A Biomimicking Polymeric Cryogel Scaffold for Repair of Critical-Sized Cranial Defect in a Rat Model

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Osteogenesis Enhancement with 3D Printed Gene-Activated Sodium Alginate Scaffolds

Natural and synthetic hydrogel scaffolds containing bioactive components are increasingly used in solving various tissue engineering problems. The encapsulation of DNA-encoding osteogenic growth factors with transfecting agents (e.g., polyplexes) into such scaffold structures is one of the promising approaches to delivering the corresponding genes to the area of the bone defect to be replaced, providing the prolonged expression of the required proteins. Herein, a comparative assessment of both in vitro and in vivo osteogenic properties of 3D printed sodium alginate (SA) hydrogel scaffolds impregnated with model EGFP and therapeutic BMP-2 plasmids was demonstrated for the first time. The expression levels of mesenchymal stem cell (MSC) osteogenic differentiation markers Runx2, Alpl, and Bglap were evaluated by real-time PCR. Osteogenesis in vivo was studied on a model of a critical-sized cranial defect in Wistar rats using micro-CT and histomorphology. The incorporation of polyplexes comprising pEGFP and pBMP-2 plasmids into the SA solution followed by 3D cryoprinting does not affect their transfecting ability compared to the initial compounds. Histomorphometry and micro-CT analysis 8 weeks after scaffold implantation manifested a significant (up to 46%) increase in new bone volume formation for the SA/pBMP-2 scaffolds compared to the SA/pEGFP ones.

Dual Delivery of BMP2 and IGF1 Through Injectable Hydrogel Promotes Cranial Bone Defect Healing

Critical-sized cranial bone defect remains a great clinical challenge. With advantages in regenerative medicine, injectable hydrogels incorporated with bioactive molecules show great potential in promoting cranial bone repair. Recently, we developed a dual delivery system by sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in microparticles (MPs), and an injectable alginate/collagen (alg/col)-based hydrogel. In this study, we aim to evaluate the effect of dual delivery of BMP2 and IGF1 in MPs through the injectable hydrogel in critical-sized cranial bone defect healing. The gelatin MPs loaded with BMP2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) MPs loaded with IGF1 were prepared, respectively. The encapsulation efficiency and release profile of growth factors in MPs were measured. A cranial defect model was applied to evaluate the efficacy of the dual delivery system in bone regeneration. Adult Sprague Dawley rats were subjected to osteotomy to make an ⌀8-mm cranial defect. The injectable hydrogel containing MPs loaded with BMP2 (2 μg), IGF1 (2 μg), or a combination of BMP2 (1 μg) and IGF1 (1 μg) were injected to the defect site. New bone formation was evaluated by microcomputed tomography, histological analysis, and immunohistochemistry after 4 or 8 weeks. Data showed that dual delivery of the low-dose BMP2 and IGF1 in MPs through alg/col-based hydrogel successfully restored cranial bone as early as 4 weeks after implantation, whose effect was comparable to the single delivery of high-dose BMP2 in MPs. In conclusion, this study suggests that dual delivery of BMP2 and IGF1 in MPs in alg/col-based hydrogel achieves early bone regeneration in critical-sized bone defect, with advantage in reducing the dose of BMP2. Impact Statement Sequential release of bone morphogenetic protein 2 (BMP2) followed by insulin-like growth factor 1 (IGF1) in two different microparticles promotes critical-sized bone defect healing. This dual delivery system reduces the dose of BMP2 by supplementing IGF1, which may diminish the potential side effects of BMP2.

Assessment of Robot-Assisted Mandibular Contouring Surgery in Comparison With Traditional Surgery: A Prospective, Single-Center, Randomized Controlled Trial

BACKGROUND

Few clinical studies on robot-assisted surgery (RAS) for mandibular contouring have been reported.

OBJECTIVES

The aim of this study was to follow the long-term effectiveness and safety of RAS for craniofacial bone surgery.

METHODS

This small-sample, early-phase, prospective, randomized controlled study included patients diagnosed with mandibular deformity requiring mandibular contouring surgery. Patients of both genders aged 18 to 30 years without complicated craniofacial repair defects were enrolled and randomly assigned in a 1:1 ratio by a permuted-block randomized assignments list generated by the study statistician. The primary outcomes were the positioning accuracy and accuracy of the osteotomy plane angle 1 week after surgery. Surgical auxiliary measurement index, patient satisfaction scale, surgical pain scale, perioperative period, and complications at 1 week, 1 month, and 6 months after surgery were also analyzed.

