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Collagen, the primary structural protein of the extracellular matrix (ECM), is widely used in biomaterials for tissue engineering and repair. However, its limited mechanical properties constrain its use in load-bearing applications. Here, we present a strategy to fabricate dense collagen–silica hybrid hydrogels (16 wt.% collagen) that have high mechanical strength, flexibility, printability, and biofunctionality. Using borate-mediated templating, we synchronize the formation of nanostructured silica networks with collagen fibrillogenesis, and subsequently covalently bind the two phases. This approach yields a compressive modulus ∼1.5 MPa for the hybrid hydrogels with a water content as high as 85%. Characterization confirms that borates act transiently during processing, allowing network formation without being retained in the final material. The hybrid hydrogels support high cell viability, elongation, and alignment in 3D cultures, while in vivo, initially cell-free scaffolds, implanted subcutaneously display minimal inflammation, vascularized tissue integration, and controlled, cell-mediated degradation. Taken together, this work establishes a robust framework for creating printable, ECM-mimetic collagen–silica hybrids with nanoscale reinforcement, offering new opportunities in regenerative medicine and scaffold fabrication.

Spinal implants have been successfully used to treat various spine conditions. However, concerns remain regarding the release of ions and particles that can cause adverse host responses. Moreover, the biological response from cells of the central nervous system to implant wear particles is not well documented. This research studied the interaction of silicon nitride, cobalt oxide, or chromium oxide particles with relevant glial cells, astrocytes and microglia, to assess their effects on viability and activation using a range of relevant concentrations. Astrocyte viability was not impaired by the particles, and expression levels of the astrocyte reactivity markers GFAP and vimentin were unaffected following 24 h of exposure. Moreover, the particles did not alter microglial phagocytic activity, or stimulate the release of the inflammatory cytokines TNF-α and IL-6. Together, these results suggest that the release of such particles from a spinal implant would not induce an inflammatory response in surrounding glial cells. Interestingly, high concentrations of SiN particles reduced microglial cell viability, potentially due to their tendency to form large agglomerates and/or their high dissolution rate. The present work highlights the importance of studying the potential effects of SiN particles on glial cells and encourages further investigations to fully understand the safety aspects of the use of SiN in spinal implants.

Powder bed fusion laser beam (PBF-LB) of Mg alloys shows strong potential for biodegradable, patient-specific implants. A key challenge is achieving adequate corrosion resistance and mechanical strength while maintaining biocompatibility. This study investigates whether varying hatch distance can balance these properties in PBF-LB processed WE43 (Mg-4Y-3RE-Zr; RE: rare earth elements). Optimal laser parameters were developed for hatch distances of 40, 50, and 60 μm (h40, h50, and h60), and samples were analyzed for microstructure, corrosion resistance, and mechanical properties. Results showed that h60 had a weaker texture and narrower grain size distribution, with fewer grains under 200 μm². It also had the lowest degradation rate while maintaining comparable ultimate tensile strength to h50, which had the highest degradation rate. The improved corrosion resistance in h60 was attributed to a more homogeneous distribution of Mg-RE precipitates due to fewer and more homogenously distributed grain boundaries. Extracts from h60 and control materials were used to culture osteoblasts, showing no cytotoxicity after 3 days. Notably, osteoblasts exposed to 3D-printed WE43 extracts produced more lactate dehydrogenase (LDH) than those exposed to extruded WE43, suggesting faster cell proliferation. This study demonstrates the importance of hatch distance in the PBF-LB processing of WE43, as well as its potential in balancing corrosion and tensile properties while maintaining a good in vitro cellular response of bone resident cells.

In this study, we developed and characterized a fully biodegradable composite bone cement reinforced with short, randomly oriented amorphous magnesium fibers. Fibers of composition Mg₆₀Zn₃₅Ca₅ (in at.%) with 50 μm diameter and 2 mm length were produced by wire spinning and then mixed with a magnesium calcium phosphate cement using fiber volume fractions between 10 and 20 %. The interface strength between the fibers and cement was improved by treating the fibers with diammonium hydrogen phosphate. Compared to the reference cement without fibers, flexural strength was increased by 18 % for the composites with 13 and 18 vol% fibers, and the work of fracture was increased by over 1000× in all cases (p < 0.05, n = 6). Immersion in simulated body fluid for two and four weeks showed that the cement's struvite phase degrades first, and overall, the composite degrades slower. The degradation rate can be tailored to the application by changing the fiber percentage or the cement/fiber composition. Murine pre-osteoblastic cells (MC3T3) cultured in extracts of reference and composite cements had significantly higher cell viability, and composites with 13 vol% fibers also had a significantly higher number of cells compared to the control, indicating that the fibers can enhance and promote pre-osteoblastic cell growth. The results demonstrate that amorphous magnesium fibers enhance both the mechanical and biological properties of ceramic bone cement, expanding their prospects for clinical application.

