Platelet-rich plasma in orthopedics: Bridging innovation and clinical applications for bone repair

Abstract

In the burgeoning domain of orthopedic therapeutic research, Platelet-Rich Plasma (PRP) has firmly established its position, transforming paradigms ranging from tissue regeneration to the management of chondral lesions. This review delves into PRP’s recent integrations with cutting-edge interventions such as 3D-printed scaffolds, its role in bone and cartilage defect management, and its enhanced efficacy when combined with molecules like Kartogenin (KGN) for fibrocartilage zone repair. Significant attention is paid to tissue engineering for meniscal interventions, where a combination of KGN, PRP, and bone marrow-derived mesenchymal stem cells are under exploration. Within the sphere of osteochondral regenerative therapy, the synergy of PRP with Bone Marrow Aspirate Concentrate (BMAC) represents a noteworthy leap towards cartilage regeneration. The innovative incorporation of PRP with biomaterials like hydroxyapatite and graphene oxide further underscores its versatility in supporting structural integrity and ensuring sustained growth factor release. However, while PRP’s autologous and nontoxic nature makes it an inherently safe option, concerns arising from its preparation methods, particularly with bovine thrombin, necessitate caution. As of 2023, despite the burgeoning promise of PRP in bone healing, the quest for its standardization, optimization, and substantiation through rigorous clinical trials continues. This comprehensive review elucidates the contemporary applications, challenges, and future trajectories of PRP in orthopedics, aiming to spotlight areas primed for further research and exploration.

Keywords

bone marrow aspirate concentrate bone repair kartogenin orthopedics platelet-rich plasma 3D-printed scaffolds

Introduction

Platelet-Rich Plasma (PRP), an autologous concentration of platelets within a diminutive plasma volume, has rapidly evolved as a focal point of interest in the realm of orthopedic therapeutic.¹ Its potent capability, defined by its role in angiogenesis, mesenchymal cell recruitment, and its status as a repository for pivotal growth factors, underscores its emerging significance in mediating the inflammatory response at bone healing site.^1,2 Recognizing PRP’s ostensible osteoinductive prowess, particularly in bolstering osteoblast proliferation and enhancing matrix formation, its adoption across diverse medical disciplines, and more notably in orthopedics, has experienced an appreciable surg.^3–6 The autologous derivation of PRP offers both economic advantages and obviates potential immunogenic complications commonly linked to exogenous recombinant growth factors. Such benefits not only mitigate the risk of disease transmission but also facilitate its application in surgical contexts.

Bone healing, an indispensable post-fracture process, can sometimes waver, culminating in nonunion - a daunting outcome where fractures persist unhealed, thus invoking the need for escalated medical measure.^6–8 Although the definition of the temporal window following which a fracture is dubbed a nonunion remains debatable, the U.S. Food and Drug Administration posits a benchmark of 9 months.^9,10 It’s crucial to comprehend the nuances of nonunions, which can be categorically segmented into atrophic, characterized by limited callus formation and suggestive of a compromised biological healing response; and oligotrophic and hypertrophic, typified by copious callus formation, albeit thwarted healing due to mechanical instabilit.^6,9 Current literature pinpoints a global nonunion incidence of approximately 2.5%, a statistic that can alarmingly amplify to 46% in the context of vascular insults.^11,12

While traditional approaches for managing these orthopedic challenges have gravitated towards mechanical stabilization, often complemented by bone grafting, PRP’s promise lies in its potential to augment tissue and bone regeneratio.^13,14 The expansive applications of PRP, spanning from synergistic use with artificial bone,^15,16 integration into 3D printed scaffold,^17,18 or in concert with muscle-derived mesenchymal stem cell,¹⁹ illuminate its dynamic utility in remedying bone defects.

This review offers an integrated exploration into the studies shedding light on PRP’s orthopedic applications, from its prowess in fundamental bone healing, its efficacy in rotator cuff repairs, to its potential to bridge bone-tendon gaps. It is our intention to provide a coherent synthesis of the available evidence, accentuating PRP’s therapeutic aptitude in bone repair, with insights garnered until July 2023.

Growth factor dynamics of PRP in osteogenesis

Platelet-Rich Plasma, distinguished by a platelet concentration exceeding 1,000,000 platelets/L in a 5 mL plasma sample, is notable for its heightened growth factor concentration.²⁰ Such concentrations have been directly linked to enhanced reparative processe.¹⁴ In the event of tissue injury, the cellular repair cascade predominantly relies on platelet.²¹ Upon activation, these platelets release an array of growth factors and cytokines.²² Remarkably, PRP inherently serves as a growth factor carrier, negating the need for external mediums.² Bones, naturally endowed with a potent regenerative capacity, utilize cellular components, growth factors, and elements of the extracellular matrix for restoratio.^23,24 PRP’s therapeutic potential stems from its rich reservoir of growth factors, especially those from its α-granules, which facilitate bone repai.²⁵ Additionally, platelets contain bioactive substances, including serotonin and histamine, that are integral to the bone healing mechanis.^26,27 In summary, growth factors associated with PRP, such as PDGF, TGFβ, VEGF, and FGF, hold pivotal roles in processes like fracture healing, tissue reconstruction, and angiogenesi.²⁸

