How to Determine a Suitable Alginate for Biofabrication Approaches using an Extensive Alginate Library?

Alginate-based hydrogels are a promising class of biomaterials due to their usability, biocompatibility, and high water-binding capacity which is the reason for their broad use in biofabrication. One challenge of these biomaterials is, however, the lack of cell adhesion motifs. This drawback can be overcome by oxidizing alginate to alginate dialdehyde (ADA) and by subsequent cross-linking with gelatin (GEL) to fabricate ADA-GEL hydrogels, which offer improved cell-material interactions. The present work investigates four pharmaceutical grade alginates of different algae sources and their respective oxidized forms regarding their molecular weight and M/G ratio using 1H NMR spectroscopy and gel permeation chromatography. In addition, three different methods for determining the degree of oxidation (% DO) of ADA, including iodometric, spectroscopic, and titration methods, are applied and compared. Furthermore, the aforementioned properties are correlated with the resulting viscosity, degradation behavior, and cell-material interactions to predict the material behavior in vitro and thus choose a suitable alginate for an intended application in biofabrication. In the framework of the present work, easy and practicable detection methods for the investigations of alginate-based bioinks were summarized and shown. In this regard, the success of oxidation of alginate was confirmed by the three aforementioned methods and was further proven by solid-state 13C NMR, for the first time in the literature, that only guluronic acid (G) was attacked during the oxidation, leading to the formation of hemiacetals. Furthermore, it was shown that ADA-GEL hydrogels of alginates with longer G-blocks are more suitable for long-term experiments due to their stability over an incubation period of 21 days, while ADA-GEL hydrogels of alginates with longer mannuronic acid (M)-blocks are more suitable for short-term applications such as sacrificial inks due to their extensive swelling and subsequent loss of shape. Finally, it was proven that the M/G ratio did not show any influence on the biocompatibility or printability of the investigated alginate-based hydrogels. The physicochemical findings provide an alginate library for tailored application in biofabrication.

Reinforced Hyaluronic Acid-Based Matrices Promote 3D Neuronal Network Formation.

3D neuronal cultures attempt to better replicate the in vivo environment to study neurological/neurodegenerative diseases compared to 2D models. A challenge to establish 3D neuron culture models is the low elastic modulus (30-500 Pa) of the native brain. Here, an ultra-soft matrix based on thiolated hyaluronic acid (HA-SH) reinforced with a microfiber frame is formulated and used. Hyaluronic acid represents an essential component of the brain extracellular matrix (ECM). Box-shaped frames with a microfiber spacing of 200 µm composed of 10-layers of poly(ɛ-caprolactone) (PCL) microfibers (9.7 ± 0.2 µm) made via melt electrowriting (MEW) are used to reinforce the HA-SH matrix which has an elastic modulus of 95 Pa. The neuronal viability is low in pure HA-SH matrix, however, when astrocytes are pre-seeded below this reinforced construct, they significantly support neuronal survival, network formation quantified by neurite length, and neuronal firing shown by Ca2+ imaging. The astrocyte-seeded HA-SH matrix is able to match the neuronal viability to the level of Matrigel, a gold standard matrix for neuronal culture for over two decades. Thus, this 3D MEW frame reinforced HA-SH composite with neurons and astrocytes constitutes a reliable and reproducible system to further study brain diseases.

Targeted Printing of Cells: Evaluation of ADA-PEG Bioinks for Drop on Demand Approaches.

A novel approach, in the context of bioprinting, is the targeted printing of a defined number of cells at desired positions in predefined locations, which thereby opens up new perspectives for life science engineering. One major challenge in this application is to realize the targeted printing of cells onto a gel substrate with high cell survival rates in advanced bioinks. For this purpose, different alginate-dialdehyde-polyethylene glycol (ADA-PEG) inks with different PEG modifications and chain lengths (1-8 kDa) were characterized to evaluate their application as bioinks for drop on demand (DoD) printing. The biochemical properties of the inks, printing process, NIH/3T3 fibroblast cell distribution within a droplet and shear forces during printing were analyzed. Finally, different hydrogels were evaluated as a printing substrate. By analysing different PEG chain lengths with covalently crosslinked and non-crosslinked ADA-PEG inks, it was shown that the influence of Schiff's bases on the viscosity of the corresponding materials is very low. Furthermore, it was shown that longer polymer chains resulted in less stable hydrogels, leading to fast degradation rates. Several bioinks highly exhibit biocompatibility, while the calculated nozzle shear stress increased from approx. 1.3 and 2.3 kPa. Moreover, we determined the number of cells for printed droplets depending on the initial cell concentration, which is crucially needed for targeted cell printing approaches.