Composite cranial implants composed of calcium phosphate cement (CPC) and titanium have improved cranioplasty procedures outcomes. The patient’s bone grows back and replaces the CPC, while the titanium remains. Therefore, fully resorbable implants could allow for an increased use in paediatric surgery and a reduced need for revision surgeries. We propose replacing the titanium by a resorbable, biocompatible, 3D-printable polymer with suitable mechanical properties and degradation rate. While the biological response to the individual materials has been thoroughly investigated in the literature, specific combinations of materials have not. These could give a different response due to e.g. pH variations. In this in vitro study, we investigate the degradation behaviour of CPC-poly-L-lactic acid (PLLA) structures and the effect of the degradation’s by-products on preosteoblastic cells.

Samples were prepared by moulding CPC around a 3D-printed dense PLLA beam, mimicking the current implants composed of a structural supporting mesh embedded in CPC tiles. The monetite CPC was obtained with β-tricalcium phosphate (βTCP) and monocalcium phosphate monohydrate (MCPM). Degradation tests were conducted in a physiologically relevant environment for parallel evaluation of cellular responses. Various techniques (e.g. Scanning Electron Microscopy, Differential Scanning Calorimetry, X-Ray Diffraction, Inductively Coupled Plasma Optical Emission Spectroscopy, pH monitoring) were applied for morphological, chemical, and thermal characterization of samples and extracts. MC3T3 preosteoblastic cells were cultured with inserts containing the samples, to gain insights into the critical early stages of bone healing and on the composite’s capability for osteoinduction. Over time, we measured cell viability (metabolic activity), progression towards osteoblastic differentiation (ALP expression and enzymatic activity), and matrix mineralization (to determine the differentiation efficacy of the osteoblasts).

This experiment was conducted to study candidate materials for new resorbable cranial implants, assessing their degradation processes and potential interactions, as well as the impact of degradation by-products on cell viability and osteogenic potential.

Rheumatoid arthritis (RA) is the most common inflammatory joint disease, and early diagnosis is key for effective disease management. CD69 is one of the earliest cell surface markers seen at the surface of activated immune cells, and CD69 is upregulated in synovial tissue in patients with active RA. In this study, we evaluated the performance of a CD69-targeting PET agent, [⁶⁸Ga]Ga-DOTA-Z_CAM241, for early disease detection in a model of inflammatory arthritis.

Methods: A model of inflammatory arthritis was induced by transferring splenocytes from KRN T-cell receptor transgenic B6 mice into T-cell–deficient I-A^g7 major histocompatibility complex class II–expressing recipient mice. The mice were examined longitudinally by [⁶⁸Ga]Ga-DOTA-Z_CAM241 PET/CT before and 3, 7, and 12 d after induction of arthritis. Disease progression was monitored by clinical parameters, including measuring body weight and scoring the swelling of the paws. The uptake of [⁶⁸Ga]Ga-DOTA-Z_CAM241 in the paws was analyzed and expressed as SUV_mean. Tissue biopsy samples were analyzed for CD69 expression by flow cytometry or immunostaining for a histologic correlate. A second group of mice was examined by a nonbinding, size-matched Affibody molecule as the control.

Results: Clinical symptoms appeared 5–7 d after induction of arthritis. The uptake of [⁶⁸Ga]Ga-DOTA-Z_CAM241 in the joints was negligible at baseline but increased gradually after disease induction. An elevated PET signal was found on day 3, before the appearance of clinical symptoms. The uptake of [⁶⁸Ga]Ga-DOTA-Z_CAM241 correlated with the clinical score and disease severity. The presence of CD69-positive cells in the joints and lymph nodes was confirmed by flow cytometry and immunostaining. The uptake of the nonbinding tracer that was the negative control also increased gradually with disease progression, although to a lesser extent than with [⁶⁸Ga]Ga-DOTA-Z_CAM241.

