Microalgae are robust microorganisms with versatile metabolic functions, including oxygen generation, making them crucial components in wastewater treatment plants, food production, or extraterrestrial life-support systems. Immobilizing microalgae in hydrogels could eliminate costly separation steps required in free-floating cultivation. Volumetric bioprinting (VBP), enabling rapid fabrication of large, complex constructs from cell-laden hydrogels, presents a promising solution. This study investigates the possibilities and limitations of VBP with microalgae in poly(ethylene glycol) diacrylate-cellulose nanofibrils (PEGDA-CNF) hydrogels. Despite chlorophyll-induced interference, the printing of stable 3D structures is achievable in high-resolution up to certain cell densities. During cultivation, printed microalgae exhibited exceptionally high viability and cell density compared to alternative bioprinting methods, and their photosynthetic efficiency remained high even in the nonphysiological PEGDA-CNF environment, as confirmed by pulse-amplitude modulated fluorometry and oxygen measurements. This work demonstrates the feasibility of integrating microalgae into VBP, enabling scalable production of photosynthetically active geometries and significantly simplifying their implementation in cascade-based processes.

Biphasic scaffolds that integrate bioactive ceramics with biodegradable polymers hold considerable potential for bone regeneration, but they present challenges in terms of interfacial integration and processability. In this study, biphasic scaffolds consisting of alternating strands of strontium-modified calcium phosphate cement (SrCPC) and poly(l-lactide-co-glycolide) (PLLA-PGA) were successfully fabricated using an optimized extrusion-based 3D printing and postprocessing protocol. Degradation studies in water showed that the presence of the SrCPC phase in the biphasic scaffolds buffered the acidic degradation products of PLLA-PGA, delaying and attenuating the pH drop over time and influencing the degradation of the polymer phase. Uniaxial compression tests revealed intermediate mechanical properties of the biphasic compared to monophasic PLLA-PGA and SrCPC scaffolds, which declined over the 24-week observation period. Aging experiments in cell culture medium under near-physiological conditions indicated a significant mutual influence of the two materials, as evidenced by an altered strontium and phosphate ion release profile from the SrCPC phase and the formation of a different surface structure on the materials in the biphasic system compared to the monophasic system. This was also reflected by the cellular response of osteoblast-like SaOS-2 cells, showing a local heterogeneity in cell-material interactions. Nevertheless, the cell experiments demonstrated the strong positive effect of the bioactive SrCPC component in the biphasic scaffolds on cell proliferation and alkaline phosphatase activity, which were significantly higher than those in the monophasic PLLA-PGA scaffolds.

To achieve bone regeneration in critical size defects, filling of the defect either with autologous bone or with a biodegradable bone substitute material possessing osteoconductivity and osteoinductivity is required. Biomimetically mineralized collagen is a nanocomposite material that closely resembles the natural bone matrix in composition and structure and has proven potential for filling bone defects. Since the mineral phase hydroxyapatite can bind proteins, the aim of the present study was to explore this biomaterial as a delivery system for the osteoinductive factor bone morphogenetic protein-2 (BMP-2) and to investigate the dependence of BMP-2 release on the mineral content. Three-dimensional scaffolds with varying mineral content were prepared by blending biomimetically mineralized collagen and non-mineralized collagen suspensions, followed by freeze-drying and chemical crosslinking. While the average pore size decreased, the stiffness of the scaffolds increased with increasing mineral content; all scaffold variants exhibited a fundamentally elastic behavior. After loading, the release of BMP-2 was investigated over 28 days. A significant influence of the mineral content on the release kinetics of BMP-2 was observed—the higher the mineral content, the stronger the retention of BMP-2 in the scaffolds. In contrast, the release of the vascular growth factor-A (VEGF-A), which was examined for comparison, was hardly influenced by the mineral content, indicating a low retention of VEGF-A by binding to the mineral phase. In summary, adjustment of the mineral content opens up the possibility of controlling the release of BMP-2 in a customized manner, but this is not transferable to VEGF-A.

