectively. However, statistical analysis revealed insignificant differences among them. On the other hand, lowest productivity of 27.69 mg dw L^-1^ d^-1^ was observed using two-fold of HEPES. These results demonstrate that doubling the concentration of any single nutrient in the WHM medium could significantly decrease the biomass productivity. Additionally, over-supplementation of WHM medium reduces the growth of Rhizoclonium sp. This suggests that initial cultivation stages of Rhizoclonium sp. may be sensitive to osmotic stress, nutrient toxicity or metabolic overload caused by excessive nutrient supply. It can be concluded that over-supplementation of all components or doubling individual components in batch culture creates unfavorable conditions for the growth of Rhizoclonium sp. Consequently, the standard 1× WHM medium is recommended as the optimal nutrient formulation for lab-scale cultivation of this alga.

Vitamin requirement

For Rhizoclonium sp. to be commercially viable as alternative textile fiber, biomass production should be cost-effective. Vitamin mixture in WHM medium contains costly components that were reported to significantly increase the production cost of algal biomass (Refolio-Samperi et al. 2025), affecting market competitiveness. Optimizing the culture medium with minimum vitamin inputs is therefore essential to ensure economic sustainability for a large-scale production. The highest biomass productivity of Rhizoclonium sp. (~ 50–55 mg dw L^-1^ d^-1^) was recorded in all treatments containing thiamin (Ti) (Fig. 5C). However, no significant differences were recorded by elimination of biotin (Bi) or cyanocobalamin (Cy), indicating that Rhizoclonium sp. does not require external supplementation of these vitamins under the tested conditions. In contrast, the absence of thiamin significantly reduced the biomass productivity of Rhizoclonium sp. which decreased to ~ 25–35 mg dw L^-1^ d^-1^. Consequently, Ti supplementation was essential in the optimized growth medium, as it is an important cofactor that ensures the optimal functionality of important enzymatic reactions in carbon metabolism within chloroplasts and mitochondria (Goyer 2010), thereby supporting efficient cell wall polysaccharide biosynthesis and overall biomass production.

Vitamin requirements of algae are species-specific, i.e. some need all three vitamins (Ti, Bi, and Cy), others need only one or two (Croft et al. 2006). While many algae can acquire Cy from associated bacteria (Croft et al. 2005), they are unable to obtain Ti directly from bacteria and it must be supplied externally (Croft et al. 2006). The present results confirmed that Ti is the only essential vitamin for the growth of Rhizoclonium sp. Excluding Bi and Cy from the culture medium would reduce the cultivation-related costs without compromising biomass productivity, thereby improving the economic feasibility of Rhizoclonium sp. fibers.

pH

In order to define the optimum pH for enhanced biomass production, Rhizoclonium sp. was cultivated in WHM medium across an initial pH range of 6–12 (Fig. 5D). Results showed that biomass productivity steadily increased from pH 6 (51.73 mg dw L^−1^ d^−1^), reaching a maximum of 58.66 mg dw L^−1^ d^−1^ at pH 8, before gradually declining at higher pH levels. Growth of filamentous algae is significantly impacted by pH levels, which affect their physiological and biochemical process (Hariz et al. 2023). The observed trend aligns with literature reports for other filamentous algae, such as Rhizoclonium riparium, which also showed the maximum growth at pH 8 (Kilroy et al. 2020). In addition, several filamentous algae such as Oedogonium,* Tribonema*,* Spirogyra* and Cladophora grow optimally within a pH range of 7.0 to 9.0 (Liu et al. 2023). Moreover, biomass productivity of Oedogonium increased by 85% and 147% when cultivated at pH 7.5 and 8.5, respectively, compared to the control pH of 9.0 (Cole et al. 2014). The present results suggest that a pH of approximately 8 provides the most favorable environment for the growth of Rhizoclonium sp. Accordingly, the optimized medium was defined as 1× WHM containing only Ti as a vitamin and adjusted at pH 8, and was further compared with the standard medium.

