Bio-Inspired 3D-Printed Modular System for Protection of Historic Floors: From Multilevel Knowledge to a Customized Solution

Abstract

Historic floors, including mosaics, stone slabs, and decorated pavements, are fragile elements that can be easily damaged during restoration works. Risks arise from falling tools, concentrated loads of scaffolding or equipment, and the repeated passage of workers. Traditional protection methods, such as plywood sheets, mats, multilayer systems, or modular plastic panels, have been applied in different sites but often present limitations in adaptability to irregular surfaces, in moisture control, and in long-term reversibility. This paper introduces an innovative approach developed within the 3D-EcoCore project. The proposed solution consists of a bio-inspired modular sandwich system manufactured by 3D printing with biodegradable polymers. Each module contains a Voronoi-inspired cellular core, shaped to match the geometry of the floor obtained from digital surveys, and an upper flat skin that provides a safe and resistant surface. The design ensures mechanical protection, adaptability to uneven pavements, and the possibility to integrate ventilation gaps, cable pathways, and monitoring systems. Beyond heritage interventions, the system also supports routine architectural maintenance by enabling safe, reversible protection during inspections and minor repairs. The solution is strictly temporary and non-substitutive, fully aligned with conservation principles of reversibility, recognizability, and minimal intervention. The Ninfeo Ponari in Cassino is presented as a guiding example, showing how multilevel knowledge and thematic mapping become essential inputs for the tailored design of the modules. The paper highlights both the technical innovation of the system and the methodological contribution of a knowledge-based design process, opening future perspectives for durability assessment, pilot installations, and the integration of artificial intelligence to optimise core configurations.

1. Introduction

Historic floors, including mosaics, stone slabs, bricks and decorated pavements, are among the most delicate elements of built heritage and are extremely vulnerable during conservation and construction activities. They can be damaged by accidental impacts, the concentrated loads of scaffolding and equipment, vibrations, or simply the repeated passage of workers. This vulnerability is even greater when pre-existing deterioration, loss of adhesion, or moisture-related decay are present. For this reason, international charters and conservation guidelines place strong emphasis on preventive measures, minimal intervention, reversibility, and the compatibility of materials. The Venice Charter of ICOMOS [1] clearly established the principle of reversibility, while later recommendations for the conservation of mosaics and decorated surfaces highlighted the importance of preventive strategies and the need to monitor the interaction between protective measures and the original fabric [2]. More recently, national agencies such as Historic England have produced specific guidance on the temporary protection of historic features during building works [3,4,5,6], and technical documents like EN 15757:2010 [6] have introduced standards for monitoring temperature and relative humidity in order to mitigate climate-induced mechanical damage [6,7].

Traditional approaches to floor protection have generally relied on simple coverings, such as plywood panels, cardboard sheets, or textile mats, and on multilayer systems that combine geotextiles, cushioning layers and sacrificial coverings. In other cases, modular road plates have been employed to spread heavy loads and allow access for machinery. Each of these solutions presents advantages and limitations. Rigid modular panels are easy to install and provide good load distribution but they do not adapt well to irregular surfaces and can concentrate stresses at contact points [8]. Multilayer coverings can better follow the geometry of uneven pavements, but they are time-consuming to install and, if they are not breathable or properly ventilated, they may trap moisture and create dangerous microclimates under the protection, with risks of salt crystallisation, efflorescence or biological growth [3]. Although conservation standards acknowledge the importance of environmental stability, very few studies have measured the microclimate beneath protective layers during building works, leaving a significant methodological gap in this field.

In recent years, developments in materials science and digital technologies have opened new perspectives for heritage protection. Composite sandwich panels, widely used in aerospace and civil engineering, offer high stiffness-to-weight ratios and can be designed for impact resistance. Life-cycle studies also show their potential environmental benefits when solutions are light, reusable and recyclable [9]. At the same time, additive manufacturing has introduced new possibilities for producing customised protection. Lattice and Voronoi-type structures, manufactured by 3D printing, can be tuned to absorb energy and to follow irregular surfaces [10,11]. Even more advanced approaches, such as 4D printing with shape-memory polymers, suggest protective systems able to recover their shape after impact and to extend their service life [12,13]. These solutions are still experimental, but they represent a promising direction for protective devices in conservation.

