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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5603_Библиотеки_им_академика_М_И_Перельмана.pdf
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N. Chowdhury etal.
[111–115]. Using PCDME instead of PAMPS yielded a substantial augmentation in
tensile strength elastic modulus and fracture stress [105, 106]. Using alginate
increased fracture energy and Young’s modulus [107–109]. A combination of a poly
(vinyl alcohol) (PVA)–(PAMPS) with nanober network DN hydrogel which contains bacterial cellulose (BC) demonstrates modulus to cartilage and comparable
strength in both compression and tension, while also exhibiting tensile fatigue
strength similar to that of cartilage after 100,000cycles [108, 109]. A synthetic gel
composed of glycerol and PHEMA was formulated by combining a 1:1 mass ratio
of glycerin and HEMA.The mechanical characteristics evaluation revealed that the
synthetic gel exhibited a hardness comparable to that of natural cartilage [110, 160].
Double network (DN) hydrogels, comprising a primary network of PAMPS and a
secondary network of P(NIPAAm-co-AAm), leverage the incorporation of
PNIPAAm improves the gels mechanical characteristics by going above the normal
physiological temperature range/thermal phase transition [111]. Double network
(DN) gels St-TPEG/PAAm were prepared using a molecular stent approach within
TPEG gels, leading to a nearly uniform rst network structure [111].
2.5.8 Triple Network Hydrogel
Single or double-network hydrogels have signicant compatible, tribological, structural properties. However, this gel doesn’t achieve the desired mechanical, tensile,
and compressive resilience of the native articular cartilage. That’s why a third network (charged, neutral, hydrophilic, hydrophobic) is incorporated within the
double- network hydrogel to increase the mechanical property while keeping the
tribological property the same [116]. Incorporating multiple networks by sequential
polymerization reactions or combining different polymerization methods allows for
enhanced toughness, strength, and resilience, mimicking the mechanical properties
of natural tissues. Examples of triple-network hydrogels include PAA/Agar/PVA
TN, PVA/B TN, PAA/Gela/PVA TN, and PVA/PVP/PAA TN, which have demonstrated exceptional fracture stress, compression strength, and compressive modulus
as shown in Figs.2.24, 2.25 and 2.26 where the synthesis techniques for different
monomer chains are explained to understand the interlinked interactions [119, 121,
122]. Furthermore, these hydrogels often possess self-healing properties, enabling
the recovery of mechanical integrity upon damage. The networks’ charge, density,
and other characteristics signicantly inuence the overall properties of triplenetwork hydrogels. Higher charge densities increase stiffness and reduce swelling;
lower charge densities enhance exibility and swelling ability. Increasing network
and crosslinking densities improve stiffness, strength, and load-bearing capacity,
but excessive densities can lead to brittleness. Adjusting polymer composition,
molecular weight, and intermolecular interactions allows modulation of the
2 Characterization ofHydrogel Properties intheAdvancement ofBio-Tribology
Fig. 2.24 BC-PAMPS-PVA triple network solution [109]
Fig. 2.25 Figure: Triple
network hydrogel structure
[121]
53
Fig. 2.26 Triple Network
hydrogel structure [122]
hydrogel’s mechanical, swelling, and degradation properties [116–120, 159, 161].
In the PAMPS-PVA-BC triple network hydrogel, BC functions akin to collagen by
providing tensile strength, while PAMPS serves as a provider of osmotic restorative
force, permanent negative charge, and like the function of cartilage proteoglycan [109].