Biomass yield and composition after optimization

Biomass yield and biochemical composition of Rhizoclonium sp. were compared between the optimized medium and the standard WHM medium as a control (Table 1). Under optimized medium, biomass productivity significantly increased by 8.6% over the control. A previous study reported protein content in filamentous algae typically ranging from 19.5%dw to 48.8%dw (Rahaman et al. 2025). In the present study, Rhizoclonium sp. showed 31.4%dw protein content in the control, which decreased by 18.4% after optimization (Table 1). Protein reduction in the biomass is advantageous for textile applications, as lower protein content is desirable to prevent yellowing during processing and to improve the final fiber’s durability (Feng et al. 2020; Gibis et al. 2021).

Table 1. Comparison of biomass and biochemical composition of Rhizoclonium sp. cultivated for 21 days under control and optimized conditionsParametersControlOptimizedBiomassYield (g L^−1^)1.11 ± 0.03^a^1.20 ± 0.03^b^Productivity (mg L^−1^ d^−1^)52.76 ± 1.52^a^57.28 ± 1.40^b^ProteinContent (%dw)31.35 ± 0.18^a^25.6 ± 0.44^b^Productivity (mg L^−1^ d^−1^)16.67 ± 0.77^a^14.65 ± 0.44^b^CarbohydratesContent (%)48.9 ± 1.1^a^57.7 ± 0.7^b^Productivity (mg L^−1^d^−1^)26.01 ± 1.01^a^33.08 ± 1.18^b^LipidsContent (%)10.3 ± 0.5^a^9.9 ± 0.19^a^Productivity (mg L^−1^d^−1^)5.49 ± 0.16^a^5.71 ± 0.25^a^Ash content (% dw)6.5 ± 0.1^a^5.7 ± 0.19^b^Series with the same letter for the same measured parameter showed insignificant differences using Tukey test (at P ≤ 0.05)

Carbohydrates represent one of the major biochemical fractions in filamentous algae (Rahaman et al. 2025), making them attractive for both bio-based materials and industrial applications. In the present study, Rhizoclonium sp. cultivated in standard WHM showed that 48.9% of dw were carbohydrates (Table 1). This finding explains the high similarity observed in FTIR analysis as previously discussed, where the spectra of Rhizoclonium sp. closely matched those of starch and cellulose. Other Rhizoclonium strains have been reported to contain 52.6–57.4%dw carbohydrates (Satpati et al. 2015), which is far higher than the carbohydrate levels commonly observed in microalgae (3.3–30.2%dw) and macroalgae (11.6–51.8%dw) (Wang et al. 2020). This high carbohydrate fraction is further complemented by a cell wall structure dominated by crystalline cellulose (up to 86.5%), with approximately 38.6% of the biomass consisting of cellulose (Chao et al. 1999). Such a special composition positions Rhizoclonium sp. as a sustainable raw material for textile fibers. Chemical treatments, such as NaOH or Na_2_SO_4_ during post-harvest cooking processes, can further enhance the carbohydrate fraction. Interestingly, optimization of growth medium enhanced carbohydrate content in Rhizoclonium sp. by 18.0% over the control (Table 1). The enhanced carbohydrate content in Rhizoclonium sp. under optimized conditions reflects carbon metabolism regulation, promoting carbon allocation toward polysaccharides. Such an improvement not only confirms the metabolic plasticity of this species but also indicates that higher carbohydrate accumulation under optimized growth conditions can directly enhance fiber quality. This finding confirms that the reduction in protein content and enhancement of carbohydrates observed under optimized conditions are not solely a dilution effect due to increased biomass but reflects a compositional reorganization of the cellular constituents. However, the mechanistic basis underlying the significant reduction in protein content and increase in carbohydrate accumulation under optimized conditions remains to be elucidated and requires further targeted physiological and molecular investigations.