In orthopedics, PRP has surfaced as a significant therapeutic modality, especially for acute long bone fractures. Derived autologously from the patient's blood, PRP’s hallmark is its dense growth factor and pro-inflammatory cytokine content, proposing an enhanced bone healing potential [Canbeyli İD et al., 2018]. Nonetheless, the precise mechanistic action of PRP remains to be elucidated. A robust study employed radiological, histopathological, and immunohistochemical approaches to assess PRP’s impact on bone healing markers: BMP-2, VEGF, and Ki-67. Surprisingly, PRP exhibited minimal influence on these markers, suggesting limited enhancement in osteogenesis or angiogenesis. Yet, it promoted mature bone formation and adeptly suppressed excessive fibroblast activity, which could otherwise impede optimal bone regeneration. The diminished presence of woven bone further endorsed PRP’s prospective merits [Canbeyli İD et al., 2018].²⁹ It’s pivotal to recognize PRP’s nuanced effects: while it augments facets of bone restoration, it doesn’t markedly modify specific molecular pathways, especially those tied to BMP-2 and VEGF. This investigation illuminated PRP’s role but also underscored knowledge gaps, emphasizing the imperative for comprehensive research. Such endeavors will clarify PRP's definitive role in osteogenesis and guide its optimal application in orthopedic treatments [Canbeyli İD et al., 2018] (Table 1).²⁹

Table 1.

Growth factors in PRP during bone repair.

Growth factors in PRP during bone repair	Reference
α-granules	³⁰
Serotonin	¹
Histamine	³¹
Platelet-derived growth factor-D (PDGF)	³²
Transforming growth factor beta (TGF-beta)	²⁸
Vascular endothelial-derived growth factor (VEGF)	³²
The fibroblast growth factor (FGF)	²⁸
Bone morphogenetic protein 2 (BMP-2)	³³
Ki-67	³⁴

Molecular underpinnings of PRP in bone repair

PRP's recognition in bone regeneration is based on its molecular composition, including inflammatory cytokines, growth factors, and angiogenic elements.¹ Upon injury, platelet aggregation and the release of growth factors play a pivotal role in tissue regeneration.²⁰ These growth factors, including PDGF, TGF-beta, serotonin, and histamine, collectively orchestrate cellular activities fundamental for tissue repair.³⁵ The efficacy of PRP in bone healing is underscored by its modulation of molecules like IL-1 in macrophages and its influence on pivotal growth factors like PDGF, TGF-beta, IGF-1, and VEGF.^2,25 Specifically, PDGF, predominantly housed in platelet alpha granules, plays a significant role in processes such as collagen synthesis and revascularization. TGFs, especially TGF-β1 and β2 present in PRP, drive bone regeneration by promoting matrix synthesis while concurrently inhibiting osteoclast formation. Another pivotal aspect in bone repair is angiogenesis, especially during endochondral ossification’s remodeling phase. PRP, with its enriched VGF content, significantly promotes vascular growth, crucial for successful bone grafting. Interestingly, PRP-infused scaffolds, both synthetic and bio-derived, have been observed to improve bone inductivity.^13,22 While PRP undoubtedly holds promise, concerns surrounding its preparation techniques and its definitive role in bone regeneration necessitate further clinical scrutiny. As we progress, ensuring cellular viability in implanted scaffolds will be of the utmost significance.

PRP in orthopedic research: potential, efficacy, and application

Role of PRP in bone healing

Platelet-Rich Plasma, characterized by its rich concentration of growth factors, has risen to prominence in orthopedic research as a potential therapeutic asset in bone healing processes. Various studies have endeavored to elucidate the effectiveness of PRP across different bone conditions. Notably, a research study incorporating 132 patients with delayed union in long bones utilized PRP therapy.³⁶ A promising 81.8% of these individuals achieved bone union following the treatment, emphasizing its potential as a valuable intervention. The treatment notably excelled in addressing delayed union of the proximal tibia, especially in cases undergoing open reduction paired with plate fixation. In contrast, it demonstrated less efficacy in situations involving the proximal humerus Table 2.³⁶

Table 2.

PRP in orthopedic research: Potential, efficacy, and application.

The directions covered by PRP in orthopedic research	Reference	The position of chapters in the article
Bone Healing	^36,37	4.1
Tendon-to-Bone regeneration post-rotator cuff repair	^38–42	4.2
Osseo-tendinous convergence	^38,43–46	4.3
Synergy with Bone marrow Stimulation (BMS) for chondral lesion management	^1,47–52	4.4

A separate observational prospective cohort study further probed the capabilities of PRP in bone healing, focusing on skeletal defects often seen in high tibial osteotomy.³⁷ Although the abundance of platelet-derived growth factors in PRP theoretically enhances its allure for augmenting bone grafts, the study’s empirical findings paint a more complex picture. The utilization of PRP raises the prospect of crafting bioengineered grafts that could potentially restrict the displacement of bone fragments within the graft, courtesy of PRP’s viscous nature, a significant consideration for individuals prone to non-unions. Its influence on osteoblasts, osteoclasts, and mesenchymal-osteoprogenitor stem cells further underscores its potential role in bone formation.³⁷