54
N. Chowdhury etal.
2.6 Tribological, Mechanical, andStructural Properties
ofPotential Cartilage Replacement Hydrogel
2.6.1 Polyacrylamide
The implementation of polyacrylamide hydrogel made a signicant impact and has
been reported to substantially diminish the friction characteristics of cartilage
explants in degradation models, exhibiting a notable reduction of 30% to 40% compared to control samples [123]. With increasing applied load, the extent of micro
plowing and plastic deformation is enhanced, leading to a reduction in brittle fracture effects. For instance, 7.5% PAAm hydrogel exhibits a wear volume ranging
from 0.01 to 0.05mm3 about cumulated dissipative energy and a wear rate of 0.1 to
0.5mm3 based on speeds ranging from 1 to 3mm/s, under varying forces of 1 to
5mN as shown in Figs.2.27 and 2.28 [115, 129]. For Gemini contact of polyacrylamide, 3–17% PAAm hydrogels have friction coefcients ranging from 0.001 to
0.025. For migrating or solid contact, the friction coefcient ranges from 0.01 to
0.05 [124, 125]. With increasing normal force, the friction coefcient decreases in
polyacrylamide [135]. The lubrication mechanisms in PAAm are thermal uctuation lubrication and polymer relaxation lubrication [124–127, 165]. Elevated temperature annealing can enhance the ability of PVA hydrogels to withstand
deformation under prolonged stress/creep resistance. Nevertheless, the annealing
process causes the collapse of pores, leading to a decrease in the level of water content and, consequently, a decrease in the hydrogel surface’s lubrication behavior. By
incorporating polyacrylamide (PAAm) within the pores, the collapse is mitigated,
allowing for better water retention and increased lubricity. The PVA-PAAm hydrogel has a friction range from 0.12 to 0.3 as shown in Figs.2.29 and 2.30 [74]. The
frictional behavior of brushy hydrogel surfaces relies on both the extent of surface
hydration and the contact surface conditions. These hydrogels demonstrate low
Fig. 2.27 Wear volume vs
speed value of
polyacrylamide hydrogel
[129]
2 Characterization ofHydrogel Properties intheAdvancement ofBio-Tribology
Fig. 2.28 Wear rate vs
fatigue fracture relation
based on the composition
of PAAm [129]
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Fig. 2.29 Coefcient of friction vs. sliding speed for different types of polyacrylamide hydrogel
(brushy/brushy, brushy/crosslinked, crosslinked/crosslinked, crosslinked/brushy) on soft contact [130]
friction (μ~0.01) that remains consistent regardless of speed when subjected to
migrating contact. This behavior is attributed to the presence of a substantial layer
of shearing liquid conned within the loosely arranged surface structure as shown
in Fig.2.30 [126, 164]. The GelMA/PAM biohybrid hydrogels exhibited increased
exibility (with a storage modulus near 1000Pa) and enhanced compressive strength
(almost 0.38 MPa). Notably, both the GelMA/PAM and the GelMA hydrogel
reduced signicantly in swelling ratio behavior compared to the PAM hydrogel.
Furthermore, the GelMA/PAM hydrogel exhibited a permeable structure that
encompassed characteristics from both GelMA and PAM hydrogels. Both GelMA
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Fig. 2.30 Coefcient of friction vs. sliding speed test results for different probe methods; ring, 4
pins, 8 pins [126]
N. Chowdhury etal.
and PAM can be incorporated and result in notable advancements in mechanical and
tribological behavior, thus holding signicant potential for cartilage replacement
applications [128].
2.6.2 PEG Hydrogel
A comprehensive investigation was conducted on the wide range of compositions of
PEG hydrogel to nd the physical properties of these hydrogels. by changing the
molecular weight of PEG concentration (3.4–10kDa), 4-arm PEG-Acr concentration (0–20wt %), and PEGDA concentration (10–30wt %), the hydrogel formulations of these PEG hydrogels were systematically varied as a result, 27 distinct
hydrogel formulations were created and subsequently characterized. The modulus
of these hydrogels varied from 10 to 250kPa as shown in Fig.2.31 [131], offering
a wide spectrum of mechanical properties suitable for various applications for varying mesh sizes of 5 to 90nm [131]. The initial storage modulus (G′) for hydrogels
of different PEG molecular weights fell within the range of 1–3kPa, with mesh
sizes varying in a range from 11 to 19nm based on molecular weight variation as
shown in Fig.2.32 [132]. Over the course of the 5-day testing period, the G′ values
consistently decreased for all hydrogels synthesized using degradable cross-linkers
[80]. The friction behavior of PEG hydrogel is shown in Fig.2.33 which indicates
signicant low friction and wear rate for varying crosslinker concentrations [132].
2 Characterization ofHydrogel Properties intheAdvancement ofBio-Tribology
Fig. 2.31 Tensile modulus
and strain vs mesh size
relationship was presented
in the study of PEG
hydrogel [176]
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Fig. 2.32 The study illustrates the variation in reduced moduli for both non-sterilized and sterilized PEG-based hydrogels concerning different concentrations of crosslinker PEGDMA [132]
2.6.3 PVA Hydrogel
The study demonstrated that hydroxyapatite (HA) nanoparticles embedded in PVA
hydrogel exhibited reduced wear when applied to stainless steel, while various alloy
particles such as Ti, steel, and HA also displayed low friction coefcients [95–98].