BACKGROUND:Localized biofilm-associated infections such as chronic wounds, osteomyelitis, and implant infections remain difficult to treat with systemic antibiotics amid rising resistance. Hydrogel delivery may enhance bacteriophage (phage) therapy by protecting phages, prolonging residence, and enabling controlled release. This systematic review summarizes in vivo evidence for hydrogel-mediated phage delivery and its translational relevance. METHODS:Following PRISMA 2020, PubMed, Web of Science were searched to 14 January 2026 using MeSH terms for bacteriophages, hydrogels/local delivery, and in vivo or clinical applications. Eligible studies reported original in vivo animal or human data; in vitro-only work was excluded. RESULTS:Nineteen studies met criteria: three clinical and sixteen preclinical. Clinical use included fracture-related, burn wound, and prosthetic joint infections treated with commercially available phage preparations in hydrogels. In a single compassionate-use fracture-related infection case managed with concurrent surgical debridement and systemic antibiotics, infection control without recurrence and good bone healing were observed at one year; locally applied phages remained detectable for approximately 72 h, indicating in vivo release and surgical compatibility, although the independent contribution of the hydrogel-phage component could not be isolated. Preclinical studies tested 28 phages against six bacterial species via topical, injected, intraoperative, oral, or irrigation delivery. Consistent benefits occurred in burn (n = 6) and wound/soft-tissue models (n = 5) with lower bacterial load, improved healing, and increased survival in two burn studies. Bone/joint models (n = 4) showed partial reduction but inconsistent eradication. Other studies demonstrated ~2000-fold pathogen reduction in colitis and decreased bacterial and inflammatory markers in endodontic infection. CONCLUSIONS:Hydrogel-based local phage therapy is a feasible strategy for infection control No major adverse effects were reported in the included studies, although safety reporting was limited. Standardized in vivo comparisons and clinical trials are needed to optimize delivery and dosing.

Type 1 diabetes mellitus (T1D) is characterized by the autoimmune destruction of pancreatic beta cells, leading to insulin deficiency and necessitating lifelong external insulin administration. The transplantation of allogenic islets is a promising therapeutic approach, whereby their macro-encapsulation offers immune protection but restricts oxygenation after transplantation. This study addresses the challenge of oxygen supply by developing a spatially structured co-culture system using bioprinting, in which both pancreatic islets and the photosynthetically active microalga Scenedesmus sp. are embedded in alginate-based hydrogels. Key environmental parameters for long-term co-cultivation were developed and systematically optimized: red light illumination was identified as non-detrimental to islet viability and function while supporting microalgal photosynthesis at the same time, and a co-culture medium was formulated to fulfill the metabolic requirements of both cell types. In direct co-culture experiments under hypoxic conditions, microalgae generated sufficient oxygen to maintain normoxic conditions, thereby preserving islet viability and glucose-stimulated insulin secretion over several days. The results demonstrate that spatially organized bioprinting enables the close proximity of islets and microalgae, facilitating effective oxygen transfer in vitro. This work establishes a robust framework for functional mammalian-microalgae co-cultures, optimizing conditions to reliably maintain cell health and function through photosynthetically generated oxygen.

Large segmental mandibular defects remain difficult to reconstruct, and patient-specific biodegradable scaffolds produced by additive manufacturing may offer an alternative to permanent alloplastic implants. This exploratory study evaluated three 3D-printed poly(DL-lactide) (PDLLA)-based implant configurations in a periosteum-preserving minipig mandibular defect model: PDLLA, PDLLA containing 10 wt% strontium-modified hydroxyapatite microparticles (PDLLA + SrHAp-P), and a biphasic PDLLA-shell/SrHAp-core implant (PDLLA/SrHAp-C). Twelve adult minipigs received patient-specific implants and titanium reconstruction plates (n = 4 per group). Bone formation was monitored by digital volume tomography and sequential fluorochrome labeling for 6 months; one animal per group underwent non-terminal follow-up to 14 months. Complications occurred in 11 of 12 animals and included dehiscence, abscess or fistula formation, implant swelling, screw loosening, and fracture or displacement of the SrHAp core. Bone bridging was radiographically observed in all animals by 6 months, including an animal in which the implant had been removed prematurely, indicating a major contribution of the preserved periosteum and host tissues. New bone formed mainly around, rather than within, the implants. Implant-associated bone ingrowth was observed only in the biphasic group, but was not a uniform finding and fibrous encapsulation was frequent. The 3 animals followed to 14 months showed continued consolidation without terminal sacrifice. These findings identify degradation-associated tissue reactions, dimensional instability, soft-tissue coverage, and construct mechanics as major limitations of large PDLLA-based mandibular implants. The biphasic architecture showed a potentially favorable local osteointegration pattern, but the small sample size and high complication rate preclude claims of efficacy or superiority. Further optimization of polymer content, ceramic architecture, porosity, mechanical stability, and soft-tissue management is required before additional translational studies.