The role of PRP in addressing skeletal defects, especially when used alongside bone grafts, remains under debate. While PRP’s innate properties might theoretically deter the displacement of bone fragments within grafts, the outcomes from various studies are not uniform. This divergence highlights the pressing need for research designed with specific clinical scenarios in mind.³⁷ However, amidst the optimism concerning PRP, findings from the high tibial osteotomy study present a more cautious perspective. Notably, while a non-union case showcased promising outcomes post-PRP treatment, the overarching bone density below the osteotomy wedge in the PRP group was not optimal. This indicates that PRP’s broad adoption should be approached with discernment, suggesting its effectiveness might be specific to certain conditions rather than a universal remedy for bone healing.^36,37 In conclusion, while PRP radiates hope in specialized bone healing avenues, its universal adaptability, especially in broader contexts, remains a subject of ongoing research.

PRP and tendon-to-bone regeneration post-rotator cuff repair

Rotator cuff interventions often confront challenges of post-operative re-tearing, an issue which persists notwithstanding progressive surgical innovations.⁵³ Traditional recuperation revolves around the vulnerable tendon-bone junction, predominantly consolidated by collagenous matrix.³⁹ Although myriad approaches pivot on factors such as suture design or anchorage systems, the biological confluence of tendon and bone has somewhat been sidelined, yielding complications more tissue-centric than instrumental or procedural.⁴² Platelet-Rich Plasma, replete with growth factors exceeding those in baseline blood, emerges as a prospective therapeutic agent.⁴¹ Its applicability, specifically in the domain of rotator cuff amelioration, remains variegated.⁵⁴ Research employing rat models illuminated PRP’s promise, delineating diminution in inflammation, amplification of tendon caliber, and increased tenacity against tendon rupture post-intervention, markedly evident during the initial post-operative window.⁴⁰ Yet, rat analogs may not aptly represent intricate human rotator cuff pathologies, and biomechanical outcomes may not extrapolate flawlessly into human therapeutic scenarios. Beyond the scope of rotator cuffs, ACL reconstruction endeavors have heralded PRP’s competence in enhancing osseo-tendinous integration, with early-phase animal trials indicating elevated efficacy.³⁸ While the latent potential of PRP is evident, investigations pivoting on human subjects are indispensable to chart its comprehensive orthopedic advantages.

PRP in osseo-tendinous convergence

Osseo-tendinous convergence is paramount within ACL reconstructive paradigms, emblematic of triumphant surgical outcomes.⁴⁵ Whereas osseous integration epitomizes optimal healing, concerns of donor site morbidity prompt the search for efficacious alternatives.⁴⁴ This quest has unveiled a plethora of promising candidates: avant-garde fixation substrates, osteogenic cytokines, hyperoxic therapies, and even extracorporeal pulse activation techniques.⁴³ Within this gamut, PRP, saturated with growth stimulants, emerges as a potential vanguard, presumably expediting wound recovery by augmenting cellular propagation, matrix deposition, vasculogenesis, and collagen fabrications.⁴³ Select studies resonate with the potentiality of PRP in fortifying the union of neo-ACLs, albeit consensus within the orthopedic fraternity remains elusive. Histomorphometric analyses depict an optimistic trajectory, underscoring enhanced bone-tendon convergence in the PRP milieu.⁴⁶ However, these examinations weren't devoid of constraints, notably the omission of biomechanical evaluations and detailed scrutiny of anchorage modalities. Yet, a lagomorph-based investigation delineated an encouraging narrative, accentuating that PRP-mediated tendinous graft integration yielded superior outcomes, starkly contrasting with non-PRP controls that exhibited diminished confluence.³⁸ In summation, PRP’s role, spanning from rotator cuff restorations to ACL overhauls, exudes transformative potential. Yet, for an unambiguous veneration of its orthopedic supremacy, a clarion call for rigorous, expansive research resonates.

PRP in synergy with bone marrow stimulation for chondral lesion management

The combined regenerative potential of PRP and Bone Marrow Stimulation (BMS) has been scrutinized for its applicability in treating cartilaginous defects.¹ Following a 6-month observational phase, Everts et al. indicated potential limitations of this combined strategy, noting minimal improvements in chondral regeneration when PRP was integrated with BMS.¹ Corroborating this, Milano et al. in an ovine model, found that while the merger of PRP gel and microfracturing did enhance certain cartilage repair metrics, it did not consistently produce the desired hyaline cartilage.⁵¹ Initial studies illustrated BMS’s potency, especially among younger patients with less pronounced cartilage defects. However, this therapeutic potential appeared to wane between 18 and 24 months, possibly due to challenges in melding fibrocartilaginous repair tissue with the native cartilage matrix.⁴⁸ While PRP alone suggested therapeutic promise in addressing degenerative chondral defects, its anticipated histological benefits appeared muted when combined with BMS, as observed by Lee et al. and Manunta and Manconi.^49,50 On a positive note, the amalgamation of PRP and BMS presented no adverse outcomes, underlining PRP’s safety profile for intra-articular usage. Additionally, Boffa et al. shed light on potential changes in the underlying bone structure, suggesting a prudent 6-week post-operative weight-bearing period after BMS interventions, particularly when focusing on the knee’s tibiofemoral region.⁴⁷ Several challenges punctuated the study, such as determining the most efficacious PRP concentrations for chondral healing and addressing platelet count inconsistencies stemming from varied preparation methods. Yet, the PRP protocols implemented aligned with therapeutic standards. In a porcine model, Olesen et al. emphasized that adding PRP to BMS did not markedly improve acute chondral injury outcomes.⁵² This necessitates further exploration to refine PRP formulations and strategies, aiming to fully leverage its regenerative capabilities.