Dual setting brushite-gelatin cement with increased ductility and sustained drug release.

A novel dual setting brushite-gelatin cement was achieved by genip ininitiated cross-linking of gelatin during cement setting. Although the combination of an inorganic and organic phase resulted in a decrease of the compressive strength from about 10 MPa without polymeric phase to 3-6-MPa for gelatin modified composites, an increase in elastic properties due to the gelatin hydrogel with a concentration of 10.0 w/v% was achieved. For a powder-to-liquid ratio of 2.5 g*mL-1, a shift of initial maximum stress value during compression testing was observed up to 5% deformation and tested samples showed a pseudo-ductile fracture behavior. The obtained composites of the different formulations were characterized regarding phase composition, porosity as well as drug loading capacity with rifampicin and vancomycin. For the latter, a sustained and prolonged release was realized with a drug release profile according to the Higuchi model and a release exponent of n = 0.5 for the formulation with a PLR of 2.5 g*mL-1 and an incorporation of 10.0 w/v% gelatin.

Oxidized Hyaluronic Acid-Gelatin-Based Hydrogels for Tissue Engineering and Soft Tissue Mimicking.

Hydrogels are ideal materials for mimicking and engineering soft tissue. Hyaluronic acid is a linear polysaccharide native to the human extracellular matrix. In this study, we first develop and characterize two hydrogel compositions built from oxidized HA and gelatin with and without alginate-di-aldehyde (ADA) crosslinked by ionic and enzymatic agents with potential applications in soft tissue engineering and tissue mimicking structures. The stability under incubation conditions was improved by adjusting crosslinking times. Through large-strain mechanical measurements, the hydrogels' properties were compared to human brain tissue and the samples containing ADA revealed similar mechanical properties to the native tissue specimens in cyclic compression-tension. In vitro characterization demonstrated a high viability of encapsulated mouse embryonic fibroblasts and a spreading of the cells in case of ADA-free samples. Impact statement Brain mimicking materials are required in several medical and industrial fields for the development of safety gear, testing of medical imaging techniques, surgical training, tissue engineering, and modeling of the mechanical behavior of tissues. The materials must resemble the microstructure, chemistry, and mechanical properties of the native tissue extracellular matrix while being adjustable in degradation to suit the various applications. In this article, different methods are used to evaluate a novel hydrogel material and its suitability as brain mimicking matrix.

Tethered TGF-ß1 in a Hyaluronic Acid-Based Bioink for Bioprinting Cartilaginous Tissues.

In 3D bioprinting for cartilage regeneration, bioinks that support chondrogenic development are of key importance. Growth factors covalently bound in non-printable hydrogels have been shown to effectively promote chondrogenesis. However, studies that investigate the functionality of tethered growth factors within 3D printable bioinks are still lacking. Therefore, in this study, we established a dual-stage crosslinked hyaluronic acid-based bioink that enabled covalent tethering of transforming growth factor-beta 1 (TGF-ß1). Bone marrow-derived mesenchymal stromal cells (MSCs) were cultured over three weeks in vitro, and chondrogenic differentiation of MSCs within bioink constructs with tethered TGF-ß1 was markedly enhanced, as compared to constructs with non-covalently incorporated TGF-ß1. This was substantiated with regard to early TGF-ß1 signaling, chondrogenic gene expression, qualitative and quantitative ECM deposition and distribution, and resulting construct stiffness. Furthermore, it was successfully demonstrated, in a comparative analysis of cast and printed bioinks, that covalently tethered TGF-ß1 maintained its functionality after 3D printing. Taken together, the presented ink composition enabled the generation of high-quality cartilaginous tissues without the need for continuous exogenous growth factor supply and, thus, bears great potential for future investigation towards cartilage regeneration. Furthermore, growth factor tethering within bioinks, potentially leading to superior tissue development, may also be explored for other biofabrication applications.