Plant lipids play important roles in cell physiology and significantly influence the properties of harvested plant material. In higher plants, lipid levels in fibers are known to affect elongation and end-use performance. For instance, total fatty acid content increases during the elongation phase of cotton fibers, i.e. during the growth, and decreases at the mature stage (Wanjie et al. 2005). While excessive lipid accumulation typically reduces cell elongation, a little lipid content can improve fiber functionality. A lipid coating on cotton fibers, for example, enhances their moisture regain, contributing to versatile applications of absorbent textiles (Yang et al. 2021). Compared to conventional terrestrial plant fibers, lipid content in filamentous algae is typically much higher and variable across species. Rhizoclonium sp. cultivated in standard WHM demonstrated a lipid content of 10.3%dw, which showed insignificant difference under optimized WHM (Table 1). The lipid content recorded in the present study falls within the reported range for this genus. Rhizoclonium africanum, for instance, was reported to contain 92.8 mg g^−1^ dw lipids (Satpati et al. 2015), while other filamentous green algae exhibit lipid contents ranging between 78 and 343 mg g^−1^ dw (Rahaman et al. 2025). The relatively high lipid fraction may require pre-extraction prior to textile processing to improve fiber characteristics such as strength and durability. This further underscores the importance of developing integrated biorefinery approaches, in which lipids can be valorized into high-value co-products.

Filamentous green algae typically contain higher ash levels than cotton fibers, which can hinder mechanical spinning and subsequent textile finishing processes (Brushwood and Perkins 1994; Clark and Durrell 2016). Interestingly, Rhizoclonium sp. cultivated in standard WHM exhibited a relatively low ash content of 6.5%dw, which decreased by 14.9% using the optimized WHM (Table 1). For instance, the marine alga Rhizoclonium sp. showed approximately 15.9%dw ash (Chao et al. 1999). The observed reduction in ash content under optimized conditions is likely linked to the physicochemical changes induced by the elevated pH under optimized conditions (Sun et al. 2018; Yu et al. 2022). pH affects mineral solubility and availability, where precipitation of Ca^2+^, Mg^2+^ and their associated anions has been reported under alkaline conditions, partially depleting dissolved minerals from the medium (Yu et al. 2022). A reduced mineral availability might contribute to a shift of cellular metabolism away from mineral-rich components toward carbohydrate-dominated biomass, explaining the decrease in ash with simultaneous increase in carbohydrates. However, transcriptomic analyses are required to elucidate in detail the underlying regulatory networks governing this compositional reorganization. Overall, these findings suggest improved fiber purity under optimized conditions and highlights the potential for further enhancing algae fibers through post-harvest treatments, thereby increasing their suitability for textile applications.

Main fiber properties

Morphology and functional groups

To validate the use of filamentous algae as alternative textile fibers, the study investigated whether the optimized medium affects the fiber structure and strength. It is of great importance as previous studies confirmed that a pH range of 4.0-11.5 showed little effect on the morphology of various algae, such as Chlorella vulgaris and Vischeria magna (Gaysina 2024). SEM revealed no visible morphological changes in the surface structure of the fibers from the control culture and that under optimized conditions (Fig. 6). However, analysis of the functional groups using FTIR showed a notable change (Fig. 6). While most major peaks were similar, a strong peak at 1480 cm^−1^, associated with protein vibrations (amide II band) and certain lipid vibrations (Movasaghi et al. 2008), appeared in the control but was absent in the optimized sample. The significant reduction of this peak under optimized conditions is attributed to the decrease in protein and lipid content as discussed in the previous section. It can be concluded that cultivating Rhizoclonium sp. under optimized conditions not only enhances the biomass yield and preserves the fiber morphology, but might also enhance the chemical structure towards better textile fibers characteristics, which was further examined.

Fig. 6. Morphology as recorded by SEM (upper panel) and FTIR spectra (lower panel) of Rhizoclonium sp. cultivated for 21 days under control and optimized conditions

Mechanical properties

The production of knitted fabrics, in which yarns are formed into flexible looped structures, places specific demands on yarns that are based less on maximum tensile strength and more on flexibility, extensibility, and the properties of the final product (Behery 2010). To comprehensively evaluate the technical suitability of Rhizoclonium sp. fibers, mechanical properties were analyzed for both dry and wet biomass of control and optimized samples (Table 2). Assessing both dry and wet states is critical because fibers undergo different mechanical stresses during processing and end-use (Catarino et al. 2025), particularly during wet finishing operations such as dyeing, washing, and steaming, where wet fiber strength ensures the integrity and performance of the textile.