Harnessing cellular and cytokine synergies: Exploring the potentials of PRP, MSCs, and combinatorial therapies in orthopedic regeneration

Muscle-derived mesenchymal stem cells and PRP

Large bone defects (LBD), resulting from tumor resections or congenital malformations, pose significant clinical challenges.⁵⁵ Traditional methods often face issues such as biomaterial incompatibility and allograft rejection. In light of this, direct autologous bone implantation is favored due to its histocompatibility and negligible immune response.⁵⁶ Recently, attention has shifted towards the use of autologous mesenchymal stem cell (MSC) implantation, especially muscle-derived MSCs (M-MSCs), for LBD treatment.⁵⁷ Originating as precursors to key connective tissue cells in adults, M-MSCs can transform into various cells, including muscle and osteocytes.⁵⁸ Unlike their bone marrow-derived counterparts, M-MSCs, abundant in adult muscle tissues, are easily accessible and cultivated.⁵⁹ This accessibility enhances their bone repair potential, especially in defects where the periosteum is compromised.⁵⁸ Beyond direct repair, M-MSCs also secrete paracrine factors crucial for the regulation of the healing process Table 3.⁵⁷

Table 3.

The potential of the synergy between cells and cytokines with PRP in orthopedic regeneration.

The potential of the synergy between cells and cytokines with PRP in orthopedic regeneration	The position of chapters in the article
Muscle-derived mesenchymal stem cells(MSC) and PRP	5.1
Kartogenin and PRP	5.2
PRP and BMAC in osteochondral regenerative therapy	5.2

In bone tissue engineering, the repair capability of seed cells isn’t solely inherent but is influenced by the environment of extracellular cytokines. Platelet-Rich Plasma, loaded with cytokines, has emerged as a promising adjunct.⁶⁰ Comprising platelets at concentrations higher than typical blood and abundant active factors, PRP facilitates wound repair.⁶⁰ However, the impact of PRP in extensive bone repair remains under-investigated. Existing studies suggest its effectiveness in enhancing periodontal cell activities, indicating its potential to stimulate M-MSC growth and speed up bone restoration.⁶¹

The question arises about PRP’s effect on M-MSC's osteogenic differentiation and its role in bolstering M-MSC's LBD regenerative capability.Yin N et al.’s pioneering study delved into this, inducing LBD in rabbit humeral bones.¹⁹ The results were eye-opening: combining M-MSCs with PRP surpassed treatments using only one component, showing noticeable bone defect remediation improvements. A 90-days post-operative assessment supported these results, revealing that the combined approach was more effective in promoting bone healing. On a molecular level, PRP was found to enhance M-MSC migration and proliferation and to increase markers like Cbfa-1 and Coll I, along with a rise in ALP activity. This study underlines the potential of integrating M-MSCs with PRP for LBD repair, highlighting the molecular mechanisms responsible for PRP’s beneficial effects on M-MSC regeneration.¹⁹ Notwithstanding this understanding, it remains essential to explore further factors, including gender and age, to truly comprehend the therapeutic potential of this combination.

Kartogenin and PRP

KGN is a small bioactive molecule initially identified for its role in the chondrogenic differentiation of bone marrow MSCs.⁶² This molecule functions by disrupting the interaction between core-binding factor β (CBFβ) and filamin A, leading to the nuclear translocation of CBFβ.⁶³ Once in the nucleus, CBFβ complexes with the runt-related transcription factor-1 (RUNX1), subsequently enhancing the expression of COL II and aggrecan. Furthermore, KGN has been reported to bolster the development of cartilage nodules and synovial joints during limb development via the transforming growth factor β (TGFβ) signaling pathway.⁶³

The tendon-bone interface, particularly its fibrocartilage zone, plays an indispensable role in facilitating a smooth transition between tendon and bone. Unfortunately, the regenerative ability of this zone post-injury is often compromised, frequently resulting in graft failures. Existing therapeutic strategies, such as growth factors, MSCs, and periosteum grafts, although promising in animal models, face significant translational challenges in clinical settings, ranging from safety to cost-effectiveness.Emerging from this backdrop, KGN appears as a beacon of hope. Recognized for its potential in promoting chondrogenic differentiation and rectifying cartilage defects as demonstrated in osteoarthritic models, its efficacy skyrockets when combined with PRP.⁶⁴ PRP, being a rich source of pivotal growth factors required for tissue repair, not only augments KGN’s activity but also prevents its undesired dispersion.⁶⁵ Preliminary studies involving rats have illuminated the potent regenerative capabilities of the KGN-PRP combination, especially concerning the fibrocartilage zone.⁶⁵ Notably, outcomes displayed superior mechanical strength in comparison to monotherapies with PRP or saline. These promising results hint at the potential application of this therapeutic combo in surgical endeavors like ACL reconstructions and rotator cuff repairs.⁶⁴

