Injectable biomaterials for minimally invasive orthopedic treatments

Injectable Functional Biomaterials for Minimally Invasive Surgery

Injectable materials represent very attractive ready-to-use biomaterials for application in minimally invasive surgical procedures. It is shown that this approach to treat, for example, vertebral fracture, craniofacial defects, or tumor resection has significant clinical potential in the biomedical field. In the last four decades, calcium phosphate cements have been widely used as injectable materials for orthopedic surgery due to their excellent properties in terms of biocompatibility and osteoconductivity. However, few clinical studies have demonstrated certain weaknesses of these cements, which include high viscosity, long degradation time, and difficulties being manipulated. To overcome these limitations, the use of sol-gel technology has been investigated, which has shown good results for synthesis of injectable calcium phosphate-based materials. In the last few decades, injectable hydrogels have gained increasing attention owing to their structural similarities with the extracellular matrix, easy process conditions, and potential applications in minimally invasive surgery. However, the need to protect cells during injection leads to the development of double network injectable hydrogels that are capable of being cross-linked in situ. This review will provide the current state of the art and recent advances in the field of injectable biomaterials for minimally invasive surgery.

PCL/β-TCP Composite Scaffolds Exhibit Positive Osteogenic Differentiation with Mechanical Stimulation

We investigated the use of Polycaprolactone (PCL)/ β-tricalcium phosphate (β-TCP) composites with applied mechanical stimulation as scaffold for bone tissue engineering. PCL-based three-dimensional (3D) structures were fabricated in a solvent-free process using a 3D-printing technique. The mass fraction of β-TCP was varied in the range 0-30%, and the structure and compressive modulus of the specimens was characterized. The shape and interconnectivity of the pores was found to be satisfactory, and the compressive modulus of the specimens was comparable with that of human trabecular bone. Human mesenchymal stem cells were seeded on the composites, and various biological evaluations were performed over 9 days. With a mass fraction of β-TCP of 30%, differentiation began earlier; however, the cell proliferation rate was lower. Through the use of mechanical stimulation, however, the proliferation rate recovered, and was comparable with that of the other groups. This stimulation effect was also observed in ECM generation and other biological assays. With mechanical stimulation, expression of osteogenic markers was lower on samples with a β-TCP content of 10 wt% than without β-TCP; however, with mechanical stimulation, the sample with a β-TCP content of 30 wt% exhibited significantly greater expression of those markers than the other samples. We found that mechanical stimulation and the addition of β-TCP interacted closely, and that a mass fraction of β-TCP of 30% was particularly useful as a bone tissue scaffold when accompanied by mechanical stimulation.

Infiltration and sustenance of viability of cells by amphiphilic biosynthetic biodegradable hydrogels

Amphiphilic biosynthetic hydrogels comprising natural polysaccharide alginate (I) and synthetic polyester polypropylene fumarate (II) units were prepared by crosslinking the copolymer of I and II with calcium ion and vinyl monomers viz, 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), butyl methacrylate (BMA) and N,N'-methylene bisacrylamide (NMBA). Three fast degradable hydrogels, ALPF-MMA, ALPF-HEMA and ALPF-BMA and one slow degradable hydrogel ALPF-NMBA were prepared. These hydrogels are amphiphilic and able to hold sufficient amount of proteins on their surfaces. All these hydrogels are found to be hemocompatible, cytocompatible and genocompatible. ALPF-NMBA promotes infiltration of L929 fibroblasts and 3D growth of H9c2 cardiomyoblasts and long-term viability.

Biosynthetic alginate–polyester hydrogels with inherent free radical scavenging activity promote cellular response

The prevention of deleterious effects of reactive oxygen species on the cell growth by biosynthetic hydrogels based on alginate–polyester copolymer was studied using H2O2 as the model ROS molecule. Chemically cross-linked biosynthetic hydrogels of alginate- co-poly(propylene fumarate)–n-butyl methacrylate, alginate- co-poly(propylene fumarate)–methyl methacrylate, alginate- co-poly(propylene fumarate)–2-hydroxyethyl methacrylate, and alginate- co-poly(propylene fumarate)– N,N′-methylene bisacrylamide with different biostabilities were prepared. We found that they were able to resist reactive oxygen species penetration into the cell to a greater extent which was evident from the live/dead assay, and increased intracellular glutathione levels compared to the H2O2-treated control. The hydrogels maintained the genomic integrity which was confirmed by comet assay. The inherent protective effects of these hydrogels without any antioxidant moiety may be mediated by dual mechanism: (a) prevention of migration of H2O2 into the cells by calcium-induced conformational changes and rigidity in phospholipids present in the surface membrane of cells by the calcium generated from degradation of hydrogel and (b) by the dilution of H2O2 by the free water in the hydrogel. These hydrogels have potential as injectable hydrogels to manage myocardial infarction and ischemia.

The mechanical and biological properties of an injectable calcium phosphate cement-fibrin glue composite for bone regeneration

Calcium phosphate cement (CPC) that can be injected to form a scaffold in situ has promise for the repair of bone defects. However, its low-strength limits the CPC to non-stress-bearing repairs. Fibrin glue (FG) with good sticking property and biocompatibility is possible used to reinforce the CPC. The objective of this study was to investigate the effects of FG on the mechanical and biological properties of CPC in an injectable CPC-FG composite. The initial setting time of this CPC-FG was delayed compared with the CPC control at different powder/liquid (P/L) mass ratio (p > 0.05). At a P/L of 5, the strength was (38.41 +/- 4.32) MPa for the CPC-FG, much higher than (27.42 +/- 2.85) MPa for the CPC alone (p < 0.05). SEM showed bone marrow stromal cells (BMSCs) with healthy spreading and anchored on the CPC-FG composite. After 14 days, the alkaline phosphatase (ALP) activity was (538 +/- 33) for the BMSCs on the CPC-FG and (517 +/- 27) for the BMSCs on the CPC alone. Both ALPs were higher than the baseline ALP (93 +/- 10) for the undifferentiated BMSCs (p < 0.05). The results demonstrate that this stronger CPC-FG scaffold may be useful for stem cell-based bone regeneration in moderate load-bearing orthopedic applications.

Reconstruction of goat tibial defects using an injectable tricalcium phosphate/chitosan in combination with autologous platelet-rich plasma

Injectable scaffolds held great promise for the reconstruction of bone defects. We prepared an injectable composite named PTC by combining TCP/chitosan (TC) with platelet-rich plasma (PRP). The objective of this study was to investigate the composite's mechanical and biological properties. First, we found that the introduction of PRP in TC showed no adverse effect on mechanical strength and that there were no significant differences in compressive strength between PTC and TC (P>0.05). In cell culture experiments, both cell count and alkaline phosphatase (ALP) activity measurements of PTC were higher than those of TC. The high levels of Cbfa1 and TGF-beta were detected early in PTC-induced MSCs by reverse transcriptase polymerase chain reaction. Bone formation following expression of collagen type I, osteocalcin, osteonectin and calcium nodules was also observed in PRP-induced MSCs. Finally, this composite was injected into the tibial bone defect in a goat model, and its ability to induce bone regeneration was observed. Sixteen weeks after the implantation of this composite, the tibial defects had completely recuperated, with significantly better formation of mature bone and less residual material than in the control. These results demonstrate that our composite, with its concomitant mechanical strength, biocompatibility, and osteoinductive properties, has significant potential as an injectable material for the treatment of bone defects.