The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period.

Bioink Platform Utilizing Dual-Stage Crosslinking of Hyaluronic Acid Tailored for Chondrogenic Differentiation of Mesenchymal Stromal Cells.

3D bioprinting often involves application of highly concentrated polymeric bioinks to enable fabrication of stable cell-hydrogel constructs, although poor cell survival, compromised stem cell differentiation, and an inhomogeneous distribution of newly produced extracellular matrix (ECM) are frequently observed. Therefore, this study presents a bioink platform using a new versatile dual-stage crosslinking approach based on thiolated hyaluronic acid (HA-SH), which not only provides stand-alone 3D printability but also facilitates effective chondrogenic differentiation of mesenchymal stromal cells. A range of HA-SH with different molecular weights is synthesized and crosslinked with acrylated (PEG-diacryl) and allylated (PEG-diallyl) polyethylene glycol in a two-step reaction scheme. The initial Michael addition is used to achieve ink printability, followed by UV-mediated thiol-ene reaction to stabilize the printed bioink for long-term cell culture. Bioinks with high molecular weight HA-SH (>200 kDa) require comparably low polymer content to facilitate bioprinting. This leads to superior quality of cartilaginous constructs which possess a coherent ECM and a strongly increased stiffness of long-term cultured constructs. The dual-stage system may serve as an example to design platforms using two independent crosslinking reactions at one functional group, which allows adjusting printability as well as material and biological properties of bioinks.

Covalently Cross-Linked Pig Gastric Mucin Hydrogels Prepared by Radical-Based Chain-Growth and Thiol-ene Mechanisms.

Mucin, a high molecular mass hydrophilic glycoprotein, is the main component of mucus that coats every wet epithelium in animals. It is thus intrinsically biocompatible, and with its protein backbone and the o-glycosidic bound oligosaccharides, it contains a plethora of functional groups which can be used for further chemical modifications. Here, chain-growth and step-growth (thiol-ene) free-radical cross-linked hydrogels prepared from commercially available pig gastric mucin (PGM) are introduced and compared as cost-efficient and easily accessible alternative to the more broadly applied bovine submaxillary gland mucin. For this, PGM is functionalized with photoreactive acrylate groups or allyl ether moieties, respectively. Whereas homopolymerization of acrylate-functionalized polymers is performed, for thiol-ene cross-linking, the allyl-ether-functionalized PGM is cross-linked with thiol-functionalized hyaluronic acid. Morphology, mechanical properties, and cell compatibility of both kinds of PGM hydrogels are characterized and compared. Furthermore, the biocompatibility of these hydrogels can be evaluated in cell culture experiments.

TEMPO/TCC as a Chemo Selective Alternative for the Oxidation of Hyaluronic Acid.

Hyaluronic acid (HA)-based hydrogels are very commonly applied as cell carriers for different approaches in regenerative medicine. HA itself is a well-studied biomolecule that originates from the physiological extracellular matrix (ECM) of mammalians and, due to its acidic polysaccharide structure, offers many different possibilities for suitable chemical modifications which are necessary to control, for example, network formation. Most of these chemical modifications are performed using the free acid function of the polymer and, additionally, lead to an undesirable breakdown of the biopolymer's backbone. An alternative modification of the vicinal diol of the glucuronic acid is oxidation with sodium periodate to generate dialdehydes via a ring opening mechanism that can subsequently be further modified or crosslinked via Schiff base chemistry. Since this oxidation causes a structural destruction of the polysaccharide backbone, it was our intention to study a novel synthesis protocol frequently applied to selectively oxidize the C6 hydroxyl group of saccharides. On the basis of this TEMPO/TCC oxidation, we studied an alternative hydrogel platform based on oxidized HA crosslinked using adipic acid dihydrazide as the crosslinker.

Bioprinting and Differentiation of Adipose-Derived Stromal Cell Spheroids for a 3D Breast Cancer-Adipose Tissue Model.

