To compare three different compositions of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) ceramic and a lithium disilicate ceramic in terms of flexural strength and translucency. Three zirconia materials of different composition and translucency, Aadva ST [ST], Aadva EI [EI] and Aadva NT [NT](GC Tech, Leuven, Belgium) were cut with a slow speed diamond saw into beams and tabs in order to obtain, after sintering, dimensions of 1.2×4.0×15.0mm and 15.0×15.0×1.0mm respectively. Blocks of IPS e.max CAD LT were cut and crystallized in the same shapes and dimensions and used as a reference group [LD]. Beams (n=15) were tested in a universal testing machine for three-point bending strength. Critical fracture load was recorded in N, flexural strength (σ in MPa), Weibull modulus (m) and Weibull characteristic strength (σ0 in MPa) were then calculated. Tabs (n=10) were measured with a spectrophotometer equipped with an integrating sphere. Contrast Ratios were calculated as CR=Yb/Yw. SEM of thermally etched samples coupled with lineal line analysis (n=6) was used to measure the tested zirconia grain size. Data were statistically analyzed. Differences in translucency, flexural strength and grain size were found to be statistically significant. CR increased and flexural strength decreased in the following order ST(σ 1215±190MPa, CR 0.74±0.01)>EI(σ 983±182MPa, CR 0.69±0.01)>NT(σ 539±66MPa, CR 0.65±0.01)>LD (σ 377±39Mpa, CR 0.56±0.02). The average grain size was different for the three zirconia samples with NT(558±38nm)>ST(445±34nm)>EI(284±11nm). The zirconia composition heavily influenced both the flexural strength and the translucency. Different percentages of Yittria and Alumina result in new materials with intermediate properties in between the conventional zirconia and lithium disilicate. Clinical indications for Zirconia Aadva NT should be limited up to three-unit span bridges.

The replacement and repair of bone lost due to trauma, cancer, or congenital defects is a major clinical challenge. Skeletal tissue engineering is a potentially powerful strategy in modern regenerative medicine, and research in this field has increased greatly in recent years. Tissue engineering strategies seek to translate research findings in the fields of materials science, stem cell biology, and biomineralization into clinical applications, demanding the use of appropriate in vivo models to investigate bone regeneration of the long bone. However, identification of the optimal in vivo segmental bone defect model from the literature is difficult due to the use of different animal species (large and small mammals), different bones (weight-bearing and nonweight bearing), and multiple protocols, including the use of various scaffolds, cells, and bioactives. The aim of this review is to summarize the available animal models for evaluating long bone regeneration in vivo. We highlight the differences not only in species and sites but also in defect size, means of defect creation, duration of study, and fixation method. A critical evaluation of the most clinically relevant models is addressed to guide the researcher in his/her choice of the most appropriate model to use in future hypothesis-driven investigations.

Thiol-ene photo-click hydrogels were prepared via step-growth polymerisation using thiol-functionalised type-I collagen and 8-arm poly(ethylene glycol) norbornene-terminated (PEG-NB), as a potential injectable regenerative device. Type-I collagen was thiol-functionalised by a ring opening reaction with 2-iminothiolane (2IT), whereby up to 80 Abs.% functionalisation and 90 RPN% triple helical preservation were recorded via 2,4,6-Trinitrobenzenesulfonic acid (TNBS) colorimetric assay and circular dichroism (CD). Type, i.e., either 2-Hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) or lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and concentration of photoinitiator were varied to ensure minimal photoinitiator-induced cytotoxicity and to enable thiol-ene network formation of collagen-PEG mixtures. The viability of G292 cells following 24 h culture in photoinitiator-supplemented media was largely affected by the photoinitiator concentration, with I2959-supplemented media observed to induce higher toxic response (0.1 → 0.5% (w/v) I2959, cell survival: 62 → 2 Abs.%) compared to LAP-supplemented media (cell survival: 86 → 8 Abs.%). In line with the in vitro study, selected photoinitiator concentrations were used to prepare thiol-ene photo-click hydrogels. Gelation kinetics proved to be largely affected by the specific photoinitiator, with LAP-containing thiol-ene mixtures leading to significantly reduced complete gelation time (τ: 187 s) with respect to I2959-containing mixtures (τ: 1683 s). Other than the specific photoinitiator, the photoinitiator concentration was key to adjusting the hydrogel storage modulus (G’), whereby 15-fold G’ increase (232 → 3360 Pa) was observed in samples prepared with 0.5% (w/v) compared to 0.1% (w/v) LAP. Further thiol-ene formulations with 0.5% (w/v) LAP and varied content of PEG-NB were tested to prepare photo-click hydrogels with porous architecture, as well as tunable storage modulus (G’: 540–4810 Pa), gelation time (τ: 73–300 s) and swelling ratio (SR: 1530–2840 wt %). The photoinitiator-gelation-cytotoxicity relationships established in this study will be instrumental to the design of orthogonal collagen-based niches for regenerative medicine.

