Page 502 - IJB-9-5

International Journal of Bioprinting Implantation of composites for cartilage repair

the full potential of these scaffolds for cartilage repair. articular cartilage (i.e., along the femoral trochlea) and
However, these results suggest that future approaches possess cartilage with a thickness comparable to human
for cartilage repair with MEW-reinforced hydrogels articular cartilage . For example, composite scaffolds
[11]
should be carefully evaluated with regard to their fixation consisting of woven polycaprolactone (PCL) and either
approach for construct retention and surrounding infilled hydrogels (i.e., self-assembling peptide-based
cartilage tissue damage. hydrogels and HA hydrogels) or bone marrow aspirate
were previously investigated for the treatment of cartilage
lesions (4 mm diameter) in Yucatan minipigs . Despite
[9]
Keywords: Melt electrowriting; Hydrogel; Cartilage the early observation of scaffold retention in defects
Repair; Mesenchymal Stromal Cells; Fibrin Glue
at 6 weeks, defects treated with composites performed
worse than those treated with microfracture. Similarly,
biphasic composites of PCL and cell-laden PEG hydrogel
were evaluated in minipig cartilage defects for 6 months;
1. Introduction explanted composites resulted in O’Driscoll scores (i.e.,
A variety of surgical approaches have been developed histological scoring) that were worse than empty defect
[6]
to treat full-thickness cartilage defects due to trauma controls, and significant bone resorption was observed .
and disease, including arthroscopic debridement, One significant challenge in implementing these
microfracture, and autologous chondrocyte implantation therapies is the successful fixation and retention of implants
(ACI) . Importantly, if cartilage defects are left untreated, within full-thickness cartilage defects [7,12,13] . A range of
[1]
they may progress to osteoarthritis (OA), which results approaches have been investigated for implant fixation ,
[14]
in significant pain and joint dysfunction for patients . including press-fitting, suturing with an overlaying
[2]
Unfortunately, these approaches fail to restore healthy periosteal flap, application of fibrin glue/sealant, and the use
cartilage structure and function, as the repair cartilage of bone anchors to integrate implants with the underlying
formed as a result of strategies such as microfracture bone, among others. While simply press-fitting an implant
typically exhibits inferior properties when compared to may be appropriate for osteochondral defects or instances
healthy articular cartilage . However, the success of each in which full-thickness cartilage defects are surrounded
[3]
of these respective approaches correlates with defect size, by healthy, thick cartilage , oftentimes chondral-only
[15]
which dictates the indication for each procedure . Bone samples are dislodged from defects due to the complex loads
[1]
marrow stimulation via subchondral microfracture is experienced within the joint [14,16] . Fibrin glue has similarly
widely considered to be the first option for treating relatively been combined with press-fitting of implants, but only
small lesions (<2.5 cm ), with defects ranging between 1 marginally improved the fixation strength and retention
2
and 2.5 cm responding well to the treatment . However, of implants [16-18] . Unfortunately, suturing of periosteal
[1]
2
microfracture has previously demonstrated poor patient flaps to secure implants within defects leads to the loss of
outcomes in the treatment of larger defects (≥4 cm ) , chondrocytes and extracellular matrix (ECM) at the local
2 [1]
which typically must be repaired with osteochondral suture site, as well as the formation of fissures reminiscent of
allografts where available. For intermediate defect sizes partial-thickness defects . Bone anchors have been shown
[19]
(2 cm ), ACI is typically used to mediate repair ; however, to ensure the retention of implants within defects more
2
[1]
ACI is not usually employed for larger defects (≥4 cm ) reliably , but they often lead to underlying subchondral
2
[9]
since there is typically a limited number of donor cells that bone remodeling or voids [18,20] . A recent study evaluated
can be readily isolated. biphasic scaffolds composed of hydroxyapatite and PCL
In response to the limitations of current approaches microfiber meshes fabricated via melt electrowriting (MEW)
for cartilage repair [4,5] , a variety of new tissue engineering in an equine osteochondral damage model. Six months after
therapies are being developed, and several have been implantation, minimal cartilaginous ECM was observed
evaluated for cartilage repair in large animals [6-9] . These have in the chondral phase of implants, while micro-computed
been met with varied success, but highlight the importance tomography (micro-CT) results showed the collapse of bone
of selecting models and time points that best recapitulate anchors used to fix the implants within defects, potentially
[7]
human cartilage damage in a clinically relevant manner. To due to improper design and fixation . Generally, both the
this end, canine, caprine, porcine, and equine models are cartilage defect size and geometry, as well as the properties
most commonly used for the investigation of new cartilage of the implant itself must be considered when selecting the
repair strategies . Porcine models are often employed optimal fixation method for scaffolds.
[10]
as large animal models for cartilage damage because In our previous work, composites of norbornene-
they permit easy operative access to non-load-bearing modified hyaluronic acid (NorHA) hydrogels mechanically

Volume 9 Issue 5 (2023) 494 https://doi.org/10.18063/ijb.775