In the broader landscape of orthopedic challenges, the meniscus, integral to the knee's function in force distribution and joint stabilization, frequently grapples with healing limitations, particularly in its avascular inner segment. This diminished reparative capacity is starkly evident in demographics such as athletes and the elderly, often manifested as chronic meniscal injuries. While conventional therapies can ameliorate symptoms, they occasionally culminate in long-term complications. This is where the realm of tissue engineering shines, capitalizing on the confluence of cells, growth factors, and biomimetic scaffolds. MSCs, renowned for their chameleon-like ability to differentiate into diverse cell types, emerge as a frontrunner in the race for meniscal repair strategies. Amplifying the regenerative prowess of MSCs is the combination of KGN and PRP, loaded with growth factors like PDGF, TGF, and VEGF.⁶⁶ This therapeutic synergy has birthed an avant-garde methodology for meniscal healing, predicated on deploying stem cells to injury sites and guiding their differentiation trajectory towards chondrocytes.⁶⁷ A cutting-edge technique encapsulates this approach, introducing a concoction of KGN, PRP, and bone marrow stromal cells(BMSCs) to the injured meniscal tissue. Rooted in the hypothesis that BMSCs, under the stewardship of KGN and PRP, metamorphose into chondrocytes, this modality aims to pioneer meniscal restoration.³⁵ Empirical studies employing rabbit femur-derived BMSCs have corroborated the efficacy of the KGN + PRP formulation in accentuating chondrogenic differentiation, underscoring its prospective clinical relevance in meniscal interventions.³⁵

PRP and BMAC in osteochondral regenerative therapy

Bone Marrow Aspirate Concentrate has garnered attention in the orthopedic domain as a regenerative powerhouse, effectively addressing diverse challenges, from osteoarthritis to intricate cartilage defects, using the body’s inherent cellular mechanisms. Its ability to confront issues like poor vascularity and limited regeneration makes it a versatile solution for not just traditional orthopedic problems but also conditions like Tennis/Golfer’s Elbow and Achilles tendinitis.Research indicates that PRP-derived growth factors are instrumental in promoting chondrogenic differentiation of BMSCs, advancing chondrocyte proliferation, and facilitating extracellular matrix synthesis.⁶⁸ Betsch et al., highlighted that the combination of PRP and BMAC enhances osteochondral defect repair, especially in specific animal models.⁶⁹

A common injury among athletes, osteochondral lesions of the talus (OCL) — often a result of recurrent trauma or ankle misalignments — demands innovative therapeutic strategies. Traditional solutions such as bone marrow stimulation and autologous grafting provide short-term relief but do raise concerns about the durability and quality of the regenerated tissue. Enter PRP and BMAC, combining stem cell regeneration and growth factor dynamics, promising enhanced tissue restoration and safety.⁷⁰ However, the validation through extensive clinical studies is still a requisite.

A study by Getgood et al. evaluated PRP and Concentrated Bone Marrow Aspirate (CBMA) combined with a biphasic collagen/glycosaminoglycan (GAG) osteochondral scaffold in ovine osteochondral defects.⁷¹ Though quantitative assessments did not reveal significant differences, a qualitative analysis suggested an inclination towards more hyaline cartilage-like tissue repair in the PRP/scaffold group.⁷¹ This evidence accentuates PRP’s potential in improving hyaline-like cartilage repair, calling for expanded research using larger animal models, especially considering its cost benefits.

Innovations in bone regeneration technology have accentuated the merits of coupling PRP with various biomaterials. For instance, a 3D printed scaffold combined PRP with gelatin microspheres, presenting both augmented mechanical resilience and an enhancement in the function of exogenous BMSCs.⁷² Another breakthrough was the PRP-GA@Lap bioink combined with PCL, exhibiting exceptional bone repair capabilities. Studies like these have emphasized the potential of bone marrow-derived mesenchymal stem cell (BMSC) sheets amalgamated with PRP gel and calcium phosphate, amplifying bone regeneration. Specifically, the combination of BMSC sheets teeming with cells and growth factors, PRP gel, and calcium phosphate particles significantly magnified bone formation.⁷³

In summation, PRP and BMAC have set the stage for groundbreaking advancements in the field of cartilage regeneration, offering a promising avenue for treating osteochondral issues. As the future unfolds, the true potential of these strategies, replete with their cellular and molecular synergies, could redefine orthopedic care. Yet, solidifying their role necessitates consistent, in-depth research to unveil their comprehensive capabilities and confirm their effectiveness.⁷⁰

