In situ precipitation of amorphous calcium phosphate nanoparticles within 3D porous collagen sponges for bone tissue engineering

Visible light-induced simultaneous bioactive amorphous calcium phosphate mineralization and in situ crosslinking of coacervate-based injectable underwater adhesive hydrogels for enhanced bone regeneration

The field of bone tissue engineering is vital due to increasing bone disorders and limitations of traditional grafts. Injectable hydrogels offer minimally invasive solutions but often lack mechanical integrity and biological functionality, including osteoinductive capacity and structural stability under physiological conditions. To address these issues, we propose a coacervate-based injectable adhesive hydrogel that utilizes the dual functionality of in situ photocrosslinking and osteoinductive amorphous calcium phosphate formation, both of which are activated simultaneously by visible light irradiation. The developed hydrogel formulation integrated a photoreactive agent with calcium ions and phosphonodiol in a matrix of tyramine-conjugated alginate and RGD peptide-fused bioengineered mussel adhesive protein, promoting rapid setting, robust underwater adhesion, and bioactive mineral deposition. The hydrogel also exhibited superior mechanical properties, including enhanced underwater tissue adhesive strength and compressive resistance. In vivo evaluation using a rat femoral tunnel defect model confirmed the efficacy of the developed adhesive hydrogel in facilitating easy application to irregularly shaped defects through injection, rapid bone regeneration without the addition of bone grafts, and integration within the defect sites. This injectable adhesive hydrogel system holds significant potential for advancing bone tissue engineering, providing a versatile, efficient, and biologically favorable alternative to conventional bone repair methodologies.

Carboxymethyl cellulose-stabilized calcium phosphate particles for injectable hydrogel-based bone tissue engineering

Calcium phosphate (CaP) is a widely used biocompatible and bioactive material for bone tissue engineering due to its similarity to the mineral component of natural bone. Amorphous calcium phosphate is a highly reactive form of CaP that can undergo a phase transformation into a more stable crystalline phase, making it an attractive candidate for bone regeneration applications. However, amorphous CaP is highly unstable in aqueous solutions, which limits its use in practical applications. To overcome this limitation, this research aimed to employ carboxymethyl cellulose (CMC), a water-soluble biopolymer, as a stabilizer for CaP particles. CMC can form a protective layer around CaP particles, enhancing their stability and dispersion in aqueous solutions. An in situ wet chemical process was used to prepare CaP/CMC particles. A concentration of 500 mg L-1 of CMC was found to effectively stabilize the synthesized CaP particles, resulting in good dispersity. These particles were then integrated into an injectable hydrogel made of methacrylated hyaluronic acid (MeHA) to create a promising material for bone regeneration applications. The use of CaP and CMC in combination with an injectable MeHA hydrogel provides a promising approach to develop a stable, injectable material for bone regeneration.

Nitric oxide-releasing thiolated starch nanoparticles embedded in gelatin sponges for wound dressing applications

This study introduces a novel wound dressing by combining nitric oxide-releasing thiolated starch nanoparticles (NO-TS NPs) with gelatin. First, starch was thiolated (TS), and then its nanoparticles were prepared (TS NPs). Subsequently, NPs were covalently bonded to sodium nitrite to obtain NO-releasing TS NPs (NO-TS-NPs) that were incorporated into gelatin sponges at various concentrations. The resulting spherical TS NPs had a mean size of 85.42 ± 5.23 nm, which rose to 100.73 ± 7.41 nm after bonding with sodium nitrite. FTIR spectroscopy confirmed S-nitrosation on the NO-TS NPs' surface, and morphology analysis showed well-interconnected pores in all sponges. With higher NO-TS NPs content, pore size, porosity, and water uptake increased, while compressive modulus and strength decreased. Composites exhibited antibacterial activity, particularly against E. coli, with enhanced efficacy at higher NPs' concentrations. In vitro release studies demonstrated Fickian diffusion, with faster NO release in sponges containing more NPs. The released NO amounts were non-toxic to fibroblasts, but samples with fewer NO-TS NPs exhibited superior cellular density, cell attachment, and collagen secretion. Considering the results, including favorable mechanical strength, release behavior, antibacterial and cellular properties, gelatin sponges loaded with 2 mg/mL of NO-TS NPs can be suitable for wound dressing applications.