Combining the volumetric fabrication of hydrogel constructs using extrusion bioprinting with highly precise drop-on-demand (DoD) bioprinting offers exciting opportunities in biofabrication. This technical report presents a technique in which a solenoid micro-pipette is operated as an additional tool in an extrusion (bio)printing system to deposit small volumes of bioinks into extrusion-printed hydrogel constructs. Using three exemplary approaches, we show that this enables the patterned placement of cells or growth factors within 3D constructs and thus influences developmental processes. Human cells within low-viscosity bioinks, deposited into extrusion-printed hydrogel constructs by filling inter-strand cavities or by injection into the hydrogel strands, maintained their viability and functionality up to 28 days. As demonstrated for salivary gland cells, the properties of the hydrogel matrix can influence the fate of the injected cells: In a stiff alginate (Alg)-based hydrogel, they formed aggregates, which is beneficial for organoid formation, and in softer hydrogels, they migrated to neighboring cell clusters. Locally injected signaling factors such as vascular endothelial growth factor (VEGF) attracted endothelial cells and fibroblasts, which migrated into previously cell-free hydrogel areas. The combination of extrusion and DoD bioprinting opens new approaches to integrate different cell types and functionalizations in one construct, facilitating the creation of more complex and dynamic models.

The development of mechanically robust, cell-instructive, and seweable small-diameter (≤ Ø 6 mm) tubular scaffolds remain a major challenge in vascular tissue engineering. Here, a hybrid biofabrication strategy is presented that combines 4D printing of alginate-methylcellulose (AlgMC) hydrogels with melt electrowritten (MEW) poly(ε-caprolactone) (PCL) reinforcement to produce tubular constructs with programmable shape-morphing capacity. The MEW fiber meshes significantly improve mechanical integrity, enabling suturing and perfusion, while preserving the anisotropic swelling behavior required for morphogenesis. Scaffold functionalization using human blood-derived protein coatings — such as fresh frozen plasma, platelet lysate, and fibrinogen — markedly enhances cellular adhesion and fibroblast proliferation without compromising structural transformation. Biological evaluation using mono and co-cultures of fibroblasts, endothelial cells (HUVEC), and vascular smooth muscle cells (vSMC) reveals the formation of organized bi-layers and phenotype-specific cell morphologies on AlgMC/PCL composites. Notably, a confluent endothelial layer promotes contractile marker expression in vSMC, while vSMC support endothelial coverage in the absence of a growth-arrested fibroblast feeder layer, indicating reciprocal stabilization. While further optimization is needed to meet the demands of small-diameter vascular grafts fully, the presented system offers a versatile and promising platform for engineering soft tissue constructs that benefit from topographical guidance, spatially controlled adhesion, and adaptive geometry.

Ideally, the combination of clinical imaging techniques with additive manufacturing processes enables the fabrication of patient-specific regenerative implants that precisely fit into the defect site, promoting native tissue restoration while gradually degrading. Osteochondral defects, affecting both cartilage and subchondral bone in joints are best visualized using magnetic resonance imaging (MRI). In this study, a workflow for computer-aided manufacturing of patient-specific osteochondral implants based on geometrical data obtained from MRI scans was evaluated in a clinically relevant setting. Artificial osteochondral defects were created in femoral condyles of human body donors and scanned with MRI. 'Computer-Aided Design' (CAD) models for bone and cartilage components served as basis for designing defect-specific trizonal implants consisting of (i) a bone, (ii) an interlocking, and (iii) a cartilage zone. These implants were fabricated using multi-channel 3D extrusion printing, using a calcium phosphate cement as a bone substitute and an alginate-based hydrogel as a cartilage substitute material - with both materials alternately printed in the interlocking zone. After fabrication, the constructs were implanted into the corresponding defects, and assessed for fit accuracy via clinical imaging. The entire process chain was successfully conducted under near-clinical conditions by an interdisciplinary team of engineers, radiologist and surgeons, during which critical points were identified. Due to the inherent resolution limitations of clinical MRI and extrusion-based 3D printing, inaccuracies in implant fitting occurred; strategies to address these challenges were identified by integrating design tolerances and applying minor intraoperative adjustments.