Enhancing bone regeneration: the convergence of PRP and biomaterials in advancing bone regeneration

Bone defects, arising from a myriad of etiologies such as trauma, congenital anomalies, or surgical necessities, pose significant therapeutic conundrums. Although conventional modalities like autografts, allografts, and vascularized bone grafts remain prevalent, they are encumbered by intrinsic limitations, including donor site morbidity and potential immunological repercussions. Contemporary strategies in addressing bone defects are increasingly leaning towards the amalgamation of PRP with a variety of biomaterials-ranging from natural polymers such as collagen to synthetic derivatives like poly(lactic-co-glycolic acid) (PLGA) — or leveraging different biomaterials to forge 3D scaffolds. These innovations not only facilitate structural support but also foster the sustained release of growth factors from PRP, thereby augmenting the bone regeneration process. Nevertheless, this promising avenue is not devoid of practical impediments. The effectiveness of such integrated systems profoundly depends on a spectrum of factors including the specific clinical situations they are deployed in, the chosen biomaterials, and their harmonization with PRP, alongside considerations of the particular preparation protocols and individual patient characteristics. To forge a path forward, it is imperative to undertake rigorous research endeavors to standardize protocols and cultivate a nuanced understanding of the intricate interactions between the materials and biological entities involved. A committed pursuit of advancing this field holds the promise to radically transform the paradigms of bone defect treatments in the near future, offering a beacon of hope for more effective solutions Table 4.

Table 4.

The convergence of PRP and biomaterials in advancing bone regeneration.

The convergence of PRP and biomaterials in advancing bone regeneration	The position of chapters in the article
The synergy of 3D printed scaffolds and PRP	6.1
PRP and Hydroxyapatite (HA)	6.2
β-tricalcium phosphate with platelet-rich plasma	6.3
Graphene oxide and PRP	6.4

The synergy of 3D printed scaffolds and PRP: Charting the future of bone regeneration

Bone defects have perennially posed therapeutic challenges in orthopedics.⁵⁵ Traditional solutions, such as autologous bone grafting, although deemed reliable, are fraught with limitations, including limited donor sites and potential nerve injuries.⁵⁵ Allografts present another solution but are not without risks of immune reactions.²¹ However, the field is currently undergoing a renaissance with the introduction of 3D-bioprinted scaffolds, which offer an amalgamation of anatomical precision and functional effectiveness.¹⁸ The innovation lies in harnessing PRP infused within these scaffolds, particularly when married to cutting-edge biomaterials, yielding enhanced biomechanical and therapeutic properties.⁷²

Liu et al.epitomize the advances in this domain, revealing the potential of 3D-printed scaffolds combined with PRP-infused gelatin microspheres.⁷² Their study demonstrates how PCL/β-TCP integrated with PRP-gelatin microspheres offers not only superior mechanical robustness but also modulates cytokine release. This novel environment augments the functionality of exogenous BMSCs, yielding significant promise in mending bone defects in vivo. Yet, challenges persist, especially in calibrating PRP concentrations and finessing scaffold design.

Cao et al. further highlight the importance of bioink selection in 3D printing for bone regeneration.⁷⁴ While growth factors like BMP-2 and VEGF show immense promise, their associated costs and potential complications spur researchers towards viable alternatives like PRP. Addressing PRP's rapid release dynamics, Cao et al. innovatively combined Methacrylated gelatin (GelMA) and Methacrylated alginate (AlgMA) with nanoclays, offering a platform for controlled growth factor release, a vital ingredient for effective bone repair. Their 3D-printed scaffold, integrating rat-derived PRP within a GelMA/AlgMA matrix modulated by Lap nanoclay, showcased promising results in both in vitro and in vivo settings, endorsing vascularization and effective bone repair in rat models.⁷⁴

In conclusion, the fusion of PRP with advanced 3D printing technologies and innovative bioinks holds the potential to revolutionize orthopedic medicine. As the field progresses, the synergistic blend of these components paves the way for groundbreaking orthopedic therapeutic strategies, portending a transformative future in bone regeneration.

PRP and hydroxyapatite in bone regeneration

Natural bone dynamics predominantly oscillate between the processes of resorption and formation. In specific clinical scenarios, there arises a need for external interventions such as autogenic grafts or bone substitutes. Although these substitutes possess osteoconductivity, their ability to accommodate osteogenic cells and vital signaling molecules is often limited. The potential benefits of combining PRP, rich in growth factors, with a bone substitute formulation of 80% tricalcium phosphate and 20% hydroxyapatite (HA) have emerged as a topic of interest in recent research.¹ Notably, Skwarcz et al. reported an increase in bone tissue density upon the inclusion of PRP.⁷⁵ Nevertheless, outcomes across different studies show variability, possibly due to differing research methodologies. This underscores the necessity for evaluations that are tailored to specific contexts.⁷⁶