In vitro and in vivo degradation, biocompatibility and bone repair performance of strontium-doped montmorillonite coating on Mg-Ca alloy

Poor bone growth remains a challenge for degradable bone implants. Montmorillonite and strontium were selected as the carrier and bone growth promoting elements to prepare strontium-doped montmorillonite coating on Mg-Ca alloy. The surface morphology and composition were characterized by SEM, EDS, XPS, FT-IR and XRD. The hydrogen evolution experiment and electrochemical test results showed that the Mg-Ca alloy coated with Sr-MMT coating possessed optimal corrosion resistance performance. Furthermore, in vitro studies on cell activity, ALP activity, and cell morphology confirmed that Sr-MMT coating had satisfactory biocompatibility, which can significantly avail the proliferation, differentiation, and adhesion of osteoblasts. Moreover, the results of the 90-day implantation experiment in rats indicated that, the preparation of Sr-MMT coating effectively advanced the biocompatibility and bone repair performance of Mg-Ca alloy. In addition, The Osteogenic ability of Sr-MMT coating may be due to the combined effect of the precipitation of Si4+ and Sr2+ in Sr-MMT coating and the dissolution of Mg2+ and Ca2+ during the degradation of Mg-Ca alloy. By using coating technology, this study provides a late-model strategy for biodegradable Mg alloys with good corrosion resistance, biocompatibility. This new material will bring more possibilities in bone repair.

Electrospun Scaffolds of Polylactic Acid, Collagen, and Amorphous Calcium Phosphate for Bone Repair

Most electrospun scaffolds for bone tissue engineering typically use hydroxyapatite (HA) or beta tricalcium phosphate (β-TCP). However, the biological activity of these crystalline compounds can be limited due to their low solubility. Therefore, amorphous calcium phosphate (ACP) may be an alternative in bone repair scaffolds. This study analyzes the morphology, porosity, mechanical strength, and surface chemistry of electrospun scaffolds composed of polylactic acid and collagen integrated with hydroxyapatite (MHAP) or amorphous calcium phosphate (MACP). In addition, the in vitro biocompatibility, osteogenic differentiation, and growth factor production associated with bone repair using human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs) are evaluated. The results show that the electrospun MHAP and MACP scaffolds exhibit a fibrous morphology with interconnected pores. Both scaffolds exhibit favorable biocompatibility and stimulate the proliferation and osteogenesis of hWJ-MSCs. However, cell adhesion and osteocalcin production are greater in the MACP scaffold compared to the MHAP scaffold. In addition, the MACP scaffold shows significant production of bone-repair-related growth factors such as transforming growth factor-beta 1 (TGF-β1), providing a solid basis for its use in bone tissue engineering.

Collagen-chitosan-hydroxyapatite composite scaffolds for bone repair in ovariectomized rats

Lesions with bone loss may require autologous grafts, which are considered the gold standard; however, natural or synthetic biomaterials are alternatives that can be used in clinical situations that require support for bone neoformation. Collagen and hydroxyapatite have been used for bone repair based on the concept of biomimetics, which can be combined with chitosan, forming a scaffold for cell adhesion and growth. However, osteoporosis caused by gonadal hormone deficiency can thus compromise the expected results of the osseointegration of scaffolds. The aim of this study was to investigate the osteoregenerative capacity of collagen (Co)/chitosan (Ch)/hydroxyapatite (Ha) scaffolds in rats with hormone deficiency caused by experimental bilateral ovariectomy. Forty-two rats were divided into non-ovariectomized (NO) and ovariectomized (O) groups, divided into three subgroups: control (empty defect) and two subgroups receiving collagen/chitosan/hydroxyapatite scaffolds prepared using different methods of hydroxyapatite incorporation, in situ (CoChHa1) and ex situ (CoChHa2). The defect areas were submitted to macroscopic, radiological, and histomorphometric analysis. No inflammatory processes were found in the tibial defect area that would indicate immune rejection of the scaffolds, thus confirming the biocompatibility of the biomaterials. Bone formation starting from the margins of the bone defect were observed in all rats, with a greater volume in the NO groups, particularly the group receiving CoChHa2. Less bone formation was found in the O subgroups when compared to the NO. In conclusion, collagen/chitosan/hydroxyapatite scaffolds stimulate bone growth in vivo but abnormal conditions of bone fragility caused by gonadal hormone deficiency may have delayed the bone repair process.