Table 2. Fiber characteristics of Rhizoclonium sp. cultivated for 21 days under control and optimized conditionsParametersWetDryControlOptimizedControlOptimizedTenacity (cN tex^−1^)2.56 ± 0.6^a^3.08 ± 0.82^b^2.36 ± 0.55^a^2.41 ± 0.61^a^Elongation (Emax, %)3.26 ± 1.41^a^4.88 ± 1.89^a^0.63 ± 0.17^c^0.68 ± 0.24^c^Linear density (dtex)2.54 ± 0.86^a^2.46 ± 0.46^a^2.25 ± 0.26^a^2.60 ± 0.36^a^Series with the same letter for the same measured parameter showed insignificant differences using LSD (at P ≤ 0.05)

Tenacity, which is a known characteristic of cellulose-based fibers (e.g., cotton, hemp) and represents fiber strength, showed a significant increase under optimized conditions, with notable differences between the wet and dry biomass, with higher value for the wet samples (Table 2). The tenacity of the control sample increases from 2.36 cN tex^−1^ (dry) to 2.56 cN tex^−1^ (wet, + 8.5%). This effect is significantly more pronounced in the sample cultivated under optimized conditions, with an increase from 2.41 cN tex^−1^ to 3.08 cN tex^−1^ (+ 27.8%). This increase in wet strength is technologically highly advantageous as it ensures the mechanical integrity of fibers during wet finishing processes (Clark 2011). However, in the context of established natural fibers, the absolute strength of the algal fiber is still to be considered low compared to conventional fibers. For instance, commercial cotton fibers reach values of 20–35 cN tex^−1^, whereas high-performance fibers like flax can reach 20–65 cN tex^−1^ and can rise to even 105–120% of their tenacity in the wet state (Elmogahzy and Farag 2018). Although the absolute tenacity of Rhizoclonium fibers remains lower than that of established natural fibers, this limitation does not exclude the practical use of this novel aquatic fibers. In many functional and technical textile applications, properties such as moisture management, comfort, and breathability are equally or more important than maximum tensile strength. In this context, Rhizoclonium fibers are particularly attractive as functional blend components, where a conventional carrier fiber provides mechanical stability while the algal fibers impart unique hygroscopic and surface-related functionalities. Future research might focus on strategies to enhance algal fiber strength, including algae screening and cultivation for thicker and more crystalline cellulosic cell walls, modulation of cultivation parameters to influence cell wall architecture and microfibril orientation, post-harvest physical or mild chemical treatments to increase microstructural cohesion, and genetic approaches targeting key pathways in cellulose biosynthesis and cell wall assembly.

Corresponding to the strength, a clear trend is also observed for elongation (Table 2). Consistent with the behavior of cellulose fibers, water absorption leads to significantly increased elongation. The elongation of the control sample significantly increased from 0.63% in the dry sample to 3.26% in the wet samples. For the optimized sample, this increase was even more pronounced, rising from 0.68% to 4.88% by wetting. This is attributed to the plasticizing effect of water, which weakens the intermolecular hydrogen bonds between the cellulose chains and increases their mobility (Miyake et al. 2000). This wet elongation is valuable for textile processing as it implies greater deformability and a lower propensity for breakage during wet process stages.

The linear density, which indicates the mass per unit length of the fiber, remained statistically unchanged between control and optimized conditions in both wet and dry states. Values ranged between 2.25 and 2.60 dtex, suggesting that the optimization process did not substantially alter filament thickness or diameter. This stability is advantageous for potential textile applications, ensuring consistent fiber morphology while improving mechanical strength. In summary, the mechanical tests confirmed that the optimization of cultivation conditions resulted in fibers with better technological properties. The significant increase in wet strength and wet elongation, combined with the strong swelling behavior, indicates a more highly ordered and stable microstructure of the fiber walls, induced by the optimized conditions.