Multiple drug-resistant bacteria are a growing life-threatening problem and novel treatment strategies are urgently needed. One promising option is the use of lytic bacteriophages, viruses that infect and kill bacteria with high specificity. To efficiently utilize bacteriophage therapy for the treatment of implant-associated infections, an effective strategy for the local, long-lasting administration of bacteriophages at the site of infection is required. With the aim of developing a defined delivery system, this study investigates the feasibility of 3D extrusion printing of bacteriophages embedded in biomaterial inks by using a Staphylococcus aureus-specific phage strain as model. It is demonstrated that a bacteriophage-loaded hydrogel blend consisting of alginate and methylcellulose (AlgMC) can be printed with high shape fidelity. After cross-linking, the hydrogel constructs release bacteriophages that maintain their activity against S. aureus over a period of 35 days when incubated in human-plasma-like medium (HPLM). The integration of the nanoclay Laponite into the AlgMC blend, known for its high binding capacity for biomolecules, does not further prolong the release under (near) physiological conditions in HPLM but may protect bacteriophages under nonphysiological conditions. In conclusion, bacteriophage-loaded AlgMC inks fulfill the requirements for local bacteriophage therapy as they release active bacteriophages in a sustained manner.

The kidneys are vital for maintaining bodily homeostasis and are susceptible to various diseases that disrupt their function. Traditionally, research on kidney diseases has relied on animal models and simplistic two-dimensional cell cultures, which do not fully replicate human tissue pathology. To address this, recent advances focus on developing advanced 3D biomimeticin vitromodels using human-derived cells. These models mimic healthy and diseased kidney tissues with specificity, replicating key elements like glomerular and tubular structures through tissue engineering. By closely mimicking human physiology, they provide a promising platform for studying renal disorders, drug-induced nephrotoxicity, and evaluating new therapies. However, the challenges include optimizing scalability, reproducibility, and long-term stability to enhance reliability in research and clinical applications. This review highlights the transformative potential of 3D biomimeticin vitrokidney models in advancing biomedical research and clinical applications. By focusing on human-specific cell cultures and tissue engineering techniques, these models aim to overcome the limitations of conventional animal models and simplistic 2D cell cultures. The review discusses in detail the various types of biomimetic kidney models currently under development, their specific applications, and the innovative approaches used to construct them. It also addresses the challenges and limitations associated with these models for their widespread adoption and reliability in research settings.

3D extrusion bioprinting, a promising and widely adopted technology in the emerging field of biofabrication, has gained considerable attention for its ability to fabricate hierarchically structured, native-mimicking tissue substitutes with precisely defined cell distributions. Despite notable advancements, the limited availability of suitably bioactive bioinks remains a major challenge, hindering the construction of volumetric tissue substitutes effectively mimicking biological functionality. Therefore, this work proposes a protein-rich, low-cost, bioactive bioink: abundantly available eggwhite powder (EWP) is leveraged to functionalize an alginate-methylcellulose (AlgMC) hydrogel matrix and enhance cellular response. The developed EWP-supplemented bioinks not only maintain favorable printability and high shape fidelity but also exhibit remarkable bioactivity. Notably, incorporating EWP into AlgMC-based bioinks enhances shear-thinning features, thereby improving the viability of encapsulated cells within the bioprinted constructs. The versatility and biofunctionality of EWP in bioprinted constructs are demonstrated using three distinct cell types, encompassing sources such as a stem cell line, human soft skin, and stiff bone tissues. Furthermore, the promising and wide applicability of the EWP-supplemented bioink for biofabrication is demonstrated exemplarily in core-shell and multi-channel bioprinting strategies as a proof-of-concept for functional tissue construction. These findings underscore the significant and versatile potential of this novel bioink in biofabrication and biomedical applications.