The integration of digital surveying techniques further reinforces this potential. Laser scanning and photogrammetry have become standard methods for documenting architectural heritage, capturing plano-altimetric irregularities with sub-centimetric precision. While these techniques are commonly applied for documentation, their use as direct input for the engineering design of protective systems is still rare [5,14]. By linking accurate 3D surveys with digital design tools, it becomes possible to fabricate protection that adapts to the actual geometry of historic pavements, ensuring uniform contact and reducing stress concentrations.

Reality-based 3D documentation and its integration with conservation workflows are well established; we build on these approaches but target temporary floor protection and a knowledge-to-design translation for tailored panels [15,16]. This positions our contribution within current practice while focusing on site-specific application.

In this framework, the present work proposes a bio-inspired modular sandwich system manufactured by 3D printing with biodegradable polymers. The modules are based on a Voronoi cellular core and a flat protective skin, while the lower surface is shaped according to the digital survey of the heritage floor. This ensures full contact with the surface, reduces localized loads, and allows the integration of ventilation channels to control rising damp. The design also foresees passages for cables and monitoring devices, thus combining temporary protection with preventive conservation. The proposed methodology is tested on the Ninfeo Ponari in Casinum (Italy), which serves as a case study to demonstrate the process from digital documentation and thematic mapping to customized module design. The aim is not only to present a technological solution but also to contribute to the development of a framework that integrates conservation standards, digital documentation and innovative manufacturing, in order to create protective systems that are reversible, compatible and effective for safeguarding historic floors during restoration.

In addition to heritage conservation and restoration, routine maintenance operations often require temporary floor protection for access, inspection, and light repair works. The proposed panels address this recurring need by providing a removable, reusable, and geometry-matched protection that reduces surface stress, impact risk, and dirt accumulation. This broader maintenance-oriented scope complements conservation practice and improves day-to-day stewardship of architectural assets.

This brief report disseminates the concept and its application on a specific heritage asset; within the same project, partner teams are finalizing detailed studies on mechanics, stiffness, adhesion, biodegradability and LCA that enabled the present solution and will be reported in dedicated publications. Basic manufacturing data are reported here to clarify process and materials. Layer thicknesses and mechanical performance are tuned per application; comprehensive datasets (compressive strength, load carrying per unit area, abrasion/erosion resistance and service durability) have been developed within the project and will be presented in dedicated partner publications. This brief report focuses on the concept and its site-specific application.

2. 3D-EcoCore Modular System

The 3D-EcoCore project is a research initiative coordinated by the University of Cassino and Southern Lazio, within Spoke 6 of the Italian MICS program. The project develops advanced sandwich structures using biodegradable and biocompatible materials produced by 3D printing.

The innovative aspect lies in the bio-inspired modular core system, designed for direct application to the protection of historic floors during restoration. The system is conceived as a set of interlocking modular panels, each fabricated by 3D printing with a Voronoi-inspired cellular structure that ensures both lightness and high energy absorption (Figure 1).

The sea urchin is used as a conceptual cue: a stiff outer skin and a lightweight graded core cooperate to diffuse contact stresses and mitigate local impacts. In our panel, the Voronoi-inspired cellular core translates this graded load diffusion, while the upper skin forms a continuous walking surface suitable for temporary works.

In order to adapt this module to the frequent irregularities of historical floors, the lower surface of each module is shaped according to the plano-altimetric configuration of the historic pavement, obtained through a digital laser-scanner survey. In this way, the protective core perfectly follows the irregularities and discontinuities of the floor, ensuring full contact and avoiding stress concentrations on single points of the historic material.

