Alginate-based biomaterials in orthopedics: What are the prospects for bacterial alginate?

Table 1 Summary of alginate-based biomaterials for bone regeneration

Biomaterial	Development of structures (scaffolds)	Physicochemical and mechanical properties	Biological activity	Ref.
Alginate	Scaffold is an oxidised alginate porogen that contains encapsulated mesenchymal stromal cells (MSCs)	On evaluating the mechanical properties, the stiffness of the scaffold was found tobe 403 ± 3.0 kPa	The in vivo results of cell regeneration and migration showed that the defect area with scaffold had a higher number of cells. (lymphocyte-like and non-lymphocyte-like) compared to pure alginate hydrogel	[30,31]
	Hydrogel construction consisting of photocrosslinked, oxidised and methacrylated alginate	The chemical structure was confirmed using H¹-NMR and FTIR methods. Mechanical testing showed that the elastic modulus of the hydrogel containing 13.55% oxidised alginate was 1315.30 Pa ± 220.77 Pa	In vitro evaluation of the proliferation and osteogenic differentiation of BMMSCs showed that the hydrogel containing the most oxidised alginate produced the weakest results
ALG/CHI	3D-printing of ALG/CHI scaffold followed by impregnation with extract CQ	Mechanical properties showed that shear curves decreased with increasing velocity for all ALG/CHI samples. Evaluation of morphology demonstrated that the scaffolds had an average fibre diameter of 845.73 ± 66.96 μm, a pore size of 357.66 ± 34.78 μm and a contact wettability angle of 42.1° ± 0.7°	Evaluation of antioxidant activity showed that the SA/CHI/CQ scaffold produced the best results (23.00% ± 1.33%). Biocompatibility evaluation demonstrated that the survival rate of the Saos-2 cell line on the SA/CHI/CQ scaffold was higher than on the bare ALG/CHI scaffold	[32-34]
	ALG/CHI scaffold with embedded EPs	The porosity of the scaffold was 89% ± 5%, and the compressive modulus was 3.69 ± 0.70 kPa	Retention and viability of MSCs on the scaffolds showed: 53% ± 12% of cells were retained and 67% ± 17% of these were viable after 21 days
	Composite ALG/CHI/β-TCP scaffold were dissolved and mixed together followed by lyphiolization	The complex shear modulus of the scaffold was greater than 10 kPa at an angular frequency greater than 100 rad/s	In vivo results showed over 23% bone formation in relation to the defect area after 4 weeks and over 60% after 8 weeks with the melatonin-included scaffold
ALG/HA	A lyophilised scaffold based on hydroxyapatite nanoparticles in a gelatin/polyvinyl alcohol/alginate matrix	The hybrid scaffolds exhibited an ultimate compressive strength of 1.1 MPa and a porosity of 70% ± 9.2%	The scaffolds exhibited excellent antibacterial activity against strains of S. epidemidis and E. coli and showed zones of inhibition with diameters of 41.8 ± 0.1 mm and 41.5 ± 0.1 after 24 hours, respectively	[35-38]
	A PHB/HA/ALG scaffold seeded with MSCs	The porosity of the PHB/HA scaffolds was 88% ± 6% and the pore size was 104 ± 25 μm. The physicochemical and mechanical properties of the PHB/HA/ALG scaffold were as follows: Young's modulus - 178.5 ± 1.8 kPa and water absorption - 241% ± 21%	In vivo studies showed that scaffold seeded with MSCs exhibited better regenerative properties compared to other materials
	3D printing using bioink, ALG/GG/HA	The bioinks exhibited linear viscoelastic behaviour, with G′ being greater than G″ up to 100% strain	Evaluation of the viability of SaOs-2 cell line on different bioinks showed that the ink with lower HA content (1%) had a higher number of live cells at all time points
	An ALG/nHA composite hydrogel incorporating the proteasome inhibitor bortezomib has been developed	The water absorption of the composite scaffold was more than 1100% after 24 hours. The compression stress-strain curves of the scaffold had significantly higher values compared to pure alginate	The survival of MC3T3 cells decreased as the concentration of nucleosome inhibitor increased; in vitro and in vivo experiments showed that scaffolds have a pronounced antitumor effect

BMMSCs: Bone marrow mesenchymal stromal cells; ALG/CHI: Alginate/chitosan; CQ: Cissus quadrangularis; EPs: Eggshell particles; ALG/CHI/β-TCP: Alginate/Chitosan/Beta-tricalcium phosphate; MSCs: Mesenchymal stem cells; ALG/HA: Alginate/Hydroxyapatite; PHB/HA/ALG: Poly(3-hydroxybutyrate)/Hydroxyapatite/Alginate; ALG/GG/HA: Alginate/Gellan gum/Hydroxyapatite; ALG/nHA: Alginate/nanohydroxyapatite; E. coli: Escherichia coli.

Table 2 Comparative costs of alginate produced by different companies from algae and bacteria

	Volume, g	Cost, $	Manufacturing companies
Bacterial	5	950-1150	Biosynth (Switzerland), USBiological Life Sciences (United States)
Algal	25	≈ 18	Flinn Scientific (Canada), Carolina Biological Supply (United States)
	500	70-270	Merck (Germany), Snow Sea (Russia), Fisher Scientific International, Inc. (United States)
	1000	125-550	Merck (Germany), MSK Ingredients (United Kingdom), Fisher Scientific International, Inc. (United States)