Advances in biomimetic collagen mineralisation and future approaches to bone tissue engineering

With an ageing world population and ~20% of adults in Europe being affected by bone diseases, there is an urgent need to develop advanced regenerative approaches and biomaterials capable to facilitate tissue regeneration while providing an adequate microenvironment for cells to thrive. As the main components of bone are collagen and apatite mineral, scientists in the tissue engineering field have attempted in combining these materials by using different biomimetic approaches to favour bone repair. Still, an ideal bone analogue capable of mimicking the distinct properties (i.e., mechanical properties, degradation rate, porosity, etc.) of cancellous bone is to be developed. This review seeks to sum up the current understanding of bone tissue mineralisation and structure while providing a critical outlook on the existing biomimetic strategies of mineralising collagen for bone tissue engineering applications, highlighting where gaps in knowledge exist.

Preparation of Collagen/Hydroxyapatite Composites Using the Alternate Immersion Method and Evaluation of the Cranial Bone-Forming Capability of Composites Complexed with Acidic Gelatin and b-FGF

Bone-substitute materials are essential in dental implantology. We prepared collagen (Col)/hydroxyapatite (Hap)/acidic gelatin (AG)/basic fibroblast growth factor (b-FGF) constructs with enhanced bone-forming capability. The Col/Hap apatite composites were prepared by immersing Col sponges alternately in calcium and phosphate ion solutions five times, for 20 and 60 min, respectively. Then, the sponges were heated to 56 °C for 48 h. Scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses showed that the Col/Hap composites contained poorly crystalline Hap precipitates on the Col matrix. Col/Hap composite granules were infiltrated by AG, freeze-dried, and immersed in b-FGF solution. The wet quaternary constructs were implanted in rat cranial bone defects for 8 weeks, followed by soft X-ray measurements and histological analysis. Animal studies have shown that the constructs moderately increase bone formation in cranial bone defects. We found that an alternate immersion time of 20 min led to the greatest bone formation (p < 0.05). Constructs placed inside defects slightly extend the preexisting bone from the defect edges and lead to the formation of small island-like bones inside the defect, followed by disappearance of the constructs. The combined use of Col, Hap, AG, and b-FGF might bring about novel bone-forming biomaterials.

Osteoinductive hybrid hydrogel membranes for in situ bone regeneration in hyperglycemia

In hyperglycemia patients, suffering from insufficient vascularization and vascular network lesion, tissue regeneration, such as bone repair, is limited and maybe delayed by the secondary injury and hyperglycemic microenvironment. Typically, dental therapies involving guided bone regeneration is facing a difficult condition in the patients with diabetes. In this study, a hybrid membrane was endowed with biomimetic function to create an angiogenesis-inductive microenvironment by calcium ion release to overcome the limitations of bone tissue regeneration in diabetic patients. Biomineralized calcium resource was Janus-structured onto the surface of hybrid hydrogel by layer-by-layer technique to enhance vascularization and improve the bone regeneration in this study. The release of calcium ions from mineralized phases was controlled by the solubility of inorganic phases and the degradation of gels, promoting HIF-1α expression and creating a key role in angiogenesis stimulation. With highly enhanced calcium signaling and blood vessel formation, the hybrid hydrogel membranes improved the recruitment, proliferation and differentiation of mesenchymal stem cells and endothelial progenitors, confirmed by the enhancement of microvascular regeneration and new bone formation in the critical-sized calvarial defect in diabetic model in vivo. Our study demonstrates a translational potential of hybrid hydrogels engineered with inorganic minerals for orthopedic applications in hyperglycemia.

Bone Tissue Regeneration by Collagen Scaffolds with Different Calcium Phosphate Coatings: Amorphous Calcium Phosphate and Low-Crystalline Apatite

Surface-mineralized collagen sponges have attracted much attention as scaffolds for bone tissue engineering. Recently, we developed amorphous calcium phosphate (ACP) and low-crystalline apatite coating processes on collagen sponges. In the present study, we applied these coating processes to granular collagen sponges (referred to as Col) to compare the bone tissue regeneration capabilities of ACP-coated and apatite-coated Col (referred to as Col-ACP and Col-Ap, respectively) using a rat cranial bone defect model. According to micro-CT and histological analyses, Col-Ap enhanced bone tissue regeneration compared to Col, whereas Col-ACP did not. These results not only demonstrated the superior bone tissue regeneration capability of Col-Ap, but also indicated limitations of the in vitro simulated body fluid (SBF) test used in our previous study. Despite the apatite-forming ability of Col-ACP in SBF, it was ineffective in improving bone tissue regeneration in vivo, unlike Col-Ap, most likely due to the quick resorption of the ACP coating in the defect site. The present results clarified the importance of the coating stability in vivo and revealed that the low-crystalline apatite coating was more beneficial than the ACP coating in the fabrication of surface-mineralized collagen sponges for use as bone tissue engineering scaffolds.