The friction behavior between PVA hydrogel and articular cartilage exhibited an
increase, ranging from 0.12 to 0.147, under a 10-N load, as the speed escalated by
varying from 10 to 20mm/s [60]. With a low hardness and elastic modulus, the PVA
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Fig. 2.33 The study compares the evolution of friction coefcient and wear rates during
200,000 cycles of wear tests between uncoated and hydrogel-coated bearing surfaces of PEG
hydrogel [132]
N. Chowdhury etal.
hydrogels possess a heterogeneous and porous structure [133]. The magnitude of
the typical kinetic friction coefcient lies between 0.04 and 0.07, compressive modulus 2–7MPa, and tensile strength of 1–7MPa for high molecular weight (30%)
PVA hydrogel [94]. The wear with time observed between PVA hydrogel and articular cartilage involved adhesive wear and surface fatigue [60]. Implantation of highwater content PVA gels (80–90% water) into rabbits subcutaneously or
intramuscularly resulted in no observed adverse effects in the surrounding tissue,
conrming the material’s biocompatibility [58, 134], orally safe [135], implantable
[136], non-toxic [137], and biocompatible [138]. The utilization of PVA inserts in
commercial hip pair (HXPE, UHMWPE, metal/ceramic sockets, metal/ceramic
heads) led to a signicant reduction of up to 98% in the value of the coefcient of
friction, reducing the coefcient average and maintained within the range of 0.002
to 0.0055 as shown in Figs.2.34 and 2.35 for commercial hip pair and PVA hydrogel friction behavior comparison [139].
2.6.4 Double Network Hydrogel
The double network structure allows for improved load-bearing capacity, replicating the high tensile and compressive strength required in articular cartilage, the
combination of two networks with contrasting properties provides enhanced toughness and resilience, enabling the hydrogel to withstand repetitive mechanical
stresses, improved hydration and lubrication characteristics of natural cartilage,
promoting reduced friction and wear, and facilitating better articulation within joint
interfaces. The incorporation of continuous PGF in PGF-PVA composite hydrogel
enhances its mechanical properties, resulting in improved mechanical properties,
with tensile and compressive strengths reaching 8.15 MPa and 2.07 MPa,
2 Characterization ofHydrogel Properties intheAdvancement ofBio-Tribology
Fig. 2.34 Friction
coefcient of commercial
hip pairs [139]
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respectively fullling the mechanical criteria necessary for cartilage repair, while
also improving the molecular structure’s crystallinity and thermal stability through
crosslinking points formation, and providing an efcient ions exchange behavior of
the PVA hydrogel matrix to the degradation of PGF leads to a change in ion concentration, creating a more conducive metabolic environment that promotes chondrocyte proliferation and induction, resulting in improved recruitment [140]. The
synthesis technique and strength behavior is depicted in Figs.2.36 and 2.37 through
the network distribution and strength testing [141, 169]. In deionized water and calf
serum, the (PHEMA)/glycerol synthetic gel demonstrated the lowest friction behavior which is 0.039 and 0.018 for knee prostheses compared to most conventional
materials [110]. In PAMPS/PNIPAAm double network hydrogels, the inclusion of
PNIPAAm enhances their mechanical properties by raising the thermal temperature
found in the natural physiological environment. Compared to traditional single network hydrogels, the PNIPAAm composed double network hydrogels claries a signicant 50 times increase in the property of compressive strength approximately
(∼25MPa, like cartilage), while also exhibiting modulus like cartilage (∼1MPa)
and hydration amount like (∼80%). Furthermore, the PNIPAAm double network
hydrogel displays a 50% less friction coefcient (COF) [114]. DN hydrogels with
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Fig. 2.35 Friction
coefcient of PVA
hydrogel [139]
N. Chowdhury etal.
Fig. 2.36 Illustrates
before and after the
necking process by
showing their network
structure [141]
2 Characterization ofHydrogel Properties intheAdvancement ofBio-Tribology
Fig. 2.37 An illustrative depiction and an image of a DN gel composed of a primary and secondary network, where the primary network is brittle, and the secondary network is ductile [177]
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Fig. 2.38 Double network hydrogels (a) friction coefcient vs speed×viscosity on DI water, (b)
friction coefcient vs speed×viscosity on FBS solution [115]
neutral or zwitterionic second networks showed lower friction and shear stresses,
surpassing cartilage performance. Lubrication responses varied more in water than
in FBS, but in both cases, the friction coefcients fell below 0.3, indicating effective
lubrication like cartilage. These DN hydrogels meet or exceed lubrication demands
for load-bearing joint cartilage replacement. Among the hydrogel samples tested,
DN-APTAC (+)-10% exhibited the highest friction behavior and the lowest surface
modulus in both FBS and water. On the other hand, though DN-AMPS (−)-10%
was stiffer than DN-APTAC (+)-10%, it had slightly lower friction behavior than
DN-APTAC(+)-10%. Double network DN-MDSAH-10% and DN-Aam-10% represented the shear stress values and lowest friction as shown in Fig.2.38 [115].
These ndings suggest that charge reorientation happens when a negative charge is
present in these gels, in a similar manner as cartilage, and is likely to result in the
most effective lubrication response [115].