Biofabrication, including printing technologies, has emerged as a powerful approach to the design of disease models, such as in cancer research. In breast cancer, adipose tissue has been acknowledged as an important part of the tumor microenvironment favoring tumor progression. Therefore, in this study, a 3D-printed breast cancer model for facilitating investigations into cancer cell-adipocyte interaction was developed. First, we focused on the printability of human adipose-derived stromal cell (ASC) spheroids in an extrusion-based bioprinting setup and the adipogenic differentiation within printed spheroids into adipose microtissues. The printing process was optimized in terms of spheroid viability and homogeneous spheroid distribution in a hyaluronic acid-based bioink. Adipogenic differentiation after printing was demonstrated by lipid accumulation, expression of adipogenic marker genes, and an adipogenic ECM profile. Subsequently, a breast cancer cell (MDA-MB-231) compartment was printed onto the adipose tissue constructs. After nine days of co-culture, we observed a cancer cell-induced reduction of the lipid content and a remodeling of the ECM within the adipose tissues, with increased fibronectin, collagen I and collagen VI expression. Together, our data demonstrate that 3D-printed breast cancer-adipose tissue models can recapitulate important aspects of the complex cell-cell and cell-matrix interplay within the tumor-stroma microenvironment.

Appreciating the First Line of the Human Innate Immune Defense: A Strategy to Model and Alleviate the Neutrophil Elastase-Mediated Attack toward Bioactivated Biomaterials.

Biointerface engineering is a wide-spread strategy to improve the healing process and subsequent tissue integration of biomaterials. Especially the integration of specific peptides is one promising strategy to promote the regenerative capacity of implants and 3D scaffolds. In vivo, these tailored interfaces are, however, first confronted with the innate immune response. Neutrophils are cells with pronounced proteolytic potential and the first recruited immune cells at the implant site; nonetheless, they have so far been underappreciated in the design of biomaterial interfaces. Herein, an in vitro approach is introduced to model and analyze the neutrophil interaction with bioactivated materials at the example of nano-bioinspired electrospun surfaces that reveals the vulnerability of a given biointerface design to the contact with neutrophils. A sacrificial, transient hydrogel coating that demonstrates optimal protection for peptide-modified surfaces and thus alleviates the immediate cleavage by neutrophil elastase is further introduced.

Differential Production of Cartilage ECM in 3D Agarose Constructs by Equine Articular Cartilage Progenitor Cells and Mesenchymal Stromal Cells.

Identification of articular cartilage progenitor cells (ACPCs) has opened up new opportunities for cartilage repair. These cells may be used as alternatives for or in combination with mesenchymal stromal cells (MSCs) in cartilage engineering. However, their potential needs to be further investigated, since only a few studies have compared ACPCs and MSCs when cultured in hydrogels. Therefore, in this study, we compared chondrogenic differentiation of equine ACPCs and MSCs in agarose constructs as monocultures and as zonally layered co-cultures under both normoxic and hypoxic conditions. ACPCs and MSCs exhibited distinctly differential production of the cartilaginous extracellular matrix (ECM). For ACPC constructs, markedly higher glycosaminoglycan (GAG) contents were determined by histological and quantitative biochemical evaluation, both in normoxia and hypoxia. Differential GAG production was also reflected in layered co-culture constructs. For both cell types, similar staining for type II collagen was detected. However, distinctly weaker staining for undesired type I collagen was observed in the ACPC constructs. For ACPCs, only very low alkaline phosphatase (ALP) activity, a marker of terminal differentiation, was determined, in stark contrast to what was found for MSCs. This study underscores the potential of ACPCs as a promising cell source for cartilage engineering.

Hyaluronic Acid-Based Bioink Composition Enabling 3D Bioprinting and Improving Quality of Deposited Cartilaginous Extracellular Matrix.