The upper surface of the modular core is flat and continuous, providing a safe and stable working platform. On this surface, an additional protective skin is applied with two main functions. First, it increases the resistance of the sandwich system to mechanical impacts (e.g., falling tools or concentrated loads from scaffolding and equipment). Second, it protects the core itself from wear during restoration activities (Figure 2). Current prototypes use PLA-based biopolymers. The cellular core and the upper skin are printed in commercial-grade PLA, while a thin sacrificial film or coating from the same family is being evaluated as a protective “skin” to reduce wear during site operations. All parts remain fully removable and replaceable as part of the temporary protection strategy.

The core is manufactured by FDM 3D printing on a Prusa XL (multi-nozzle) using commercial PLA. A removable support (PolySupport) enables printing of the open Voronoi lattice. After printing, the modules are cleaned and bonded with two-component structural epoxies (e.g., 3M EC 9323 B/A, Loctite EA 9309.3NA, EA 9396) selected for compatibility with thermoplastics. A flat PLA upper skin is printed to provide a continuous, non slip walking surface and to protect the core during site operations. Prototype demonstrators use a typical core thickness of about 20 mm, while cover layers for LCA demonstrators consist of recycled stone agglomerates with thicknesses in the 7–12 mm range depending on the application.

Within the same project, the system underwent essential verification steps that informed the final design used here. Printed cores and sandwich panels were tested in compression and in dynamic conditions to assess stiffness and energy absorption under trampling and accidental local impacts. Core–skin bonding was qualified through adhesive selection and surface preparation checks, and reinforced-skin prototypes were developed to improve overall panel response. A walking co-simulation coupled with the measured material law was used to verify contact stress levels under typical site operations. These activities enabled the tailored configuration applied on the heritage floor. Full test protocols, datasets and statistical analyses are being finalized by partner teams and will be presented in separate publications. Detailed mechanical and durability datasets are being finalized by partner teams and will be reported in separate publications.

Furthermore, the skin can be customized by printing the exact map of the underlying pavement, allowing workers to identify the configuration of the historic floor even when it is completely covered. This feature supports monitoring and reversibility, in line with established conservation principles.

The material choice addresses end-of-life options rather than short on-site exposure. Under indoor, dry service typical of temporary protection, PLA-based parts show negligible short-term degradation; main ageing modes are stiffness loss and embrittlement if heat or moisture are high. Under industrial composting, hydrolysis and subsequent biodegradation lead to innocuous products (lactic-acid intermediates, CO₂, water). Within the present project, a partner research team has specifically investigated degradation pathways, time scales and mitigation through protective skins; their results are being finalized for submission to specialized journals.

The system has also been conceived as multifunctional. While primarily developed as a temporary protective layer, the modular core can also serve as a ventilated underfloor void system. This function is particularly valuable in historic buildings where moisture accumulation and rising damp are major causes of degradation. By creating a controlled air gap beneath the protective skin, the EcoCore modules promote natural ventilation and drying of the underlying pavement, mitigating humidity-related risks such as efflorescence, salt crystallization, or biological growth. In this way, the system not only prevents mechanical damage during restoration works but also actively contributes to the long-term conservation of historic floors.

Additionally, the core can be adapted as an innovative screed system capable of integrating articulated installations (pipes, electrical conduits, or underfloor sensors). This multifunctional approach highlights the flexibility and future potential of the EcoCore technology, which can serve both as a temporary protective solution and as a permanent enhancement for the durability and functionality of heritage pavements.

The system is lightweight and modular to allow safe handling in heritage sites. Panels are transported in reusable crates and moved indoors with non-marking carts or dollies. Two operators place each panel using manual grips or optional suction-cup lifters. The underside follows the survey-based contact surface, a small perimeter clearance avoids contact with walls and thresholds, and adjacent panels connect through simple interlocks and edge seams. No anchors or adhesives are applied to the original floor. Dismantling follows the reverse order with basic hand tools (release of interlocks, panel lifting, crate packaging). Each panel is inspected, cleaned and labelled for reuse. This reversible workflow limits risk for the substrate and reduces time on site.