One such comprehensive study, conducted by Segundo et al., delved into the combined efficacy of PRP, HA, and chitosan in promoting bone and cartilage regeneration within the rabbit femoral trochlea.⁷⁷ Their findings accentuated the value of HA, especially when combined with ceramics, in boosting bone tissue repair. However, the study did not furnish a direct comparison between the collective and isolated impacts of these biomaterials, leaving a data interpretation gap. Yet, the primary outcomes suggest the composite’s promising role in bone and cartilage restoration. This potential is further echoed in several animal trials which validate PRP’s effectiveness, especially when merged with substances like calcium phosphate cement and HA, in mending bone deficiencies. Still, the definitive role of PRP in cartilage rejuvenation remains contested, marking an avenue for future explorations. Expanding the perspective to bone tissue engineering, novel approaches are emerging that prioritize stem cells, growth modulators, and tailored biocompatible scaffolds. A standout innovation is the melding of HA with organic polymers, such as the nanohydroxyapatite/polyamide 66 scaffold. This combination has garnered attention for its biomimicry traits.⁷⁸

Addressing LBDs poses ongoing clinical challenges. Traditional techniques like autografts and vascularized bone grafts often come with constraints. PRP, rich in platelets and growth factors, holds promise in enhancing vascularization and osteogenesis. This potential is echoed in the work by Li et al. showcasing sintered porous Ti6Al4V scaffolds incorporated with mesenchymal stem cells and PRP. Further affirmation comes from Liu et al., elucidating the integrated merits of PRP gel, HUMSCs, and the nHA-PA66 scaffold. By the end of the 12-week period, this combined scaffold exhibited significant advancements in cellular growth and bone recovery.⁷⁸ Collectively, these studies highlight the promising application of the HUMSCs-PRP-gel/nHA-PA66 scaffold in addressing LBDs.⁷² Lastly, another research by Segundo FAS et al.focused on the synergistic therapeutic effects of PRP, HA, and chitosan. Their results suggest that the combined application of chitosan and PRP yields superior results than their isolated use.⁷⁷ Furthermore, incorporating ceramics, such as hydroxyapatite, enhances bone tissue recovery. Although the study didn't differentiate between the joint and individual effects, the primary observations emphasize the potential of the combined approach in bone and cartilage healing.⁷⁷ In a subsequent study by Segundo FAS et al., the synergistic therapeutic effects of PRP, HA, and chitosan were evaluated.⁷⁷ Their findings suggest a better outcome from the combined application of chitosan and PRP compared to their separate applications. Additionally, the inclusion of ceramics like hydroxyapatite has proven beneficial for bone tissue recovery.Moreover, Gu et al. introduced a three-dimensional porous scaffold made from a specific borosilicate bioactive glass (13-93B1) via a foam replication technique.⁷⁹ When tested, these scaffolds showed good integration with newly formed bone and conversion to hydroxyapatite.⁷⁹ Notably, bone regeneration was amplified when these scaffolds were complemented with PRP, emphasizing their regenerative and biocompatible properties.⁷⁹ In conclusion, the combined use of PRP and HA shows significant promise in the field of bone regeneration, with various studies underscoring its potential benefits and paving the way for further research.

Preparation of a new composite combining strengthened β-tricalcium phosphate with platelet-rich plasma as a potential scaffold for the repair of bone defects

To address bone defects, clinicians often employ autogenic grafts, allogeneic grafts, or industrially manufactured bone substitutes.⁸⁰ These can be sourced from demineralised bone matrices or synthesized derivatives, predominantly based on calcium phosphates such as hydroxyapatite or tricalcium phosphate.⁸¹ Notably, while these substitutes offer impressive osteoconductive attributes, they generally lack the indispensable osteogenic cells and pivotal signaling molecules required for optimal bone regeneration.In recent years, attention has shifted towards PRP. Wang et al. pioneered this approach, crafting a composite scaffold that melded strengthened β-TCP with PRP.⁸² The composite bore morphological resemblances to the fungus Boletus kermesinus and displayed superior mechanical strength and biocompatibility compared to β-TCP on its own. SEM imaging further highlighted BMSCs flourishing on this composite, indicating its potential for bone tissue engineering.⁸²

However, the application of PRP in bone regeneration has garnered contention. Skwarcz et al. delved into the efficacy of a bone substitute comprising 80% tricalcium phosphate and 20% hydroxyapatite combined with PRP.⁷⁵ While their MicroCT imaging demonstrated heightened bone tissue density with PRP inclusion, other assessments in the study discerned no substantial advantages. Discrepancies like these in findings across diverse studies can potentially stem from methodological variations.⁷⁵ To conclude, PRP undeniably showcases promise as a potent enhancer in bone regeneration. Yet, its real-world clinical effectiveness remains under discussion. Comprehensive evaluations considering the myriad of factors influencing outcomes in distinct clinical scenarios are imperative for establishing its definitive role in bone regeneration.