In 3D bioprinting, bioinks with high concentrations of polymeric materials are frequently used to enable fabrication of 3D cell-hydrogel constructs with sufficient stability. However, this is often associated with restricted cell bioactivity and an inhomogeneous distribution of newly produced extracellular matrix (ECM). Therefore, this study investigates bioink compositions based on hyaluronic acid (HA), an attractive material for cartilage regeneration, which allow for reduction of polymer content. Thiolated HA and allyl-modified poly(glycidol) in varying concentrations are UV-crosslinked. To adapt bioinks to poly(ε-caprolactone) (PCL)-supported 3D bioprinting, the gels are further supplemented with 1 wt% unmodified high molecular weight HA (hmHA) and chondrogenic differentiation of incorporated human mesenchymal stromal cells is assessed. Strikingly, addition of hmHA to gels with a low polymer content (3 wt%) results in distinct increase of construct quality with a homogeneous ECM distribution throughout the constructs, independent of the printing process. Improved ECM distribution in those constructs is associated with increased construct stiffness after chondrogenic differentiation, as compared to higher concentrated constructs (10 wt%), which only show pericellular matrix deposition. The study contributes to effective bioink development, demonstrating dual function of a supplement enabling PCL-supported bioprinting and at the same time improving biological properties of the resulting constructs.

Comparison of Hydrogels for the Development of Well-Defined 3D Cancer Models of Breast Cancer and Melanoma.

Bioprinting offers the opportunity to fabricate precise 3D tumor models to study tumor pathophysiology and progression. However, the choice of the bioink used is important. In this study, cell behavior was studied in three mechanically and biologically different hydrogels (alginate, alginate dialdehyde crosslinked with gelatin (ADA-GEL), and thiol-modified hyaluronan (HA-SH crosslinked with PEGDA)) with cells from breast cancer (MDA-MB-231 and MCF-7) and melanoma (Mel Im and MV3), by analyzing survival, growth, and the amount of metabolically active, living cells via WST-8 labeling. Material characteristics were analyzed by dynamic mechanical analysis. Cell lines revealed significantly increased cell numbers in low-percentage alginate and HA-SH from day 1 to 14, while only Mel Im also revealed an increase in ADA-GEL. MCF-7 showed a preference for 1% alginate. Melanoma cells tended to proliferate better in ADA-GEL and HA-SH than mammary carcinoma cells. In 1% alginate, breast cancer cells showed equally good proliferation compared to melanoma cell lines. A smaller area was colonized in high-percentage alginate-based hydrogels. Moreover, 3% alginate was the stiffest material, and 2.5% ADA-GEL was the softest material. The other hydrogels were in the same range in between. Therefore, cellular responses were not only stiffness-dependent. With 1% alginate and HA-SH, we identified matrices that enable proliferation of all tested tumor cell lines while maintaining expected tumor heterogeneity. By adapting hydrogels, differences could be accentuated. This opens up the possibility of understanding and analyzing tumor heterogeneity by biofabrication.

Improving alginate printability for biofabrication: establishment of a universal and homogeneous pre-crosslinking technique.

Many different biofabrication approaches as well as a variety of bioinks have been developed by researchers working in the field of tissue engineering. A main challenge for bioinks often remains the difficulty to achieve shape fidelity after printing. In order to overcome this issue, a homogeneous pre-crosslinking technique, which is universally applicable to all alginate-based materials, was developed. In this study, the Young's Modulus after post-crosslinking of selected hydrogels, as well as the chemical characterization of alginate in terms of M/G ratio and molecular weight, were determined. With our technique it was possible to markedly enhance the printability of a 2% (w/v) alginate solution, without using a higher polymer content, fillers or support structures. 3D porous scaffolds with a height of around 5 mm were printed. Furthermore, the rheological behavior of different pre-crosslinking degrees was studied. Shear forces on cells as well as the flow profile of the bioink inside the printing nozzle during the process were estimated. A high cell viability of printed NIH/3T3 cells embedded in the novel bioink of more than 85% over a time period of two weeks could be observed.

Permanent Hydrophilization and Generic Bioactivation of Melt Electrowritten Scaffolds.

Melt electrowriting (MEW) is an emerging additive manufacturing technology that direct-writes low-micron diameter fibers into 3D scaffolds with high porosities. Often, the polymers currently used for MEW are hydrophobic thermoplastics that induce unspecific protein adsorption and subsequent uncontrolled cell adhesion. Here are developed a coating strategy for MEW scaffolds based on six-arm star-shaped NCO-poly(ethylene oxide-stat-propylene oxide) (sP(EO-stat-PO)). This permanently hydrophilizes the PCL through the formation of a hydrogel coating and minimizes unspecific interactions with proteins and cells. It also provides the option of simultaneous covalent attachment of bioactive molecules through reaction with isocyanates before these are hydrolyzed. Furthermore, a photoactivatable chemical functionalization is introduced that is not dependent on the time-limited window of isocyanate chemistry. For this, photo-leucine is covalently immobilized into the sP(EO-stat-PO) layer, resulting in a photoactivatable scaffold that enables the binding of sterically demanding molecules at any timepoint after scaffold preparation and coating and is decoupled from the isocyanate chemistry. A successful biofunctionalization of MEW scaffolds via this strategy is demonstrated with streptavidin and collagen as examples. This hydrogel coating system is a generic one that introduces flexible specific and multiple surface functionalization, potentially for a spectrum of polymers made from different manufacturing processes.