3. Proposal for Application to Ninfeo Ponari

The Ninfeo Ponari is part of a luxurious Roman domus built in the 1st century BC in the ancient city of Casinum, located on the lower slopes of Montecassino hill, in Italy. The monument consists of a rectangular vaulted chamber with wall niches, richly decorated with mosaics, shells, colored glass, and painted plasters (Figure 3). The floor presents a mosaic made of polychrome tesserae and marble fragments, while traces of decorative plaster and shell incrustations still survive on the walls.

Historically, the building probably functioned as a coenatio aestiva (summer dining room) enriched with fountains, confirming its role as a private nymphaeum within the domus.

The monument was rediscovered in the 20th century after being buried for centuries by debris and slope material [17]. Recent archaeological campaigns and structural studies have highlighted both its cultural importance and its vulnerability to humidity, slope instability, and material degradation [18]. Geotechnical-structural investigations, including 3D laser scanning, photogrammetry, and finite element modeling, were carried out by the Authors to understand soil–structure interaction, wall deformation, and local failure mechanisms [19,20,21]. The results confirm the need for integrated conservation strategies combining archaeological, structural, and environmental knowledge.

In the Ninfeo Ponari case, the floor was surveyed with a terrestrial 3D laser scanner (FARO Focus X130) from multiple stations covering the entire room. Spherical targets enabled registration into a single dense point cloud. The dataset was cleaned, subsampled and meshed, then processed in CloudCompare to extract the plano-altimetric surface and to delineate tile edges and joint lines. This workflow captures small level differences and wear patterns between adjacent tiles and provides the contact geometry used to shape the underside of the protective modules.

Phases Preliminary to the Design of the EcoCore System

To ensure the safe restoration and conservation of the Ninfeo Ponari floor, the design of the proposed EcoCore system necessarily requires important preliminary phases of knowledge, summarized in the following.

A complete 3D digital survey of the pavement, here already available from laser scanner data, is necessary to provide a detailed plano-altimetric map of the floor geometry (Figure 4). A dense point cloud across the whole paved surface was preferred to detect small inter-tile displacements, joint widths and local level variations that are critical for a reliable contact geometry. The resulting contact surface is exported for CAD/CAM to shape the underside of each module and to minimise stress concentrations at tile edges.

The data collected by the survey (instrumental and visual) have to be converted into interactive thematic maps of the pavement, in close collaboration with archaeologists (Figure 5). This map will necessarily include:

(a)

Constituent materials in different floor zones, their fragility, and degradation state.

(b)

Moisture distribution, highlighting areas affected by rising damp where specific ventilation levels must be ensured.

(c)

Functional pathways, identifying the routing of cables for lighting systems and structural health monitoring devices, which are part of the conservation project.

(d)

Zones subjected to the presence of significant concentrated loads due to apparatuses or

Other information depending on the specificity of the case can be included.

Based on the survey and thematic map, modular panels will be then designed. Each module will have:

(a)

lower surface shaped to the irregularities of the pavement, ensuring full contact without concentrating stresses particularly in the zones where from the map emerges fragile elements;

(b)

a flat upper surface, providing a safe working platform for restoration teams;

(c)

an external protective skin, resistant to impacts and customizable with the printed map of the underlying pavement. This allows workers to recognize the hidden historic surface while it remains fully protected.

The EcoCore modules will be 3D-printed and assembled directly in the Ninfeo (Figure 6). Once installed, they will allow safe transit of operators and equipment, while simultaneously providing ventilation beneath the protective skin, crucial to counteract moisture and reduce long-term risks of degradation. The system will also integrate pathways for cables and monitoring sensors, ensuring both conservation and continuous control of the monument’s condition.

