With respect to the composition of natural bone, we established a degradable dual setting system of different poly(ethylene glycol) (PEG)-based hydrogels combined with a brushite cement. The idea was to reinforce the inorganic calcium phosphate mineral phase with an organic, polymeric phase to alter the cement’s properties towards ductility and elasticity. Extremely flexible samples were produced via this dual setting approach with a fully reversible elasticity of the samples containing high molecular weight PEG-based hydrogel precursors. Using the decalcifying agent EDTA, the whole inorganic phase was dissolved due to Ca²⁺-complexation and dimensionally stable hydrogels were obtained, indicating a homogenous polymeric phase within the composites. This was also confirmed by SEM-analysis, where no discontiniuites or agglomerations of the phase were observed. Additional XRD-measurements proved a significant influence of the coherent polymeric matrix on the conversion from β-TCP/MCPA to brushite with a decrease in signal intensity. The results confirmed a parallelly running process of setting reaction and gelation without an inhibition of the conversion to brushite and the formation of interpenetrating networks of hydrogel and cement. The strengths of this newly developed dual setting system are based on the material degradability as well as flexibility, which can be a promising tool for bone regeneration applications in non-load bearing craniomaxillofacial defects.

Statement of significance

Brushite based calcium phosphate cements (CPCs) are known as bone replacement materials, which degrade in vivo and are replaced by native bone. However, the pure inorganic material shows a brittle fracture behavior. Here, the addition of a polymeric phase can influence the mechanical properties to create more ductile and flexible materials. This polymeric phase should ideally form during cement setting by a polymerization reaction to achieve high polymer loads without altering cement viscosity and it should be degradable in vivo similar to the cement itself. Therefore, we developed a dual setting system based on simultaneous cement setting of brushite and lactide modified poly(ethylene glycol) dimethacrylate (PEG-PLLA-DMA)-based hydrogel. It was evident that the gels form a continuous phase within the cement after radical polymerization with a strong reduction of cement brittleness.

Brushite based calcium phosphate cements (CPCs) are known as bone replacement materials, which degrade in vivo and are replaced by native bone. However, the pure inorganic material shows a brittle fracture behavior. Here, the addition of a polymeric phase can influence the mechanical properties to create more ductile and flexible materials. This polymeric phase should ideally form during cement setting by a polymerization reaction to achieve high polymer loads without altering cement viscosity and it should be degradable in vivo similar to the cement itself. Therefore, we developed a dual setting system based on simultaneous cement setting of brushite and lactide modified poly(ethylene glycol) dimethacrylate (PEG-PLLA-DMA)-based hydrogel. It was evident that the gels form a continuous phase within the cement after radical polymerization with a strong reduction of cement brittleness.

中文翻译：

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基于PEG-水凝胶和透钙磷石水泥的高度灵活且可降解的双重固化系统

关于天然骨的组成，我们建立了一种可降解的双重凝固体系，该体系由不同的基于聚乙二醇（PEG）的水凝胶与透钙磷石胶结剂组成。想法是用有机聚合相增强无机磷酸钙矿物相，以改变水泥的延展性和弹性。通过这种双重固化方法可生产出极具弹性的样品，其中包含高分子量基于PEG的水凝胶前体的样品具有完全可逆的弹性。使用脱钙剂EDTA，由于Ca ²⁺溶解了整个无机相获得了复合物和尺寸稳定的水凝胶，表明复合物中的聚合物相是均匀的。SEM分析也证实了这一点，其中未观察到相的不连续或团聚。额外的XRD测量证明，相干聚合物基质对从β-TCP/ MCPA转变为透钙磷石的转化具有显着影响，且信号强度降低。结果证实了平行进行的设定反应和凝胶化的过程，而没有抑制向透钙磷石的转化以及水凝胶和水泥互穿网络的形成。这种新开发的双重固定系统的优势是基于材料的可降解性和柔韧性，这对于非承重颅颌面缺损的骨再生应用而言可能是很有前途的工具。

重要声明

透钙磷石基磷酸钙水泥（CPC）被称为骨替代材料，其在体内降解并被天然骨替代。但是，纯无机材料表现出脆性断裂行为。在此，聚合物相的添加会影响机械性能，从而产生更具延展性和柔性的材料。理想地，该聚合物相应在水泥固化过程中通过聚合反应形成，以在不改变水泥粘度的情况下实现高聚合物负载，并且应在体内降解类似于水泥本身。因此，我们基于透钙磷石和丙交酯改性的聚（乙二醇）二甲基丙烯酸酯（PEG-PLLA-DMA）基水凝胶的同时水泥固化，开发了一种双重固化系统。显然，在自由基聚合后，凝胶在水泥内形成连续相，从而大大降低了水泥的脆性。

透钙磷石基磷酸钙水泥（CPC）被称为骨替代材料，其在体内降解并被天然骨替代。但是，纯无机材料表现出脆性断裂行为。在此，聚合物相的添加会影响机械性能，从而产生更具延展性和柔性的材料。理想地，该聚合物相应在水泥固化过程中通过聚合反应形成，以在不改变水泥粘度的情况下实现高聚合物负载，并且应在体内降解类似于水泥本身。因此，我们基于透钙磷石和丙交酯改性的聚（乙二醇）二甲基丙烯酸酯（PEG-PLLA-DMA）基水凝胶的同时水泥固化，开发了一种双重固化系统。显然，在自由基聚合后，凝胶在水泥内形成连续相，从而大大降低了水泥的脆性。