RESULTS

One patient was lost to follow-up, resulting in a total of 14 patients in the traditional surgery group and 15 in the robot-assisted group (mean [standard deviation] age, 22.65 [3.60] years). Among the primary outcomes, there was a significant difference in the positioning accuracy (2.91 mm vs 1.65 mm; P < 0.01) and angle accuracy (13.26º vs 4.85º; P < 0.01) between the 2 groups. Secondary outcomes did not significantly differ.

CONCLUSIONS

Compared to traditional surgery, robot-assisted mandibular contouring surgery showed improved precision in bone shaving, as well as higher safety.

LEVEL OF EVIDENCE: 2

Stereocomplexation Reinforced High Strength Poly(L-lactide)/Nanohydroxyapatite Composites for Potential Bone Repair Applications

Composite materials composed of polylactide (PLA) and nano-hydroxyapatite (n-HA) have been recognized as excellent candidate material in bone repai The difference in hydrophilicity/hydrophobicity and poor interfacial compatibility between n-HA filler and PLA matrix leads to non-uniform dispersion of n-HA in PLA matrix and consequent poor reinforcement effect. In this study, an HA/PLA nanocomposite was designed based on the surface modification of n-HA with poly(D-lactide) (PDLA), which not only can improve the dispersion of n-HA in the poly(L-lactide) (PLLA) matrix but also could form a stereocomplex crystal with the matrix PLLA at the interface and ultimately lead to greatly enhanced mechanical performance The n-HA/PLA composites were characterized by means of scanning electron microscopy, Fourier transform infrared spectroscopy, X-Ray diffraction, thermal gravity analysis, differential scanning calorimetry, and a mechanical test; in vitro cytotoxicity of the composite material as well as its efficacy in inducing osteogenic differentiation of rat bone marrow stromal cells (rMSCs) were also evaluated. Compared with those of neat PLLA, the tensile strength, Young’s modulus, interfacial shear strength, elongation at break and crystallinity of the composites increased by 34%, 53%, 26%, 70%, and 17%, respectively. The adhesion and proliferation as well as the osteogenic differentiation of rMSCs on HA/PLA composites were clearly evidenced. Therefore, the HA/PLA composites have great potential for bone repai.

Synergistic Effect of Whitlockite Scaffolds Combined with Alendronate to Promote Bone Regeneration

BACKGROUND

Due to the increasing aging of society, the number of patients suffering from senile diseases is increasing. Patients suffering from osteoporosis, which is a representative senile disease, take a long time to recover from fractures, and the resulting mortality rate is very high. Alendronate (Ald), which is widely used as a treatment for osteoporosis, alleviates osteoporosis by inhibiting osteoclasts. In addition, whitlockite (WH) promotes the osteogenic differentiation of bone cells and improves bone regeneration. Therefore, we intended to bring about a synergistic effect by using these substances together.

METHODS

In this study, a scaffold composed of gelatin/heparin was fabricated and applied to effectively use WH and Ald together. A scaffold was constructed using gelatin and heparin was used to effectively utilize the cations released from WH. In addition, it formed a porous structure for effective bone regeneration. In vitro and in vivo osteoclast inhibition, osteogenic differentiation, and bone regeneration were studied using the prepared scaffolds.

RESULTS

The inhibition of osteoclast was much higher when WH and Ald were applied in combination rather than individually. The highest level of osteogenic differentiation was observed when both substances were applied simultaneously. In addition, when applied to bone regeneration through the mouse calvarial defect model, combined treatment showed excellent bone regeneration.

CONCLUSION

Therefore, this study showed the synergistic effect of WH and Ald, and it is suggested that better bone regeneration is possible by applying this treatment to bones with fractures that are difficult to regenerate.

Parameterized design and fabrication of porous bone scaffolds for the repair of cranial defects

In bone tissue engineering, the structure of a scaffold is very important for cell growth and bone regeneration. It is better to make the scaffold resemble the native cancellous bone because natural cancellous bone can promote scaffold revascularization, which then accelerates cell proliferation. This study presents a parameterized design and fabrication method for cranial scaffold construction. A native human cranial sample was first scanned using micro computed tomography (CT), followed by 3D reconstruction, after which the internal structure of the bone trabecula was created. Based on an extracted negative bone trabecula model, the design components of "cavity", "connecting pipe" and "spatial framework" were proposed to describe the scaffold model. Then, by using the parameterized component model and an assembly and deformation algorithm, the bionic scaffold was designed. Its porous distribution, connection, porosity and area size were easily controlled. Finally, a biomaterial scaffold case was fabricated using a gelcasting process, and cell culture testing was performed in vitro to verify the scaffold's biocompatibility. The results show that the scaffold can promote cell growth and that cells accumulate in the form of a mass within three days.