The design of photo-active collagen systems is presented as a basis for establishing biomimetic materials with varied network architecture and programmable macroscopic properties. Following in-house isolation of type I collagen, reaction with vinyl-bearing compounds of varied backbone rigidity, i.e. 4-vinylbenzyl chloride (4VBC) and glycidyl methacrylate (GMA), was carried out. TNBS colorimetric assay, ¹H-NMR and ATR-FTIR confirmed covalent and tunable functionalization of collagen lysines. Depending on the type and extent of functionalization, controlled stability and thermal denaturation of triple helices were observed via circular dichroism (CD), whereby the hydrogen-bonding capability of introduced moieties was shown to play a major role. Full gel formation was observed following photo-activation of functionalized collagen solutions. The presence of a covalent network only slightly affected collagen triple helix conformation (as observed by WAXS and ATR-FTIR), confirming the structural organization of functionalized collagen precursors. Photo-activated hydrogels demonstrated an increased denaturation temperature (DSC) with respect to native collagen, suggesting that the formation of the covalent network successfully stabilized collagen triple helices. Moreover, biocompatibility and mechanical competence of obtained hydrogels were successfully demonstrated under physiologically-relevant conditions. These results demonstrate that this novel synthetic approach enabled the formation of biocompatible collagen systems with defined network architecture and programmable macroscopic properties, which can only partially be obtained with current synthetic methods.

Chemical crosslinking of collagen is a general strategy to reproduce macroscale tissue properties in physiological environment. However, simultaneous control of protein conformation, material properties and biofunctionality is highly challenging with current synthetic strategies. Consequently, the potentially-diverse clinical applications of collagen-based biomaterials cannot be fully realised. In order to establish defined biomacromolecular systems for mineralised tissue applications, type I collagen was functionalised with 1,3-phenylenediacetic acid (Ph) and investigated at the molecular, macroscopic and functional levels. Preserved triple helix conformation was observed in obtained covalent networks via ATR-FTIR (A_III/A₁₄₅₀ ∼ 1) and WAXS, while network crosslinking degree (C: 87–99 mol%) could be adjusted based on specific reaction conditions. Decreased swelling ratio (SR: 823–1285 wt%) and increased thermo-mechanical (T_d: 80–88 °C; E: 28–35 kPa; σ_max: 6–8 kPa; ε_b: 53–58%) properties were observed compared to state-of-the-art carbodiimide (EDC)-crosslinked collagen controls, likely related to the intermolecular covalent incorporation of the aromatic segment. Ph-crosslinked hydrogels displayed nearly intact material integrity and only a slight mass decrease (M_R: 5–11 wt%) following 1 week incubation in either PBS or simulated body fluid (SBF), in contrast to EDC-crosslinked collagen (M_R: 33–58 wt%). Furthermore, FTIR, SEM and EDS revealed deposition of a calcium–phosphate phase on SBF-retrieved samples, whereby an increased calcium phosphate ratio (Ca/P: 0.84–1.41) was observed in hydrogels with higher Ph content. 72 hours material extracts were well tolerated by L929 mouse fibroblasts, whereby cell confluence and metabolic activity (MTS assay) were comparable to those of cells cultured in cell culture medium (positive control). In light of their controlled structure–function properties, these biocompatible collagen hydrogels represent attractive material systems for potential mineralised tissue applications.