Chitosan/alginate/hyaluronic acid polyelectrolyte composite sponges crosslinked with genipin for wound dressing application

Wound dressing composed of polyelectrolyte complexes (PECs), based on chitosan/alginate/hyaluronic acid (CS/ALG/HYA) crosslinked by genipin, was prepared by freeze-dried molding. Genipin as excellent natural biological crosslinker was chose for high biocompatibility and improving mechanical properties of materials. The CS/ALG/HYA sponges (CAHSs) were characterized by FTIR, XRD, DSC and SEM. Porosity, swelling behavior and mechanical properties and in vitro degradation of CAHSs were investigated. The cytotoxicity assay was carried out on HUVEC cells in vitro and the result proves the good biocompatibility of CAHSs. Hemolysis tests indicated that the prepared CAHSs were non-hemolytic material (hemolysis ratio < 5%, no cytotoxicity). PT and aPPT coagulation tests demonstrated that CAHS2 and CAHS3 could both activate the extrinsic and intrinsic coagulation pathway and thus accelerated blood coagulation. Further, in a rat full-thickness wounds model, the CAHS2 sponge significantly facilitates wound closure compared to other groups. CAHSs exhibited adjustable physical, mechanical and biological properties. Thus, the chitosan-based polyelectrolyte composite sponges exhibit great potential as promising wound dressings.

Osteogenic differentiation system based on biopolymer nanoparticles for stem cells in simulated microgravity

An efficient long-term intracellular growth factor release system in simulated microgravity for osteogenic differentiation was prepared based on polylactic acid (PLA) and polyhydroxyalkanoate (PHA) nanoparticles for loading of bone morphogenetic protein 2 (BMP2) and bone morphogenetic protein 7 (BMP7) (defined as sB2-PLA-NP and sB7-PHA-NP), respectively, associated with osteogenic differentiation of human adipose derived stem cells (hADSCs). On account of soybean lecithin (SL) as biosurfactants, sB2-PLA-NPs and sB7-PHA-NPs had a high encapsulation efficiency (>80%) of BMPs and uniform small size (<100 nm), and showed different slow-release to provide BMP2 in early stage and BMP7 in late stages of osteogenic differentiation within 20 days, due to degradation rate of PLA and PHA in cells. After uptake into hADSCs, by comparison with single sB2-PLA-NP or sB7-PHA-NP, the Mixture NPs, compound of sB2-PLA-NP and sB7-PHA-NP with a mass ratio of 1:1, can well-promote ALP activity, expression of OPN and upregulated related osteo-genes. Directed osteo-differentiation of Mixture NPs was similar to result of sustained free-BMP2 and BMP7-supplying (sFree-B2&B7) in simulated microgravity, which demonstrated the reliability and stability of Mixture NPs as a long-term osteogenic differentiation system in space medicine and biology in future.

Macroporous chitosan/methoxypoly(ethylene glycol) based cryosponges with unique morphology for tissue engineering applications

Three-dimensional porous scaffolds are widely employed in tissue engineering and regenerative medicine for their ability to carry bioactives and cells; and for their platform properties to allow for bridging-the-gap within an injured tissue. This study describes the effect of various methoxypolyethylene glycol (mPEG) derivatives (mPEG (-OCH₃ functionality), mPEG-aldehyde (mPEG-CHO) and mPEG-acetic acid (mPEG-COOH)) on the morphology and physical properties of chemically crosslinked, semi-interpenetrating polymer network (IPN), chitosan (CHT)/mPEG blend cryosponges. Physicochemical and molecular characterization revealed that the –CHO and –COOH functional groups in mPEG derivatives interacted with the –NH₂ functionality of the chitosan chain. The distinguishing feature of the cryosponges was their unique morphological features such as fringe thread-, pebble-, curved quartz crystal-, crystal flower-; and canyon-like structures. The morphological data was well corroborated by the image processing data and physisorption curves corresponding to Type II isotherm with open hysteresis loops. Functionalization of mPEG had no evident influence on the macro-mechanical properties of the cryosponges but increased the matrix strength as determined by the rheomechanical analyses. The cryosponges were able to deliver bioactives (dexamethasone and curcumin) over 10 days, showed varied matrix degradation profiles, and supported neuronal cells on the matrix surface. In addition, in silico simulations confirmed the compatibility and molecular stability of the CHT/mPEG blend compositions. In conclusion, the study confirmed that significant morphological variations may be induced by minimal functionalization and crosslinking of biomaterials.