Tuning the Product Spectrum of a Glycoside Hydrolase Enzyme by a Combination of Site-Directed Mutagenesis and Tyrosine-Specific Chemical Modification.

Selective chemical modification of proteins plays a pivotal role for the rational design of enzymes with novel and specific functionalities. In this study, a strategic combination of genetic and chemical engineering paves the way for systematic construction of biocatalysts by tuning the product spectrum of a levansucrase from Bacillus megaterium (Bm-LS), which typically produces small levan-like oligosaccharides. The implementation of site-directed mutagenesis followed by a tyrosine-specific modification enabled control of the product synthesis: depending on the position, the modification provoked either enrichment of short oligosaccharides (up to 800 % in some cases) or triggered the formation of high molecular weight polymer. The chemical modification can recover polymerization ability in variants with defective oligosaccharide binding motifs. Molecular dynamic (MD) simulations provided insights into the effect of modifying non-native tyrosine residues on product specificity.

Influence of charged groups on the cross-linking efficiency and release of guest molecules from thiol-ene cross-linked poly(2-oxazoline) hydrogels.

We describe the preparation of hydrogels using highly functionalized poly(oxazoline) based polymeric precursors and cross-linking via UV mediated radical thiol-ene chemistry. Random copolymers were synthesized based on the combination of the more hydrophilic 2-methyl-2-oxazoline or the less hydrophilic monomer 2-ethyl-2-oxazoline with 2-(3-butenyl)-2-oxazoline. These copolymers were functionalized via a post-polymerization technique with thiol or cysteine functionality at the side chain. Hence, hydrogels were obtained, for which the thermo-responsive behavior, network density and correlated properties such as swelling and mechanics, as well as the possibility of electrostatic interaction, can be tuned. Cell culture tests demonstrated good cytocompatibility of the synthesized copolymers and hydrogels. A study with two low molecular weight substances, methylene blue and fluorescein sodium, was performed to investigate how the thermo-responsive behavior or the positive charge incorporated by cysteine could influence the interaction with the compounds. It was found that the interaction with the hydrogel network was strongly influenced by the chemical properties of the dye. A hydrophilic and positively charged hydrogel network was shown to be a promising candidate for the uptake and prolonged release of negatively charged low molecular weight substances.

Tough and Elastic α-Tricalcium Phosphate Cement Composites with Degradable PEG-Based Cross-Linker.

Dual setting cements composed of an in situ forming hydrogel and a reactive mineral phase combine high compressive strength of the cement with sufficient ductility and bending strength of the polymeric network. Previous studies were focused on the modification with non-degradable hydrogels based on 2-hydroxyethyl methacrylate (HEMA). Here, we describe the synthesis of suitable triblock degradable poly(ethylene glycol)-poly(lactide) (PEG-PLLA) cross-linker to improve the resorption capacity of such composites. A study with four different formulations was established. As reference, pure hydroxyapatite (HA) cements and composites with 40 wt% HEMA in the liquid cement phase were produced. Furthermore, HEMA was modified with 10 wt% of PEG-PLLA cross-linker or a test series containing only 25% cross-linker was chosen for composites with a fully degradable polymeric phase. Hence, we developed suitable systems with increased elasticity and 5⁻6 times higher toughness values in comparison to pure inorganic cement matrix. Furthermore, conversion rate from α-tricalcium phosphate (α-TCP) to HA was still about 90% for all composite formulations, whereas crystal size decreased. Based on this material development and advancement for a dual setting system, we managed to overcome the drawback of brittleness for pure calcium phosphate cements.