Calcium phosphate cements (CPC) are widely used materials for filling bone defects and bone augmentation. Developments in CPC formulations have led to a practically unlimited processability, allowing to use these formulations for new fabrication methods like extrusion-based 3D-printing. This study shows the application of INNOTERE 3D scaffolds, printed from a CPC paste and allowed to set, for open wedge high tibial osteotomy. It is the first time that a 3D-printed, certified medical device in this product class is used in a routine clinical application. The objective of this retrospective clinical evaluation is to assess the safety and clinical performance in regards to bone healing, osteointegration and resorption. In comparison to the also commercially available OSferion, a conventional, sintered ceramic, the 3D-printed scaffolds show no inferiority. This marks the first time that such a 3D-printed medical product is used in a broad evaluation regarding its clinical outcome.

Bioprinting, a technology with the potential to support long-term space missions, offers medical solutions for human settlements on the Moon and Mars. Moreover, 'green bioprinting' presents a promising approach to address terrestrial environmental challenges. Effective and cost-efficient implementation of this technology beyond the Earth requires leveragingin situresources on celestial bodies. Consequently, this study examines the integration of Lunar and Martian regolith into bioprintable hydrogels as mechanically stabilizing and protective components as well as nutrient sources. Hydrogel blends composed of alginate and methylcellulose were supplemented with regolith simulants. Rheological characterization revealed maintenance of shear thinning and shear recovery properties, ensuring optimal printability. In regards to cultivation of microalgae, the ion release/uptake of the regolith simulants in culture medium was investigated, indicating that regolith has potential to serve as nutrient source. The microalgaChlorella vulgarisand bacteriaButtiauxella sp. MASE-IM-9 andSalinisphaera shabanensiswere bioprinted in regolith-based inks. Results demonstrate that the microalgae maintained their photosynthetic efficiency in regolith-containing bioinks during cultivation, exhibiting high viability and growth. The bacteria exhibited an enhanced resistance to desiccation as well as temperature and radiation stress when regolith simulants were present in the hydrogels. This study confirms the feasibility of employing Lunar and Martian regolith simulants in bioinks for green bioprinting and bacterial bioprinting. Such an approach could minimize the volume of stored printing materials and culture media, optimizing rocket transport capacity.

A promising therapeutic option for the treatment of critical-size mandibular defects is the implantation of biodegradable, porous structures that are produced patient-specifically by using additive manufacturing techniques. In this work, degradable poly(DL-lactide) polymer (PDLLA) was blended with different mineral phases with the aim of buffering its acidic degradation products, which can cause inflammation and stimulate bone regeneration. Microparticles of CaCO3, SrCO3, tricalcium phosphates (α-TCP, β-TCP), or strontium-modified hydroxyapatite (SrHAp) were mixed with the polymer powder following processing the blends into scaffolds with the Arburg Plastic Freeforming 3D-printing method. An in vitro degradation study over 24 weeks revealed a buffer effect for all mineral phases, with the buffering capacity of CaCO3 and SrCO3 being the highest. Analysis of conductivity, swelling, microstructure, viscosity, and glass transition temperature evidenced that the mineral phases influence the degradation behavior of the scaffolds. Cytocompatibility of all polymer blends was proven in cell experiments with SaOS-2 cells. Patient-specific implants consisting of PDLLA + CaCO3, which were tested in a pilot in vivo study in a segmental mandibular defect in minipigs, exhibited strong swelling. Based on these results, an in vitro swelling prediction model was developed that simulates the conditions of anisotropic swelling after implantation.