The protective panel is derived from the survey-based contact surface of the Ninfeo floor. Its underside follows the measured geometry to ensure uniform support, while the upper skin provides a flat, continuous, non-slip walking surface suitable for safe access and maneuvering during works.

Through this application, the EcoCore system will act not only as a temporary protective solution during restoration but also as a preventive conservation tool, addressing two major risks for the Ninfeo Ponari floor: mechanical damage during works and persistent deterioration caused by humidity.

4. Conclusions

This study has focused on the temporary protection of historic floors during restoration and has presented the innovative 3D-EcoCore system. The solution is based on modular sandwich panels made of 3D-printed bio-inspired cores, designed with a Voronoi-type internal pattern, combined with a flat protective surface and an external skin. The system can adapt to irregular pavements, distribute concentrated loads, absorb impacts, allow ventilation and cable routing, and remain fully reversible. These features make it a sustainable and flexible alternative to conventional solutions such as plywood sheets or multilayer mats, which often show limits in adaptability, moisture control, and traceability of the covered surfaces.

An important contribution of this paper is that, beyond describing the physical characteristics of the proposed modules, it has analysed the design process that leads from the knowledge of the monument to the realisation of the protective system. Each historic floor is unique, with its own materials, geometry, fragility, and degradation processes. For this reason, a protection strategy cannot be standard, but must be adapted to the specific case. The methodology developed here shows that it is possible to create tailored interventions: information coming from surveys and thematic maps is not only recorded but directly used to design the internal structure of the cores. In practice, thematic maps provide data on materials, fragility, moisture distribution, and functional pathways, and these data are then translated into design parameters. This means that the internal pattern of the cores can change from one zone to another, ensuring that each part of the floor receives the level of protection it actually needs.

The strong interaction between archaeologists, architects, engineers, and material scientists is therefore essential, since the contribution of each discipline becomes part of the design process of the protection system. This integrated and interdisciplinary approach represents one of the main strengths of the EcoCore methodology.

Another relevant point is that the system has already been tested in terms of impact resistance, punching, and concentrated loads in other studies carried out within the 3D-EcoCore project, which are currently under review in scientific journals and conference proceedings. These experimental works confirm that the proposed solution shows excellent performance, and that this performance can be tuned in the design stage by modifying the internal pattern of the core. This result supports the approach described in the present paper and shows that the proposed solution is not only conceptual but already supported by consistent laboratory evidence.

Even though further steps are needed, the perspectives are promising. Future research will investigate the long-term durability of the biodegradable materials, the behaviour of the skin–core interface in site conditions, and the microclimatic performance under the panels, in order to ensure that no risks are introduced during use. Within the same project, a dedicated partner team is finalizing detailed biodegradation studies and protective-skin strategies; those results will be reported in separate publications.

Pilot applications will also be fundamental to verify installation and removal procedures, to test multifunctional aspects such as integration with sensors, and to collect practical feedback from restorers.

Another important direction will be the use of artificial intelligence tools: data from thematic surveys could be processed automatically to generate input for the design phase, and optimisation algorithms could define the best internal configuration of the cores in each area of the floor. This integration between survey, AI, and digital manufacturing will open new opportunities for highly efficient, case-specific, and reproducible solutions.

In conclusion, the 3D-EcoCore project does not only introduce an innovative protective system but also defines a new design methodology. By combining digital survey, thematic mapping, interdisciplinary interaction, advanced materials, and digital manufacturing, it demonstrates that temporary protection of historic floors can evolve from generic solutions to customised, modular, and reversible systems. This approach makes it possible to preserve fragile pavements more effectively during restoration, while also creating a methodological framework that can be applied to different historic sites. For this reason, the 3D-EcoCore solution represents not just a technical innovation but a new paradigm in the way conservation science and engineering can work together to protect cultural heritage.

The system here presented is designed as a temporary, reversible protective layer, not as a substitute for the original floor, and serves both conservation tasks and routine maintenance with minimal risk and full removability.