Conclusion: The uptake of [⁶⁸Ga]Ga-DOTA-Z_CAM241 in the inflamed joints preceded the clinical symptoms in the KRN T-cell transfer model of inflammatory arthritis, in accordance with immunostaining for CD69. [⁶⁸Ga]Ga-DOTA-Z_CAM241 is thus a promising PET imaging marker of activated immune cells in tissue during RA onset.

Study Design: Experimental porcine anterior cervical discectomy and fusion (ACDF) model: a proof-of-concept study.Objective.The effect of monetite synthetic bone graft (SBG) containing calcium pyrophosphate and beta-tricalcium phosphate on cervical spinal fusion in a noninstrumented two-level large animal model.

Summary of Background Data: ACDF is the gold standard surgical technique for the treatment of degenerative cervical spinal diseases. However, pseudarthrosis associated with increased patient morbidity occurs in similar to 2.6% of the surgeries. SBG may enhance bony fusion and subsequently decrease the risk of pseudarthrosis. Recent studies on monetite-based SBGs for use in large cranial defects in humans have shown promising bone healing results, necessitating further investigation of their use in cervical spinal fusion.

Materials and Methods: Four adult female Danish G & ouml;ttingen minipigs received partial cervical anterior discectomy and intervertebral defects at an upper and lower level. One defect was filled with SBG, and the other was left empty. Bony fusion was evaluated using computed tomography (CT) at three-month intervals for 12 months. Fifteen months postsurgery, the animals were euthanized for further ex vivo qualitative histopathologic and micro-CT evaluations. Fusion rates were compared using the Fisher exact test at each time point.Results.Increased interbody bony fusion rates were observed at SBG levels (4/4) compared with control levels (0/4) evaluated by CT at 6 and 9 months postsurgery (P=0.029). Fusion was observed at all SBG levels 12 months postsurgery and at only one control level. Histopathologic evaluation confirmed high-quality interbody bony fusion at all SBG levels and fusion by spondylosis at one control level.

Conclusion: This proof-of-concept study provides preliminary evidence of a novel, calcium pyrophosphate-containing, and beta-tricalcium phosphate-containing monetite SBG that promotes bony fusion compared with a negative control in a clinically relevant porcine model of ACDF.

In cranioplasty procedures, composite cranial implants using calcium phosphate cement (CP) and 3D-printed titanium alloy have shown improved surgical outcomes [1,2]. While CP is replaced by the patient’s bone over time, the titanium remains.  A fully resorbable implant would enable expansion to applications in pediatric surgery and reduce the need for revision surgeries. We propose using a resorbable, biocompatible, and 3D-printable polymer with suitable mechanical properties and degradation rates instead of titanium. While biological responses to individual materials are well-studied, interactions within specific material combinations are less explored. This study investigates the degradation behavior of CP combined with poly-L-lactic acid (PLLA) [3,4] and its effects on preosteoblastic cells.

Implant-like samples were prepared by molding CP around a 3D-printed dense PLLA beam and tested in a physiologically relevant environment, enabling a concurrent assessment of cellular responses. Techniques including Scanning Electron Microscopy, X-Ray Diffraction, Inductively Coupled Plasma Optical Emission Spectroscopy and mass monitoring were used for characterization. MC3T3 preosteoblastic cells cultured with these samples provided insights into early bone healing and the composite's osteoinductive potential, with evaluations of cell viability, osteoblastic differentiation, and matrix mineralization. 

While limited degradation occurred over 28 days, changes in calcium and phosphorus levels influenced early biological responses, delaying cell proliferation, metabolic activity, and differentiation. However, by the end of the study, degradation by-products did not adversely affect cell metabolic activity or osteogenic potential. These findings suggest that the CP-PLLA composite structure holds promise and is comparable to the clinically established CP in terms of in vitro preosteoblastic cell response.

References

[1] L. Kihlström Burenstam Linder et al., World Neurosurgery, 2019, 122:e399–407. doi: 10.1016/j.wneu.2018.10.061.

[2] S. Lewin et al., Acta Biomaterialia, 2021, 128:502–13. doi: 10.1016/j.actbio.2021.04.015.

[3] E. Capuana et al., Polymers, 2022, 14(6):1153. doi: 10.3390/polym14061153.

[4] T. Ahlfeld et al., Biomaterials Science, 2023. doi: 10.1039/d2bm02071h.