One of the biggest challenges in tissue engineering and regenerative medicine is to ensure oxygen supply of cells in the (temporary) absence of vasculature. With the vision to exploit photosynthetic oxygen production by microalgae, co-cultivated in close vicinity to oxygen-consuming mammalian cells, we are searching for culture conditions that are compatible for both sides. Herein, we investigated the impact of long-term illumination on mammalian cells which is essential to enable photosynthesis by microalgae: four different cell types—primary human fibroblasts, dental pulp stem cells, and osteoblasts as well as the murine beta-cell line INS-1—were continuously exposed to warm white light, red or blue light over seven days. We observed that illumination with red light has no adverse effects on viability, metabolic activity and growth of the cells whereas exposure to white light has deleterious effects that can be attributed to its blue light portion. Quantification of intracellular glutathione did not reveal a clear correlation of this effect with an enhanced production of reactive oxygen species. Finally, our data indicate that the cytotoxic effect of short-wavelength light is predominantly a direct effect of cell illumination; photo-induced changes in the cell culture media play only a minor role.

The co-cultivation of mammalian cells with microalgae is an innovative concept to overcome one major limitation in tissue engineering and regenerative medicine: shortage of oxygen. Under illumination, photosynthetically active microalgae can produce oxygen, consequently increasing the potential construct dimension. In such co-cultures, mammalian cells are exposed to light, which does not reflect their natural conditions and can negatively influence their viability and functionality. In this study, 3D extrusion bioprinted pancreatic murine Islets of Langerhans should be co-cultivated with the bioprinted green microalgae species Scenedesmus sp. to improve the oxygen supply of the Islets in a potential insulin-producing implant. After defining the microalgae partner and a suitable co-culture medium that supported the functionality of both cell types, the focus was put on the effects of long-term red, blue and white light illumination on this system. First, the direct influence of light of different wavelengths on both microalgae and different mammalian cell types was investigated to find an ideal illumination regime, followed by an investigation into the influence of light on the culture medium. It was found that long-term exposure to blue or white light is detrimental to mammalian cells itself as well as the medium, while long-wave light has no effect on the function of mammalian cells. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the CIRP BioM 2024

In vitro liver models are pivotal in early drug development as they serve in assessing drug toxicity. Currently, most of the liver models include static cultures of liver derived cell spheroids. Mimicking dynamic conditions (similar to native liver - such as blood flow, glucose gradients etc.) in in vitro liver models would be essential for studying drug induced liver injury (DILI). The current work investigated and developed a simple bioink composed of gelatin and alginate blends (GA) that can be used to 3D bioprint hepatocyte laden scaffolds, serving as an in vitro liver model for drug toxicity assays. Rheological evaluation (using a rotary rheometer) of various compositions of GA blends was performed to assess their printability with an extrusion bioprinter. Suitable GA compositions with human liver carcinoma cells (HepG2) were 3D bioprinted. The scaffolds were stabilized by crosslinking the alginate (using calcium chloride) and gelatin (using microbial transglutaminase). Cell viability and proliferation of HepG2 in bioprinted scaffolds was assessed for 28 days. Further work includes fabrication of HepG2 laden hollow tubes and colonization of inner lumen with human umbilical vein endothelial cells (HUVEC), followed by DILI studies in long-term perfusion culture. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

Calcium phosphate cements (CPC) and mesoporous bioactive glasses (MBG) are two well studied biomaterial groups widely under investigation on their applicability to treat bone defects in orthopaedics and maxillofacial surgery. Recently the extrusion properties of CPC-MBG composites using a pasty CPC based on a hydrophobic carrier-liquid were studied in our group demonstrating that such composites are suitable for low temperature 3D plotting. Based on this work, we show in this study that by variation of the MBG content in the composite the degradation of the final scaffolds can be influenced. Furthermore, by modifying the cement phase and/or the MBG with therapeutically active ions like strontium, the released ion concentration can be varied over a wide range. In a second step the MBG was functionalized exploiting the high specific surface area of the glass as a carrier system for proteins like lysozyme or grow factors. We developed a protocol that allows the incorporation of protein-laden MBG in CPC pastes without impairing the extrudability of the CPC-MBG composites. Additionally, we found that released proteins from pure MBG or 3D plotted composite-scaffolds maintained their biological activity. Therefore, the combination of CPC and MBG allows the creation of a highly flexible composite system making it a promising candidate for bone tissue engineering.