Graphene oxide and PRP

The combination of graphene oxide (GO) and PRP has shown significant promise in advancing tendon-bone healing, particularly in a rabbit model of supraspinatus tendon reconstruction.⁷ The impetus for combining GO with PRP is underpinned by the former’s ability to enhance material properties and the latter’s rich growth factor profile conducive for healing. Research has indicated the 0.5 GO/PRP gel formulation's superiority in terms of mechanical attributes, biocompatibility, and stimulation of bone marrow mesenchymal stem cell (BMSC) proliferation and differentiation.⁷ Conventional surgical procedures often do not sufficiently restore the intricate structure of tendon-bone interface (TBI), which is crucial in rotator cuff repair, highlighting the potential of GO/PRP innovations.⁷ Despite PRP’s sporadic effectiveness in tendon repair, attributed to diverse preparation methods and the ephemeral nature of growth factors, the inclusion of GO seeks to overcome these challenges. GO’s integration not only amplifies the gel’s mechanical robustness but also bolsters nutrient exchange and elongates the release of growth factors, acting as a reliable delivery system.⁷ A sustained release of TGF-β1 for over a fortnight is particularly remarkable. Nonetheless, high concentrations of GO can lead to extended, intense growth factor release, presenting potential drawbacks. The efficacy of GO in cellular activities, including adhesion, growth, and differentiation, has been consistently validated. Notably, upon GO’s introduction, BMSC proliferation was conspicuously accelerated within 5 days. However, elevated GO concentrations can elicit cytotoxic effects, accentuating the need for precise concentration calibration.⁷ In vivo trials on rabbit models, simulating human tendon injuries, confirmed the 0.5 GO/PRP gel’s stellar efficacy, proficiently replicating the natural tendons in structure and biomechanics without any discernible toxicity. The study, though illuminating, harbored certain constraints, such as its concentration on acute injuries and specific cells. Given its reliance on animal models, rigorous preclinical evaluations are essential before progressing to human trials. To encapsulate, the GO and PRP amalgamation in the formulated gel offers significant potential in treating rotator cuff tears, chiefly with its regulated growth factor release and augmented TBI healing. PRP's established role as a therapeutic medium for tendon recuperation, paired with GO’s prowess as a tissue repair stimulant and biomaterial property enhancer, makes the GO-PRP blend a propitious strategy for rotator cuff injury treatments.⁷

Controversies and limitations

The repair of large segmental bone defects due to trauma, inflammation, and tumor surgery remains a major clinical problem. Animal models were developed to test bone repair by tissue engineering approaches, mimicking real clinical situations. Studies differed with regard to animals, treated bone, chemistry, and structure of the scaffolds. As the advantage of PRP as a matrix for cells is that PRP is autologous and nontoxic, it is inherently safe, and any concerns of disease transmission such HIV, hepatitis, or Creutzfeldt-Jakob disease or immunogenic reactions that exist with allograft or xenograft preparations are eliminated. However, the preparation of PRP involves isolation of the PRP, after which gel formation is accelerated using calcium chloride and bovine thrombin. The use of bovine thrombin has been reported to be associated with the development of antibodies to factors V and XI, resulting in the risk of life-threatening coagulopathies.⁸³ Despite some benefits demonstrated to date, it must be acknowledged that the uses of PRP in bone healing applications are still weakly supported. Inferences regarding the potential establishment of platelet therapy as a reliable, efficacious, and safe therapy in managing the bone wound will require the completion of high-quality clinical trials with long-term followup. In particular, the supply of oxygen and nutrients to the cells in the inner part of the implanted scaffolds remains a major concern, requiring additional investigations.¹

Future directions

In summation, these insights underscore the vast therapeutic potential of PRP in the realm of bone repair. While more research and clinical trials are essential to refine and expand upon these findings, the future for PRP in orthopedic and regenerative medicine seems promising. As the field continues to evolve, it is anticipated that PRP, with its rich repository of growth factors and healing properties, will play an increasingly pivotal role in bone repair methodologies.

Conclusion

In the rapidly advancing domain of orthopedic therapeutic research, the profound implications of PRP have garnered substantial attention. Its autologous nature augments its appeal, offering both economic and immunological benefits, effectively sidelining concerns affiliated with exogenous growth factors. As highlighted in this review, the confluence of PRP with cutting-edge modalities like 3D-printed scaffolds and Kartogenin reveals promising trajectories, particularly in the niche of tissue engineering and meniscal interventions. Despite these promising advancements, challenges such as standardization, cost-effectiveness, and potential complications demand judicious consideration. The dynamic interface between PRP and biomaterials, underscored by its synergistic potential with diverse biomaterials and clinical contexts, forms the crux of modern orthopedic therapeutic research. As the trajectory of PRP in orthopedic healing oscillates between optimism and circumspection, the immediate research horizon should center on randomized large-scale studies, honing in on PRP’s optimal concentrations and preparation methodologies. It is anticipated that with systematic research endeavors and strategic interdisciplinary collaborations, PRP’s full potential in orthopedic treatments can be realized, fostering enhanced patient outcomes.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the Jiangxi Province Traditional Chinese Medicine Research Project (Project Number: 2019A417) and the Jiangxi Provincial Health Committee Research Plan Project (Project Number: 20197506 and 202410934).

Consent for publication

All authors of this manuscript have read and approved its content and have agreed to the journal’s submission policies and conditions. They confirm that the content of the manuscript has not been published or submitted for publication elsewhere.

Ethical statement

ORCID iDs

Liangbo Zhu

Ping Li

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