Moisture regain capacity

Moisture regain is a crucial property for wearing comfort, processability, and antistatic performance of textile fibers. The present results indicate that Rhizoclonium fibers possess a high moisture regain capacity, surpassing that of commonly used plant-based textile fibers (Table 3). The standard and optimized media showed insignificant differences in moisture regain (12.14 and 11.61%, respectively). However, algae fibers exhibited more than twice moisture regain of cotton (5.50%) and ˃34% of lyocell (8.62%). These findings suggest that the intrinsic morphology and biochemical composition of Rhizoclonium fibers contribute to superior hygroscopic behavior compared to established natural fibers. Specifically, the reduction in protein (-18.4%) and ash (-14.9%) contents together with an increase in total carbohydrates (+ 18.0%), indicates a shift toward a more cellulose-dominated biomass. The previously discussed FTIR analysis further supported this, showing the disappearance of the amide/lipid-associated peak under optimized conditions . Interestingly, despite a relatively higher lipid content compared to cotton, Rhizoclonium sp. fibers exhibited higher moisture regain, which may be attributed to the localization of lipids predominantly in the cytosol rather than within the cell wall, a hypothesis that requires further validation. Mechanistically, the exceptional moisture regain of Rhizoclonium fibers can be attributed to the architecture of the cell wall. Unlike cotton, which is dominated by highly crystalline cellulose limiting water accessibility, green algae cell walls are composite structures with cellulose microfibrils embedded in an amorphous matrix of hydrophilic polysaccharides (Michalak and Messyasz 2020; Fuertes-Rabanal et al. 2025). These amorphous regions contain abundant hydroxyl and carboxyl groups, preventing tight packing of cellulose fibrils. This can be confirmed from the FTIR spectra, where a strong broad O-H stretching band (3600 –3000 cm^−1^) and pronounced polysaccharide-associated vibrations in the 1200 –900 cm^−1^ region were recorded (Fig. 6), indicating highly accessible hydrophilic functional groups. Together, the compositional shift toward carbohydrates and the accessible polysaccharide-rich cell wall matrix in the optimized growth medium could enhance the hydrogen bonding, swelling behavior, and load transfer within the fiber matrix, explaining the observed improvements in elongation and moisture regain. Such a high moisture regain is an outstanding and unique characteristic, indicating an unparalleled potential for wearing comfort and breathability.

Table 3. Comparison of moisture regain (MR, %) of Rhizoclonium sp. cultivated for 21 days under control and optimized conditions with other conventional cellulosic fibersFibers MR Experimental

MR Literature ReferencesRhizoclonium sp. (Control)12.14 ± 0.27^a^ na This studyRhizoclonium sp. (Optimized)11.61 ± 0.70^a^ na This studyCotton5.50 ± 0.50^b^5.25–6.52(Adamu and Gao 2022)Lyocell8.62 ± 0.07^c^9.23(Okubayashi et al. 2004)Values in the same column with the same letter showed insignificant differences using LSD (at P ≤ 0.05)MR is measured at 65% relative humidityna Not available

Overall, the optimized Rhizoclonium fibers not only compete with performance of comfort fibers but even surpasses them in terms of moisture management. This property predestines it as a specialty material for textiles where maximum moisture absorption is required, such as in performance sportswear, functional textiles, or special hygiene and medical products. Future work should focus on optimizing Rhizoclonium sp. cultivation to maximize fiber yield and functional properties, while investigating the structural and biochemical factors that govern moisture regain, elongation, and tenacity. Scaling up through pilot- and industrial-scale production together with textile processing and product development are essential to evaluate economic feasibility and environmental impact, ensuring a sustainable fiber supply. Additionally, incorporating natural bioactive compounds from the algae could enable multifunctional fabrics with antimicrobial, antioxidant, or UV-protective features.

Conclusions

The present study demonstrated that filamentous freshwater algae, specifically Rhizoclonium sp., can serve as a sustainable and versatile alternative to traditional textile fibers. Through targeted strain selection and optimized cultivation, both biomass yield and crucial fiber properties were significantly enhanced, including a notable increase in carbohydrate content and reductions in proteins and ash. These improvements were accompanied with fibers having outstanding moisture regain (~ 12%), exceeding cotton and high-performance fibers like lyocell, as well as acceptable wet strength and elongation. The folded surface morphology of algae fibers retains flexibility and promotes cohesion, making it suitable for yarn production, breathable fabrics, and innovative binder-free nonwovens. Aquatic algae fibers have the potential for new generation of high-comfort, functional, and eco-friendly textiles. Future research is required to evaluate the scale-up cultivation, integrate biorefinery approaches for maximal resource utilization, and thoroughly evaluate processing at pilot- and industrial-scale.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary Material 1

Supplementary Material 2

Supplementary Material 3